results of 2002 virginia - chesapeake bay finfish …...all fish were collected in 2002 by the...

Results of 2002 Virginia - Chesapeake Bay

Finfish Ageing

by

Stephen J. Bobko, Cynthia M. Jones, and

Eric M. Robillard

VMRC/ODU Age and Growth Laboratory

Center for Quantitative Fisheries Ecology

Old Dominion University

Norfolk, VA 23529-0456

October 1, 2003

Final Report

Development and Support of Facilities to Provide

Finfish Ageing for Virginia Catches and

Application of Virtual Population Analysis to

Provide Management Advice

by

Stephen J. Bobko, Cynthia M. Jones, and

Eric M. Robillard

VMRC/ODU Age and Growth Laboratory


Old Dominion University

October 1, 2003

Funded by contract No. RF 02-12 from the Virginia Saltwater Recreational

Development Fund through the Virginia Marine Resources Commission

VMRC final report on finfish ageing, 2002

Center for Quantitative Fisheries Ecology Old Dominion University

Page i

Table of Contents Page

Executive Summary iii

Acknowledgements iv

Chapter 1 Atlantic croaker Introduction 1

Methods 1

Results 2

Chapter 2 black drum

Introduction 5

Methods 5

Results 6

Chapter 3 bluefish

Introduction 9

Methods 9

Results 10

Chapter 4 cobia

Introduction 14



Page ii

Methods 14

Results 15

Chapter 5 red drum

Introduction 18

Methods 18

Results 19

Chapter 6 spadefish

Introduction 22

Methods 22

Results 23

Table of Contents (continued) Page

Chapter 7 Spanish mackerel Introduction 26

Methods 26

Results 29

Chapter 8 spot Introduction 34

Methods 34



Page iii

Results 35

Chapter 9 spotted seatrout

Introduction 37

Methods 37

Results 38

Chapter 10 striped bass Introduction 41

Methods 41

Results 44

Chapter 11 summer flounder

Introduction 49

Methods 49

Results 52

Chapter 12 tautog Introduction 55

Methods 55

Results 56

Chapter 13 weakfish Introduction 60

Methods 60



Page iv

Results 61



Page v

Executive Summary

In this report we present the results of ageing finfish collected from catches made in Virginia’s

marine waters in 2002. All fish were collected in 2002 by the Virginia Marine Resources

Commission’s (VMRC) Stock Assessment Program and aged in 2003 at the Center for Quantitative

Fisheries Ecology’s Age and Growth Laboratory at Old Dominion University. This report is broken

down into chapters, one for each of the 13 species we aged. For each species, we present measures of

ageing precision and bias, graphs of year-class distributions, and age-length keys.

For three species: summer flounder, Paralichthys dentatus, (n=329); striped bass, Morone saxatilis,

(n=863); and tautog, Tautoga onitis, (n=374) multiple bony structures were used for determining fish

age. Scales and otoliths were used to age summer flounder and striped bass, and opercula and otoliths

were used to age tautog. Comparing alternative hard parts allowed us to assess their usefulness in

determining fish age as well as the relative precision of each structure. Ages were determined from

otoliths for the following species collected in Virginia waters during 2002: Atlantic croaker,

Micropogonias undulatus, (n=362); black drum, Pogonias cromis, (n=89); bluefish, Pomatomus

saltatrix, (n=716); cobia, Rachycentron canadum, (n=65); red drum, Sciaenops ocellatus, (n=65);

spadefish, Chaetodipterus faber, (n=351); spot, Leiostomus xanthurus, (n=354); spotted seatrout,

Cynoscion nebulosus, (n=405); and weakfish, Cynoscion regalis, (n=646).

In total, we made 14,406 age readings from 6,403 scales, otoliths and opercula collected during 2002.

A summary of the age ranges for all species aged is presented in Table I.

Table I. Summary of numbers aged and age ranges for the 13 marine fish species

collected for age determination in Virginia during 2002.

Number of Number of Number of Minimum Maximum

Species Fish Hard-Parts Age Readings Age Age

Atlantic croaker 362 360 820 1 12

black drum 89 88 276 0 51

bluefish 716 710 1520 0 9

cobia 65 65 230 2 15

red drum 65 64 228 1 31

spadefish 351 336 772 0 16

Spanish mackerel 895 856 1812 0 9

spot 354 353 806 0 5

spotted seatrout 405 405 910 0 5

striped bass 863 1145 2490 2 22

summer flounder 329 632 1464 1 10

tautog 374 743 1686 2 18

weakfish 646 646 1392 1 10

Totals 5514 6403 14406



Page vi

As part of our continued public outreach focused at recreational anglers, we again participated in the

CCA’s Kid’s Fishing Day at Lynnhaven Fishing Pier. This was the third year our staff volunteered

their time to participate in the event. We are currently working on a spotted seatrout Species Update

report, which will be the fifth report in the series. Each report includes an overview of what is known

about a fish species’ biology, age and growth data and analyses generated in our lab, and interesting

information on fish in general.

In 2003 we upgraded our Age & Growth Laboratory website, which can be accessed at

http://web.odu.edu/fish. The website includes electronic versions of this document along with more

detailed explanations of the methods and structures we use in age determination.

Acknowledgements

We thank Roxanne Torres, Becky Taylor, and Susan McKeel for their technical expertise in preparing

otoliths, scales, and opercula for age determination. Roxanne, Becky, Susan, Serena Turner, Forrest

Crock, and Kathleen McNamee all put in long hours processing “tons” of fish in our lab. We are also

thankful for Dr. William Persons’ III hard work on our Spcies Updates and web page. A special note

of appreciation to Ron Owens, Troy Thompson, Joanie Beatley, and Myra Thompson for their many

efforts in this cooperative project. This work was funded by the Virginia Saltwater Recreational

Development Fund.

The image on the front cover is an otolith thin-section from a 315 mm (12.4 inch) total length, 5 year-

old male spot. The fifth annulus is forming at the edge of the otolith.

http://web.odu.edu/fish

VMRC final report on finfish ageing, 2002 Atlantic croaker


Page i

Chapter 1 Atlantic Croaker

Micropogonias

undulatus INTRODUCTION

Three hundred sixty two (362) Atlantic croaker,

Micropogonias undulatus, were collected by the

VMRC’s Stock Assessment Program for age

and growth analysis in 2002. We were unable

to age two fish due to the poor quality of their

otoliths. For the 360 fish we were able to age,

the average age was 5.6 years, and the standard

deviation and standard error were 2.3 and 0.1,

respectfully. Twelve age classes (1 to 12) were

represented, comprising fish from the 1990-

2001 year-classes. Fish from the 1996 through

1998 year-classes dominated the sample

METHODS

Handling of collection Otoliths were

received by the Age & Growth Laboratory in

labeled coin envelopes. In the lab they were

sorted by date of capture, their envelope labels

were verified against VMRC’s collection data,

and each fish was assigned a unique Age and

Growth Laboratory identification number. All

otoliths were stored dry in labeled cell well

plates.

Preparation Otoliths were processed

following the methods described in Barbieri et

al. (1994) with a few modifications. Briefly, the

left or right sagittal otolith was randomly

selected and attached to a glass slide with

Aremco's clear Crystalbond™ 509 adhesive. At

least two serial transverse sections were cut

through the core of each otolith with a Buehler

Isomet low-speed saw equipped with a three

inch, fine grit Norton diamond-wafering blade.

Otolith sections were placed on labeled glass

slides and covered with a thin layer of Flo-texx

mounting medium, that not only adhered the

sections to the slide, but more importantly,

provided enhanced contrast and greater

readability by increasing light transmission

through the sections.

Readings Sectioned otoliths were aged by

two different readers using a Leica MZ-12

dissecting microscope with transmitted light and

dark-field polarization at between 8 and 20

times magnification. Each reader aged all of the

otolith samples. The ageing criteria reported in

Barbieri et al. (1994) were used in age

determination, particularly regarding the

location of the first annulus (Figure 1).

All samples were aged in chronological order,

based on collection date, without knowledge of

previously estimated ages or the specimen

lengths. When the readers’ ages agreed, that age

was assigned to the fish. When the two readers

disagreed, both readers sat down together and



Page ii

re-aged the fish, again without any knowledge

of previously estimated ages or lengths, and

assigned a final age to the fish. When the

readers were unable to agree on a final age, the

fish was excluded from further analysis.

Comparison Tests Age estimates from

reader 1 were plotted against age estimates from

reader 2 to assess deviation from 1:1

equivalence (Campana et al. 1995). A test for

symmetry was used to detect any systematic

difference between the two readers (Hoenig et al.

1995). Also, a random sub-sample of 50 fish

was selected for second readings to measure

reader precision and age reproducibility. To

detect any changes or drift in our ageing

methods, both readers re-aged the otoliths of 50

randomly selected fish previously aged in 2000.

We considered a reader to be biased if the

readings revealed consistent over or under

ageing.

RESULTS

Measurements of reader self-precision were

high, with both readers able to reproduce the

ages of previously read otoliths (100%

agreement for reader 1 and reader 2). There was

no evidence of systematic disagreement

between reader 1 and reader 2 (test of symmetry,

2 = 7.3, df = 8, P = 0.5). In Figure 2 we

present a graph of the results for between-reader

ageing precision. The average between-reader

coefficient of variation (CV) of 0.4% was not

significant and much lower than the CV of 1.7%

from 2001. There was no evidence of drift in

age determination with the CV’s from 2000

precision fish with 100% agreement for reader 1

and reader 2.

(a)

(b)

Figure 1. Otolith cross-

sections of a) a 5 year old

croaker with a small 1st

annulus, and b) a 6 year

old croaker with a large

1st annulus.

Figure 2. Between-reader comparison of otolith

age estimates for Atlantic croaker.

123456789101112

Reader 1

1

2

3

4

5

6

7

8

9

10

11

12

Reader 2

(10)

(13)(1)

(22)

(63)(1)

(1)(108)(1)

(60)

(2)(9)

(1)(20)(1)

(2)(14)

(1)(15)

(1)(6)

(8)

Otolith Ages (years)



Page iii

Of the 360 fish aged with otoliths, 12 age

classes (1 to 12) were represented (Table 1).

The average age for the sample was 5.6 years,

and the standard deviation and standard error

were 2.3 and 0.1, respectfully.

Year-class data (Figure 3) indicate that

recruitment into the fishery begins at age 1, but

large numbers are not seen until age 3, which

corresponds to the 1999 year-class for Atlantic

croaker collected in 2002. While the ratio of

males to females shows an overall higher

number of females, both sexes show trends of

high abundance for the 1996 through 1997 year-

classes.

Age-Length-Key In Table 2 we present an

age-length-key that can be used in the

conversion of numbers-at-length in the

estimated catch to numbers-at-age using otolith

ages. The table is based on VMRC’s stratified

sampling of landings by total length inch

intervals.

REFERENCES

Barbieri, L.R., M.E. Chittenden, and C.M. Jones.

1994. Age, growth, and mortality of

Atlantic croaker, Micropogonias

undulatus, in the Chesapeake Bay region,

with a discussion of the apparent

geographical changes in population

dynamics. Fish. Bull. 92:1-12.

Campana, S.E., M.C. Annand, and J.I.

McMillan. 1995. Graphical and

statistical methods for determining the

consistency of age determinations. Trans.

Am. Fish. Soc. 124:131-138.

Hoenig, J.M., M.J. Morgan, and C.A. Brown.

1995. Analysing differences between two

age determination methods by tests of

symmetry. Can. J. Fish. Aquat. Sci.

52:364-368.

S-Plus. 1999. S-Plus 4.5 Guide to Statistics.

Data Analysis Products Division. Math

Soft, Inc. Seattle, Washington.

Figure 3. Year-class distribution for Atlantic

croaker collected for ageing in 2002.

Distributions are broken down by sex.

199019911992199319941995199619971998199920002001

Year Class

0

20

40

60

80

100

Number of Fish

Females n = 256

Males n = 99

Unknown n = 5



Page iv



Page i

Table 1. The number of Atlantic croaker assigned to each total length-at-age category for 360

fish sampled for age determination in Virginia during 2002.

Length Age (years)

1-inch 1 2 3 4 5 6 7 8 9 10 11 12

intervals Totals

7 - 7.99 7 0 0 0 0 0 0 0 0 0 0 0 7

8 - 8.99 0 5 0 0 0 0 0 0 0 0 0 0 5

9 - 9.99 2 8 7 2 1 0 0 0 0 0 0 0 20

10 - 10.99 1 0 9 19 8 2 1 0 0 0 0 0 40

11 - 11.99 0 0 6 23 17 4 1 0 1 0 0 0 52

12 - 12.99 0 0 1 15 38 13 2 2 0 1 0 1 73

13 - 13.99 0 0 0 1 25 8 4 0 0 0 0 0 38

14 - 14.99 0 0 0 2 14 19 0 3 3 2 0 1 44

15 - 15.99 0 0 0 0 7 6 2 6 4 3 3 1 32

16 - 16.99 0 0 0 1 0 5 1 3 5 2 0 0 17

17 - 17.99 0 0 0 0 0 3 1 5 0 2 0 1 12

18 - 18.99 0 0 0 0 0 1 0 1 2 4 2 2 12

19 - 19.99 0 0 0 0 0 0 0 0 1 3 0 1 5

20 - 20.99 0 0 0 0 0 0 0 0 1 0 1 0 2

21 - 21.99 0 0 0 0 0 0 0 0 0 0 0 1 1

Totals 10 13 23 63 110 61 12 20 17 17 6 8 360

Table 2. Age-Length key, as proportions-at-age in each 1 inch length-class, based on otolith

ages for Atlantic croaker sampled for age determination in Virginia during 2002.

Length Age (years)

1-inch 1 2 3 4 5 6 7 8 9 10 11 12

intervals N

7 - 7.99 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 7

8 - 8.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 5

9 - 9.99 0.100 0.400 0.350 0.100 0.050 0.000 0.000 0.000 0.000 0.000 0.000 0.000 20

10 - 10.99 0.025 0.000 0.225 0.475 0.200 0.050 0.025 0.000 0.000 0.000 0.000 0.000 40

11 - 11.99 0.000 0.000 0.115 0.442 0.327 0.077 0.019 0.000 0.019 0.000 0.000 0.000 52

12 - 12.99 0.000 0.000 0.014 0.205 0.521 0.178 0.027 0.027 0.000 0.014 0.000 0.014 73

13 - 13.99 0.000 0.000 0.000 0.026 0.658 0.211 0.105 0.000 0.000 0.000 0.000 0.000 38

14 - 14.99 0.000 0.000 0.000 0.045 0.318 0.432 0.000 0.068 0.068 0.045 0.000 0.023 44

15 - 15.99 0.000 0.000 0.000 0.000 0.219 0.188 0.063 0.188 0.125 0.094 0.094 0.031 32

16 - 16.99 0.000 0.000 0.000 0.059 0.000 0.294 0.059 0.176 0.294 0.118 0.000 0.000 17

17 - 17.99 0.000 0.000 0.000 0.000 0.000 0.250 0.083 0.417 0.000 0.167 0.000 0.083 12

18 - 18.99 0.000 0.000 0.000 0.000 0.000 0.083 0.000 0.083 0.167 0.333 0.167 0.167 12

19 - 19.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.200 0.600 0.000 0.200 5

20 - 20.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.500 0.000 0.500 0.000 2

21 - 21.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000 1

Sample Size 360



Page i

VMRC final report on finfish ageing, 2002 black drum


Page i

Chapter 2 Black Drum

Pogonias cromis

INTRODUCTION

A total of 88 black drum, Pogonias cromis, was

collected by the VMRC’s Stock Assessment

Program for age and growth analysis in 2002.

The average age of the sample was 18.1 years,

with a standard deviation of 14.9 and a standard

error of 1.6. The youngest fish was a young-of-

the-year (YOY) and the oldest fish was 51 years

old, representing the 2002 and 1951 year-classes,

respectively.

METHODS

Handling of collection


labeled coin envelopes. In the lab they were

sorted by date of capture, their envelope labels

were verified against VMRC’s collection data,

and each fish was assigned a unique Age and

Growth Laboratory sample number. All otoliths

were stored dry in their original VMRC coin

envelopes.

Preparation Otoliths were processed for

ageing following the methods described in

Bobko (1991) and Jones and Wells (1998).

Briefly, at least two serial transverse sections

were cut through the nucleus of each otolith

with a Buehler Isomet low-speed saw equipped

with a three inch, fine grit diamond-wafering

blade (Norton). A thin layer of Flo-texx

mounting medium was applied to the otolith

section to increase light transmission through

the translucent zones, which provided enhanced

contrast and greater readability.

Readings


dissecting microscope with transmitted light at

between 8 and 20 times magnification (Figure

1). Each reader aged all of the otolith samples.

All samples were aged in chronological order,









Figure 1. Otolith thin-section from a 20 year-old black drum.



Page ii



Comparison Tests








reader precision and age reproducibility. We

considered a reader to be biased if the readings

revealed consistent over or under ageing.

RESULTS

No bias was discovered in any of the self-

precision tests of otolith age estimates, with

both readers equally able to reproduce the ages

of previously read samples (reader 1’s CV =

0.09% and reader 2’s = 2.69%). The average

between reader coefficient of variation (CV) of

0.2% was not significant, and much lower than

the CV of 3.9% reported for black drum

collected in 2001. Figure 2 illustrates the

between readers’ precision of age estimates,

with no differences greater than one year. There

was no evidence of systematic disagreement


2 = 7, df = 7, P = 0.43).

Of the 88 fish aged with otoliths, 35 age classes

were represented (Figure 3). The average age of

the sample was 18.1 years, with a standard

deviation of 14.9 and a standard error of 1.6.

The youngest fish was a young-of-the-year

(YOY) and the oldest fish was 51 years old,

representing the 2002 and 1951 year-classes,

respectively. Year-class data indicate that older

fish continued to dominate the fishery, although

we observed good representation from the 1995

through 2002 year-classes. The strongest year-

classes were 1967, 1998, and 1999. Black drum

collected in 2002 were predominately males, a

trend observed by Jones (1998) for the years

1990-1996.







intervals.

REFERENCES

Bobko, S. J. 1991. Age, growth, and

reproduction of black drum, Pogonias

cromis, in Virginia. M.S. thesis. Old

Dominion University, Norfolk, VA.




Figure 3. Year-class distribution for black drum

collected for ageing in 2002.


1940195019601970198019902000

Year Class

0

2

4

6

8

10

12

Number of Fish

Females n = 27

Males n = 40

Unknown n = 21



Page iii

consistency of age determinations.

Trans. Am. Fish. Soc. 124:131-138.

Hoenig, J.M., M.J. Morgan, and C.A.

Brown. 1995. Analysing differences

between two age determination

methods by tests of symmetry. Can. J.

Fish. Aquat. Sci. 52:364-368.

Jones, C.J. 1998. Report on black drum

studies for the period 1990-1996.

Study of important recreational

fishes in the Chesapeake Bay.

Federal Aid in Sport Fish

Restoration Act project F-88-R-3.

Jones, C.J. and B.K. Wells. 1998. Age,

growth, and mortality of black drum,

Pogonias cromis, in the Chesapeake

Bay region. Fish. Bull. 96:451-461.


age estimates for black drum.

0 10 20 30 40 50

Reader 1

0

10

20

30

40

50Reader 2

(2)(2)(1)(10)(12)(4)(1)(2)

(1)(3)(2)(2)(1)(1)(1)

(3)(4)

(1)

(2)

(1)

(1)(2)(3)

(3)(1)(1)(1)(3)(1)(4)(1)(1)(2)(2)

(1)

(1)

(1)(1)(1)

(1)


VMRC final report on finfish ageing, 2002 bluefish


Page i

Tab

le 1

. Age

-Len

gth

key

, as

pro

po

rtio

ns-

at-a

ge in

eac

h 1

inch

len

gth

-cla

ss, b

ased

on

oto

lith

age

s fo

r b

lack

dru

m s

amp

led

fo

r ag

e

det

erm

inat

ion

in

Vir

gin

ia d

uri

ng

20

02.

Tota

l len

gth

no

t re

po

rted

fo

r tw

o f

ish

.



Page ii

Chapter 3 Bluefish

Pomatomus

saltatrix

INTRODUCTION

A total of 716 bluefish, Pomatomus saltatrix,

was collected by the VMRC’s Stock

Assessment Program for age and growth

analysis in 2002. We were unable to age six

fish due to the poor quality of their otoliths.

The average age for the 710 aged fish was 1.9

years, and the standard deviation and standard

error were 1.6 and 0.1, respectfully. The 1999

and 2000 year-classes dominated the sample.

METHODS



labeled coin envelopes. Once in our hands, they

were sorted based on date of capture, their

envelope labels were verified against VMRC’s

collection data, and assigned unique Age and

Growth Laboratory sample numbers. All

otoliths were stored in dry in labeled cell well

plates.

Preparation We used a “bake and thin-

section” technique to process bluefish otoliths

for age determination. Otolith preparation began

by randomly selecting either the right or left

otolith. Each otolith was mounted with Crystal

Bond onto a standard microscope slide with its

distal surface orientated upwards. Once

mounted, a small mark was placed on the otolith

surface directly above the otolith focus. The

slide, with attached otolith, was then secured to

an Isomet saw equipped with two diamond

wafering blades separated by a 0.5 mm spacer,

which was slightly smaller in diameter than the

diamond blades. The otolith was positioned so

that the wafering blades straddled each side of

the otolith focus ink mark. It was crucial that

this cut be perpendicular to the long axis of the

otolith. Failure to do so resulted in

“broadening” and distortion of winter growth

zones. A proper cut resulted in annuli that were

clearly defined and delineated. Once cut, the

otolith section was placed into a ceramic

“Coors” spot plate well and baked in a

Thermolyne 1400 furnace at 400oC. Baking

time was otolith size dependent and gauged by

color, with a light caramel color desired. Once

a suitable color was reached the baked thin-

section was placed on a labeled glass slide and

covered with a thin layer of Flo-texx mounting

medium, which provided enhanced contrast and

greater readability by increasing light

transmission through the sections.

Readings Two different readers using a

LEICA MZ-12 dissecting microscope with

transmitted light and dark-field polarization at

between 8 and 100 times magnification aged all

sectioned otoliths (Figure 1). If an otolith was



Page iii

properly sectioned the sulcal groove came to a

sharp point within the middle of the focus.

Typically the first year’s annulus was found by

locating the focus of the otolith, which was

characterized as a visually distinct dark oblong

region found in the center of the otolith. The

first year’s annulus had the highest visibility

proximal to the focus along the edge of the

sulcal groove. Once located, the first year’s

annulus was followed outward from the sulcal

groove towards the dorsal perimeter of the

otolith. Often, but not always, the first year was

associated with a very distinct crenellation on

the dorsal surface and a prominent protrusion on

the ventral surface. Unfortunately both these

landmarks had a tendency to become less

prominent in older fish.

Even with the bake and thin-section technique,

interpretation of the growth zones from the

otoliths of young bluefish was difficult. Rapid

growth within the first year of life prevents a

sharp delineation between opaque and

translucent zones. When the exact location of

the first year was not clearly evident, and the

otolith had been sectioned accurately, a

combination of surface landscape (1st year

crenellation) and the position of the second

annuli were used to help determine the position

of the first annulus.

What appeared to be “double annuli” were

occasionally observed in bluefish four years of

age and older. This annulus formation typically

occurred within years 4 to 7, and was

characterized by distinct and separate annuli in

extremely close proximity to each other. We do

not know if the formation of these double annuli

were two separate annuli, or in fact only one,

but they seemed to occur during times of

reduced growth after maturation. “Double

annuli” were considered to be one annulus when

both marks joined to form a central origin. The

origins being the sulcal groove and at the outer

peripheral edge of the otolith. If these annuli

did not meet to form a central origin they were

considered two annuli, and counted as such.

All samples were aged in chronological order






















Figure 1. Otolith thin-section from a 869mm TL

10 year-old female bluefish.



Page iv

RESULTS

The measurement of reader self-precision was

high for both readers (reader 1’s CV = 0.3% and

reader 2’s CV = 2.8%). There was evidence of

systematic disagreement between reader 1 and

reader 2 (test of symmetry, 2 = 18.9, df = 9,

P = 0.03), with reader 2 ageing fish older than

reader 1. Although this disagreement was

statistically significant, it was not considered

practically significant, with disagreements

occurring for only 35 out of 710 fish aged.

Figure 2 illustrates the between readers’

precision of age estimates, with no differences

greater than one year. The average coefficient of

variation (CV) of 1.6% was much lower than

the CV of 3.1% reported in 2001.

Of the 710 fish aged with otoliths 10 age classes

were represented (Table 1). The average age for

the sample was 1.9 years, and the standard


respectfully.

Year-class data (Figure 3) indicates that

recruitment into the fishery began at age 0,

which corresponded to the 2002 year-class for

bluefish caught in 2002. One-year-old fish were

the dominant year-class in the 2002 sample.







intervals.

REFERENCES





Am. Fish. Soc. 124:131-138.





52:364-368.





age estimates for bluefish.

0123456789

Reader 1

0

1

2

3

4

5

6

7

8

9

Reader 2

(6)(1)

(1)(435)(1)

(10)(145)(1)

(2)(12)(1)

(6)(6)

(36)(2)

(5)(21)(1)

(1)(9)

(2)(4)

(1)(2)




Page v

Figure 3. Year-class distribution for bluefish


Distribution is broken down by sex.

1993199419951996199719981999200020012002

Year Class

0

100

200

300

400

Number of FishFemales n = 392

Males n = 278

Unknown n = 40



Page vi

Table 1. The number of bluefish assigned to each total length-at-age category for 710

fish collected for age determination in Virginia in 2002 (length not reported for 4 fish).Length Age (years)

1-inch 0 1 2 3 4 5 6 7 8 9

intervals Totals

6 - 6.99 0 3 0 0 0 0 0 0 0 0 3

7 - 7.99 0 10 0 0 0 0 0 0 0 0 10

8 - 8.99 0 1 0 0 0 0 0 0 0 0 1

9 - 9.99 0 4 0 0 0 0 0 0 0 0 4

10 - 10.99 0 8 0 0 0 0 0 0 0 0 8

11 - 11.99 1 33 0 0 0 0 0 0 0 0 34

12 - 12.99 1 68 0 0 0 0 0 0 0 0 69

13 - 13.99 5 71 0 0 0 0 0 0 0 0 76

14 - 14.99 1 84 0 0 0 0 0 0 0 0 85

15 - 15.99 0 78 12 1 0 0 0 0 0 0 91

16 - 16.99 0 32 27 2 0 0 0 0 0 0 61

17 - 17.99 0 23 33 0 0 0 0 0 0 0 56

18 - 18.99 0 18 14 1 0 0 0 0 0 0 33

19 - 19.99 0 9 6 2 0 0 0 0 0 0 17

20 - 20.99 0 3 13 0 0 0 0 0 0 0 16

21 - 21.99 0 0 5 0 0 0 0 0 0 0 5

22 - 22.99 0 0 9 0 0 0 0 0 0 0 9

23 - 23.99 0 0 6 0 0 0 0 0 0 0 6

24 - 24.99 0 0 13 1 0 0 0 0 0 0 14

25 - 25.99 0 0 7 1 0 0 0 0 0 0 8

27 - 27.99 0 0 0 0 5 7 0 0 0 0 12

28 - 28.99 0 0 0 3 0 15 2 1 0 0 21

29 - 29.99 0 0 0 0 3 10 5 1 1 0 20

30 - 30.99 0 0 0 0 0 9 9 3 0 0 21

31 - 31.99 0 0 0 0 0 4 5 4 3 1 17

32 - 32.99 0 0 0 0 1 0 1 1 1 1 5

33 - 33.99 0 0 0 0 0 0 0 2 0 0 2

34 - 34.99 0 0 0 0 0 0 1 0 0 0 1

35 - 35.99 0 0 0 0 0 0 1 0 0 0 1

Totals 8 445 145 11 9 45 24 12 5 2 706



Page vii

Table 2. Age-Length key, as proportions-at-age in each 1 inch length-class, based

on otolith ages, for bluefish collected for age determination in Virginia during 2002.Length Age (years)

1-inch 0 1 2 3 4 5 6 7 8 9

intervals N

6 - 6.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 3

7 - 7.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 10

8 - 8.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

9 - 9.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 4

10 - 10.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 8

11 - 11.99 0.029 0.971 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 34

12 - 12.99 0.014 0.986 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 69

13 - 13.99 0.066 0.934 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 76

14 - 14.99 0.012 0.988 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 85

15 - 15.99 0.000 0.857 0.132 0.011 0.000 0.000 0.000 0.000 0.000 0.000 91

16 - 16.99 0.000 0.525 0.443 0.033 0.000 0.000 0.000 0.000 0.000 0.000 61

17 - 17.99 0.000 0.411 0.589 0.000 0.000 0.000 0.000 0.000 0.000 0.000 56

18 - 18.99 0.000 0.545 0.424 0.030 0.000 0.000 0.000 0.000 0.000 0.000 33

19 - 19.99 0.000 0.529 0.353 0.118 0.000 0.000 0.000 0.000 0.000 0.000 17

20 - 20.99 0.000 0.188 0.813 0.000 0.000 0.000 0.000 0.000 0.000 0.000 16

21 - 21.99 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 5

22 - 22.99 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 9

23 - 23.99 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 6

24 - 24.99 0.000 0.000 0.929 0.071 0.000 0.000 0.000 0.000 0.000 0.000 14

25 - 25.99 0.000 0.000 0.875 0.125 0.000 0.000 0.000 0.000 0.000 0.000 8

27 - 27.99 0.000 0.000 0.000 0.000 0.417 0.583 0.000 0.000 0.000 0.000 12

28 - 28.99 0.000 0.000 0.000 0.143 0.000 0.714 0.095 0.048 0.000 0.000 21

29 - 29.99 0.000 0.000 0.000 0.000 0.150 0.500 0.250 0.050 0.050 0.000 20

30 - 30.99 0.000 0.000 0.000 0.000 0.000 0.429 0.429 0.143 0.000 0.000 21

31 - 31.99 0.000 0.000 0.000 0.000 0.000 0.235 0.294 0.235 0.176 0.059 17

32 - 32.99 0.000 0.000 0.000 0.000 0.200 0.000 0.200 0.200 0.200 0.200 5

33 - 33.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 2

34 - 34.99 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000 1

35 - 35.99 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000 1

Sample Size 706

VMRC final report on finfish ageing, 2002 cobia


Page i

Chapter 4 Cobia

Rachycentron

canadum

INTRODUCTION

A total of 65 cobia, Rachycentron canadum,



analysis in 2002. The average age of the sample

was 5.4 years, and the standard deviation and

standard error were 2.7 and 0.3, respectfully.

The 1995, 1997, 1998, and 1999 year-classes

dominated the sample.

METHODS









plates.

Preparation Individual otoliths were placed

into 14 mm x 5 mm x 3 mm wells (Ladd

Industries silicon rubber mold) filled with

Loctite adhesive. Each otolith was rolled

around in the Loctite to remove all trapped air

bubbles and ensure complete coverage of the

otolith surface. The otoliths were oriented

sulcal side down with the long axis of the otolith

exactly parallel with the long axis of the mold

well. Once the otoliths were properly oriented,

the mold was placed under UV light and left to

solidify overnight. Once dry, each embedded

otolith was removed from the mold and

mounted with Crystal Bond onto a standard

microscope slide. Once mounted, a small mark

was placed on the otolith surface directly above

the otolith focus. The slide, with attached otolith,

was then secured to an Isomet saw equipped

with two diamond wafering blades separated by

a 0.5 mm spacer, which was slightly smaller in

diameter than the diamond blades. The otolith

was positioned so that the wafering blades

straddled each side of the focus ink mark. The

glass slide was adjusted to ensure that the blades

were exactly perpendicular to the long axis of

the otolith. The otolith wafer section was

viewed under a dissecting microscope to

determine which side (cut surface) of the otolith

was closer to the focus. The otolith section was

mounted best-side up onto a glass side with

Crystal Bond. The section was then lightly

polished on a Buehler Ecomet 3 variable speed

grinder-polisher with Mark V Laboratory 30-

micron polishing film. After drying, a thin layer

of Flo-texx mounting medium was applied over

the polished otolith surface.



Page ii

Readings Two different readers using a

LEICA MZ-12 dissecting microscope with

transmitted light and dark-field polarization at

between 8 and 100 times magnification aged all

sectioned otoliths (Figure 1). Both age readers

aged all of the otolith samples.























RESULTS



ages of previously read otoliths (reader 1’s CV

= 0.8% and reader 2’s CV = 0.9%). There was

no evidence of systematic disagreement


2 = 5, df = 4, P = 0.3). Figure 2 illustrates the

between

Figure 1. Otolith thin-section from a 1524mm TL

6 year old cobia.


age estimates for cobia.

23456789101112131415

Reader 1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Reader 2(2)

(10)

(21)(2)(1)

(5)(1)

(2)

(1)(13)

(1)

(2)

(2)

(2)


Figure 3. Year-class distribution for cobia



19871988198919901991199219931994199519961997199819992000

Year Class

0

5

10

15

20

Number of Fish

Females n = 46

Males n = 15

Unknown n = 4



Page iii

readers’ precision of age estimates, with a

difference greater than one year observed for

only one fish. The average coefficient of

variation (CV) of 1.4% was considered not to be

significant, and slightly less than the CV of

1.8% reported last year.

Of the 65 fish aged, 10 age classes were

represented (Table 1). The average age of the

sample was 5.4 years, and the standard


respectfully.


recruitment into the fishery begins at age 2,

which corresponds to the 2000 year-class for

cobia caught in 2002. The year-classes 1995,

1997, 1998, and 1999 dominated the sample.







intervals.

REFERENCES

Franks, J.S., J.R. Warren, and M.V. Buchanan.

1999. Age and growth of cobia,

Rachycentron canadum, from the

northeastern Gulf of Mexico. Fish. Bull.

97:459-471.





Am. Fish. Soc. 124:131-138.





52:364-368.






Page iv

Table 1. The number of cobia assigned to each total length-at-age category for 65 fish

sampled for age determination in Virginia during 2002. (lengths not reported for four fish)

Length Age (years)

1-inch 2 3 4 5 6 7 8 9 12 15

intervals Totals

29 - 29.99 1 0 0 0 0 0 0 0 0 0 1

31 - 31.99 1 0 0 0 0 0 0 0 0 0 1

36 - 36.99 0 0 1 0 0 0 0 0 0 0 1

37 - 37.99 0 1 0 0 0 0 0 0 0 0 1

38 - 38.99 0 1 1 0 0 0 0 0 0 0 2

39 - 39.99 0 1 1 1 0 0 0 0 0 0 3

40 - 40.99 0 2 0 0 0 0 0 0 0 0 2

41 - 41.99 0 2 1 0 0 0 0 0 0 0 3

42 - 42.99 0 0 2 0 0 0 0 0 0 0 2

43 - 43.99 0 1 3 0 0 0 0 0 0 0 4

44 - 44.99 0 0 0 0 0 1 0 0 0 0 1

45 - 45.99 0 0 1 0 0 1 0 0 0 0 2

46 - 46.99 0 0 3 0 0 0 0 0 0 1 4

47 - 47.99 0 0 6 0 0 0 0 0 0 0 6

48 - 48.99 0 0 2 0 0 1 0 0 0 0 3

49 - 49.99 0 0 0 1 0 0 0 0 0 0 1

50 - 50.99 0 1 2 2 1 0 0 0 0 0 6

51 - 51.99 0 0 0 0 0 1 0 0 0 0 1

52 - 52.99 0 0 0 2 1 0 0 0 0 0 3

53 - 53.99 0 0 0 1 0 0 0 0 0 0 1

54 - 54.99 0 0 0 0 0 1 0 0 1 0 2

56 - 56.99 0 0 0 0 0 2 0 0 0 0 2

57 - 57.99 0 0 0 0 0 1 1 0 0 0 2

58 - 58.99 0 0 0 0 0 0 0 1 0 0 1

60 - 60.99 0 0 0 0 0 1 0 0 0 0 1

61 - 61.99 0 0 0 0 0 1 0 0 0 1 2

62 - 62.99 0 0 0 0 0 1 0 1 0 0 2

64 - 64.99 0 0 0 0 0 0 0 0 1 0 1

Totals 2 9 23 7 2 11 1 2 2 2 61



Page i


on otolith ages for cobia sampled for age determination in Virginia during 2002.

Length Age (years)

1-inch 2 3 4 5 6 7 8 9 12 15

intervals N

29 - 29.99 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

31 - 31.99 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

36 - 36.99 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

37 - 37.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

38 - 38.99 0.000 0.500 0.500 0.000 0.000 0.000 0.000 0.000 0.000 0.000 2

39 - 39.99 0.000 0.333 0.333 0.333 0.000 0.000 0.000 0.000 0.000 0.000 3

40 - 40.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 2

41 - 41.99 0.000 0.667 0.333 0.000 0.000 0.000 0.000 0.000 0.000 0.000 3

42 - 42.99 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 2

43 - 43.99 0.000 0.250 0.750 0.000 0.000 0.000 0.000 0.000 0.000 0.000 4

44 - 44.99 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000 0.000 1

45 - 45.99 0.000 0.000 0.500 0.000 0.000 0.500 0.000 0.000 0.000 0.000 2

46 - 46.99 0.000 0.000 0.750 0.000 0.000 0.000 0.000 0.000 0.000 0.250 4

47 - 47.99 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 6

48 - 48.99 0.000 0.000 0.667 0.000 0.000 0.333 0.000 0.000 0.000 0.000 3

49 - 49.99 0.000 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 1

50 - 50.99 0.000 0.167 0.333 0.333 0.167 0.000 0.000 0.000 0.000 0.000 6

51 - 51.99 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000 0.000 1

52 - 52.99 0.000 0.000 0.000 0.667 0.333 0.000 0.000 0.000 0.000 0.000 3

53 - 53.99 0.000 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 1

54 - 54.99 0.000 0.000 0.000 0.000 0.000 0.500 0.000 0.000 0.500 0.000 2

56 - 56.99 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000 0.000 2

57 - 57.99 0.000 0.000 0.000 0.000 0.000 0.500 0.500 0.000 0.000 0.000 2

58 - 58.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 1

60 - 60.99 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000 0.000 1

61 - 61.99 0.000 0.000 0.000 0.000 0.000 0.500 0.000 0.000 0.000 0.500 2

62 - 62.99 0.000 0.000 0.000 0.000 0.000 0.500 0.000 0.500 0.000 0.000 2

64 - 64.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000 1

Sample Size 61

VMRC final report on finfish ageing, 2002 red drum


Page i

Chapter 5 Red Drum

Sciaenops

ocellatus

INTRODUCTION

Sixty-four red drum, Sciaenops ocellatus, were

collected for age and growth analysis in 2002.

Fifty-seven of the fish were five years-of-age or

less, while the remaining seven fish ranged in

age from 12 to 31 years old.

METHODS








otoliths were stored dry in their original labeled

coin envelopes.


ageing following the methods described in

Bobko (1991) for black drum. Briefly, otoliths

were mounted on glass slides with Crystal Bond.

At least two serial transverse sections were cut

through the nucleus of each otolith with a

Buehler Isomet low-speed saw equipped with a

three inch, fine grit diamond-wafering blade

(Norton). After drying, a thin layer of Flo-texx


section to increase light transmission through

the translucent zones, which provided enhanced

contrast and greater readability.

Readings Two different readers aged all

sectioned otoliths using a Leica MZ-12



times magnification (Figure 1).








Figure 1. Otolith thin-section from 26 year old

red drum.



Page ii





Red drum ages were based on a biological

birthdate of September 1, while year-class

assignment was based on a January 1 annual

birthdate. Red drum were treated in this manner

because of the timing of spawning and the fact

that the first annulus is not seen on an otolith

until a fish’s second spring. For example, a red

drum that was born in September of 1997 and

captured in March of 1999 would not have any

visible annuli on it’s otoliths, but would be aged

as a 1 year-old fish since it lived beyond one

September (September 1998). But this 1 year-

old fish caught in 1999 would be mistakenly

assigned to the 1998 year-class. In order to

properly assign the fish to it’s correct year-class,

1997, a January birthdate was used which would

make the fish 2 years-old (since the fish lived

past January 1998 and 1999) and year-class

would be assigned correctly.







1995). Also, both readers aged all 30 fish a

second time to measure reader precision and age

reproducibility. We considered a reader to be

biased if the readings revealed consistent over

or under ageing.

RESULTS


high, with both readers able to reproduce 100 %

of the ages of previously read otoliths. Figure 2

illustrates the between readers’ precision of age

estimates. There was also 100% agreement

between readers.

Of the 64 fish aged with otoliths, 11 age classes

were represented (Table 1). The average age of

the sample was 4.7 years, and the standard


respectfully.

Year-class data (Figure 3) indicate that the 1996

through 2001 year-classes dominated the fishery.

Indicative of the trend in the recreational fishing,

very few older fish were collected in 2002.






age estimates for red rum.

135791113151719212325272931

Reader 1

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

31

Reader 2

(21)(20)(3)(10)(3)

(1)

(1)

(1)

(1)(1)

(2)


Figure 3. Year-class distribution for red drum



1971197319751977197919811983198519871989199119931995199719992001Year Class

0

5

10

15

20

Number of Fish

Females n = 7

Males n = 25

Unknown n = 32



Page iii



intervals.

REFERENCES

Bobko, S. J. 1991. Age, growth, and

reproduction of black drum, Pogonias

cromis, in Virginia. M.S. thesis. Old

Dominion University, Norfolk, VA.





Am. Fish. Soc. 124:131-138.





52:364-368.






Page iv

Table 1. The number of red drum assigned to each total length-at-age

category for 64 fish sampled for age determination in Virginia during 2002.

Length Age (years)

1-inch 1 2 3 4 5 12 20 24 28 29 31

intervals Totals

10 - 10.99 1 0 0 0 0 0 0 0 0 0 0 1

11 - 11.99 3 0 0 0 0 0 0 0 0 0 0 3

12 - 12.99 6 0 0 0 0 0 0 0 0 0 0 6

13 - 13.99 2 0 0 0 0 0 0 0 0 0 0 2

14 - 14.99 1 0 0 0 0 0 0 0 0 0 0 1

15 - 15.99 1 0 0 0 0 0 0 0 0 0 0 1

16 - 16.99 1 0 0 0 0 0 0 0 0 0 0 1

17 - 17.99 2 0 0 0 0 0 0 0 0 0 0 2

18 - 18.99 3 0 0 0 0 0 0 0 0 0 0 3

19 - 19.99 1 1 0 0 0 0 0 0 0 0 0 2

20 - 20.99 0 2 0 0 0 0 0 0 0 0 0 2

21 - 21.99 0 4 0 0 0 0 0 0 0 0 0 4

22 - 22.99 0 1 0 0 0 0 0 0 0 0 0 1

23 - 23.99 0 2 0 0 0 0 0 0 0 0 0 2

24 - 24.99 0 3 0 0 0 0 0 0 0 0 0 3

25 - 25.99 0 6 0 0 0 0 0 0 0 0 0 6

26 - 26.99 0 1 0 0 0 0 0 0 0 0 0 1

27 - 27.99 0 0 0 1 0 0 0 0 0 0 0 1

28 - 28.99 0 0 1 3 0 0 0 0 0 0 0 4

29 - 29.99 0 0 0 1 0 0 0 0 0 0 0 1

30 - 30.99 0 0 0 3 0 0 0 0 0 0 0 3

31 - 31.99 0 0 0 2 0 0 0 0 0 0 0 2

32 - 32.99 0 0 1 0 0 0 0 0 0 0 0 1

34 - 34.99 0 0 1 0 0 0 0 0 0 0 0 1

35 - 35.99 0 0 0 0 2 0 0 0 0 0 0 2

38 - 38.99 0 0 0 0 1 0 0 0 0 0 0 1

40 - 40.99 0 0 0 0 0 0 1 0 0 0 0 1

41 - 41.99 0 0 0 0 0 0 0 1 0 0 0 1

42 - 42.99 0 0 0 0 0 0 0 0 1 1 0 2

45 - 45.99 0 0 0 0 0 1 0 0 0 0 0 1

47 - 47.99 0 0 0 0 0 0 0 0 0 0 2 2

Totals 21 20 3 10 3 1 1 1 1 1 2 64



Page v


on otolith ages for red drum sampled for age determination in Virginia during 2002.

Length Age (years)

1-inch 1 2 3 4 5 12 20 24 28 29 31

intervals N

10 - 10.99 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

11 - 11.99 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 3

12 - 12.99 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 6

13 - 13.99 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 2

14 - 14.99 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

15 - 15.99 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

16 - 16.99 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

17 - 17.99 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 2

18 - 18.99 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 3

19 - 19.99 0.500 0.500 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 2

20 - 20.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 2

21 - 21.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 4

22 - 22.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

23 - 23.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 2

24 - 24.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 3

25 - 25.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 6

26 - 26.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

27 - 27.99 0.000 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

28 - 28.99 0.000 0.000 0.250 0.750 0.000 0.000 0.000 0.000 0.000 0.000 0.000 4

29 - 29.99 0.000 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

30 - 30.99 0.000 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 3

31 - 31.99 0.000 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 2

32 - 32.99 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

34 - 34.99 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

35 - 35.99 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 2

38 - 38.99 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 1

40 - 40.99 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000 0.000 1

41 - 41.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000 1

42 - 42.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.500 0.500 0.000 2

45 - 45.99 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 1

47 - 47.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000 2

Sample Size 64

VMRC final report on finfish ageing, 2002 spadefish


Page i

Chapter 6 Atlantic Spadefish

Chaetodipterus

faber

INTRODUCTION

A total of 336 spadefish, Chaetodipterus faber,

was collected for age and growth analysis in

2002. The average age of the sample was 3.1

years, and the standard deviation and standard

error were 3.1 and 0.2, respectfully.

METHODS









trays.


ageing using a bake and thin-section technique.

Each otolith was mounted onto a glass slide

with Aremco's clear Crystalbond™ 509

adhesive and a transverse cut was made just

outside the focus with a Buehler Isomet saw

equipped with a single three inch, high

concentration diamond wafering blade (Buehler

Series 15HC). The half of the sectioned otolith

with the focus was baked in a Thermolyne 1400

furnace at 400C for approximately one to two

minutes. The sectioned surface (through the

otolith focus) of the otolith half was attached to

a glass slide with Loctite 349 photo-active

adhesive. We then used a Hillquist Thin Section

machine to grind the embedded otolith half to a

thickness of 0.3 to 0.5mm. The otolith section

was polished on a Buehler Ecomet 3 variable

speed grinder-polisher Mark V Laboratory 30

micron polishing film. After polishing, a thin

layer of Flo-texx mounting medium was applied

to the otolith section to increase light

transmission through the translucent zones,

which provided enhanced contrast and greater

readability.




Figure 1. Sectioned otolith from a 3-year-old

female spadefish.



Page ii


times magnification (Figure 1).























RESULTS



ages of previously read otoliths (reader 1’s CV

= 2.5% and reader 2’s CV = 5.4%). Figure 2

illustrates the between readers’ precision of age

estimates, with only six age difference greater

than one year. There was no evidence of

systematic disagreement between reader 1 and

reader 2 (test of symmetry, 2 = 18, df = 16, P

= 0.32). The average coefficient of variation

(CV) of 5.6% was considered not to be

significant, but a bit higher than the CV of 1.7%

reported in 2001.


classes were represented (Table 1). The average

age of the sample was 3.1 years, and the

standard deviation and standard error were 3.1

and 0.2, respectfully. Year-class data (Figure 3)

show good representation from the 1995, 1999,

2000, and 2001 year-classes.


age estimates for spadefish.

01234567891011121314151617

Reader 1

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

Reader 2

(1)(135)(7)

(14)(31)(6)

(2)(51)(3)

(1)(4)(14)(2)

(2)(6)(3)(1)

(3)(3)

(2)(18)

(2)

(3)

(2)(2)(1)

(2)(1)(3)

(2)

(1)(1)(1)(1)

(2)

(1)(1)


Figure 3. Year-class distribution for spadefish



198619881990199219941996199820002002

Year Class

0

50

100

150

Number of Fish

Females n = 160

Males n = 176



Page iii







intervals.

REFERENCES





Am. Fish. Soc. 124:131-138.





52:364-368.

Kimura, D.K. 1980. Likelihood methods for

the von Bertalanffy growth curve. Fish.

Bull. 77:765-776.






Page iv

Table 1. The number of spadefish assigned to each total length-at-age category for 336 fish


Length Age (years)

1-inch 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

intervals Totals

4 - 4.99 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1

5 - 5.99 0 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4

6 - 6.99 0 79 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 83

7 - 7.99 0 59 12 3 0 0 0 0 0 0 0 0 0 0 0 0 0 74

8 - 8.99 0 13 11 6 0 0 0 0 0 0 0 0 0 0 0 0 0 30

9 - 9.99 0 1 6 8 0 0 0 0 0 0 0 0 0 0 0 0 0 15

10 - 10.99 0 0 0 8 2 0 0 0 0 0 0 0 0 0 0 0 0 10

11 - 11.99 0 0 0 7 1 0 0 0 0 0 0 0 0 0 0 0 0 8

12 - 12.99 0 0 0 10 0 0 0 0 0 0 0 0 0 0 0 0 0 10

13 - 13.99 0 0 0 11 2 1 0 0 0 0 0 0 0 0 0 0 0 14

14 - 14.99 0 0 0 7 2 0 1 0 0 0 0 0 0 0 0 0 0 10

15 - 15.99 0 0 0 5 6 1 1 0 0 0 0 0 0 0 0 0 0 13

16 - 16.99 0 0 0 0 2 3 0 0 0 0 0 0 0 0 0 0 0 5

17 - 17.99 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1

18 - 18.99 0 0 0 0 1 3 1 4 0 0 0 0 0 0 0 0 0 9

19 - 19.99 0 0 0 0 0 1 0 3 1 0 0 0 0 0 0 0 0 5

20 - 20.99 0 0 0 0 0 0 4 8 1 1 3 0 1 0 0 0 0 18

21 - 21.99 0 0 0 0 0 0 0 4 0 2 0 3 1 0 0 1 0 11

22 - 22.99 0 0 0 0 0 0 0 3 0 0 1 3 3 1 0 0 2 13

23 - 23.99 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 2

Totals 1 156 33 65 17 9 7 22 2 3 4 6 5 1 1 2 2 336



Page v

Table 2. Age-Length key, as proportions-at-age in each 1 inch length-class, based on otolith

ages for spadefish sampled for age determination in Virginia during 2002.

Length Age (years)

1-inch 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

intervals N

4 - 4.99 1.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1

5 - 5.99 0.00 1.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 4

6 - 6.99 0.00 0.95 0.05 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 83

7 - 7.99 0.00 0.80 0.16 0.04 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 74

8 - 8.99 0.00 0.43 0.37 0.20 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 30

9 - 9.99 0.00 0.07 0.40 0.53 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 15

10 - 10.99 0.00 0.00 0.00 0.80 0.20 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 10

11 - 11.99 0.00 0.00 0.00 0.88 0.13 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 8

12 - 12.99 0.00 0.00 0.00 1.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 10

13 - 13.99 0.00 0.00 0.00 0.79 0.14 0.07 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 14

14 - 14.99 0.00 0.00 0.00 0.70 0.20 0.00 0.10 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 10

15 - 15.99 0.00 0.00 0.00 0.38 0.46 0.08 0.08 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 13

16 - 16.99 0.00 0.00 0.00 0.00 0.40 0.60 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5

17 - 17.99 0.00 0.00 0.00 0.00 1.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1

18 - 18.99 0.00 0.00 0.00 0.00 0.11 0.33 0.11 0.44 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 9

19 - 19.99 0.00 0.00 0.00 0.00 0.00 0.20 0.00 0.60 0.20 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5

20 - 20.99 0.00 0.00 0.00 0.00 0.00 0.00 0.22 0.44 0.06 0.06 0.17 0.00 0.06 0.00 0.00 0.00 0.00 18

21 - 21.99 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.36 0.00 0.18 0.00 0.27 0.09 0.00 0.00 0.09 0.00 11

22 - 22.99 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.23 0.00 0.00 0.08 0.23 0.23 0.08 0.00 0.00 0.15 13

23 - 23.99 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.50 0.50 0.00 2

Sample Size 336

VMRC final report on finfish ageing, 2002 Spanish mackerel


Page i

Chapter 7

Spanish Mackerel

Scomberomorous

maculatus

INTRODUCTION

The Spanish mackerel is a common visitor to

the Chesapeake Bay from spring to autumn,

known to appear as far north as the mouth of the

Patuxent River. It is a nearshore, schooling

species that undertakes long-distance migrations.

Spanish mackerel enter the Chesapeake Bay by

May, when the water temperatures exceed

approximately 17C (63F). Spawning occurs

off the coast of Virginia from late spring

through late summer, with fish returning to

Florida waters in autumn to overwinter (Murdy

1997).

Spanish mackerel support important recreational

and commercial fisheries along the Atlantic

coast of the United States. In Virginia (ocean to

3 miles, Chesapeake Bay and tributaries), the

five-year average catch for Spanish mackerel

(1997-2001) was 176,975 pounds per year.

Two major gears accounted for 99% of the

harvest, pound net (81% of the harvest) and gill

net (18% of the harvest) and. Virginia

Recreational anglers’ average harvest of

Spanish mackerel over the same five-year

period was 99,845 fish per year.

The Atlantic Coast Cooperative Statistical

Program (ACCPS) has identified Spanish

mackerel, Scomberomorous maculatus, as a

species with no established harvest targets in the

Northeast or Southeast. This is the first

extensive biological sampling program for

Spanish mackerel in Virginia, with the goal of

collecting data ultimately useful in making

informative management decisions on future

harvests.

A total of 2124 Spanish mackerel,

Scomberomorous maculatus, was collected by

the Virginia Marine Resource Commission

(VMRC) Stock Assessment Program and the


(CQFE). Age was determined for 857 Spanish

mackerel using sagittal otoliths. Fifteen of the

fish were young-of-the-year fish and ranged in

size from 230 to 407.5 mm total length. The

average total length for the remaining 842 fish

was 476.7 mm and the average age was 2.1

years old. Ten age classes were observed (0 –

9), representing fish from the 1993 through

2002 year-classes.

METHODS

Sampling – A total of 2124 Spanish mackerel

was collected from May through October 2002

by CQFE and VMRC (Table 1). Each fish was

measured for total length, fork length, standard

length, sex, maturity stage and total weight.

Sagittal otoliths were removed for age and



Page ii

growth analysis for 895 of the 2124 measured

fish.

Handling of collection All otoliths and

associated data were transferred to the Center

for Quantitative Fisheries Ecology’s Age and

Growth Laboratory as they were collected. In

the lab they were sorted by date of capture, their

envelope labels verified against VMRC’s

collection data, and each fish was assigned a

unique Age and Growth Laboratory sample

number. All otoliths were stored dry in labeled

cell well plates.

Preparation Spanish mackerel otoliths were

separated into two classes based on the total

length of the fish, (1) 500 mm and (2) 500

mm. Otoliths from fish less than 500 mm were

aged whole, with no processing required.

Otoliths from fish greater than or equal to 500

mm total length were processed using an Age

and Growth Laboratory thin section technique

modified to deal with the fragile nature of

Spanish mackerel otoliths. Briefly, an otolith

from one of these larger fish was first embedded

in a 9.5 mm x 4.5 mm x 4.5 mm silicon mold

well with Loctite 349 photo-active adhesive.

The mold was placed under ultraviolet light to

cure and harden the Loctite. Th embedded

otolith was removed from the silicon mold and

the location of the core of the otolith was then

marked with an extra fine point permanent

marker. A thin transverse section was made

using a Buelher Isomet saw equipped with two

high concentration diamond wafering blades

separated by a 0.5 mm plastic spacer. The thin-

section was then covered with a thin layer of

Flo-texx mounting medium, which not only

adhered the section to the slide but also


readability by increasing light transmission

through the sections.

Readings By convention, a birthdate of

January 1 is assigned to all Northern

Hemisphere fish species. We use a system of

age determination that assigns age class

according to the date of sacrifice with respect to

this international accepted birthdate and the

timing of annulus formation. Although an

otolith annulus is actually the combination of an

opaque and translucent band, when ageing

otliths we actually enumerate only the opaque

bands, but still refer to them as annuli. Spanish

mackerel otolith annulus formation occurs

between the months of April and June, with

younger fish tending to lay down annuli earlier

than older fish. Fish age is written first

followed by the actual number of annuli visible

listed within parentheses (e.g., 3(3)). The

presence of a “+” after the number in the

parentheses indicates new growth, or “plus

growth” visible on the structure’s margin.

Using this method, a fish sacrificed in January

before annulus formation with three visible

annuli would be assigned the same age, 4(3+),

Table 1

Summary of the total number of Spanish mackerel sampled and aged by month.

Month October-May June July August September Total

Number of fish measured 144 589 721 509 161 2124

Number of fish aged 108 381 222 108 38 857

Percent Aged 75 64.7 30.8 21.2 23.6 40.4



Page iii

as a fish with four visible annuli sacrificed in

August after annulus formation, 4(4+). Year-

class is then assigned once the reader

determines the fish’s age and takes into account

the year of capture.

Whole otoliths were aged in a petri dish filled

with water at between 8 and 40 times

magnification using a Leica MZ-12 dissecting

microscope with polarized transmitted light.

The first annulus on whole otoliths was often

easy to identify. However, determining if plus

growth beyond the first annulus was from

otolith growth after the current year’s annulus

formation or if the fish were in fact getting

ready to deposit a second annulus was

extremely difficult to determine. Consequently

young-of-the-year and one-year old fish were

differentiated from older fish based, in part, on

the greater transparency of their whole otoliths

(Figure 1). Fish older than age two and two-

year old fish depositing their second annulus on

the edge of the otolith were difficult to age with

whole otoliths (Figures 2 and 3).

Sectioned otoliths were aged with a Leica MZ-

12 dissecting microscope with polarized

transmitted light at between 8 and 40 times

magnification. The first annulus on sectioned

otoliths was often quite distant from the core,

with subsequent annuli regularly spaced along

the sulcal groove out towards the proximal

(inner-face) edge of the otolith (Figures 2 and 3).

Without knowledge of previously estimated

ages or the specimen lengths, two different

readers aged all otoliths in chronological order

based on collection date. When the readers’

ages agreed, that age was assigned to the fish.

When the two readers disagreed, both readers

sat down together and re-aged the fish, again

without any knowledge of previously estimated

ages or lengths, and assigned a final age to the

fish. When the readers were unable to agree on

a final age, the fish was excluded from further

analysis.

Figure 1. Unbaked whole otoliths from a) a 1

year-old Spanish mackerel b) a 2 year-old

Spanish mackerel.

(a)

(b)

(a)

(b)

Figure 2. A three year old spanish mackerel

otolith from a 0.6 kg male a) thin-section b)

whole otolith with part of the tip broken off.



Page iv

Collaboration with other laboratories ageing

spanish mackerel All otoliths were sent to

the National Marine Fisheries Service (NMFS)

Panama City, Florida for second readings. At

the time of submitting this report the NMFS

data were not available for comparative analysis.







1995).

Growth Curves von Bertalanffy Growth

Functions (VBGF) were fit to length-at-age data

for pooled sexes, and for males and females fit

separately using the function nls of S-PLUS (S-

PLUS 1999). A likelihood ratio test (Kimura

1980) was used to determine if differences exist

between VBGF parameter estimates for mean

length at age data from males and females.

RESULTS

Sampling Two major gears, pound nets

(81%) and gill nets (18%), account for the

largest percentage of historical Spanish

mackerel harvests in Virginia. Consequently,

our sampling targeted these gears. Collections

from pound nets made up 86.4% of all measured

fish and 90.5% of all aged fish (Table 2). In

addition, 9.1% of the measured fish and 3.4% of

the aged fish were collected from gill nets.

Random sampling of Spanish mackerel

provided length data representative of Virginia’s

commercial harvest. Collected Spanish

mackerel ranged from 230 mm to 800 mm in

total length and 0.07 kg to 2.9 kg in total weight.

Sampling for age determination was

proportional to the observed number at length,

with over-representation of fish from the

extremes of the length frequency distribution

(Figure 4).

Age Determination We were only able to

age 857 of the 895 Spanish mackerel collected.

The otoliths from 27 fish were unable to be aged

because they were either broken to the point that

they could not be aged whole or could not be

thin-sectioned. Age readers could not agree on

an age for 11 fish. These 38 fish were excluded

from further age and growth analysis.

(a)

(b)

Figure 3. An eight year old spanish

mackerel otolith from a 1 kg female a)

thin-section b) whole otolith.



Page v

The average between-reader coefficient of

variation (CV) was 13.6%. Figure 5 illustrates

the between readers’ precision of age estimates.

There was evidence of systematic disagreement


2 = 194.4, df = 9, P < 0.001), with reader 2

ageing young fish older than reader 1. The final

ageing criteria listed in the Methods – Readings

section of this document were a result of the

large numbers of disagreements. Using a Leica

MZ-8 dissection microscope with a two-head

discussion tube, both readers reaged all otoliths

for which the readers disagreed using these

finalized ageing criteria.

Of the 857 Spanish mackerel aged with otoliths,

ten age classes were represented (Table 3). The

average age was 2.0 year old, and the standard


Table 2

Percent measured by gear Percent aged by gear

Pound net 86.4 90.5

Gill Net 9.1 3.4

Haul seine 4.5 6.1

Summary of the percentage of Spanish mackerel measured and aged by gear.

230268306344382420458496534572610648686724762800

Total Length (mm)

0

50

100

150

Frequency

Measured for Length

Fish Aged

Figure 4. Length frequency distribution of Spanish mackerel collected for regular length

sampling and for age determination.



Page vi

respectfully. Year-class data (Figure 6) show

that the fishery was comprised of ten year-

classes, comprising fish from the 1993 through -

2002 year-classes, with fish primarily from the

1999 and 2001 year-classes.

Likelihood ratio tests of VBGFs fitted to mean

size at age data showed a significant difference

between the sexes ( 2 = 28.2, df = 3, P <

0.001). Based on these results, we recommend

that separate VBGF parameter estimates be used

for each sex. Length-at-age data with

corresponding VBGF curves and equations are

presented in Figure 7.







intervals.

REFERENCES



statistical methods for determining

the consistency of age eterminations.


Hoenig, J.M., M.J. Morgan, and C.A.

Brown. 1995. Analyzing

differences between two age

determination methods by tests of


52:364-368.

Kimura, D.K. 1980. Likelihood methods for

the von Bertalanffy growth curve. Fish.

Bull. 77:765-776.

Murphy E.O., R.S. Birdsong, J.A. Musick.

1997. Fishes of the Chesapeake Bay.

Smithsonian Institute Press.

Washington and London.

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002

Year Class

0

100

200

300

400

500

Nu

mb

er

of

Fis

h

Females n = 593

Males n = 254

Unknown n = 10

Figure 6. Year-class frequency distribution

for Spanish mackerel collected for ageing

in 2002. Distribution for otolith ages is

broken down by sex.

0 1 2 3 4 5 6 7 8 9 10

Reader 1

0

1

2

3

4

5

6

7

8

9

10

Read

er

2

(11)

(3) (252) (12) (1)

(168) (82) (6)

(4) (54) (134) (3)

(16) (65) (7)

(6) (21)

(4) (3)

(6)

(1) (2)

(4)

(2)


Figure 5. Between-reader comparison of

otolith age estimates for Spanish mackerel.



Page vii

Figure 7. Plots of separate sex length-at-

age data for Spanish mackerel collected in

2002 with fitted von Bertalanffy growth

curves and equations.

1 3 5 7 9

Age (years)

300

400

500

600

700

800

Total Length (mm)Females (n = 592 )

Males (n = 254 )

Lt = 605.85 *(1-e(- 0.27 *(age-( -2.94 ))))

Lt = 820.98 *(1-e(- 0.22 *(age-( -2.35 ))))



Page 8

Table 3. The number of Spanish mackerel assigned to each total length-at-age category for

857 fish sampled for age determination in Virginia during 2002 (no length for 1 fish).

Length Age (years)

1-inch 0 1 2 3 4 5 6 7 8 9

intervals Totals

9 - 9.99 4 0 0 0 0 0 0 0 0 0 4

10 - 10.99 2 0 0 0 0 0 0 0 0 0 2

11 - 11.99 5 1 0 0 0 0 0 0 0 0 6

12 - 12.99 1 1 0 0 0 0 0 0 0 0 2

13 - 13.99 1 9 0 0 0 0 0 0 0 0 10

14 - 14.99 0 45 0 0 0 0 0 0 0 0 45

15 - 15.99 1 141 1 1 0 0 0 0 0 0 144

16 - 16.99 1 168 0 0 1 0 0 0 0 0 170

17 - 17.99 0 65 9 9 0 0 0 0 0 0 83

18 - 18.99 0 20 19 33 1 0 0 0 0 0 73

19 - 19.99 0 11 17 25 1 0 0 0 0 0 54

20 - 20.99 0 6 5 29 8 1 0 0 0 0 49

21 - 21.99 0 4 3 33 6 1 1 0 0 1 49

22 - 22.99 0 1 5 17 6 2 0 0 1 0 32

23 - 23.99 0 0 3 17 12 3 1 0 0 3 39

24 - 24.99 0 0 1 7 17 4 0 1 0 0 30

25 - 25.99 0 0 0 3 11 3 0 0 0 0 17

26 - 26.99 0 0 0 2 8 3 1 1 0 0 15

27 - 27.99 0 0 0 1 10 7 0 2 0 0 20

28 - 28.99 0 0 0 0 3 2 0 1 1 1 8

29 - 29.99 0 0 0 0 0 0 0 2 0 1 3

30 - 30.99 0 0 0 0 0 1 0 0 0 0 1

Totals 15 472 63 177 84 27 3 7 2 6 856



Page 9

Table 4. Age-Length key, as proportions-at-age in each 1 inch length-class, based on

otolith ages for Spanish mackerel sampled for age determination in Virginia during 2002.

Length Age (years)1-inch 0 1 2 3 4 5 6 7 8 9

intervals N

9 - 9.99 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 4

10 - 10.99 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 2

11 - 11.99 0.833 0.167 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 6

12 - 12.99 0.500 0.500 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 2

13 - 13.99 0.100 0.900 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 10

14 - 14.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 45

15 - 15.99 0.007 0.979 0.007 0.007 0.000 0.000 0.000 0.000 0.000 0.000 144

16 - 16.99 0.006 0.988 0.000 0.000 0.006 0.000 0.000 0.000 0.000 0.000 170

17 - 17.99 0.000 0.783 0.108 0.108 0.000 0.000 0.000 0.000 0.000 0.000 83

18 - 18.99 0.000 0.274 0.260 0.452 0.014 0.000 0.000 0.000 0.000 0.000 73

19 - 19.99 0.000 0.204 0.315 0.463 0.019 0.000 0.000 0.000 0.000 0.000 54

20 - 20.99 0.000 0.122 0.102 0.592 0.163 0.020 0.000 0.000 0.000 0.000 49

21 - 21.99 0.000 0.082 0.061 0.673 0.122 0.020 0.020 0.000 0.000 0.020 49

22 - 22.99 0.000 0.031 0.156 0.531 0.188 0.063 0.000 0.000 0.031 0.000 32

23 - 23.99 0.000 0.000 0.077 0.436 0.308 0.077 0.026 0.000 0.000 0.077 39

24 - 24.99 0.000 0.000 0.033 0.233 0.567 0.133 0.000 0.033 0.000 0.000 30

25 - 25.99 0.000 0.000 0.000 0.176 0.647 0.176 0.000 0.000 0.000 0.000 17

26 - 26.99 0.000 0.000 0.000 0.133 0.533 0.200 0.067 0.067 0.000 0.000 15

27 - 27.99 0.000 0.000 0.000 0.050 0.500 0.350 0.000 0.100 0.000 0.000 20

28 - 28.99 0.000 0.000 0.000 0.000 0.375 0.250 0.000 0.125 0.125 0.125 8

29 - 29.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.667 0.000 0.333 3

30 - 30.99 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000 0.000 1

Sample Size 856

VMRC final report on finfish ageing, 2002 spot


Page 10

Chapter 8 Spot

Leiostomus

xanthurus

INTRODUCTION

A total of 405 spot, Leiostomus xanthurus,



analysis in 2002. The average age for the

sample was 1.5 year old, and the standard

deviation and standard error were 1.0 and

0.04, respectfully. Six age classes (0 to 5)

were represented, comprising fish from the

1997-2002 year-classes, with fish

predominantly from the 2001 year-class.

METHODS


received by the Age & Growth Laboratory

in labeled coin envelopes. Once in our

hands, they were sorted based on date of

capture, their envelope labels were verified

against VMRC’s collection data, and

assigned unique Age and Growth

Laboratory sample numbers. All otoliths

were stored dry in labeled cell well trays.


ageing using a thin-sectioning technique.

The first step in otolith preparation was to

grind down the otolith in a transverse plane

to its core using a Hillquist thin section

machine’s 320-mesh diamond cup wheel. To

prevent distortion of the reading surface, the

otolith was ground exactly perpendicular to

the reading plane. The ground side of the

otolith was then placed face down in a drop

of Loctite 349 photo-active adhesive on a

labeled glass slide and placed under

ultraviolet light to allow the adhesive to

harden (approximately ten minutes). The

Hillquist thin section machine’s cup wheel

was used again to grind the otolith,

embedded in Loctite, to a thickness of 0.3 to

0.5mm. Finally, a thin layer of Flo-texx


section to increase light transmission

through the translucent zones, which


readability.

Figure 1. Sectioned otolith from a 1 year old male

spot.



Page 11



dissecting microscope with transmitted light

and dark-field polarization at between 8 and

100 times magnification (Figure 1).

All samples were aged in chronological

order based on collection date, without

knowledge of previously estimated ages or

the specimen lengths. When the readers’

ages agreed, that age was assigned to the

fish. When the two readers disagreed, both

readers sat down together and re-aged the

fish, again without any knowledge of

previously estimated ages or lengths, and


readers were unable to agree on a final age,

the fish was excluded from further analysis.


reader 1 were plotted against age estimates

from reader 2 to assess deviation from 1:1

equivalence (Campana et al. 1995). A test

for symmetry was used to detect any

systematic difference between the two

readers (Hoenig et al. 1995). Also, a random

sub-sample of 50 fish was selected for

second readings to measure reader precision

and age reproducibility. To detect any

changes or drift in our ageing methods, both

readers re-aged otoliths of 50 randomly

selected fish previously aged in 2000. We

considered a reader to be biased if the

readings revealed consistent over or under

ageing.

RESULTS

Measurements of reader precision were

high, with age disagreements for only 3 out

of 405 fish aged. Figure 2 illustrates the

between readers’ precision of age estimates.

Both reader 1 and reader 2 had 100 %

agreement for precision age reading. There

was no evidence of drift in age

determination, with 100% agreement on the

2000 precision fish for both readers.


classes were represented (Table 1). The

average age for the sample was 1.5 year old,

Figure 2. Between-reader comparison of otolith age

estimates for spot.

0 1 2 3 4 5

Reader 1

0

1

2

3

4

5

Reader 2

(26)

(247)(1)

(2)(57)

(56)

(15)

(1)


Figure 3. Year-class distribution for spot collected

for ageing in 2002. Distribution is

broken down by sex.

199719981999200020012002

Year Class

0

40

80

150

190

230

270

Number of Fish

Females n = 261

Males n = 118

Unknown n = 26



Page 12

and the standard deviation and standard


Year-class data (Figure 3) show that the

fishery was comprised of 6 year-classes,

with fish spawned in 2001 dominating the

catch.

Age-Length-Key In Table 2 we present

an age-length-key that can be used in the


estimated catch to numbers-at-age using

otolith ages. The table is based on VMRC’s

stratified sampling of landings by total

length inch intervals.

REFERENCES







1995. Analysing differences between

two age determination methods by

tests of symmetry. Can. J. Fish. Aquat.

Sci. 52:364-368.


Data Analysis Products Division.

Math Soft, Inc. Seattle, Washington.



Page 13

Table 1. The number of spot assigned to each totallength-at-age category for 405 fish sampled for agedetermination in Virginia during 2002 (Length not reported for 2 fish).

Length Age

1-inch 0 1 2 3 4 5

intervals Totals

6 - 6.99 2 0 0 0 0 0 2

7 - 7.99 14 32 0 0 0 0 46

8 - 8.99 9 87 1 0 0 0 97

9 - 9.99 0 79 9 0 0 0 88

10 - 10.99 0 37 19 1 0 0 57

11 - 11.99 0 12 21 26 3 0 62

12 - 12.99 0 1 7 17 10 1 36

13 - 13.99 0 0 1 12 2 0 15

Totals 25 248 58 56 15 1 403

Table 2. Age-Length key, as proportions-at-age ineach 1 inch length-class, based on otolith ages for spotsampled for age determination in Virginia during 2002(Length not reported for 2 fish).

Length Age

1-inch 0 1 2 3 4 5

intervals N

6 - 6.99 1.000 0.000 0.000 0.000 0.000 0.000 2

7 - 7.99 0.304 0.696 0.000 0.000 0.000 0.000 46

8 - 8.99 0.093 0.897 0.010 0.000 0.000 0.000 97

9 - 9.99 0.000 0.898 0.102 0.000 0.000 0.000 88

10 - 10.99 0.000 0.649 0.333 0.018 0.000 0.000 57

11 - 11.99 0.000 0.194 0.339 0.419 0.048 0.000 62

12 - 12.99 0.000 0.028 0.194 0.472 0.278 0.028 36

13 - 13.99 0.000 0.000 0.067 0.800 0.133 0.000 15

Sample Size 403

VMRC final report on finfish ageing, 2002 spotted seatrout


Page 14

Chapter 9 Spotted Seatrout

Cynoscion nebulosus

INTRODUCTION

A total of 354 spotted seatrout, Cynoscion

nebulosus, was collected by the VMRC’s

Stock Assessment Program for age and

growth analysis in 2002. We were unable to

age one fish due to the poor quality of

otoliths. The average age for the sample

was 1.5 years old, and the standard deviation

and standard error were 1.1 and 0.06,

respectfully. Six age classes (0 to 5) were

represented, comprising fish from the 1997-

2002 year-classes, with fish primarily from

the 2000 and 2001 year-classes.

METHODS



in labeled coin envelopes. They were sorted

based on date of capture, their envelope

labels were verified against VMRC’s

collection data, and each fish assigned a

unique Age and Growth Laboratory sample

number. All otoliths were stored dry in

labeled cell well trays.

Preparation The first step in seatrout

otolith preparation was to make a transverse

cut just off center of the otolith with a

Hillquist thin section machine’s cut-off saw

equipped with an HCR-100 diamond blade.

To prevent distortion of the reading surface,

the cut surface of the otolith half containing

the focus was ground down on a Hillquist

thin section machine’s 320 mesh diamond

cup wheel until perpendicular to the reading

plane. The otolith’s ground surface was

then placed face down in a drop of Loctite

349 photo-active adhesive on a labeled glass

slide and placed under ultraviolet light to

allow the adhesive to harden (approximately

ten minutes). The Hillquist thin section

machine’s cup wheel was used again to

grind the otolith, embedded in Loctite, to a

thickness of 0.3 to 0.5mm. Finally, a thin

layer of Flo-texx mounting medium was

applied to the otolith section to increase

light transmission through the translucent

zones, which provided enhanced contrast

and greater readability.



Page 15





100 times magnification (Figure 1). All

samples were aged in chronological order

based on collection date, without knowledge

of previously estimated ages or the specimen

lengths. When the readers’ ages agreed, that

age was assigned to the fish. When the two

readers disagreed, both readers sat down

together and re-aged the fish, again without

any knowledge of previously estimated ages

or lengths, and assigned a final age to the

fish. When the readers were unable to agree

on a final age, the fish was excluded from

further analysis.







readers (Hoenig et al. 1995). Also, both

readers aged all 50 fish a second time to

measure reader precision and age

reproducibility. To detect any changes or

drift in our ageing methods, both readers re-

aged otoliths of 50 randomly selected fish

previously aged in 2000. We considered a

reader to be biased if the readings revealed

consistent over or under ageing.

RESULTS



both readers equally able to reproduce the

ages of previously read samples. There was

also 100 percent agreement between reader

age estimates. Figure 2 illustrates the


There was no evidence of drift in age

determination from the 2000 precision fish

with 100% agreement for both readers.



average age for the sample was 1.5 years old,

and the standard deviation and standard


Figure 1. Sectioned otolith from an 8 year old

male spotted seatrout.



Page 16


fishery was comprised of 6 year-classes,

comprising fish from the 1997-2002 year-

classes, with fish primarily from the 2000

and 2001 year-classes.








REFERENCES










Sci. 52:364-368.





age estimates for spotted seatrout.

0 1 2 3 4 5

Reader 1

0

1

2

3

4

5

Reader 2

(61)

(121)

(129)

(19)

(17)

(6)


Figure 3. Year-class distribution for spotted

seatrout collected for ageing in 2002.


199719981999200020012002

Year Class

0

40

80

120

Number of Fish

Females n = 174

Males n = 179



Page 17

Table 1. The number of spotted seatrout assigned to each total length-at-age category for

353 fish sampled for age determination in Virginia during 2002 (no length for 1 fish).

Length Age (years)

1-inch 0 1 2 3 4 5

intervals Totals

11 - 11.99 36 0 0 0 0 0 36

12 - 12.99 24 2 0 0 0 0 26

13 - 13.99 1 5 0 0 0 0 6

14 - 14.99 0 2 0 0 0 0 2

15 - 15.99 0 13 0 0 0 0 13

16 - 16.99 0 17 2 0 0 0 19

17 - 17.99 0 30 6 0 0 0 36

18 - 18.99 0 24 5 0 0 0 29

19 - 19.99 0 14 25 0 0 0 39

20 - 20.99 0 11 29 4 0 0 44

21 - 21.99 0 2 9 3 1 0 15

22 - 22.99 0 0 20 5 4 0 29

23 - 23.99 0 0 19 2 4 1 26

24 - 24.99 0 0 12 1 6 3 22

25 - 25.99 0 0 2 2 1 1 6

26 - 26.99 0 0 0 1 1 0 2

28 - 28.99 0 0 0 1 0 0 1

29 - 29.99 0 0 0 0 0 1 1

Totals 61 120 129 19 17 6 352



Page 18


otolith ages for spotted seatrout sampled for age determination in Virginia during 2002.

Length Age (years)

1-inch 0 1 2 3 4 5

intervals N

11 - 11.99 1.000 0.000 0.000 0.000 0.000 0.000 36

12 - 12.99 0.923 0.077 0.000 0.000 0.000 0.000 26

13 - 13.99 0.167 0.833 0.000 0.000 0.000 0.000 6

14 - 14.99 0.000 1.000 0.000 0.000 0.000 0.000 2

15 - 15.99 0.000 1.000 0.000 0.000 0.000 0.000 13

16 - 16.99 0.000 0.895 0.105 0.000 0.000 0.000 19

17 - 17.99 0.000 0.833 0.167 0.000 0.000 0.000 36

18 - 18.99 0.000 0.828 0.172 0.000 0.000 0.000 29

19 - 19.99 0.000 0.359 0.641 0.000 0.000 0.000 39

20 - 20.99 0.000 0.250 0.659 0.091 0.000 0.000 44

21 - 21.99 0.000 0.133 0.600 0.200 0.067 0.000 15

22 - 22.99 0.000 0.000 0.690 0.172 0.138 0.000 29

23 - 23.99 0.000 0.000 0.731 0.077 0.154 0.038 26

24 - 24.99 0.000 0.000 0.545 0.045 0.273 0.136 22

25 - 25.99 0.000 0.000 0.333 0.333 0.167 0.167 6

26 - 26.99 0.000 0.000 0.000 0.500 0.500 0.000 2

29 - 29.99 0.000 0.000 0.000 0.000 0.000 1.000 1

Sample Size 352

VMRC final report on finfish ageing, 2002 striped bass


Page 19

Chapter 10 Striped Bass

Morone

saxatilis

INTRODUCTION

A total of 863 striped bass, Morone saxatilis,



analysis in 2002. Only otoliths were

collected from 12 fish and only scales were

collected from 565 fish, leaving 284 fish

from which both scales and otoliths were

collected. The average scale age was 8.0

years, with 17 age classes (2 to 16, 18, and

19) comprising fish from the 1983, 1984,

and 1986-2000 year-classes. The average

otolith age was 7.9 years, with 17 age

classes (2 to 14, 18, and 20 to 22)

comprising fish from the 1980-1982, 1984,

and 1988-2000 year-classes.

METHODS

Handling of collection Otoliths and

scales were received by the Age & Growth

Laboratory in labeled coin envelopes. Once

in our hands, they were sorted based on date

of capture, their envelope labels were

verified against VMRC’s collection data,

and each fish assigned a unique Age and

Growth Laboratory sample number. All


plates, while scales were stored in their

original coin envelopes.

Preparation

Scales – Striped bass scales were prepared

for age and growth analysis by making

acetate impressions of the scale

microstructure. Due to extreme variation in

the size and shape of scales from individual

fish, we selected only those scales that had

even margins and uniform size. We selected

a range of four to six preferred scales (based

on overall scale size) from each fish, making

sure that only non-regenerated scales were

used. Scale impressions were made on

extruded clear 020 acetate sheets (25mm x

75mm) with a Carver Laboratory Heated

Press (model “C”). The scales were pressed

with the following settings:

Pressure: 15000 psi

Temperature: 77°C (170°F)

Time: 5 to 10 min



Page 20

Striped bass scales that were the size of a

quarter (coin) or larger, were pressed

individually for up to twenty minutes. After

pressing, the impressions were viewed with

a Bell and Howell microfiche reader and

checked again for regeneration and

incomplete margins. Impressions that were

too light, or when all scales were

regenerated a new impression was made

using different scales from the same fish.

Otoliths We used a “thin-section and

bake” technique to process striped bass

otoliths for age determination. Otolith

preparation began by randomly selecting

either the right or left otolith. The otolith

was mounted with Crystal Bond onto a

standard microscope slide with its distal

surface orientated upwards. Once mounted,

a small mark was placed on the otolith


slide, with attached otolith, was then secured

to an Isomet saw equipped with two

diamond wafering blades separated by a 0.5

mm spacer, which was slightly smaller in

diameter than the diamond blades. The

otolith was positioned so that the wafering

blades straddled each side of the otolith

focus ink mark. It was crucial that this cut be

perpendicular to the long axis of the otolith.

Failure to do so resulted in “broadening”

and distortion of winter growth zones. A

proper cut resulted in annuli that were

clearly defined and delineated. Once cut,

the otolith section was placed into a ceramic



time was otolith size dependent and gauged

by color, with a light caramel color desired.

Once a suitable color was reached the baked

thin-section was placed on a labeled glass

slide and covered with a thin layer of Flo-

texx mounting medium, which provided

enhanced contrast and greater readability by

increasing light transmission through the

sections.



Hemisphere fish species. We use a system

of age determination that assigns age class

according to the date of sacrifice with

respect to this international accepted

birthdate and the timing of annulus

formation, which occurs between the months

of May and June for striped bass. Once the

reader decides how many annuli are visible

on the ageing structure, the year class is

assigned. The year class designation, or age,

is written first followed by the actual

number of annuli visible listed within

brackets (e.g. 3(3)). The presence of a “+”

after the number in the brackets indicates

new growth, or “plus growth” visible on the

structure’s margin. Using this method, a

fish sacrificed in January before annulus

formation with three visible annuli would be

assigned the same age, 4(3), as a fish with

four visible annuli sacrificed in July after

annulus formation, 4(4).

Two different readers aged all samples in

chronological order based on collection date,

without knowledge of previously estimated

ages or the specimen lengths. When the

readers’ ages agreed, that age was assigned

to the fish. When the two readers disagreed,

both readers sat down together and re-aged

the fish, again without any knowledge of



age readers were unable to agree on a final



Page 21

age, the fish was excluded from further

analysis.

Scales - We determined fish age by viewing

acetate impressions of scales (Figure 1) with

a standard Bell and Howell R-735

microfiche reader equipped with 20 and 29

mm lenses.

Annuli on striped bass scales are identified

based on two scale microstructure features,

“crossing over” and circuli disruption.

Primarily, “crossing over” in the lateral

margins near the posterior\anterior interface

of the scale is used to determine the origin

of the annulus. Here compressed circuli

(annulus) “cross over” the previously

deposited circuli of the previous year’s

growth. Typically annuli of the first three

years can be observed transversing this

interface as dark bands. These bands remain

consistent throughout the posterior field and

rejoin the posterior\anterior interface on the

opposite side of the focus. Annuli can also

be observed in the anterior lateral field of

the scale. Here the annuli typically reveal a

pattern of discontinuous and suddenly

breaking segmented circuli. This event can

also be distinguished by the presence of

concentric white lines, which are typically

associated with the disruption of circuli.

Annuli can also be observed bisecting the

perpendicular plain of the radial striations in

the anterior field of the scale. Radii emanate

out from the focus of the scale towards the

outer corner margins of the anterior field.

These radial striations consist mainly of

segmented concave circuli. The point of

intersection between radii and annuli results

in a “straightening out” of the concave

circuli. This straightening of the circuli

should be consistent throughout the entire

anterior field of the scale. This event is

further amplified by the presence of concave

circuli neighboring both directly above and

below the annulus.

The first year’s annulus can be difficult to

locate on some scales. It is typically best

identified in the lateral field of the anterior

portion of the scale. The distance from the

focus to the first year’s annulus is typically

larger with respect to the following few

annuli. For the annuli two through six,

summer growth generally decreases

proportionally. For ages greater than six, a

crowding effect of the annuli near the outer

margins of the scale is observed. This

crowding effect creates difficulties in edge

interpretation. At this point it is best to

focus on the straightening of the circuli at

the anterior margins of the scale.

When ageing young striped bass, zero

through age two, extreme caution must be

taken as not to over age the structure.

Young fish have no point of reference to aid

in the determination of the first year; this

invariably results in over examination of the

scale and such events as hatching or

Figure 1. Scale impression of a 5-year-old male

striped bass.



Page 22

saltwater incursion marks (checks) may be

interpreted as the first year.

Otoliths – Sectioned otoliths were aged by





By convention an annulus is identified as the

narrow opaque zone, or winter growth.

Typically the first year’s annulus can be

determined by first locating the focus of the

otolith. The focus is generally located,

depending on preparation, in the center of

the otolith, and is visually well defined as a

dark oblong region. The first year’s annulus

can be located directly below the focus,

along the outer ridge of the sulcal groove on

the ventral and dorsal sides of the otolith.

This insertion point along the sulcal ridge

resembles a check mark (not to be confused

with a false annulus). Here the annulus can

be followed outwards along the ventral and

dorsal surfaces where it encircles the focus.

Subsequent annuli also emanate from the

sulcal ridge, however, they do not encircle

the focus, but rather travel outwards to the

distal surface of the otolith. To be

considered a true annulus, each annulus

must be rooted in the sulcus and travel

without interruption to the distal surface of

the otolith. The annuli in striped bass have a

tendency to split as they advance towards

the distal surface. As a result, it is critical

that reading path proceed in a direction

down the sulcal ridge and outwards to the

distal surface.










and age reproducibility. We considered a



RESULTS

Figure 2. Otolith thin-section of a 5-year-old

male striped bass.



Page 23

Scales Measurements of reader self-

precision were high, with both readers able

to reproduce the ages of previously read

scales (reader 1’s CV = 4.4% and reader 2’s

CV = 3.5%). In Figure 3 we present a graph

of the results for between-reader scale

ageing precision. There was good between-

reader agreement for scale age readings,

with age differences between the two

readers one year or less for 93.2% of all

aged fish. The average between-reader

coefficient of variation (CV) of 4.3% was

not significant, and comparable to the CV of

4.4% from 2001. There was evidence of

systematic disagreement between reader 1

and reader 2 (test of symmetry, 2 = 78.4,

df = 37, P < 0.01), with reader 1 tending to

age fish older than reader 2.

Of the 849 striped bass aged with scales, 17

age classes (2 to 16, 18, and 19) were

represented. The average age for the sample

was 8.0 years. The standard deviation and



recruitment into the fishery typically begins

at age 3, which corresponds to the 1999

year-class for striped bass caught in 2002.

Striped bass appear to fully recruit to the

fishery at age 6 (1996 year-class).

Otoliths There was good between-reader

agreement for otolith age readings using

sectioned otoliths, with age differences

between the two readers one year or less for

97.6% of all aged fish (Figure 5). The

between reader average CV for otolith age

estimates was only 1.5%, slightly less than

the CV of 2.4% reported for 2001 fish.

Unlike scale ages, there was no evidence of



df = 17, P = 0.08.

Figure 4. Year-class frequency distribution for

striped bass collected for ageing in

2002. Distribution of scale ages is

broken down by sex.

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000Year Class

0

50

100

150

Number of Fish

Females n = 242

Males n = 267

Unknown n = 340

Figure 3. Between-reader comparison of scale

age estimates for striped bass.

2345678910111213141516171819

Reader 1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

Reader 2

(2)

(1)(13)(1)(1)

(7)(24)(2)

(8)(45)(9)(1)

(1)(18)(113)(15)(1)(1)

(1)(36)(91)(10)(6)

(4)(36)(52)(28)(2)

(6)(19)(88)(12)(2)(1)

(1)(1)(35)(32)(5)(1)(1)

(7)(10)(26)(5)(3)

(1)(2)(6)(13)(6)(1)(3)

(1)(1)(2)(10)(1)(1)

(1)(2)(2)(3)(1)

(1)(1)(1)

(1)

(1)

(1)(1)

(1)

scale Ages (years)



Page 24



ages of previously read otoliths (Reader 1’s

CV = 0.2% and Reader 2’s CV = 1.7%).

Seventeen age classes (2-14, 18, and 20-22)

were represented for striped bass aged with

otoliths. The average age for the sample was

7.8 years. The standard deviation and


Comparison of Scale and Otolith Ages

While the CV of otolith and scales age

estimates was only 6.3%, there was

significant evidence of systematic

disagreement between otolith and scale ages

(test of symmetry, 2 = 64.3, df = 28, P <

0.01). Scales were assigned a lower age

than otoliths for 32% of the fish. Only

14.8% of the time were scales assigned a

higher age than otoliths (Figure 6). There

was also evidence of bias between otolith

and scale ages using an age bias plot (Figure

7), again with scales generally assigned

lower ages than otoliths.





scale ages. The table is based on VMRC’s



RECOMMENDATIONS

We recommend that VMRC and ASMFC

use otoliths for ageing striped bass.

Although there is more preparation time for

otoliths compared to scales, as the mean age

of striped bass increases in the recovering

fishery, otoliths should provide more

reliable estimates of age. We will continue

to compare the age estimates between

otoliths and scales.


otolith age estimates for striped

bass.

2345678910111213141516171819202122

Reader 1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22Reader 2

(4)(1)(12)(1)(9)(1)(4)(1)(1)(67)(4)(43)(1)(4)(2)(16)(3)(2)(62)(9)(13)(1)(1)(10)(1)(3)(2)(1)(8)(1)(1)(1)(1)(2)

(1)(1)(1)

(1)


Figure 6. Comparison of otolith and scale age

estimates for striped bass.

2345678910111213141516171819202122

Otolith Age (years)

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

Scale Age (years)

(1)(3)(7)(4)(6)(3)

(1)

(4)(1)(10)(45)(14)(2)(1)

(2)(13)(25)(5)(1)

(4)(4)(6)(1)

(1)

(2)(8)(18)(39)(3)(1)

(1)(4)(10)(1)(4)(5)(1)

(2)(3)(2)(3)(2)(3)(1)

(2)(1)

(1)

(1)

(1)

(1)



Page 25

REFERENCES










Sci. 52:364-368.

S-PLUS. 1999. Guide to Statistics, Vol 1.

Data Analysis and Products Division.

MathSoft, Inc. Seattle, Washington.

Figure 7. Age-bias plot for striped bass scale

and otolith age estimates.

246810121416182022

Otolith Age (years)

2

4

6

8

10

12

14

16

18

20

22

Scale Age +/- 95% Confidence Intervals



Page 26

Table 1. The number of striped bass assigned to each total length-at-age category for fish


Length Age (years)

1-inch 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 18 19

intervals Totals

12 - 12.99 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1

13 - 13.99 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1

14 - 14.99 0 3 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4

15 - 15.99 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2

16 - 16.99 1 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4

17 - 17.99 0 1 2 1 1 0 0 0 0 0 0 0 0 0 0 0 0 5

18 - 18.99 1 2 8 2 3 1 0 0 0 0 0 0 0 0 0 0 0 17

19 - 19.99 1 3 5 16 8 1 0 0 0 0 0 0 0 0 0 0 0 34

20 - 20.99 0 0 5 11 17 10 0 2 0 0 0 0 0 0 0 0 0 45

21 - 21.99 0 1 3 5 16 12 2 3 0 0 0 0 0 0 0 0 0 42

22 - 22.99 0 1 2 8 20 15 3 4 0 1 0 0 0 0 0 0 0 54

23 - 23.99 0 0 2 6 15 10 5 8 2 0 0 0 0 0 0 0 0 48

24 - 24.99 0 1 1 4 8 8 11 4 1 0 0 0 0 0 0 0 0 38

25 - 25.99 0 0 0 2 12 10 7 13 2 0 0 0 0 0 0 0 0 46

26 - 26.99 0 0 0 1 10 8 5 4 4 1 0 0 0 0 0 0 0 33

27 - 27.99 0 0 0 1 12 10 8 4 1 0 0 0 0 0 0 0 0 36

28 - 28.99 0 0 0 1 13 12 4 4 1 0 1 0 0 0 0 0 0 36

29 - 29.99 0 0 0 0 6 8 5 7 1 0 0 0 0 0 0 0 0 27

30 - 30.99 0 0 0 0 3 13 5 4 2 0 0 0 0 1 1 0 0 29

31 - 31.99 0 0 0 0 1 8 5 8 2 0 0 1 0 0 1 0 0 26

32 - 32.99 0 0 0 0 1 5 9 20 1 1 0 1 0 1 0 0 0 39

33 - 33.99 0 0 0 0 0 5 5 19 8 2 3 1 1 0 0 0 0 44

34 - 34.99 0 0 0 0 0 3 6 22 10 4 8 2 0 0 0 1 0 56

35 - 35.99 0 0 0 0 1 0 9 19 9 4 6 1 0 0 0 0 0 49

36 - 36.99 0 0 0 0 1 1 2 12 10 10 3 5 0 0 0 0 0 44

37 - 37.99 0 0 0 0 0 1 1 5 8 9 1 3 1 0 1 0 0 30

38 - 38.99 0 0 0 0 1 0 1 4 2 5 4 1 0 0 0 0 0 18

39 - 39.99 0 0 0 0 0 0 0 1 3 3 0 2 0 2 0 0 0 11

40 - 40.99 0 0 0 0 0 0 0 0 0 3 0 1 2 0 1 0 0 7

41 - 41.99 0 0 0 0 0 0 0 0 0 2 1 0 0 1 0 0 0 4

42 - 42.99 0 0 0 0 0 0 0 1 0 2 0 1 1 0 0 1 0 6

43 - 43.99 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 2

44 - 44.99 0 0 0 0 0 0 0 0 0 0 1 0 0 1 1 0 0 3

45 - 45.99 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 2

46 - 46.99 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1

49 - 49.99 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1

Totals 3 18 30 58 149 141 93 169 67 48 28 19 5 7 7 2 1 845



Page 27

Table 2. Age-Length key, as proportions-at-age in each 1 inch length-class, based on scale ages

for striped bass sampled for age determination in Virginia during 2002.Length Age (years)

1-inch 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 18 19

intervals N

12 - 12.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

13 - 13.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

14 - 14.99 0.000 0.750 0.250 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 4

15 - 15.99 0.000 0.500 0.500 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 2

16 - 16.99 0.250 0.750 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 4

17 - 17.99 0.000 0.200 0.400 0.200 0.200 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 5

18 - 18.99 0.059 0.118 0.471 0.118 0.176 0.059 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 17

19 - 19.99 0.029 0.088 0.147 0.471 0.235 0.029 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 34

20 - 20.99 0.000 0.000 0.111 0.244 0.378 0.222 0.000 0.044 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 45

21 - 21.99 0.000 0.024 0.071 0.119 0.381 0.286 0.048 0.071 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 42

22 - 22.99 0.000 0.019 0.037 0.148 0.370 0.278 0.056 0.074 0.000 0.019 0.000 0.000 0.000 0.000 0.000 0.000 0.000 54

23 - 23.99 0.000 0.000 0.042 0.125 0.313 0.208 0.104 0.167 0.042 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 48

24 - 24.99 0.000 0.026 0.026 0.105 0.211 0.211 0.289 0.105 0.026 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 38

25 - 25.99 0.000 0.000 0.000 0.043 0.261 0.217 0.152 0.283 0.043 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 46

26 - 26.99 0.000 0.000 0.000 0.030 0.303 0.242 0.152 0.121 0.121 0.030 0.000 0.000 0.000 0.000 0.000 0.000 0.000 33

27 - 27.99 0.000 0.000 0.000 0.028 0.333 0.278 0.222 0.111 0.028 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 36

28 - 28.99 0.000 0.000 0.000 0.028 0.361 0.333 0.111 0.111 0.028 0.000 0.028 0.000 0.000 0.000 0.000 0.000 0.000 36

29 - 29.99 0.000 0.000 0.000 0.000 0.222 0.296 0.185 0.259 0.037 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 27

30 - 30.99 0.000 0.000 0.000 0.000 0.103 0.448 0.172 0.138 0.069 0.000 0.000 0.000 0.000 0.034 0.034 0.000 0.000 29

31 - 31.99 0.000 0.000 0.000 0.000 0.038 0.308 0.192 0.308 0.077 0.000 0.000 0.038 0.000 0.000 0.038 0.000 0.000 26

32 - 32.99 0.000 0.000 0.000 0.000 0.026 0.128 0.231 0.513 0.026 0.026 0.000 0.026 0.000 0.026 0.000 0.000 0.000 39

33 - 33.99 0.000 0.000 0.000 0.000 0.000 0.114 0.114 0.432 0.182 0.045 0.068 0.023 0.023 0.000 0.000 0.000 0.000 44

34 - 34.99 0.000 0.000 0.000 0.000 0.000 0.054 0.107 0.393 0.179 0.071 0.143 0.036 0.000 0.000 0.000 0.018 0.000 56

35 - 35.99 0.000 0.000 0.000 0.000 0.020 0.000 0.184 0.388 0.184 0.082 0.122 0.020 0.000 0.000 0.000 0.000 0.000 49

36 - 36.99 0.000 0.000 0.000 0.000 0.023 0.023 0.045 0.273 0.227 0.227 0.068 0.114 0.000 0.000 0.000 0.000 0.000 44

37 - 37.99 0.000 0.000 0.000 0.000 0.000 0.033 0.033 0.167 0.267 0.300 0.033 0.100 0.033 0.000 0.033 0.000 0.000 30

38 - 38.99 0.000 0.000 0.000 0.000 0.056 0.000 0.056 0.222 0.111 0.278 0.222 0.056 0.000 0.000 0.000 0.000 0.000 18

39 - 39.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.091 0.273 0.273 0.000 0.182 0.000 0.182 0.000 0.000 0.000 11

40 - 40.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.429 0.000 0.143 0.286 0.000 0.143 0.000 0.000 7

41 - 41.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.500 0.250 0.000 0.000 0.250 0.000 0.000 0.000 4

42 - 42.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.167 0.000 0.333 0.000 0.167 0.167 0.000 0.000 0.167 0.000 6

43 - 43.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.500 0.000 0.000 0.000 0.000 0.500 0.000 0.000 2

44 - 44.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.333 0.000 0.000 0.333 0.333 0.000 0.000 3

45 - 45.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.500 0.000 0.000 0.000 0.000 0.000 0.000 0.500 0.000 0.000 2

46 - 46.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000 1

49 - 49.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000 1

Sample Size 845

VMRC final report on finfish ageing, 2002 summer flounder


Page 28

Chapter 11 Summer Flounder

Paralichthys

dentatus

INTRODUCTION

A total of 324 summer flounder,

Paralichthys dentatus, was collected by the

VMRC’s Stock Assessment Program for age

and growth analysis in 2002. Only otoliths

were collected from 5 fish and only scales

were collected from 21 fish, leaving 303 fish

for which both scales and otoliths were

collected. The average scale age was 2.9

years, representing 9 year-classes (1992, and

1995 to 2002). Fish from the 1998-2001

year-classes dominated the collection. The

average otolith age was 3.0 years,

representing 9 year-classes (1992, and 1994

to 2001).

METHODS


scales were received by the Age & Growth

Laboratory in labeled coin envelopes. Once

in our hands, they were sorted based on date

of capture, their envelope labels were

verified against VMRC’s collection data,

and each fish assigned a unique Age and

Growth Laboratory sample number. All


plates, while scales were stored in their

original coin envelopes.

Preparation

Scales – Summer flounder scales were

prepared for age and growth analysis by

making acetate impressions of the scale

microstructure. Due to extreme variation in

the size and shape of scales from individual

fish, we selected only those scales that had

even margins and uniform size. We selected

a range of five to ten preferred scales (based

on overall scale size) from each fish, making

sure that only non-regenerated scales were

used. Scale impressions were made on

extruded clear 020 acetate sheets (25mm x

75mm) with a Carver Laboratory Heated

Press (model “C”). The scales were pressed

with the following settings:

Pressure: 12000 to 15000 psi

Temperature: Room temperature

Time: two to three minutes



Page 29

Otoliths – The left otoliths of summer

flounder are symmetrical in relation to the

otolith nucleus, while right otoliths are

asymmetrical (Figure 1). The right otolith

was mounted with Crystal Bond onto a

standard microscope slide with its distal

surface orientated upwards. Once mounted,

a small mark was placed on the otolith


slide, with attached otolith, was then secured

to an Isomet saw equipped with two

diamond wafering blades separated by a 0.5

mm spacer, which was slightly smaller in

diameter than the diamond blades. The

otolith was positioned so that the wafering

blades straddled each side of the otolith

focus ink mark. It was crucial that this cut be

perpendicular to the long axis of the otolith.

Failure to do so resulted in “broadening”

and distortion of winter growth zones. A

proper cut resulted in annuli that were

clearly defined and delineated. Once cut,

the otolith section was placed into a ceramic



time was otolith size dependent and gauged

by color, with a light caramel color desired.

Once a suitable color was reached the baked

thin-section was placed on a labeled glass

slide and covered with a thin layer of Flo-

texx mounting medium, which provided

enhanced contrast and greater readability by

increasing light transmission through the

sections.



Hemisphere fish species. The Age and

Growth Lab uses a system of age

determination that assigns age class

according to the date of sacrifice with

respect to this international accepted

birthdate and the timing of annulus

formation, which occurs in Virginia’s waters

between the months of February and April.

Using this method, a fish sacrificed in

January before annulus formation with three

visible annuli will be assigned the same age

as a fish with four visible annuli sacrificed

in July after annulus formation. Once the

reader has decided how many annuli are

visible on the ageing structure, the year class

is assigned. The year class designation, or

age, is written first followed by the actual

number of annuli visible listed within

brackets (e.g. 3(3)). The presence of a “+”

after the number in the brackets indicates

new growth, or “plus growth” visible on the

structure’s margin.










(a) (b)

Figure 1. Whole otoliths from a 485 mm (total

length) female summer flounder. (a) left otolith

(b) right otolith.



Page 30




Scales - We determined fish age by viewing

the acetate impressions of scales (Figure 2)

with a standard Bell and Howell R-735

microfiche reader equipped with 20 and 29

mm lenses.

Annuli on summer flounder scales are

primarily identified by the presence of

crossing over of circuli. Crossing over is

most evident on the lateral margins near the

posterior/anterior interface of the scale.

Here compressed circuli (annulus) “cross

over” the deposited circuli of the previous

year’s growth. Typically the annulus will

protrude partially into the ctenii of the

posterior field, but not always. Following

the annulus up into the anterior field of the

scale reveals a pattern of discontinuous and

suddenly breaking segmented circuli. This

event can also be distinguished by the

presence of concentric white lines, which

are associated with the disruption of circuli.

This pattern should be continuous

throughout the entire anterior field of the

scale. Locating the first annulus can be

difficult due to latitudinal differences in

growth rates and changes in the size of the

first annulus due to a protracted spawning

season. We consider the first annulus to be

the first continuous crossing over event

formed on the scale.

Otoliths – Sectioned otoliths were aged by





Summer flounder otoliths are composed of

visually distinct summer and winter growth

zones. By convention, an annulus is

identified as the narrow opaque zone, or

winter growth band. With sectioned otoliths,

to be considered a true annulus, these

growth bands must be rooted in the sulcus

and able to be followed, without interruption

to the distal surface of the otolith. The

annuli in summer flounder have a tendency

to split as they advance towards the distal

surface. As a result, it is critical that the

reading path proceeds in a direction from the

sulcus to the proximal surface. The first

annulus is located directly below the focus

and near the upper portion of the sulcal

groove. The distance from the focus to the

first year is moderate, with translucent zone

deposition gradually becoming smaller as

consecutive annuli are deposited towards the

outer edge.

Figure 2. Scale impression of a 590 mm female

summer flounder collected in

November and aged as 4-years-old

with scales. The question mark is

located at a possible “3rd” annulus.



Page 31













RESULTS

Scales Measurements of reader self-



scales (reader 1’s CV = 1.6% and reader 2’s

CV = 1.9%). There was no evidence of



df = 9, P = 0.2). In Figure 4 we present a

graph of the results for between-reader scale

ageing precision. The average between-

reader coefficient of variation (CV) of 3.5%

was not significant, and slightly lower than

the CV of 4.2% from 2001.

Of the 324 fish aged with scales, 9 age-

classes (0 to 7, and 10) were represented

(Table 1). The average scale age was 2.9

years, and the standard deviation and

standard error were 1.4 and 0.1,

respectfully.

Year-class data (Figure 5) indicate that

recruitment into the fishery began at age 0,

which corresponds to the 2002 year-class for

summer flounder caught in 2002. Year-class

abundance was high for the 1999–2001

year-classes, but declined sharply in the

1998 year-class and remained low for the

Figure 3. Otolith section from a 590 mm, 6-

year-old female summer flounder

collected in November. Same fish as

Figure 2.

Figure 5. Scale year-class distribution for

summer flounder collected in 2002.


19921993199419951996199719981999200020012002

Year Class

0

20

40

60

80

100

Number of Fish

Females n = 305

Males n = 14

Unknown n = 5

Figure 4. Between-reader comparison of scale

age estimates for summer flounder.

012345678910

Reader 1

0

1

2

3

4

5

6

7

8

9

10

Reader 2

(1)

(44)(3)

(5)(74)(2)

(6)(99)(3)

(11)(31)(2)

(1)(2)(16)(1)

(1)(4)(11)(2)

(3)(1)

(1)

scale Ages (years)



Page 32

earlier years.

Otoliths Measurements of reader self-



otoliths (reader 1’s CV = 0.0% and reader

2’s CV = 0.6%). There was no evidence of


and reader 2 (test of symmetry, 2 = 3, df

= 4, P = 0.56). In Figure 6 we present a

graph of the results for between-reader

otolith ageing precision. The average

between-reader coefficient of variation (CV)

of 0.3% was not significant, and less than

the CV of 1.6% reported in 2001.

Of the 308 fish aged with otoliths, 9 age-

classes (1 to 8, and 10) were represented.

The average age for the sample was 3.0

years. The standard deviation and standard


Comparison of Scale and Otolith Ages

Otolith and scales ages were similar, with an

average CV of 3.2% for the 303 fish for

which both otoliths and scales were

collected. There was no evidence of

systematic disagreement between otolith and

scale ages (test of symmetry, 2 = 9.5, df

= 12, P = 0.66). In Figure 7 we present a


otolith/scale ageing precision. There was

some evidence of bias between otolith and

scale ages for the oldest fish in the sample

(Figure 8), but this could be due to the

extremely small number of fish in these age

categories.





otolith ages. The table is based on VMRC’s Figure 6. Between-reader comparison of otolith

age estimates for summer flounder.

12345678910

Reader 1

1

2

3

4

5

6

7

8

9

10

Reader 2

(47)

(70)(1)

(1)(112)(1)

(36)(1)

(18)

(16)

(2)(1)

(2)

(1)


Figure 7. Comparison of otolith and scale age

estimates for summer flounder.

12345678910

Otolith Age (years)

1

2

3

4

5

6

7

8

9

10

Scale Age (years)

(44)

(1)

(1)

(1)

(63)

(4)

(7)

(100)

(5)

(1)

(3)

(30)

(3)

(1)

(1)

(14)

(2)

(1)

(3)

(11)

(1)

(1)

(1)

(2)

(1)

(1)

Figure 8. Age-bias plot for summer flounder

scale and otolith age estimates.

12345678910

Otolith Age (years)

1

2

3

4

5

6

7

8

9

10

Scale Age +/- 95% Confidence Intervals



Page 33



REFERENCES

Bolz, G., R. Monaghan, K. Lang, R. Gregory,

and J. Burnett. 1999. Proceedings of

the summer flounder ageing workshop,

1-2 February 1999, Woods Hole, MA. .

NOAA Tech. Memo, in press.










Sci. 52:364-368.






Page 34

Table 1. The number of summer flounder assigned to each total length-at-age

category for 324 fish sampled for age determination in Virginia during 2002.

Length Age (years)

1-inch 0 1 2 3 4 5 6 7 10

intervals Totals

9 - 9.99 1 0 0 0 0 0 0 0 0 1

11 - 11.99 0 1 0 0 0 0 0 0 0 1

12 - 12.99 0 2 0 0 0 0 0 0 0 2

13 - 13.99 0 8 1 0 0 0 0 0 0 9

14 - 14.99 0 24 15 0 0 0 0 0 0 39

15 - 15.99 0 10 19 9 0 2 1 0 0 41

16 - 16.99 0 2 19 19 2 2 0 0 0 44

17 - 17.99 0 1 15 38 6 1 0 0 0 61

18 - 18.99 0 0 9 29 10 1 1 0 0 50

19 - 19.99 0 0 1 13 7 6 1 0 0 28

20 - 20.99 0 0 1 1 8 4 2 0 0 16

21 - 21.99 0 0 0 3 3 2 2 1 0 11

22 - 22.99 0 0 0 1 2 0 4 0 1 8

23 - 23.99 0 0 0 0 1 3 1 0 0 5

24 - 24.99 0 0 0 0 0 0 4 1 0 5

25 - 25.99 0 0 0 0 0 1 0 0 0 1

26 - 26.99 0 0 0 0 0 0 1 1 0 2

Totals 1 48 80 113 39 22 17 3 1 324



Page 35


scale ages for summer flounder sampled for age determination in Virginia during 2002.

Length Age (years)

1-inch 0 1 2 3 4 5 6 7 10

intervals N

9 - 9.99 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

11 - 11.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

12 - 12.99 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 2

13 - 13.99 0.000 0.889 0.111 0.000 0.000 0.000 0.000 0.000 0.000 9

14 - 14.99 0.000 0.615 0.385 0.000 0.000 0.000 0.000 0.000 0.000 39

15 - 15.99 0.000 0.244 0.463 0.220 0.000 0.049 0.024 0.000 0.000 41

16 - 16.99 0.000 0.045 0.432 0.432 0.045 0.045 0.000 0.000 0.000 44

17 - 17.99 0.000 0.016 0.246 0.623 0.098 0.016 0.000 0.000 0.000 61

18 - 18.99 0.000 0.000 0.180 0.580 0.200 0.020 0.020 0.000 0.000 50

19 - 19.99 0.000 0.000 0.036 0.464 0.250 0.214 0.036 0.000 0.000 28

20 - 20.99 0.000 0.000 0.063 0.063 0.500 0.250 0.125 0.000 0.000 16

21 - 21.99 0.000 0.000 0.000 0.273 0.273 0.182 0.182 0.091 0.000 11

22 - 22.99 0.000 0.000 0.000 0.125 0.250 0.000 0.500 0.000 0.125 8

23 - 23.99 0.000 0.000 0.000 0.000 0.200 0.600 0.200 0.000 0.000 5

24 - 24.99 0.000 0.000 0.000 0.000 0.000 0.000 0.800 0.200 0.000 5

25 - 25.99 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000 1

26 - 26.99 0.000 0.000 0.000 0.000 0.000 0.000 0.500 0.500 0.000 2

Sample Size 324

VMRC final report on finfish ageing, 2002 tautog


Page 36

Chapter 11 Tautog

Tautoga

onitis

INTRODUCTION

A total of 374 tautog, Tautoga onitis, was

collected by the VMRC’s Stock Assessment

Program for age and growth analysis in

2002. Otoliths were not collected from 3 fish

and opercula were not collected from 2 fish,

leaving 369 fish for which both otoliths and

opercula were collected. Our results and

analyses are based on operculum ages,

unless otherwise noted, to allow our data to

be directly comparable to other tautog age

and growth studies. The average operculum

age for the sample was 4.8 years, and the

standard deviation and standard error were

2.8 and 0.1, respectfully. Fourteen age-

classes (2-14, and 16) were represented,

comprising fish from the 1986 and 1988

through 2000 year-classes.

METHODS


opercula were received by the Age &

Growth Laboratory in labeled coin

envelopes. Once in our hands, they were

sorted based on date of capture, their

envelope labels were verified against

VMRC’s collection data, and each fish

assigned a unique Age and Growth

Laboratory sample number. All otoliths

were stored dry in labeled cell well plates,

while opercula were stored frozen in their

original coin envelopes until processed.

Preparation

Opercula – Tautog opercula were boiled for

several minutes to remove any attached skin

and muscle tissue. After boiling, opercula

were examined to determine whether they

were collected whole or in some way

damaged. Opercula were allowed to dry and

finally stored in new labeled coin envelopes.

Otoliths – Because of the small size of a

tautog otolith, it required extra steps in

preparation for ageing. An otolith was first

baked in a Thermolyne 1400 furnace at

400 C for one to two minutes until it turned

a medium brown color (caramel). The

location of the core of the otolith was

marked with a felt pen and the entire otolith

was embedded in Loctite 349 adhesive,

placed under UV light, and allowed to

harden overnight. The otolith was then

transversely sectioned through the felt pen

mark with a low speed Buehler Isomet saw

equipped with double wafering blades

separated by a 0.5 mm spacer. The sectioned

side of the otolith was then placed face



Page 37

down in a drop of Loctite 349 photo-active

adhesive on a labeled glass slide and placed

under ultraviolet light to allow the adhesive

to harden (approximately ten minutes). The

otolith section was then polished using a

Buehler Ecomet 3 variable speed grinder-

polisher with Mark V Laboratory 30-micron

polishing film. After polishing, a thin layer

of Flo-texx mounting medium was applied

to the otolith section to increase light

transmission through the translucent zones,

which provided enhanced contrast and

greater readability.

Readings

table with no magnification (Figure 1).

Sectioned otoliths were aged by two

different readers using a Leica MZ-12





chronological order based on collection

date, without knowledge of previously

estimated ages or the specimen lengths.

When the readers’ ages agreed, that age

was assigned to the fish. When the two

readers disagreed, both readers sat down

together and re-aged the fish, again without

any knowledge of previously estimated ages

or lengths, and assigned a final age to the

fish. When the readers were unable to agree

on a final age, the fish was excluded from

further analysis.












consistent over or under ageing

RESULTS

Figure 1. Operculum from a 13 year-old male

tautog.

Figure 2. Otolith section from a 13 year-old

male tautog. Same fish as Figure 1.



Page 38

Opercula Measurements of reader self-



opercula (Reader 1’s CV = 1.0% and Reader

2’s CV = 3.8%). In Figure 3 we present a


operculum ageing precision. There was no

evidence of systematic disagreement

between reader 1 and reader 2 (test of

symmetry, 2 = 24.1, df = 17, P = 0.12).

The average between-reader coefficient of

variation (CV) of 3.6% was slightly lower

than the 4.3% reported last year.

The average operculum age for the sample

was 4.8 years, and the standard deviation

and standard error were 2.8 and 0.1,

respectfully.

Year-class data (Figure 4) indicate that full

recruitment into the fishery occurred at age

three, which corresponds to the 1999 year-

class for tautog caught in 2002. Year-class

abundance was high for the 1996–2000

year-classes.

Otoliths Measurements of reader self-



otoliths (reader 1’s CV = 0.7% and reader

2’s CV = 0.9%). There was no evidence of



df = 13, P = 0.48). In Figure 5 we present a


otolith ageing precision. The average

between-reader coefficient of variation (CV)

of 0.9 % was not significant, and slightly

smaller than the CV of 1.4% reported last

year.


operculum age estimates for tautog.

2345678910111213141516

Reader 1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

Reader 2

(55)(9)

(7)(85)(5)

(1)(10)(44)(9)

(2)(40)(3)

(4)(23)(1)

(4)(4)(1)

(1)(19)(4)

(7)(3)

(2)(10)(1)(1)

(1)(2)(1)(1)

(1)(2)(1)(1)

(1)(2)(1)

(2)

(1)

Opercle Ages (years)

Figure 4. Operculum year-class distribution for

tautog collected in 2002.


1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

Year Class

0

20

40

60

80

100

Number of Fish

Females n = 173

Males n = 198

Unknown n = 1

Figure 6. Comparison of otolith and operculum

age estimates for tautog.

23456789101112131415161718

Otolith Age (years)

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

Operculum Age (years)

(54)

(6)

(1)

(7)

(93)

(11)

(1)

(38)

(4)

(1)

(4)

(45)

(7)

(2)

(22)

(1)

(2)

(2)

(1)

(2)

(19)

(1)

(1)

(1)

(7)

(1)

(3)

(13)

(1)

(1)

(3)

(1)

(4)

(3)

(1)

(1)

(1)(2)

(1)



Page 39

Of the 374 fish aged with otoliths, 14 age-

classes (2 through 14, and 18) were

represented. The average age for the sample

was 4.8 years. The standard deviation and


Comparison of Operculum and Otolith

Ages The between-structure average CV

of 3.1% was comparable to the within

structure CV’s. There was no evidence of

systematic disagreement between otolith and

operculum ages (test of symmetry, 2 =

26.8, df = 19, P = 0.1), with operculum ages

generally younger than otolith ages. In

Figure 6 we present a graph of the results for

between-reader otolith ageing precision.

There was no evidence of bias between

otolith and operculum ages for tautog

(Figure 7).





operculum ages. The table is based on

VMRC’s stratified sampling of landings by

total length inch intervals.

REFERENCES










Sci. 52:364-368.



Math Soft, Inc. Seattle,

Washington.

White, G.G., J.E. Kirkley, and J.A. Lucy.

1997. Quantitative assessment of

fishing mortality for tautog, Tautoga

onitis, in Virginia. Preliminary report

23456789101112131415161718

Otolith Age (years)

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

Operculum Age +/- 95% Confidence IntervalsFigure 7. Age-bias plot for tautog otolith and

operculum age estimates.


age estimates for tautog.

23456789101112131415161718

Reader 1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

Reader 2

(61)(1)

(110)

(2)(42)(3)

(52)(1)

(2)(25)

(5)(1)

(1)(18)(2)

(2)(6)(2)

(11)(2)(1)

(1)(3)(4)

(5)(1)(1)

(1)(2)

(1)(1)

(1)




Page 40

to the Virginia Marine Recreational

Advisory Board and Virginia Marine

Resources Commission. Newport

News, VA.



Page 41

Table 1. The number of tautog assigned to each total length-at-age category for 372 fish

sampled for operculum age determination in Virginia during 2002.

Length Age (years)

1-inch 2 3 4 5 6 7 8 9 10 11 12 13 14 16

intervals Totals

10 - 10.99 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1

11 - 11.99 2 5 0 0 0 0 0 0 0 0 0 0 0 0 7

12 - 12.99 1 9 3 0 0 0 0 0 0 0 0 0 0 0 13

13 - 13.99 22 19 11 5 2 0 0 0 0 0 0 0 0 0 59

14 - 14.99 28 27 13 4 3 0 0 0 0 0 0 0 0 0 75

15 - 15.99 8 13 6 10 8 0 6 3 0 0 0 1 0 0 55

16 - 16.99 0 16 13 10 5 2 6 1 4 1 1 1 0 0 60

17 - 17.99 0 10 6 10 8 1 1 1 2 1 3 0 0 0 43

18 - 18.99 0 2 2 6 2 0 4 3 4 2 1 0 0 0 26

19 - 19.99 0 0 2 5 2 1 1 1 2 0 0 1 1 0 16

20 - 20.99 0 0 0 1 1 1 1 1 0 0 0 1 2 0 8

21 - 21.99 0 0 0 0 0 0 1 0 1 0 1 0 0 0 3

22 - 22.99 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1

23 - 23.99 0 0 0 0 0 1 1 0 0 0 0 0 0 0 2

24 - 24.99 0 0 0 0 0 0 0 0 1 0 0 0 0 0 1

25 - 25.99 0 0 0 0 0 0 0 1 0 0 0 0 0 1 2

Totals 62 101 56 51 31 6 21 12 14 4 6 4 3 1 372



Page 42


operculum ages for tautog sampled for age determination in Virginia during 2002.Length Age (years)

1-inch 2 3 4 5 6 7 8 9 10 11 12 13 14 16

intervals N

10 - 10.99 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1

11 - 11.99 0.286 0.714 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 7

12 - 12.99 0.077 0.692 0.231 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 13

13 - 13.99 0.373 0.322 0.186 0.085 0.034 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 59

14 - 14.99 0.373 0.360 0.173 0.053 0.040 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 75

15 - 15.99 0.145 0.236 0.109 0.182 0.145 0.000 0.109 0.055 0.000 0.000 0.000 0.018 0.000 0.000 55

16 - 16.99 0.000 0.267 0.217 0.167 0.083 0.033 0.100 0.017 0.067 0.017 0.017 0.017 0.000 0.000 60

17 - 17.99 0.000 0.233 0.140 0.233 0.186 0.023 0.023 0.023 0.047 0.023 0.070 0.000 0.000 0.000 43

18 - 18.99 0.000 0.077 0.077 0.231 0.077 0.000 0.154 0.115 0.154 0.077 0.038 0.000 0.000 0.000 26

19 - 19.99 0.000 0.000 0.125 0.313 0.125 0.063 0.063 0.063 0.125 0.000 0.000 0.063 0.063 0.000 16

20 - 20.99 0.000 0.000 0.000 0.125 0.125 0.125 0.125 0.125 0.000 0.000 0.000 0.125 0.250 0.000 8

21 - 21.99 0.000 0.000 0.000 0.000 0.000 0.000 0.333 0.000 0.333 0.000 0.333 0.000 0.000 0.000 3

22 - 22.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 1

23 - 23.99 0.000 0.000 0.000 0.000 0.000 0.500 0.500 0.000 0.000 0.000 0.000 0.000 0.000 0.000 2

24 - 24.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 1

25 - 25.99 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.500 0.000 0.000 0.000 0.000 0.000 0.500 2

Sample Size 372

VMRC final report on finfish ageing, 2002 weakfish


Page 43

Chapter 13 Weakfish

Cynoscion regalis

INTRODUCTION

A total of 646 weakfish, Cynoscion regalis,



analysis in 2002. The average age was 3.6

year old, and the standard deviation and

standard error were 1.5 and 0.06,

respectfully. Nine age classes (1 to 8, and

10) were represented, comprising fish from

the 1992 and 1994-2001 year-classes, with

fish primarily from the 1998 through 2001

year-classes.

METHODS



in labeled coin envelopes. Once in our

hands, they were sorted based on date of

capture, their envelope labels were verified

against VMRC’s collection data, and

assigned unique Age and Growth

Laboratory sample numbers. All otoliths

were stored dry in labeled cell well trays.

Preparation The first step in otolith

preparation was to grind down the otolith in

a transverse plane to its core using a

Hillquist thin section machine’s 320-mesh

diamond cup wheel cup wheel. To prevent

distortion of the reading surface, the otolith

was ground exactly perpendicular to the

reading plane. The otolith’s ground surface

was then placed face down in a drop of

Loctite 349 photo-active adhesive on a

labeled glass slide and placed under

ultraviolet light to allow the adhesive to

harden (approximately ten minutes). The

Hillquist thin section machine’s cup wheel

was used again to grind the otolith,

embedded in Loctite, to a thickness of 0.3 to

0.5mm. Finally, a thin layer of Flo-texx


section to increase light transmission

through the translucent zones, which


readability.



Page 44





100 times magnification (Figure 1). Each

reader aged all of the otolith sections using

ageing criteria listed in Lowerre-Barbieri et

al. (1994). All samples were aged in
























RESULTS



both readers equally able to reproduce the

ages of previously read samples. There was

also 100 percent agreement between reader

age estimates. Figure 2 illustrates the


Figure 1. Sectioned otolith from a 7 year old

female weakfish.

Figure 3. Year-class frequency distribution for

weakfish collected for ageing in 2002.


1992199319941995199619971998199920002001

Year Class

0

50

100

150

200

Number of Fish

Females n = 409

Males n = 236

Unknown n = 1



Page 45

Of the 646 fish aged with otoliths, nine age


average age was 3.0 years old, and the

standard deviation and standard error were

1.6 and 0.06, respectfully.


fishery was comprised of nine year-classes,

comprising fish from the 1992 and 1994

through 2001 year-classes, with fish

primarily from the 1998 through 2001 year-

classes.








REFERENCES










Sci. 52:364-368.

Lowerre-Barbieri, S.K., M.E. Chittenden Jr.,

and C.M. Jones. 1994. A comparison

of a validated otolith method to age

weakfish, Cynoscion regalis, with the

traditional scale method. Fish Bull.

92:555-568.




Figure 2. Between-reader comparison of otolith age

estimates for weakfish.

12345678910

Reader 1

1

2

3

4

5

6

7

8

9

10

Reader 2

(119)

(141)

(189)

(87)

(55)

(32)

(21)

(1)

(1)




Page 46

Table 1. The number of weakfish assigned to each total length-at-age category for

644 fish sampled for age determination in Virginia during 2002 (no lengths for 2 fish).

Length Age (years)

1-inch 1 2 3 4 5 6 7 8 10

intervals Totals

8 - 8.99 17 1 0 0 0 0 0 0 0 18

9 - 9.99 70 12 1 0 0 0 0 0 0 83

10 - 10.99 22 82 27 1 0 0 0 0 0 132

11 - 11.99 3 35 31 3 0 0 0 0 0 72

12 - 12.99 6 7 14 3 0 0 0 0 0 30

13 - 13.99 1 2 19 7 0 0 0 0 0 29

14 - 14.99 0 1 16 12 1 0 0 0 0 30

15 - 15.99 0 1 13 13 5 1 1 0 0 34

16 - 16.99 0 0 13 7 4 4 0 0 0 28

17 - 17.99 0 0 4 4 4 2 0 0 0 14

18 - 18.99 0 0 6 7 3 0 0 0 0 16

19 - 19.99 0 0 6 4 6 2 0 0 0 18

20 - 20.99 0 0 8 3 7 4 0 0 0 22

21 - 21.99 0 0 9 6 7 5 0 0 0 27

22 - 22.99 0 0 10 7 5 3 1 0 0 26

23 - 23.99 0 0 6 5 6 3 3 0 0 23

24 - 24.99 0 0 4 1 3 3 2 0 0 13

25 - 25.99 0 0 0 3 2 1 1 0 0 7

26 - 26.99 0 0 1 0 0 1 2 0 0 4

27 - 27.99 0 0 1 0 1 2 3 0 1 8

28 - 28.99 0 0 0 0 1 1 2 0 0 4

29 - 29.99 0 0 0 0 0 0 3 1 0 4

30 - 30.99 0 0 0 0 0 0 2 0 0 2

Totals 119 141 189 86 55 32 20 1 1 644



Page 47


otolith ages for weakfish sampled for age determination in Virginia during 2002.

Length Age (years)1-inch 1 2 3 4 5 6 7 8 10

intervals N

8 - 8.99 0.944 0.056 0.000 0.000 0.000 0.000 0.000 0.000 0.000 18

9 - 9.99 0.843 0.145 0.012 0.000 0.000 0.000 0.000 0.000 0.000 83

10 - 10.99 0.167 0.621 0.205 0.008 0.000 0.000 0.000 0.000 0.000 132

11 - 11.99 0.042 0.486 0.431 0.042 0.000 0.000 0.000 0.000 0.000 72

12 - 12.99 0.200 0.233 0.467 0.100 0.000 0.000 0.000 0.000 0.000 30

13 - 13.99 0.034 0.069 0.655 0.241 0.000 0.000 0.000 0.000 0.000 29

14 - 14.99 0.000 0.033 0.533 0.400 0.033 0.000 0.000 0.000 0.000 30

15 - 15.99 0.000 0.029 0.382 0.382 0.147 0.029 0.029 0.000 0.000 34

16 - 16.99 0.000 0.000 0.464 0.250 0.143 0.143 0.000 0.000 0.000 28

17 - 17.99 0.000 0.000 0.286 0.286 0.286 0.143 0.000 0.000 0.000 14

18 - 18.99 0.000 0.000 0.375 0.438 0.188 0.000 0.000 0.000 0.000 16

19 - 19.99 0.000 0.000 0.333 0.222 0.333 0.111 0.000 0.000 0.000 18

20 - 20.99 0.000 0.000 0.364 0.136 0.318 0.182 0.000 0.000 0.000 22

21 - 21.99 0.000 0.000 0.333 0.222 0.259 0.185 0.000 0.000 0.000 27

22 - 22.99 0.000 0.000 0.385 0.269 0.192 0.115 0.038 0.000 0.000 26

23 - 23.99 0.000 0.000 0.261 0.217 0.261 0.130 0.130 0.000 0.000 23

24 - 24.99 0.000 0.000 0.308 0.077 0.231 0.231 0.154 0.000 0.000 13

25 - 25.99 0.000 0.000 0.000 0.429 0.286 0.143 0.143 0.000 0.000 7

26 - 26.99 0.000 0.000 0.250 0.000 0.000 0.250 0.500 0.000 0.000 4

27 - 27.99 0.000 0.000 0.125 0.000 0.125 0.250 0.375 0.000 0.125 8

28 - 28.99 0.000 0.000 0.000 0.000 0.250 0.250 0.500 0.000 0.000 4

29 - 29.99 0.000 0.000 0.000 0.000 0.000 0.000 0.750 0.250 0.000 4

30 - 30.99 0.000 0.000 0.000 0.000 0.000 0.000 1.000 0.000 0.000 2

Sample Size 644

results of 2002 virginia - chesapeake bay finfish …...all fish were collected in 2002 by the...

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