Validation of Daily lncrement Formation on Otoliths with Applications to Wild Striped Bass (Morone saxatilis) at the Northern Limit of Its Range

Scott G. Douglas

B.Sc., University of Prince Edward Island, 1995

Thesis submitted in partial fulfilhent of the requirements for

the Degree of Master of Science (Biology)

Acadia University Spring Convocation 2001

O by Scott G. Douglas, 2001

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TABLE OF CONTENTS

TABLE OF CONTENTS ................................................................................................. iv

LIST OF TABLES .......................................................................................................... vi

. . LIST OF FIGURES ........................................................................................................ vii

ABSTRACT .................................................................................................................... ix

ACKNOWLEDGEMENTS ............................................................................................... x

................................................................................ ........................ INTRODUCTION .,. 1

Overview of Otolith Development ..................... .. ...................................................... 1

Striped Bass in the Eastern Canadian Provinces ......................................................... 4

Northwest Miramichi River Population ......................................................................... 5

Shubenacadie - Stewiacke River Population ............................................................... 7

Ecological Importance of Daily Age Validation ............................................................. 8

................................................................................................................... Objectives 9

MATERIALS AND METHODS ..................................................................................... I O

Miramichi Striped Bass .............................................................................................. 10

Shubenacadie Striped Bass ..................................... .. ................... 11

Comparative Growth Experiments ............................................................................. 11

Oxytetracycline Marking ...................................... .. . . 12

........................................................................................................ Field Collections 13

Otolith Preparation ........................ .. ........................................................................ 13

Validation of Daily lncremerit Formation .................................................................... 14

...................................................................................................... Birthdate Analysis 15

........................................................................................................ Growth Analysis 16

RESULTS ..................................................................................................................... 17

Light Microscopy ....................................................................................................... 17

Validation by Real Age .............................................................................................. 18

Validation by OTC Marking ........................................................................................ 19

Hatchery Growth ....................................................................................................... 20

lnterpretation of Ages for Wild Mirarnichi Striped Bass .......................................... 21

Wild Growth ............................................................................................................... 21

Birthdate Analysis ...................................................................................................... 22

DISCUSSION ............................................................................................................. 46

....................................................................................................... Lig ht Microscopy 46

Daily lncrement Validation ......................................................................................... 48

.......................................................................................................... Otolith Marking 49

Hatchery Growth .................................................................................................. 50

Age lnterpretations of Wild Miramichi Striped Bass ................................................... 54

Birthdate Analysis ...................................................................................................... 55

............................................................................................................... Wild Growth 59

SUMMARY AND CONCLUSIONS ................................ .. .......................................... 63

LIST OF TABLES

Table 1. Sampling scheme and otofiths available for validation analysis. NA not available. ...................................................................................................................... 23

Table 2. Summary of the catch per individual trap per 24h and the mean 2 1 standard deviation (SD) catch of striped bass for each day that the 1996 gaspereau fishery on the Northwest Miramichi River was sampled for bycatch (from Bradford and Chaput 1997). ................................................................................ 24

Table 3. Results of validation analysis by real age for the two populations reared at differenf facilities. SE standard error, CI confidence interval, significance as it relates to a slope of 1. .................................................................................................. 24

Table 4. Results from ANCOVAs between Shubenacadie striped bass and different groups of Miramichi striped bass for daily increment technique validation

........................ by real age and by OTC marking. ............................................... 25

Table 5. Results of validation analysis by OTC marking for the two populations reared at different facilities. SE standard error, CI confidence interval, significance as it relates to a slope of 1. ....................................................................... 25

Table 6. Observed and predicted growth parameters (logistic curve) for Shubenacadie and Miramichi striped bass reared at Two Rivers Bass Hatchery. TL total Iength; NA not availabfe. .................................................................................. 26

Table 7. Logistic growth parameters K (maximum total length attained by the end of the first growing season), a (estimate of total Iength at hatch), and R (innate capacity for growth) for TRBH-reared Shubenacadie, TRBH-reared Miramichi, and wild Miramichi striped bass. SE standard error, CI confidence interval. ................. 27

Table 8. Observed growth parameters for wild Miramichi striped bass. TL total length; NA not available. ............................................................................................... 27

LIST OF FIGURES

Figure 1. River systerns of the Canadian provinces where striped bass currently spawn or have been extirpated. The only remaining spawning populations exist in the Northwest Miramichi River in New Brunswick, and the Shubenacadie - Stewiacke River in Nova Scotia. ............................... .. .................................................. 28

Figure 2. Northwest Miramichi River identifying location of trapnets, beach ............ seining sites and commercial smelt fishery site in Loggieville (Miramichi River) 29

Figure 3. Sagittal otoliths of hatchery reared striped bass. A. Miramichi larvae 3 dph; nucleus is obvious, however daily increment formation has not begun (Magnification 1000x oil immersion). B. Miramichi larvae 10 dph (Magnification 630x oil immersion). C. Polished transverse section of a sagitta from a Shubenacadie juvenile 27 dph (Magnification 250x). ...................... .. ................... 30 Figure 4. Sagitta from a wild Miramichi juvenile striped bass collected in November (-150 dph). Arrows indicate a change in growth axis corresponding to daily growth increments 30 - 40. Magnification 250x. ................................................... 31

Figure 5. Regression between real age and increments counted on the otoliths of TRBH-reared Shubenacadie and Miramichi striped bass .......................................... 31

Figure 6. Regression between real age and increments counted on the combined otoliths of TRBH-reared and MSEC-reared Miramichi striped bass ............................. 32

Figure 7. Regression between real age and increments counted on the otoliths of MSEC-reared Miramichi larval striped bass (1997). Individual points rnay represent several observations. ................................................................................ 32

Figure 8. Regression between real age and increments counted on the combined otoliths of TRBH-reared Miramichi, MSEC-reared Miramichi, and MSEC-reared Miramichi larval striped bass ......................................................................................... 33

Figure 9. Striped bass sagitta aged 27 dph. Arrows indicate stress mark at ............................................................ increment 14. Magnification 630x oil immersion 33

Figure 10. Regression between days elapsed since marking and increments formed after the stress mark for TRBH-reared Shubenacadie and Miramichi striped bass. ................................................................................................................. 34

Figure 11. Regression between days elapsed since rnarking and increments formed after the stress mark for TRBH-reared Miramichi and MSEC-reared Miramichi striped bass. ................................................................................................. 34

Figure 12. Length frequency distribution of TRBH-reared Shubenacadie striped bass .............................................................................................................................. 35

Figure 13. Length frequency distribution of TRBH-reared Miramichi striped bass. ........ 35

vii

Figure 14. Logistic growth curves for TRBH-reared Shubenacadie and Miramichi striped bass. ......................... ..,,........... ......................................................................... 36

Figure 1 5. Polynomial growth curves of TRBH-reared Shubenacadie and Miramichi striped bass. ................................................................................................. 36

Figure 16. Sagitta of a wild Miramichi striped bass collected in November (-150 dph). Note the decrease in increment widths at increments 110-120 (lower parenthesis) and further decreases in increment widths at the edge (upper parenthesis). Magnification 630x oil immersion ............................................................. 37

Figure 17. Length frequency distributions of wild Miramichi striped bass sampled in July, Septernber and November 1996. ...................................................................... 37

Figure 18. Regression of age and total length for wild Miramichi striped bass collected July 30 and 31, 1996 (upper panel), and September 4 and 5, 1996 (lower panel) ................................................................................................................. 38

Figure 19. Logistic growth cunre for wild Miramichi striped bass collected July 30 - 31 and September 4 - 5, 1996. Total lengths of November samples have been included on the line but not used in the calculation. .................................................... 39

Figure 20. Age distribution of juvenile Miramichi striped bass collected on July ................................................................................................................. 30-31 , 1996. 39

Figure 21. Age distribution of juvenile Miramichi striped bass collected on September 4-5, 1996. ................................................................................................... 40

Figure 22. Birthdate distributions of young-of-the-year striped bass collected in the Miramichi River on JuIy 30-31, and September 4-5, 1996 ....................................... 40

Figure 23. Birthdate distribution of young-of-the-year Miramichi striped bass collected on July 30, 1996 (n = 13) and total adult bycatch in the NW gaspereau fishery. The birthdate distribution has been adjusted by three to six days ..................... 41

Figure 24. Birthdate distribution of young-of-the-year Miramichi striped bass collected on July 31, 1996 (n = 17) and total adult bycatch in the NW gaspereau fishery. The birthdate distribution has been adjusted by three to six days ..................... 42

Figure 25. Birthdate distribution of young-of-the-year Miramichi striped bass collected on Septernber 4, 1996 (n = 25) and total adult bycatch in the NW gaspereau fishery. The birthdate distribution has been adjusted by three to six days .............................................................................................................................. 43

Figure 26. Birthdate distribution of young-of-the-year Miramichi striped bass collected on September 5, 1996 (n = 13) and total adult bycatch in the NW gaspereau fishery. The birthdate distribution has been adjusted by three to six

............................................................................................................................ days.. 44

Figure 27. Mean daily water temperatures from the Northwest Miramichi River near Hackett's Beach, 1 996. ......................................................................................... 45

viii

ABSTRACT

Aging young-of-the-year with otoliths was validated for striped bass (Morane saxatilr's) at

the northern end of the species range using garden-style hatchery rearing and

oxytetracycline marking. The target populations of striped bass were from two eastern

Canadian rivers: the Northwest (NW) Miramichi in New Brunswick, which discharges into

the Gulf of St. Lawrence, and the Shubenacadie - Stewiacke river in Nova Scotia, which

discharges into the inner Bay of Fundy. Initial increment formation was at 4 days post

hatch (dph) for hatchery-reared Shubenacadie striped bass, but ranged from 2 - 4 dph

for hatchery-reared Miramichi striped b a s . Results indicated that increments were

formed on a daily basis for both populations. Otolith increments of hatchery-reared fish

were highIy discernible with light microscopy at 11 3 dph (end of experiment). Hatchery

growth was 1.14 mm/d for Shubenacadie fish and 1.06 mm/d for Miramichi fish, but

these were not significantly different. The logistic growth equations for hatchery-reared

Shubenacadie and Miramichi striped bass were Lt = 166.4 1 1 + e3-38-0-041t and Lt = 153.4

/ 1 + e3.47 - 0.042t , respectively. The polynomial growth equations for hatchery-reared

Shubenacadie and Miramichi striped bass were: Total length = (O.Ol*age in d a y ~ ) ~ c

(0.31eage in days) + 2.65, and Total length = (O.Ol*age in d a y ~ ) ~ + (0.22*age in days) + 3.38, respectively. Results suggest that either population should have similar growth

rates of progeny for the commercial aquaculture industry or resource agency stocking

initiatives. Aging criteria developed here applied to wild Miramichi striped bass indicated

a bimodal birthdate distribution in 1996. These two peaks of spawning activity correlated

closely with the adult bycatch in the NW Miramichi gaspereau commercial fishery. Daily

increments in otoliths of wild Miramichi striped bass could not be resolved with Iight

microscopy beyond 11 0-120 days post hatch. Total length was not a good predictor of

age for wild-caught Miramichi fish. Wild, Septernber samples had a modal age of 86

days but ranged by nearly 60 mm in total length. Daily growth of wild Miramichi striped

bass in 1996 was 0.83 mm/d at the beginning of Septernber, which is less than similarly

aged Mirarnichi or Shubenacadie striped bass reared in the hatchery. Growth of wild

young-of-the-year is likely controlled by density-independent exogenous factors.

ACKNOWLEDGEMENTS

1 thank the mernbers of rny thesis comrnittee, Drs. Roger Rulifson, Rod Bradford,

Mike Dadswell, and Dan Toews for allowing me freedom and time to explore other

opportunities while preparing my thesis. Special thanks are due to Elizabeth Laban of

the National Marine Fisheries Service, Southeast Fisheries Center, Beaufort Laboratory

in North Carolina for training me in the proper techniques of hand polishing otoliths. 1 am

most grateful to Gérald Chaput, Rod Bradford, and Dave Moore of the Department of

Fisheries and Oceans who have provided enormous arnounts of logistic support in the

form of lab and office space, microscope and computer use, boats, and sampling gear.

This work could not have been completed without funding through surnmer employment

with the Department of Fisheries and Oceans as a student in the Federal Student Work

Employment Program (FSWEP) in 1997-98 and as a biologist in 1999-2001. Mark

flambrook and Joe Sheasgreen of the Miramichi Fish Hatchery (formerly the Miramichi

Salmonid Enhancement Center) aided in the colIection of Miramichi broodstock and

provided tank space for spawning and rearing of Miramichi striped bass. Owners of Two

Rivers Bass Hatchery -- Bill Stone, Ralph Meadows, and Bob Covert -- provided

hatchery facilities and space for growth studies in Nova Scotia. I am indebted to Aaron

Perry, who was working for Two Rivers Bass Hatchery during the course of the growth

experiments and took much care and impeccable records in my absence. Dr. James

Duston of the Nova Scotia Agricultural College provided aquaria for the growth

experiments. 1 am grateful to Renée Bernier, Dave Moore, Chris Ward, Rod Bradford,

Gérald Chaput, John Hayward, John MacMillan and lan Patterson for assistance during

field collections. Sincere thanks go to the gaspereau and smelt fishermen of the

Miramichi River who helped in broodstock collections and provided sampies of young-of-

the-year striped bass. Special thanks are due to many employees of the Departrnent of

Fisheries and Oceans (Moncton), in particular, Tom Hurlbut for the use of his isomet

saw, and Mary Stephenson and Sharon MCGladdery for use and assistance with

microscope photography. Gérald Chaput and Manon Mallet of the Department of

Fisheries and Oceans (Moncton), and Jarnie Gibson of the Acadia Centre for Estuarine

Research provided invaluable statistical guidance. Teaching assistantships granted by

Acadia University and East Carolina University are acknowledged. Roger Rulifson and

farnily provided accommodations during my stays in North Carolina, and lan Patterson

and Glenys Gibson provided accommodations during visits to Wolfville.

I am especially thankful to my family and Renée who supported me in every way.

INTRODUCTION

Overview of Otolith Development

Otoliths are calcified structures that are located in the heads of teleost fish, which

function in equilibrium maintenance and sound detection. Although ages are encoded on

virtually al1 hard body parts of bony fish, otoliths are especially reliable at recording the

timing of important life-history events. The early formation of otoliths during fish

development, their protected location, and their non-resorptive quatities, allows accurate

annual and daily age determinations (Jones 1992). Sagittal otoliths, often the largest of

the three pairs, are used most frequently in otolith microstructure analyses (Secor et al.

1 992).

The formation of daily increments on fish otoliths was discovered in the early

1970s (Pannella 1971). Since that tirne, many studies on otolith microstructure and its

use in fisheries science have been generated. Many researchers believe that

recruitment to the forming year class is determined before the eariy Iife history stages

are completed, so accurate aging of larvae and juveniles from otolith daily increments is

an important advancement in fisheries science. Aging fish with the daily increment

technique has applications in growth studies (Struhsaker and Uchiyama 1976; Wilson

and Larkin 1982; Partridge and DeVries 1999), birthdate distribution analysis (Methot

1983; Alvarez and Alemany 1997), mortality estimates (Essig and Cole 1986; Rooker et

al. 1999), stock and cohort discrimination (Rutherford and Houde 1995; Mosegaard and

Madsen 1996), and migration tracking (Secor et al. 1993). The timing of life history

events has been documented with the daily aging technique (Brothers and McFarland

1981 ; Brothers et al. 1983; Wright et al. 1991), and recently, the analysis of otolith

microchemistry from fossils has proven useful in tracing the evolution of climates (Smith

and Patterson 1994).

The formation of growth increments on otoliths occurs by the accretion of calcium

carbonate (CaC03) and protein (Mugiya et al. 1981). The accretion of these two

substances occurs with a diel rhythm and results in the deposition of a bipartite feature

on the otolith. The bipartite features, referred to as daily growth increments, are formed

concentrically around the nucleus of the otolith. Because photoperiod, water

temperature, and feeding regimes also have diel cycles, much effort has been devoted

to identifying how each of these environmental variables affects the periodicity of daily

increment formation. Results from such tests suggest that: 1) different environmental

stimuli affect species differently, 2) a single environmental stimulus is not the

determining factor in the production of daily increments, and 3) there is an endogenous

circadian rhythm involved in ring formation (Campana and Neilson 1985). It has been

demonstrated that a 12 hour light - 12 hour dark cycle caused daily increment formation

in Lepomis (Taubert and Coble 1977), Tilapia (Tanaka et al. 1981), and Fundulus

(Radtke and Dean 1982). However, contradictory studies using constant light conditions

(Campana and Neiison 1982; Geffen 1982; Neilson and Geen 1982) or constant dark

conditions (Neilson and Geen 1982) did not alter the daily periodicity of increment

formation. Neilson and Geen (1982, 1985) demonstrated that chinook salmon

(Oncorhynchus tshawytscha) fed several tirnes a day produced less than one increment

per day, but a direct relationship was not established. Striped bass (Morone saxatilis)

starved or fed intermittently produced fewer increments than one per day (Jones and

Brothers 1987), but feeding frequency did not disrupt daily increment formation in starry

flounder (Platichthys stellatus), steelhead trout (Salmo gairdneri), (Campana 1983a) or

Tilapia (Tanaka et al. 1981). Diel temperature fluctuations also have been suggested as

the factor responsible for the production of daiiy increments in fish (Brothers 1981).

Campana and Neilson (1982) and Neilson and Geen (1982) reported that temperature

effects were iimited and that ternperature fluctuations did not disrupt the periodicity of

increment formation from daily.

The mechanism behind daily incrernent formation is not weIl understood, and the

existence of the phenornenon among al1 fish is undetermined. The focus of many works

has been the validation of the daily aging technique for a wide variety of species (see

Campana and Neilson 1985; Jones 1986 for reviews). Validation studies are achieved

by examining either otoliths from larvae or juveniles of known age, or by examining

otoliths that have been marked on a predetermined date. Marking otoliths requires that

the fish be subjected to a chemical compound or dye that wiil incorporate into the otolith

and will be visible after preparation. Fish exposed to appropriate concentrations of

oxytetracycline (OTC) or calcein, by immersion (Hettier 1984; Reinert et al. 1998; Secor

et al. 1991), by injection (Campana and Neilson 1982; Campana 1983a), or in food

(Burnguardner 1991) have resulted in marks deposited on otoliths, which fluoresce

under ultraviolet Iight. Dyes, such as Alizarin compounds, also have been successful in

marking otoliths (Beckman and Schulz 1996). Otoliths that develop checks due to

handling stress (Ralston and Miyamoto 1983; Campana 1983b; Volk et al. 1984;

Boehlert and Yoklavich 1985), temperature fluctuations (Nishirnura and Yamada 1984;

Mosegaard et al. 19883 or marks associated with life-history events (Brothers et al. 1983;

Victor 1982) also have been used to validate daily aging for a variety of species (see

Geffen 1992 for review).

Studies validating daily increment formation can be compromised depending on

the techniques employed to prepare and read otolith samples. Campana and Moksness

(1991) demonstrated that a direct relationship exists between the time and effort

required for preparing otoliths, and the resultant accuracy and precision of age

interpretation. Otoliths with longer preparation times often result in better increment

visibility and thus more accurate age determinations. Many light microscopy techniques

have been used to validate daily increment deposition for various species (Geffen 1992).

Scanning electron microscopy (SEM) has been recommended as a validation check for

any light microscopy study (Campana and Neilson 1985; Jones 1986), especially when

difficulty arises in discerning sub-daily from daily increments (Campana et al. 1987).

Striped Bass in the Eastern Canadian Provinces

The striped bass (Morone sauatilis) (Walbaum, 1792) is an anadromous percoid

that spawns in many estuaries along the eastern seaboard of North America, and

returns to the marine environment to feed and mature. The natural range of the striped

bass extends along the western Atlantic Ocean from the St. Lawrence River in Québec,

Canada, to the St. John's River in Florida, but is only considered anadromous north of

Cape Hatteras, North Carolina (Scott and Scott 1988). Throughout its range, the striped

bass is one of the most important species for many recreational and commercial

fisheries. UntiI recently, the majority of the knowledge pertaining to the biology and

aquaculture of the species has originated from the study of populations in the US.

lnterest in striped bass as a recreational and aquaculture species has recently increased

in eastern Canada (Peterson 1991), and as a result, research on the species' biology at

the northern limit of its range is growing (Rulifson et al. 1987; Harris 1988; Rulifson and

Dadswell 1995; Robichaud-LeBlanc et al. 1996, 1998; Paramore 1 998; Rulifson and Tull

1999, Robinson 2000).

Historical documentation of striped bass spawning exists for five eastern

Canadian rivers. Populations from the St. Lawrence River in Québec, and the Saint John

River in New Brunswick are believed to be extirpated, whiie the population from the

Annapolis River in Nova Scotia is considered to be severely depressed (Jessop 1995).

The two remaining, self-sustaining populations of striped bass in the Maritime Provinces

represent the northern geographic limit of the species spawning range. New Brunswick's

population is confined to the southern Gulf of St. Lawrence and demonstrates high

fidelity to the Northwest (NW) Miramichi River in the northeastern part of the province

(N46'58' & W65'36') (Figure 1). The other population exists in the Shubenacadie -

Stewiacke River system which flows into the inner Bay of Fundy (N45'09 & W63'23')

(Figure 1). Striped bass stocking has never been conducted in either the Miramichi or

Shubenacadie - Stewiacke watershed and both populations are considered to be

genetically discrete from one another (Wirgin et al. 1993; Robinson 2000).

Northwest Miramichi River Population

Striped bass spawning in the Northwest Miramichi River represents the northern

most self-sustaining population of striped bass in North Arnerica. Stock assessments

conducted for Miramichi striped bass each year since 1993 (Bradford et al. 1995;

Bradford and Chaput 1996, 1997, 1998; Bradford et al. 2001 ; Douglas et al. 2001 ) reveal

that this population is generally of low abundance with occasional recruitment of strong

year-classes (high of 50,000 in 1995 to a present low of approximately 3,000-5,000 fish).

Striped bass in the NW Miramichi River have not met the conservation requirement

since 1996 and therefore have been protected by a management regime of no

commercial or recreational harvest. Large annual variability in population size has been

attributed to overfishing and year-class failures caused by adverse environmental

conditions (Bradford and Chaput 1997).

Mature adult and immature striped bass enter the NW Miramichi during mid-May

to early June. Bycatch data from the commercial gaspereau fishery indicate that striped

bass spawning is usually brief (Bradford and Chaput 1997). Young-of-the-year occur in

near-shore habitats throughout the summer (Robichaud-LeBlanc et al. 1998) and are

believed to migrate downriver to mesohaline habitats during late summer, where they

are present in large numbers by October (Bradford et al. 1995; Bradford and Chaput

1998). Recent studies suggest that O+ striped bass may exhibit an increased distribution

beyond the Miramichi Estuary (Robinson 2000). Although striped bass spawning activity

was not detected in the Kouchibouguac and Richibucto rivers for years 1996-98, Young-

of-the-year were present in beach seine and fyke net surveys within those estuaries, and

along the coast between the Mirarnichi and Richibucto Rivers for those same years

(Robinson 2000). There were no genetic differences in the genome studied from fish

sarnpled in the Mirarnichi and Richibucto Estuaries (Robinson 2000).

Evidence suggests that striped bass size at age may Vary throughout its range,

but it is unclear whether growth rates are related to environmental conditions, to unique

growth characteristics of the population, or both (Scott and Scott 1988; Conover et al.

1997). Robichaud-LeBlanc et al. (1 998) reported that the growth rate of young-of-the-

year striped bass frorn the Miramichi River was faster and that length attained by winter

was greater than for the species in the center of its range. This supports Conover's

(1990) "countergradient variation" model, which demonstrates an inverse relationship

between growth rate and the length of the growing season over different latitudes.

Growth was fastest at higher latitudes before the onset of winter for Atlantic silversides

Menidia menidia (Conover and Present 1990), American shad Alosa sapidissima,

mummichog Fundulus heteroclitus, and striped bass (Conover 1990). Secor et al. (2000)

however, determined that young-of-the-year distributions within estuaries, particularly

with respect to different salinity gradients, could alter the expected latitudinal gradient in

growth rates for striped bass. Bernier (1996) back-calculated lengths of NW Miramichi

striped bass aged 2+ and determined that juveniles needed to attain a minimum body

Iength of about 10 cm by the end of the first growing season in order to survive the first

winter. Furthermore, Hurst and Conover (1 998) demonstrated size-dependent mortality

for striped bass in the Hudson River during severe winter conditions.

Shu benacadie - Stewiacke River Population

Striped bass spawning in the Shubenacadie River system represent the only self-

sustaining population of striped bass in Nova Scotia. Biological characteristics and the

size of the Shubenacadie adult population were described recently by Paramore (1 998).

The first federal stock assessments of the population were recently attempted (1999-

2000), and conservation requirements for this population are currently the suoject of

investigation (R. Bradford, BI0 Dartmouth NS, persona1 communication). The present

allocation scheme for commercial shad fishermen in the Shubenacadie watershed is a

maximum of three striped bass per day (2 68cm) for personal use, whereas commercial

fishers elsewhere in the Bay are permitted to retain only one striped bass daily. The daily

bag limit for recreational anglers in the inner Bay of Fundy is one striped bass (2 68cm).

The Shubenacadie River flows from Grand Lake near Halifax to the inner Bay of

Fundy where it becomes transformed by the harsh environment of a tidal bore. The

Shubenacadie River is believed to be the only tidal bore river that has a seIf-sustaining

population of striped bass (Rulifson and Dadswell 1995). The tidal bore of the

Shubenacadie - Stewiacke watershed can alter the elevation and salinity of the water by

as much as 3.7 m and 20 ppt in one hour respectively (Tull 1997). Tull (1 997) described

four peak spawning events in 1994 (first on June 2; last on June 20) and suggested that

this population has adapted methods of handling the harsh tidal bore environment.

Rulifson and Tull (1999) also described a specialized mechanism for striped bass egg

transport in the Shubenacadie - Stewiacke River systern.

Local fishermen report that the two traditional spawning sites of the

Shubenacadie watershed near the head of tide are now limited to a single site on the

Stewiacke River (approximately 3 - 6 km above the confluence). Striped bass enter the

Shubenacadie system in late May or early June and spawning is generally cued to water

temperature (Rulifson and Dadswell 1995). From tagging studies (Rulifson et al. l987),

we know that at least a portion of the 2+ and older fish frequenting the inner Bay of

Fundy during summer and fall ascend the Shubenacadie River and ovenivinter in Grand

Lake. Spring run adult fish descend frorn the fresh waters of Grand Lake to the spawning

grounds, while a second run of adults is believed to ascend the river from the inner Bay.

Both groups of fish are believed to spawn near the confluence of the Shubenacadie and

Stewiacke Rivers (Rulifson et al. 1987; Rulifson and Dadswell 1995; Paramore 1998).

The life-history of wild juvenile Shubenacadie striped bass is not well understood,

but is under current investigation (R. Bradford, BI0 Dartmouth NS, personal

communication).

Ecological Importance of Daily Age Validation

The ability to age wild young-of-the-year striped bass from the Miramichi and

Shubenacadie - Stewiacke Rivers would be of profound ecological importance for both

populations. The daily aging technique has been validated for striped bass in the

southern part of the species range (South Carolina, Santee-Cooper broodstock (Secor

and Dean 1989)), presumably the center of the species range (New York, unknown

broodstock (Jones and Brothers 1987)), but not the northern part of the species range.

In light of the possible different genetic make-up and environmental conditions

encountered by striped bass in the north, validation of the daily increment technique is

required before any studies dealing with daily ages of wild young-of-the-year are

conducted.

Understanding the first year's growth for northern striped bass populations is

critical, not only for the aquaculture industry but also for fisheries managers. If

broodstock collected from northern striped bass populations produced faster growing

progeny, the tirne required to attain either marketable-size and/or stocking-size fish

would be reduced, resulting in a substantial savings to the aquaculture industry. Also,

maximal growth during the first year of life rnay be essential for sumiva! throughout the

first winter at the northern Iimit of the species range (Chaput and Robichaud 1995;

Bernier 1996; Robichaud-LeBlanc et al. 1998). This rnay be especiafly true for the NW

Miramichi population, which currently is at a depressed level.

The advantages for young-of-the-year fish to be spawned early or late in the

spawning season remains debated (McGovern and Olney 1996). Although the spawning

season for northern striped bass is short (one to three weeks), the relative importance of

being spawned early or Iate could be deterrnined with daily ages and birthdate

distributions of young-of-the-year. Bulak et al. (1 997) reported that survival in 1988 and

1990 in the Santee-Cooper system, South Carolina was highest when striped bass eggs

hatched during the early half of the spawning season. Conversely, Ulanowicz and Polgar

(1980) concluded that survival of young-of-the-year was largely dependent on

environmental factors. In the north, tirne of spawning may be important if O+ striped bass

must reach a critical size before the onset of winter. In some years, early spawned fish

may set the pace for growth throughout the rest of the summer and ultimately define the

recruitment process for northern populations of striped bass. Also, the relative

importance in the timing of the adult striped bass spawning run in relation to the

commercial fisheries around the Maritimes could be addressed.

Objectives

The objectives of this study were:

(1) To determine whether striped bass at the northern limit of its breeding range

deposited daily increments on sagittal otoliths;

(2) To investigate the periodicity of daily increment deposition in two populations of

striped bass at the northern limit of its breeding range;

(3) To establish daily aging criteria required for aging studies on northern wild

populations;

(4) To determine the intrinsic growth rates of northern striped bass under laboratory

conditions; and

(5) To apply newly developed aging criteria to ascertain the intrinsic growth rates and

birthdate distributions of northern populations, using wild Miramichi striped bass as a

model.

MATERIALS AND METHODS

Miramichi Striped Bass

Miramichi larvae for growth experiments were obtained by artificial rearing from

the egg stage at the Miramichi Salmonid Enhancement Center (MSEC), Miramichi, New

Brunswick. Broodstock were collected on June 5, 1996 from commercial alewife, Alosa

pseudoharengus and blueback herring, A. aestivalis (collectively termed gaspereau)

trapnets located in the striped bass spawning area of the NW Miramichi River (Figure 2).

Four ripe females and two ripe males were transported to the MSEC for natural

spawning (Le., fish were not induced to spawn). Broodstock were maintained in a

covered, 2.4-m diameter x 1.2-m deep circufar, fiberglass tank supplied with a once-

through flow system of ambient brook (Stewart Brook; Figure 2) water. Spawning

occurred during the evening of June 5, 1996 at a water temperature of 17% and salinity

of O ppt. Fertilized eggs were incubated in aerated hatching jars at a mean water

ternperature of 17.7OC and salinity of O ppt. Hatching began approximately 52 hours after

fertilization and was complete by hour 60. Miramichi larvae were transferred to rearing

tanks of water quality the same as that of the hatching jars, and assigned a hatch date of

June 8, 1996. A natural light/dark photoperiod was used for egg incubation, with

fluorescent light supplementing the arnbient sunlight through hatchery windows during

the day.

Shubenacadie Striped Bass

Shubenacadie broodstock held in a 3.6-m diameter x 1 -2-m deep steel circular

tank spawned naturally on June 6, 1996 at the Two Rivers Bass Hatchery (TRBH) facility

near Stewiacke, Nova Scotia. Fertilized eggs were transferred to aerated hatching jars

and held under natural light conditions at a mean water temperature of 19.4OC and

salinity of O ppt. Hatching started on June 8, 1996, approxirnately 50 hours after

fertilization. Larvae were transferred to rearing tanks of water quality sirnilar to that in the

hatching jars and assigned a hatch date of June 8, 1996. Water from the Shubenacadie

Rivet was aerated in the hatching jars for egg incubation and in the rearing tanks for

grow-out.

Comparative Growth Experiments

Growth experiments were conducted at the Two Rivers Bass Hatchery in a

greenhouse under ambient photoperiod and Iight conditions using Shubenacadie River

water from grow-out ponds. At two days post hatch (dph), Mirarnichi larvae were

transported in sealed buckets (half water, half cornpressed oxygen) to the TRBH facility

for growth experiments. Initially, TRBH-reared Miramichi and Shubenacadie larvae were

placed into six 55-L glass aquaria (three replicates per group) at a density of

approximately 10 larvaell. Striped bass larvae were counted individually into aquaria

through clear tubing used as a siphon. Aquaria were positioned in a linear, alternate

faskiion. High mortality of TRBH-reared Mirarnichi larvae during the first few days

necessitated combining rernaining individuals into a single aquarium to maintain original

stocking densities. Because of the normal hatchery procedures and lirnited tank

avaiiability, both groups of fish were transferred to square 1 -2-m x 1.2-m x 1.8-m rearing

tanks on August 1. Larvae from both groups were kept under identical conditions

throughout the experiment. Temperature (OC), salinity (ppt), and dissolved oxygen (mg/L)

were recorded three tirnes daily for each aquarium. Larvae were fed Artemia ad libitum

(three times daily) for approximately one month, at which time they were weaned ont0 a

prepared dry food diet (0.5 granular). Ration levels of both Artemia and milled feed were

measured in graduated cylinders and administered by hand. Water in the rearing tanks

was changed every two days by siphoning off 3/4 of the water and replenishing the

aquaria with an equivalent amount of Shubenacadie River water. Throughout the

experiment, fish from both groups were sacrificed periodically to determine growth (total

length measured to the nearest 0.1 mm) then preserved in 95% ethanol for later

extraction of otoliths. Samples were arbitrarily selected by seining together al1 fish in the

aquaria and using an aquarium dip net to retrieve the sample. Having enough fish to

sample at the end of the growth experiments was a consideration that was reflected in

the number of individuals sacrificed throughout the experirnent.

Oxytetracycline Marking

At 16 dph, TRBH-reared Shubenacadie and Mirarnichi striped bass larvae were

placed in an oxytetracycline (OTC) solution (0.35 mg/[) for three hours to mark the

otoliths at a known age (Secor et al. 1991). SeveraI Miramichi striped bass beionging to

the same brood as those transported to TRBH were maintained at MSEC (hereafter

referred to as MSEC-reared Miramichi striped bass) for growth trials in a cornpanion

study (Hambrook, unpublished data). At 14 dph, MSEC-reared Miramichi larvae were

immersed in an OTC solution (0.35 mg/l for three hours) identical to that used for larvae

at Two Rivers Bass Hatchery. Otoliths were acquired from MSEC-reared larvae on one

occasion in 1996 (Table 1) and stored in 95% ethanol.

Field Collections

Wild striped bass juveniles were collected in 1996 during daylight from the NW

Miramichi River at MCKay Cove on July 30 (n = 13)' and from Hackett's Beach on July 31

(n = 17), September 4-5 (n = 25, 30)' and October 4 (n = O). Fish were collected with a

beach seine measuring 30-m long x 1.2-m deep constructed of 6-mm ace mesh. Striped

bass were sacrificed and immediately returned to the laboratory. Fish were measured for

total length (nearest 0.1 mm) prior to storage in 95% ethanol. Otoliths were extracted

from the preserved samples within Wo months of capture and stored in 95% ethanol.

Young-of-the-year striped bass were also collected on November 1, 1996 (n =

67), from a commercial smelt (Osmerus mordax) fisherman in the Miramichi Estuary

(Figure 2). Since the bycatch of juvenile striped bass in this fishery can be large, a

length-stratified subsample was taken (a maximum of five striped bass per 5-mm TL size

classes). These fish were measured for total length to the nearest 1 mm and frozen for

otolith extraction at a later date.

Otolith Preparation

Both sagittal otoliths were removed from each juvenile via the gill cavity (Secor et

al. 1992) under a Wild M3 dissecting microscope (maximum magnification 400x). The

right sagittal otolith was arbitrarily selected for preparation unless it was crystalline in

nature, cracked, or obviously deformed, in which case the left sagitta was substituted.

The remaining left sagittal otoliths were labeled and stored in a 95% ethanol solution for

reference if necessary. Each otolith selected for examination was mounted on a glass

slide using the embedding medium, Embed 812 (Electron Microscopy Sciences). A thin

transverse section (approximately 1 mm) containing the otolith core region was obtained

using a Buehler isornet low speed saw. Sections were then mounted on individual glass

slides with Crystal Bond for grinding and polishing. Grinding was completed by hand

using 400-pm and 600-pm grit wetldry sandpaper; final polishing was with a 0.3-pm

alurnina slurry. OIder otoliths (>15 dph) were polished to within 10 prn of the core on

each side of the nucleus to ensure the best resolution of increments possible given the

above procedure. Polishing ceased in al1 cases when the core could be resolved within

10 Fm. Younger otoliths (< 14 dph) were mounted permanently in Embed 81 2 and not

polished. Otolith polishing was rnonitored at 250x with an Olympus BH-2 light

microscope. Right sagittae that were over-polished, broken or lost during polishing, were

discarded and replaced with corresponding left sagittae. AI1 otoliths were read with the

Olympus light microscope at 1OOOx oit immersion. Otoliths were read according to

Tanaka et al. (1 981), in which an increment consists of a discontinuous zone followed by

an incremental zone. lncrernent counts began from the core, extended along the ventral

or dorsal axis of the sagitta, and ended at the peripheral edge. Each otolith was read

blind (unknown chronological age and origin) at least twice by the reader; samples were

random and groups not consecutive. lncrement counts of individual samples were

averaged and the mean reported as age in days post hatch (dph).

VaIidation of Daily lncrement Formation

The experimental design of the validation study allowed the daily increment

formation technique to be validated in two ways. The first method validated daily

increment formation by calculating the number of elapsed days between the day of

hatching and the day of sampling, while the second method calculated the nurnber of

elapsed days between the day of oxytetracycline (OTC) marking and the day of

sampling. No significant difference occurred in the mean number of incrernent counts

between aquaria for TRBH-reared fish of the same age and from the same population,

so data were pooled as representative of either Miramichi or Shubenacadie stock.

Sarnples available for the validation analyses are summarized in Table 1.

Linear regression was used to model the periodicity of increment deposition

(slope) and the day of initial increment formation (y-intercept) for both validation

techniques. Initial regression equations were calculated independently for TRBH-reared

Shubenacadie and TRBH-reared Miramichi striped bass. MSEC-reared Miramichi

striped bass were included with TRBH-reared Miramichi striped bass, and a new

regression equation calculated. The day of initial increment formation for MSEC-reared

l a ~ a e (3, 4, 5, 6, and 8 dph) in 1997 (Table 1) was also modelled with linear regression.

Residuat plots of al1 regressions were examined for outliers, time sequences (correlation

between residuals), and gross departure from normality. Analysis of covariance

(ANCOVA) tested sirnilarities between regression equations for both populations of

striped bass.

Birthdate Analysis

Otoliths of wild-caught young-of-the-year striped bass from the Miramichi River

were prepared and read similarly to those of the hatchery validation study (this study).

The 1996 striped bass spawning season occurred over a two-week period. The brevity

of the spawning period negated the need to correct for proportional differences in

abundance at age due to differences in cumulative natural mortality, which for some

species is assurned to be greater for early spawned fish. Since the day of initial

increment formation for Miramichi striped bass was calculated to be two to four dph (this

study), and striped bass eggs generally require two to three days before hatching, the

ages interpreted from otoliths were adjusted by three to six days to obtain an accurate

birthdate distribution for the year. Ages interpreted frorn otoliths of wild Miramichi striped

bass were adjusted by three, four, five, and six days in order to correlate birthdate

distributions with adult striped bass bycatch in the commercial gaspereau fishery, which

were standardized to fish/trap/day (Bradford and Chaput, 1997). Birthdate distributions

were tested for similarity by one-way analysis of variance (ANOVA).

Growth Analysis

Growth rate was calculated as the mean total length at the end of a sampling

period minus the mean total length at the beginning of the sampling period, then divided

by the duration of the sarnpling period.

A least squares application of the logistic growth equation L, = K / 1 + eadt (Krebs

1972) was used to model growth for Shubenacadie and Miramichi striped bass reared at

Two Rivers Bass Hatchery, where:

Lt = length at time t (day),

K = the maximum value of L (TL attained at the end of the first growing season),

a = constant defining the position of the curve relative to the origin (approximate

estimate of length at hatch), and

R = the innate capacity for growth.

The parameter R (innate capacity for growth) from the logistic equations for both

populations was tested for similarity with the Fisher-Behren's statistic (Quinn and Deriso

1999):

where:

Gi = estimate of the parameter of interest (growth rate) from the Rh dataset, and

Si = the estimated standard error of the parameter.

The test statistic (R) was compared with the critical value of a standard normal

distribution (Kingsley 1979), at a significance level of a.

The polynomial growth equation Lt = mx c b + c2 was also used to mode1 growth

for the two populations of striped bass reared at TRBH, where:

Lt = length at time t (day),

m = capacity for growth (mmld),

b = approximate estirnate of length at hatch, and

c2 = constant defining the position of the curve relative to the origin.

Residual plots of growth data for hatchery-reared striped bass were examined for

outliers, time sequences (correlation between residuals) and gross departure from

normality. Differences in growth between the two populations of hatchery-reared striped

bass were tested for similarity by analysis of covariance (ANCOVA).

Similarly to TRBH-reared striped bass, Krebs' (1 972) logistic equation was used

to describe growth of wild Miramichi striped bass.

RESULTS

Light Microscopy

Daily increments observed on the otoliths of hatchery-reared larval and juvenile

Shubenacadie and Miramichi striped bass were highly discernible with Iight microscopy

(Figure 3). Eoth groups dernonstrated many similarities in the otolith microstructure. For

older otoliths (> 40 dph), a change in growth axis occurred between increments 30 and

40 (Figure 4), which made counting along the ventral axis in this area difficult. When a

shift in growth axis occurred along a counting transect, the last increment to be counted

was tracked to a more suitable transect extending to the edge. This technique permitted

a compfete count of the otolith, and no increments were rnissed in areas of transitional

growth.

Validation by Real Age

Linear regression of the daily ages and corresponding increment counts of

TRBH-reared Shubenacadie otoliths demonstrated a slope of 1 -00 (95% CI: 1 -00 - 1.01)

(Figure 5; Table 3) indicating that the periodicity of increment deposition was daily. The

corresponding intercept from the regression equation suggested that initiation of

incremental growth was at approximately 4 dph (95% CI: 4.79 - 3.73 days; Table 3).

The regression equation calculated for TRBH-reared Miramichi striped bass

(Figure 5) demonstrated a slope of 0.97 (95% CI: 0.95 - 0.981, which was significantly

different from 1, indicating that increment formation on these otoliths was less than daiIy.

The day of initial increment formation for TRBH-reared Miramichi fish appeared to be

approximately one day earlier than Shubenacadie fish (Table 3). Analysis of covariance

indicated that the slopes ( p c 0.001) and intercepts (p < 0.05) were significantly different

between regression equations for the two populations of striped bass reared at TRBH

(Table 4).

After increment counts of MSEC-reared Miramichi striped bass were combined

with increment counts of TRBH-reared Miramichi striped bass, the slope of the new

regression equation increased and the intercept decreased (Figure 6). Analysis of

covariance indicated that the periodicity of increment formation for the combined

Miramichi group continued to be significantly different from that of TRBH-reared

Shubenacadie striped bass (Table 4). Furthermore, the initiation of incremental growth

for the combined group of Miramichi striped bass continued to be significantly different (p

< 0.005) from that of the Shubenacadie population, offering further evidence that day of

initial increment formation for Miramichi fish occurred one day earlier than for

Shubenacadie fish (Table 3 ).

The lower intercept calculated for TRBH-reared Mirarnichi striped bass

corresponded with results obtained from MSEC-reared Miramichi larvae sampled in

1997 to determine the day of initial increment formation (Figure 7). Initial increment

formation for MSEC-reared Miramichi larvae in 1997 was at two dph (intercept = 2.1 1,

Table 3). When daily increment counts of the 1997 Miramichi larvae were combined with

TRBH-reared and MSEC-reared Miramichi increment counts, the regression equation

remained about the same (y = 0.97(age) - 2.83) (Figure 8).

Validation by OTC Marking

Immersion in the OTC solution failed to produce a mark that fluoresced under

ultra violet light, but the process did result in a stress mark laid down in the otolith matrix

on the day of application. Stress marks were highly visible with Iight rnicroscopy and

appeared as a single, very dark increment with an obvious disruption during formation

(Figure 9). Stress marks were visible in 100% of the otoliths examined from striped bass

reared at TRBH and MSEC. The difference between real age and the day of OTC

marking was approximately 4 days for both populations of striped bass. TRBH-reared

Shubenacadie and Miramichi fish marked at 16 dph had stress marks laid down at an

average increment of 12.5 and 12.8 dph, respectively. For MSEC-reared Mirarnichi

striped bass immersed in the OTC bath at 14 dph, stress marks were formed at an

average increment of 10.3 dph.

Results of the regression between the number of days elapsed since marking,

and the count of increments after the stress mark, indicated a slope of 1 .O for TRBH-

reared Shubenacadie striped bass (Figure 10; Table 5). Linear regression results for

TRBH-reared Miramichi striped bass were significantly different from Shubenacadie fish

reared at TRBH (Figure 10; Table 4). The same analysis with inclusion of the MSEC-

reared Miramichi fish with TRBH-reared Miramichi fish resulted with a similar equation (y

= 0.96(days elapsed since rnarking) + 0.86) (Figure 11 ; Table 5).

Hatchery Growth

80th Shubenacadie and Miramichi striped bass exhibited an approximate 19-fold

increase in total length during the 103 days between the beginning and the end of

sarnpling. Observed rnean TL increased from 6.8 mm to 129.3 mm for Shubenacadie

fish, and 6.4 mm to 11 9.5 mm for Miramichi fish, from 10 dph to 11 3 dph (Figures 12, 13;

Table 6). Growth rates increased progressively throughout al1 sampling periods with

fastest rates of 1.55 mrn/d (Shubenacadie) and 1.45 mm/d (Miramichi) observed

between August and September (Table 6).

Observed growth (TL) of Shubenacadie and Miramichi striped bass closely

resembled that of the predicted logistic curves ( R ~ = 0.99) (Figure 14; Table 6). Logistic

growth curves for both populations remained similar until 20 dph, at which point

Shubenacadie fish demonstrated an apparent increase in growth over Miramichi fish.

From the logistic equation, Shubenacadie striped bass had a predicted maximum length

of 166 mm, slightly Iarger than Miramichi fish (1 53 mm) by the end of the experiment, but

predicted lengths at time O and growth coefficients between the two populations were

the same (Table 7). The Fisher-Behren's statistic for the growth coefficient parameter

(R) for the logistic equations between TRBH-reared Shubenacadie and Miramichi striped

bass was not significantly different (p = 0.61). The polynomial function used to describe

growth between the two populations reared in the hatchery demonstrated that

Shubenacadie striped bass had a higher growth rate (0.31 mmfday) than Miramichi

striped bass (0.22 mm/day) over the duration of the study (Figure 15). Shubenacadie

striped bass started off smaller than Miramichi fish but compensated with an overall

increased growth rate. Growth between the two populations of hatchery-reared striped

bass, as inferred from the polynomial equations, was not significantly different (ANCOVA

p = 0.31).

lnterpretation of Ages for Wild Miramichi Striped Bass

Daily increments on otoliths of wild Miramichi striped bass resembled increments

of hatchery produced fish (this study) including a change in growth towards a different

axis between increments 30 and 40. Complete counts of daily increments were possible

with Iight microscopy for wild Miramichi striped bass collected in July and September but

not for samples collected in November. Daily increments of November samples could be

counted up to 110 - 120 dph, at which point they grew too close together for accurate

daily age interpretation (Figure 16). The Novernber results did not correspond with those

of the validation study, where daily ages were enumerated beyond 110 dph for TRBH-

reared Miramichi fish. Qualitative interpretation suggested that increment widths for

hatchery produced striped bass were greater at the 11 0 dph stage than wild striped bass

of similar age.

Wild Growth

Peripheral increments in otoliths collected in November were too close for

accurate aging (Figure 16) and therefore were ornitted from growth analyses. Wild

Miramichi striped bass increased in mean total length from 36 mm to 11 5 mm between

the end of July and the first of November 1996 (Figure 17; Table 8). Linear regression

provided a poor fit to obsewed growth within samples from July and September (Figure

18) suggesting that length was not a good predictor of daily ages in wild-spawned fish in

1996. Wild Miramichi striped bass exhibited an increase of 1.33 mm/d between the end

of July and the first of September 1996 (Table 8).

Observed growth (TL) of wild Miramichi striped bass closely resembled that of

the predicted logistic growth curve (? = 0.89) (Figure 19). Although striped bass

coflected in November could not be aged, the predicted line intersected the November

distribution of total lengths evenly, suggesting that the equation was likely a fair

representation of YOY growth in 1996 (Figure 19).

Birthdate Analysis

Only otoliths from samples collected in July and September were used for

birthdate analysis. Birthdate distributions were not consistent for juveniles collected in

July and September (ANOVA p < 0.001), suggesting that spawning in 1996 was more

protracted than previously believed (Bradford and Chaput, 1997). Mean birth dates for

samples collected on July 30, July 31, Septernber 4, and September 5, were June 6,

June 5, June 12, and June 13, respectively. Ages of sarnples coilected in July spanned

14 days, while September ages spanned 12 days (Figures 20 and 21). The birthdate

distribution for July-collected otoliths indicated that these fish were approximately one

week older than juveniles collected in September (Figure 22). Minimal overlap in

birthdate distributions existed between samples collected in July and samples collected

in September (Figure 22).

The validated daily increment technique for Miramichi striped bass (this study)

indicated that the day of initial increment formation was 3 dph. Assuming striped bass

eggs behaved "normally" in 1996, and required 48-72 hours at 16-1 8% before hatching

(Peterson et al. 1996), the addition of five or six days to the birth date distribution should

suggest the timing of spawning for that year. The addition of five days to the birthdate

distributions of samples collected on July 31, September 4, and September 5 most

closely followed the total adult bycatch intercepted in the gaspereau fishery of the NW

Miramichi in 1996 (Figures 23-26).

Table 1. Sampling scheme and otoliths available for validation analysis. NA not available.

Otolith samples for validation Population Date Hatchery Age (dph) Marked (dph) By real age By OTC marking

1996 Miramichi 18-Jun TRBH 10 NA 10 Miramichi 5-Jul TRBH 27 16 10 Miramichi 7-Aug TRBH 60 16 9 Miramichi 9-Aug MSEC 62 14 23 Miramichi 29-Sep TRBH 113 16 8

Shubenacadie 18-Jun TRBH 10 NA 12 Shubenacadie 5-Jul TRBH 27 16 34 Shubenacadie 7-Aug TRBH 60 16 25 Shubenacadie 29-Sep TRBH 113 16 18

1997 Miramichi 20-Jun MSEC 3 NA 7 NA Miramichi 21 -Jun MSEC 4 NA 11 NA Miramichi 22-Jun MSEC 5 NA 11 NA Miramichi 23-Jun MSEC 6 NA 10 NA Miramichi 25-Jun MSEC 8 NA 8 NA

Table 2. Summary of the catch per individual trap per 24h and the mean I 1 standard deviation (SD) catch of striped bass for each day that the 1996 gaspereau fishery on the Northwest Miramichi River was sampled for bycatch (from Bradford and Chaput 1997).

Traps Catch per trap per 24 hours Date Fished Sarnpled 1 2 3 4 5 6 Mean SD 24-May-9 6 2 2 1.3 0.8 1 .O 0.3 29-May-96 4 4 6.0 2.0 5.0 2.0 3.8 1.8 31 -May-96 11 5 11.5 6.5 14.0 57.0 22.0 22.2 18.1

Table 3. Results of validation analysis by real age for the two populations reared at different facilities. SE standard error, CI confidence interval, significance as it relates to a dope of 1.

S Io pe lntercept 95% CI Significance 95% CI

Group N Counts SE Low High P < 0.05 < P Counts SE Low High P

TRBH-reared Shubenacadie 89 1.00 0.00 1-00 1.01 > 0.05 -4.26 0.27 -4.79 -3.73 1 .O0

TRBH-reared Miramichi 37 0.97 0.01 0.95 0.98 c 0.05 -3.15 0.41 -3.97 -2.33 1.00

TRBH-reared Miramichi + 60 0.97 0.01 0.96 0.99 c 0.05 -2.77 0.47 -3.70 -1.83 1-00 MSEC-reared Miramichi

MSEC-reared Miramichi 47 0.83 0.04 0.75 0.91 < 0.05 -2.1 1 0.22 -2.54 -1.67 0.91 Larvae (1 997)

TRBH-reared Miramichi + 107 0.97 0.00 0.97 0.98 c 0.05 -2.83 0.18 -3.19 -2.47 1.00 MSEC- reared Miramichi + MSEC- reared Miramichi larvae

Table 4. Results from ANCOVAs between Shubenacadie striped bass and different groups of Miramichi striped bass for daily increment technique validation by reaI age and by OTC marking.

P Value Between grour, Validation method Slope Interce~t

TRBH-reared Shubenacadie and TRBH-reared Miramichi

TRBH-reared Shubenacadie and TRBH-reared + MSEC-reared Miramichi

TRBH-reared S hu benacadie and TRBH-reared + MSEC-reared Miramichi + MSEC-reared larvae (1 997)

TRBH-reared Shubenacadie and TRBH-reared Miramichi

TRBH-reared S hu benacadie TRBH-reared + MSEC-reared Miramichi

Real age < 0.001 0.020

Real age < 0.001 0.004

Real age < 0.001 < 0.001

OTC marking < 0.001 0.147

OTC marking < 0.001 0.003

Table 5. Results of validation analysis by OTC marking for the two populations reared at different facilities. SE standard error, CI confidence interval, significance as it relates to a slope of 1.

Slope lntercept 95% CI Significance 95% CI

Group N Counts SE Low High P <0.05 < P Counts SE Low High 6

TRBH-reared Shubenacadie T7 1 .O1 0.01 1 .O0 1.02 > 0.05 -1.06 0.29 -1.64 -0.48 1.00

TRBH-reared Miramichi 27 0.96 0.01 0.94 0.98 c 0.05 -0.19 0.52 -1.26 0.88 1.00

TRBH-reared Miramichi t 50 0.96 0.01 0.94 0.98 c 0.05 0.86 0.60 -0.36 2-07 0.99 MSEC- reared Miramichi

Table 6. Obsewed and predicted growth parameters (logistic curve) for Shubenacadie and Miramichi striped bass reared at Two Rivers Bass Hatchery. TL total length; NA not available.

Obsewed Predicted Real MeanTL Meangrowth Mean growth (mmtd) TL Mean growth Growth (mdd)

Population Date age (d) N (mm) (rndd) between sampling periods (m m) (mmld) between sampling periods

Shubenacadie 18-Jun 10 15 6.8 0.68 Shubenacadie 5 4 27 34 16.1 O. 60 Shubenacadie 7-Aug 60 30 47.3 0.79 Shubenacadie 29-Sep 113 20 129.3 1.14

Miramichi 18-Jun 10 15 6.4 0.64 N a>

Miramichi 5-Jul 27 10 14.2 0.53 Miramichi 7-Aug 60 10 42.4 0.71 Mirarnlchi 29-Sep 113 8 119.5 1 .O6

Table 7. Logistic growth parameters K (maximum total length attained by the end of the first growing season), a (estimate of total length at hatch), and R (innate capacity for growth) for TRBH-reared Shubenacadie, TRBH-reared Miramichi, and wild Miramichi striped bass. SE standard error, CI confidence interval.

95% CI Population Origin Parameter Estimate SE Lower Upper

Shubenacadie hatchery K 166.4 6.6 153.3 179.4 Shubenacadie hatchery a 3.38 0.06 3.25 3.50 Shubenacadie hatchery R 0.041 0.002 0.037 0.045

Miramichi hatchery K 153.4 9.4 134.4 172.5 Miram ichi hatchery a 3.47 0.10 3.27 3.67 Miramichi hatchery R 0.042 0.003 0.036 0.048

Miramichi wild K 125.7 50.6 24.7 226.6 Miramichi wild a 3.49 0.36 2.77 4.22 Miramichi wild R 0.046 0.016 0.014 0.077

Table 8. Observed growth parameters for wild Miramichi striped bass. TL total length; NA not available.

Observed

Mean age Mean TL Mean growth Mean growth (mmld)

Date N t5days (mm) hm/d) between sarnpling periods

July 30-31 32 6 1 35.9 0.59

September 4-5 40 90 74.6 0.83

November 1 452 NA 1 14.8 NA

Figure 3. Sagittal otoliths of hatchery reared striped bass. A. Miramichi larvae 3 dph; nucleus is obvious, however daily increment formation has not begun (Magnification 1000x oil immersion). B. Miramichi larvae 10 dph (Magnification 630x oil immersion). C. Polished transverse section of a sagitta from a Shubenacadie juvenile 27 dph (Magnification 250x).

(-i50 dph). ~ r rows indicate a change in growth axis corresponding to daily growth increments 30 - 40. Magnification 250x.

Shubenacadie y = 1 .OOX - 4.26 P = 1.00 n = 89

fi -. ,~ .-benacadie

Miramic hi

Miramichi y = 0.97~ - 3.15

P = 1-00

Figure 5. Regression between real age and increments counted on the otoliths of TRBH- reared Shubenacadie and Miramichi striped bass.

Figure 6. Regression between real age and increments counted on the combined otoliths of TRBH-reared and MSEC-reared Miramichi striped bass.

Figure 7. Regression between real age and increments counted on the otoliths of MSEC-reared Miramichi larval striped bass (1997). Individual points rnay represent several observations.

Figure 8. Regression between real age and increments counted on the combined otoliths of TRBH-reared Miramichi, MSEC-reared Miramichi, and MSEC-reared Miramichi larval striped bass.

Figure 9. Striped bass sagitta aged 27 dph. Arrows indicate stress mark at increment 14. Magnification 630x oil immersion.

33

Shubenacadie y = 1 . 0 1 ~ - 1.06

P = 1-00 n = 77 S hubenacadie

Miramichi

Miramichi y = 0.96~ - 0.1 9

P = 1-00 n = 27

O I I I i 1 i t

O 20 40 60 80 1 O0 120

Days elapsed since marking

Figure 10. Regression between days elapsed since marking and increments formed after the stress mark for TRBH-reared Shubenacadie and Miramichi striped bass.

Days elapsed since rnarking

Figure 11. Regression between days elapsed since marking and increments formed after the stress mark for TRBH-reared Miramichi and MSEC-reared Miramichi striped bass.

4 12 20 28 36 44 52 60 68 76 84 92 100 108 116 124 132 140

Total length (mm)

C O .-

0.09 - Q 2 L une 18

Figure 12. Length frequency distribution of TRBH-reared Shubenacadie striped bass.

July 5

1 1 1

August 7 Septem ber 29

August 7 September 29

k

44 52 60 68 76 84 92 100 108 116 124 132 140

Total length (mm)

1 , Il I UIII I I j i i

Figure 13. Length frequency distribution of TRBH-reared Miramichi striped bass.

Shubenacadie Lt =l66.4/1 + e 338-a041'

9 = 0.99 n=99

Figure 14. Logistic growth curves for TRBH-reared Shubenacadie and Miramichi striped bass.

Shubenacadie y = 0.01x2 + 0.31~ + 2.65 8 = 0.99 n = 99

Figure 15. Polynomial growth curves of TRBH-reared Shubenacadie and Miramichi striped bass.

Note the decrease in increment widths a t increments 1 10-1 20 (lower parenthesis) and further decreases in increment widths at the edge (upper parenthesis). Magnification 630x oil immersion.

0.15 7

I Nowm ber 1

Septem ber 4-5

28 33 38 4 3 48 53 62 67 72 77 82 87 92 97 102107 83 109135

Total length (mm)

Figure 17. Length frequency distributions of wild Mirarnichi striped bass sampled in July, Septernber and November 1996.

Figure 18. Regression of age and total length for wild Miramichi striped bass collected July 30 and 31, 1996 (upper panel), and September 4 and 5, 1996 (lower panel).

Figure 19. Logistic growth curve for wild Miramichi striped bass collected July 30 - 31 and September 4 - 5, 1996. Total lengths of November samples have been included on the iine but not used in the calculation.

Figure 20. Age distribution of juvenile Miramichi striped bass collected on July 30-31, 1996.

Figure 21. Age distribution of juvenile Miramichi striped bass collected on September 4- 5, 1996.

July n = 30

mseptember n = 38

Birt hdate

Figure 22. Birthdate distributions of young-of-the-year striped bass collected in t h e Miramichi River on July 30-31, and September 4-5, 1996.

23- 26- 29- 1- 4- 7- 10- 13- 16- 19- May May Vay Jun Jun Jun Jun Jun Jun Jun

Date + O days

23- 26- 29- 1- 4- 7- 10- 13- 16- 19- May May May Jun Jun Jun Jun Jun Jun Jun

Date + 3 days

23- 26- 29- 1- 4- 7- 10- 13- 16- 19- May May May Jun Jun Jun Jun Jun Jun Jun

Date + 4 days

May May May Jun Jun Jun Jun Jun Jun Jun

Date t 5 days

23- 26- 29- 1- 4- 7- 10- 13- 16- 19- May May May Jun Jun Jun Jun Jun Jun Jun

Date + 6 days

Figure 23. Birthdate distribution of young-of-the-year Miramichi striped bass collected on July 30, 1996 (n = 13) and total adult bycatch in the NW gaspereau fishery. The birthdate distribution has been adjusted by three to six days.

23- 26- 29- 1- 4- 7- 10- 13- 16- 19- May May May J u n J u n J u n Jun Jun J u n J u n

Date t O days

23- 26- 29- 1- 4- 7- 10- 13- 16- 19- May May May J u n J u n J u n Jun Jun J u n J u n

ûate + 3 days

23- 26- 29- 1- 4- 7- 10- 13- 16- 19- May May May J u n Jun J u n Jun Jun J u n J u n

Date + 4 days

23- 26- 29- 1- 4- 7- 10- 13- 16- 19- May May May J u n J u n J u n Jun Jun J u n J u n

Date + 5 days

23- 26- 29- 1- 4- 7- 10- 13- 16- 19- May May May J u n J u n J u n Jun Jun J u n J u n

Date + 6 days

1 - JwerileB irt- 1 -Addt Catch

Figure 24. Birthdate distribution of young-of-the-year Miramichi striped bass collected on July 31, 1996 (n = 17) and total adult bycatch in the NW gaspereau fishery. The birthdate distribution has been adjusted by three to six days-

24- 27- 30- 2- 5- 8- 11- 14- 17- 20- May May May Jun Jun Jun Jun Jun Jun Jun

Date + O days

24- 27- 30- 2- 5- 8- 11- 14- 17- 20- May May May Jun Jun Jun Jun Jun Jun Jun

Date + 3 days

24- 27- 30- 2- 5- 8- 11- 14- 17- 20- May May May Jun Jun Jun Jun Jun Jun Jun

Da!e + 4 days

May May May Jun Jun Jun Jun Jun Jun Jun

Date t- 5 days

24- 27- 30- 2- 5- 8- 11- 14- 17- 20- May May May Jun Jun Jun Jun Jun Jun Jun

Date + 6 days

Figure 25. Birthdate distribution of young-of-the-year Miramichi striped bass collected on September 4, 1996 (n = 25) and total adult bycatch in the NW gaspereau fishery. The birthdate distribution has been adjusted by three to six days.

t

5 0.20 - c. 71 g 0.10 - -Adilt Cdch

&- 0.00 r

24- 27- 30- 2- 5- 8- 11- 14- 17- 20- May May May Jun Jun Jun Jun Jun Jun Jun

Date + O days

24- 27- 30- 2- 5- 8- 1 1 - 14- 17- 20- May May May Jun Jun Jun Jun Jun Jun Jun

Cate + 3 days

24- 27- 30- 2- 5- 8- I l - 14- 17- 20- Wy May May Jun Jun Jun Jun Jun Jun Jun

Date + 4 days

24- 27- 30- 2- 5- 8- 11 - 14- 17- 20- hky May May Jun Jun Jun Jun Jun Jun Jun

Date + 5 days

May May May Jun Jun Jun Jun Jun Jun Jun Date + 6 days

Figure 26. Birthdate distribution of young-of-the-year Miramichi striped bass collected on September 5, 1996 (n = 13) and total adult bycatch in the NW gaspereau fishery. The birthdate distribution has been adjusted by three to six days.

Figure 27. Mean daily water temperatures from the Northwest Miramichi River near Hackett's Beach, 1996.

DISCUSSION

Light Microscopy

Results of this study support the contention that high quality Iight microscopy,

coupied with good preparation techniques, are adequate for enumerating daily

increments on otoliths of northem stnped bass populations with minimal error and robust

confidence intervals. Light microscopy has been used for age validation for a nurnber of

species including striped bass (Jones and Brothers 1987; Secor and Dean 1989).

Apparently light microscopy works welt for validation of daily otolith increments of well-

fed striped bass, but underestimates true age when bass are fed at suboptimal levels

(Jones and Brothers 1987). Striped bass reared at Two Rivers Bass Hatchery and fed

ad libitum did not exhibit any abnormality in the otolith microstructure. Also, no

environmental variables were manipulated and al1 aquaria were treated similarly, which

provided ail fish the same opportunity for normal otolith growth.

In studies of underfed striped bass larvae, scanning electron microscopy (SEM)

can increase the accuracy of age interpretations. Jones and Brothers (1987) had better

success with age validation of underfed striped bass larvae using SEM compared to Iight

microscopy. Some researchers suggest that SEM be used to check increment counts

after light microscope counts, and especially when the daily increment technique is

being vafidated the first time for a species. However, for rnany researchers, access to

SEM equipment is difficult and costly, and sarnples require longer preparation times than

traditional light microscopy techniques.

The accuracy and precision of age determinations are directly related to the

quality of otolith preparation and the experience of the reader (Campana and Moksness

1991). For this study, otolith samples older than 10 dph wàre polished on eacti side of

the nucleus to within IO um of the core, This polishing technique permitted easy

resolution and identification of al1 increments except for those ventrally and dorsally

corresponding to 30 to 40 dph. This area of the sagitta dernonstrated transitional growth

towards a different axis, but was not a consequence of preparation techniques or

capabilities of the Iight microscope. Tracing increments back proximally or distally on the

otolith sample always produced a suitable transect for increment counts through the

transitional growth. If researchers wish to measure incrernent widths of ventral or dorsal

transects on otoliths that have been cut in the transverse plane, SEM would be

recommended for northern striped bass greater than one month old.

Daily otolith increments of hatchery-reared Shubenacadie and Miramichi striped

bass were read reliably up to age 113 dph with Iight microscopy techniques. These

results do not correspond with those of Kline (1990), who suggested that otoliths are

reliably aged for striped bass < 80 dph, but fish > 80 dph and c 110 dph require age

correction factors. Kline (1 990) ais0 concluded that striped bass > 11 0 dph cannot be

reliably aged with light microscopy. In my study however, daily ages of striped bass

having maximum ages of 11 3 dph were enurnerated using Iight microscopy without the

need for a correction factor.

The ability to age hatchery-reared northern striped bass to 11 0 dph suggests that

there is a high likelihood of observing similar microstructure in otoliths of wild fish.

Sirnilar otolith preparation techniques should permit the aging of northern caught wild

striped bass during the sumrner months (Le., frorn June until the end of September) with

relatively minor expense. The ability to age wild fish over their first three or four months

of life would be useful in isolating ecological issues related to growth during the sumrner

and survival through the first winter. A sampie of otoliths frorn hatchery-reared fish older

than 113 dph would have been useful for reference, especiaily during aging of wild fish

of similar age.

Daily lncrement Validation

lncrements on the otoliths of hatchery-reared Shubenacadie striped bass were

formed daily, similar to those of more southern populations (Jones and Brothers 1987;

Secor and Dean l989), but hatchery-reared Miramichi striped bass formed increments

less than daily. Although increment deposition rates for both groups were statistically

different, results from the regression equations were similar, suggesting that the

difference probably is not biologically significant. For example, if the precision of the

increment counts for either population was less, thereby creating a greater degree of

error, the regression equations would not have been significantIy different. In addition,

the small sample size (n = 8) of the oldest TRBH-reared Miramichi fish (1 13 dph) was

likely a major factor in causing the difference between the regression equations for the

two populations; differences in increment counts between the two groups were only

significant at 1 13 dph (ANOVA p = 0.002). The higher variance of the 113 dph Miramichi

counts resulted in the deviation of the regression lines at that point and caused the slope

of the Miramichi line to decrease to less than one (Figure 5). It is Iikely that a larger

sample size of Miramichi striped bass aged 113 dph would have resulted with a slope

not significantly different from 1 .O.

Deterrnining the time at which the first otolith increment is formed is important for

accurate age interpretations as well as back-calculating the date of hatch. The initiation

of increment formation for TRBH-reared Shubenacadie fish was at approximately 4 dph,

which corresponds closely with that of southern populations (Jones and Brothers 1987;

Secor and Dean 1989). Jones and Brothers (1987) suggested that initial increment

formation for striped bass reared in New York (unknown broodstock) was between 3 and

5 dph. Secor and Dean (1989) reported that incremental growth begins between 4 and 5

dph for Santee Cooper striped bass. Linear regression results for TRBH-reared

Miramichi striped bass suggested that initial increment formation was at 3 dph, which

was significantly different from that of Shubenacadie fish reared at the same location

and under the same conditions. Miramichi larvae of 3, 4, 5, 6, and 8 dph coilected in

1997 for initial increment analysis provided clear evidence that increment formation in

Miramichi fish began earlier than for Shubenacadie striped bass (Table 3).

Reasons why Miramichi striped bass exhibited incremental growth before

Shubenacadie striped bass did are not obvious. Water temperature is known to affect

the initiation of incremental growth for striped bass (Houde and Morin 1990). Houde and

Morin (1990) demonstrated earlier increment formation for laboratory-reared striped

bass when water temperatures were elevated. Verification of water temperature effects

on initial increment fornation could be accomplished with laboratory rearing of Miramichi

and Shubenacadie striped bass at various water temperatures. Also, researchers trying

to identify stimuli affecting initial increment formation in striped bass may wish to look at

physiological issues such as egg size and the amount of yoIk, size at hatch, and duration

of yolk sac depletion.

Otolith Marking

Oxytetracycline (OTC) marks in the otoliths did not fluoresce under ultraviolet

Iight even though the concentration of OTC used was the same as that successfully

used to mark southern striped bass (Secor et al. 1991 ). Secor et al. (1 991 ) reported that

OTC-marked otoliths were identifiable for at least five to seven months for larvae and

juvenile striped bass, respectively. There are no obvious explanations as to why the

OTC did not incorporate into otoliths of northern striped bass. Two possibilities are that

exposure time was too short, or that concentrations of OTC higher than that

recomrnended in the Iiterature should have been used. A number of species show

variable success in marking otoliths with OTC (Secor et al. 1991 ; Thomas et al. 1995),

calcein (Beckman et al. 1990; Hales and Hurley 1991 ; Thomas et a1.1995), and alizarin

complexone (Powell et al. 2000).

However, both Shubenacadie and Mirarnichi groups exposed to the OTC bath

did form highly identifiable marks on otoliths, most likely associated with marking stress.

These marks were formed on the same day as the OTC marking event. Handling

procedures during the marking process did not prornote additional mortality, but rnay

have been adequate to record a stress mark on otoliths of these fish. Tetracycline has

been demonstrated to cause stress, and mortality, for some species (Tsukamoto et al.

1989; Bumguardner and King 1996).

Although the incorporation of a stress mark on otoliths of northern striped bass

was fortuitous, the marking of otoliths using stress has worked well as a biological aging

marker for other species (Boehlert and Yoklavich 1985; Volk et al. 1984). Manipulations

of environmental stimuli, such as temperature fluctuations (Mosegaard et al. 1988),

photoperiod (Wright 1991), handling stress (Ralston and Miyarnoto 1983), and anaerobic

stress (Mugiya and Uchimura 1989) have been successful in producing stress marks on

otoliths. Marking otoliths with stress dismisses the need for fish to be exposed to

chernicals and eliminates the need for elaborate microscope equiprnent to detect the

marks.

Hatchery Growth

Similar growth rates between the two populations were observed in the hatchery,

but several factors may have influenced the outcome of the experiment. The original

study design incorporated replicate tanks in an atternpt to quantify potential variability in

growth within each of the populations. However, mortalities in each of the aquaria

reduced the stocking densities to such a level that al1 Miramichi larvae had to be

combined into one aquarium to maintain original stocking densities. This action resulted

in loss of replicates, thereby elirninating the ability to test for tank effects on growth. Any

environmental differences between tanks, such as light intensity, ammonia, pH, or

accumulation of solid wastes could influence growth rate. However, both tanks were

treated the same, and water was changed every two days, so these parameters should

have been very sirnilar if not equaf. Therefore, I believe that any tank influences on

growth should have been similar between tanks and resulted in minimal effect on the

outcome of the experiment.

Conover's (1990) countergradient variation rnodel suggests that growth in fish is

under genetic control and that because of the earlier onset of winter in the north, many

fish, including striped bass, exhibit faster growth to compensate for the relatively short

growing season. If his hypothesis is correct, striped bass frorn the Miramichi should

exhibit faster growth rates than Shubenacadie striped bass, (albeit a very srnall

latitudinal difference between provinces), as well as any other striped bass population in

the world. If Mirâmichi striped bass were to exhibit faster rates of growth, they would be

the obvious choice for grow-out in both the aquaculture industry and for stocking-

restocking programs. Identifying growth characteristics that maximized size in the

shortest amount of tirne would reduce time to market andfor time in pond or tank culture

before stocking. Also, attaining a critical size at the end of the first growing season may

be especially important in the north if survival and recruitment is driven by size

dependent winter rnortality.

Growth of Shubenacadie and Miramichi striped bass reared under identical

conditions at Two Rivers Bass Hatchery was not significantly different. There are several

possibilities for this result. The distance between the Gulf of St. Lawrence and the Bay of

Fundy rnay not be adequate to differentiate growth rates of the two populations based on

Conover's (1990) "countergradient variation modeln. Results from this study are not the

first to disagree with the countergradient variation hypothesis. Conover et al. (1997)

studied striped bass from rivers that nearly covered the entire range of the species. Their

work showed that striped bass from the Santee-Cooper systern in South Carolina were

the slowest growing, white Hudson River fish were not only the fastest growing but

outgrew Shubenacadie striped bass, which originated from a more northern latitude.

Over their 10-day experiments, Conover et al. (1 997) noted that growth in total length for

Shubenacadie, Hudson, and Chesapeake striped bass was not significantly different.

Genetic work was not conducted on the broodstock from these rivers, which according to

Rulifson and Laney (1999), has been stocked with progeny from numerous broodstock

across different US latitudes. Also, Brown et al. (1 998) conducted a striped bass growth

study similar to Conover et al. (1997) but was unable to place striped bass growth rates

in the correct ascending order from south to north. Finally, problems with the

"countergradient variation hypothesis" have transcended the genetic boundaries and

recently have been linked to environmental aspects. Secor et al. (2000) determined that

growth of young-of-the-year striped bass is affected by salinity and therefore cautioned

that growth in conjunction with different saiinity gradients within estuaries would be

sufficient to alter the expected latitudinal gradient of young-of-the-year growth rates.

Environmental variables and not necessarily genetics of a population may control

growth of northern striped bass. Studies dernonstrating the effects of environmental

manipulations, such as water temperature, salinity, and ration level (Kerby 1986;

Peterson et al. 1996) on growth of striped bass under laboratory conditions are

numerous. Both groups of northern striped bass in this study were reared under identical

conditions and did not show any differences in growth over the duration of the study,

suggesting that abiotic factors play an important role in growth. My results cannot ruie

out the possibility that genetic differences between these populations may be so srnaIl

as to be masked by environmental effects. Additional studies to determine the relative

influences of the environment and genetics on growth of northern striped bass are

warranted.

Miramichi eggs hatched and larvae were rnaintained at the MSEC for two days

before they were transported to TRBH. During this time, Miramichi fish were held at an

approximate rnean water temperature 2OC lower than Shubenacadie fish at TRBH.

Although the tirne before transport was short, the difference of 2OC may have been

enough for Shubenacadie fish to get "a head startn on the Miramichi fish. According to

the polynomial functions, Shubenacadie striped bass started out smaller but soon

compensated with an increased growth rate over Miramichi fish. Miramichi striped bass

undewent the stress of transport and placement in "unfamiliai' water, while

Shubenacadie striped bâss were not subjected to this stress. Shubenacadie fish had the

advantage of being hatched and reared in constant conditions throughout the study and

were rnaintained in river water that undoubtedly contained natural food that would have

been available at the time of first feeding. It is unknown how Shubenacadie striped bass

would have fared if they were faced with the sarne stresses as Miramichi fish. It is

unfortunate that a simultaneous growth study with both populations of striped bass was

not possible ai MSEC.

With interest in striped bass aquaculture gaining in the Maritimes (Peterson

1991), the question of which population it is best to derive broodstock has surfaced.

Results presented here suggest that broodstock frorn either the Shubenacadie or

Miramichi population would grow at similar rates. Over the duration of this study (1 13

dph), obsewed daily increases in length for TRBH-reared Shubenacadie and Miramichi

striped bass were 1-14 mm and 1.06 mm respectively. If the aquaculture industry wants

to pursue either of these populations for striped bass production, further growth studies

under practical and intense culture are highly recornmended. Southem Gulf of St.

Lawrence striped bass have been reared in hatcheries around the Maritimes (DFO

hatchery Cardigan, PEI), but generally studies have been lirnited to feasibility

experiments and growth has not been monitored scientifically. Shubenacadie striped

bass, however, have been reared at several hatcheries around the Maritimes and the

US where growth was monitored successfully (Peterson et al. 1996; Conover et al.

1997). The growth rate of laboratory-reared Shubenacadie striped bass was 0.78 mrnld

and was not significantly different frorn growth rates calculated for striped bass from the

Hudson or Choptank Rivers during the same 10-day experiment (Conover et al. 1997)

Age Interpretations of Wild Miramichi Striped Bass

Daily increments on otoliths collected in November could be counted up to 110 -

120 dph, at which point they grew too close together for complete counts given the

equipment and techniques employed.

One explanation for the tight incremental growth may be due to change in water

ternperatures. Water temperatures began decreasing dramatically the second week in

Septernber 1996 (Figure 27), which may have caused spacing of incremental growth to

decrease. Thus it appears that aging of wild juvenile striped bass at the northern limit of

its breeding range is possible with light microscopy up to approximately 110 days old. If

daily ages of striped bass are required beyond 1 I O to 120 dph, then other techniques

such as SEM may have to be employed. Low temperatures can result in little or no

incremental growth on otoliths. Casas (1998) dernonstrated a threshold temperature

level that must be exceeded for increments to be discernible for winter flounder

(Pleuronectes amencanus) larvae. Marshall and Parker (1982) showed that increment

formation in juvenile sockeye salmon (Oncorhynchus nerka) otoliths ceased when water

temperatures reached 5%. Taubert and Coble (1 977) deterrnined that cessation of daily

ring production in bluegill (Lepomis macrochirus) was the result of an interruption in fish

growth due to temperatures below 10°C. Furthermore, increment widths are known to

increase when water temperatures are high and decrease when water temperatures are

low for Atlantic silverside Menidia menidia (Barkrnan and Bengtson 1987) and chinook

salmon Oncorhynchus tshawytscha (Neilson and Geen 1982).

A second explanation for tightening of otolith increments may be related to a

possible shift in habitat later in the growing season. Young striped bass shift habitats by

moving downstream from upper freshwater areas toward lower estuarine areas, as the

season progresses. The transition from predominantly freshwater to estuarine waters

toward the bay could cause changes in otolith growth patterns. Changes in otolith

microstructure corresponding to entry into estuarine habitats for chum sa!mon

Oncorhynchus keta have been reported (Simenstad et al. 1980), and Ruzycki and

Wurtsbaugh (1 999) demonstrated ring patterns on the otoliths of the endemic Bear Lake

sculpin Cottus extensus corresponding to a habitat shift from the profundal zone to the

littoral zone. Also, Zhang et al. (1 995) dernonstrated changes in microstructure patterns

on the otoliths of chinook salmon corresponding to the time of release into the wild from

the hatchery. Changes in incrernent widths corresponded to larval metamorphosis of

starry flounders (Campana 1984).

Birthdate Analysis

Given the 1996 birthdate distributions, daily increments between 1 10 - 120

would correspond to the first and second week in October. Interestingly, no striped bass

were captured during the beach seine survey at that time of year (this study).

Furthermore, Robichaud-LeBlanc et al. (1 998) reported an absence of juveniles in their

upstream beach seining survey during the same time of year in 1992. Robichaud-

LeBlanc et al. (1998) interpreted their findings as a downstream migration of young-of-

the-year to the more saline waters of the estuary. It is possible that increments f o n e d

after 110 - 120 dph coincide with the days when young-of-the-year striped bass are

migrating from shallow, inshore, riverine habitats to the estuary.

Birthdate distributions of wild Miramichi larvae indicate that there were two major

peaks of spawning activity in 1996, the first between May 29 - June 1, and the second

between June 5 - 8. Bradford and Chaput (1997) reported that adult striped bass were

intercepted twice in the gaspereau fishery of the NW Mirarnichi in 1996, once as they

ascended the river to spawn, and again after spawning dunng emigration, Birthdate

distributions presented here are consistent with the observation and timing of the two

peak adult catches (Bradford and Chaput 1997), and would suggest that both "runsn of

fish were captured during their up-river spawning migration. Only striped bass larvae

collected in July had birth dates similar to what would be expected from the single

spawning event (June 1- June 3) reported by Bradford and Chaput (1997).

Mean birth dates differed by six to eight days between July and September

samples, and minimal overlap existed between birthdate distributions. These results

suggest that juveniles spawned early in the season were not available to capture in

September, and alternatively, that fish spawned Iater in the season were not available to

capture in July.

The apparent non-availability of late spawned striped bass in the samples

collected in July is perplexing. Robichaud-LeBlanc et al. (1998) reported an absence of

young-of-the-year striped bass during midchannel trawls at the end of June in the

Miramichi River, but noted that nurnbers of juveniles were increasing in near-shore

beach seine surveys. If these interpretations are accurate, then young-of-the-year

spawned in 1996 should have had ample tirne to take up residence in the near-shore

shallows of the river and would have been available to capture by beach seine.

Distribution of early- and late-spawned cohorts in different areas of a river is common

(Ulanowicz and Polgar 1980), but the six to eight day difference in birthdate distributions

of Miramichi striped bass in 1996 is not Iikely enough time to observe complete

separation of both cohorts in different areas of the river,

However, my results cannot rule out the possibility that the preferred rearing

habitats for early and late spawned juveniles are in different locations of the river

throughout the summer. Robichaud-LeBlanc et al. (1998) reported a size-related

downstream migration of the young-of-the-year between June and September, which

would indicate that juveniles were always in a state of transition, increasing their

distribution downstream. Presumably, early-run fish spawn first, the product of their

spawn hatch downstream of the spawning grounds first, and the newly hatched lawae

are already on their downstream migration by the time late-run fish spawn. it is possible

then, that in a downstream direction, younger cohorts are progressively and continuously

replacing all of the areas in the freshwater section of the river. Thus, by autumn of any

given year, the only remaining juveniles in the freshwater section of the river should be

the youngest; i.e., those spawned last.

The birthdate distribution for September sarnples supports this hypothesis. Early

spawned juveniles were not available to capture at the same location as they were in

July. Furtherrnore, genetic research conducted on young-of-the-year collected in

Kouchibouguac and Richibucto estuaries in August of 1997 (Robinson 2000) indicated

that these juveniles were of Miramichi origin. It is possible that juveniles occurring

outside of the estuary (Robinson 2000) were those that are spawned eariiest. A sample

of otoliths from juveniles intercepted outside of Miramichi Bay may confirrn this

suspicion. Otolith microstructure of the endemic Bear Lake sculpin revealed that they

undenvent an ontogenetic habitat shift from the cooler, less productive profundal zone to

the warm, food-rich littoral zone (Ruzycki and Wurtsbaugh 1999).

Early-spawned juveniles, which were not apparent in September samples, could

have had poor survival. Losses of fish due to natural mortality are believed to be

cumulative; fish spawned earliest are subjected to more mortality than fish spawned later

and consequently, fewer older fish relative to younger fish remain. Campana and Jones

(1992) recommended that birthdate analysis studies should correct for mortality rates

associated with the population, species, or life stage of the species in question. A variety

of methods for correcting rnortality rates have been used when birthdate distributions

extend over one month (Yoklavich and Bailey 1990) or several months (Methot 1983).

The difference between hatch date distributions for Miramichi striped bass in the current

study was six to eight days. The possible differences in natural rnortality over this short

period (one week) is not likely since the occurrence of any environmental event during

that period would have affected al1 cohorts similarly.

Numerous striped bass studies in the US (Rutherford and Houde 1995; Cooper

et al. 1998) have used the daily aging technique to discriminate between cohorts of the

same spawning season. Spawning seasons for US striped bass are longer, occur over

weeks and can produce several cohorts from one spawning season. Although striped

bass spawning in Canada is generally much shorter and usually only occurs over days

(Rulifson and Dadswell 1995), aging criteria presented here wilf ailow for discrimination

between cohorts at the northern Iimit of the species breeding range. In the event that the

Miramichi population rebuilds to its historic levels, the spawning season rnay be

expected to become more protracted and will require the use of this daily aging criteria

to distinguish between cohorts. SimiIarfy, the daily aging criteria can be extended to the

Shubenacadie population where spawning in 1999 was more protracted than Miramichi

striped bass (R. Bradford, B I0 Dartmouth NS, personal communication).

It is unfortunate that samples collected from the estuary in November could not

be aged with the equipment and techniques used. An accurately aged sample of

juveniles from that time of year could determine whether or not the birth date

distributions converged on the overwintering grounds of the young-of-the-year. Also, if

Miramichi striped bass must reach a critical size during their first growing season

(Bernier i996), a known-aged sample of f ish at length at the end of the first growing

season would be useful in determining the relative importance of early versus late

spawned fish. Higher survival rates have been demonstrated in young-of-the-year that

were spawned later in the spawning seasorn (Ulanowicz and Polgar 1980; Rutherford

and Houde 1995; McGovern and Olney 1996:+ If this idea is taken a step further for the

Miramichi population, the importance of run ttirning of the adults in the spring could be

addressed. Since the Miramichi spawning season is so short and the population is

reduced, the ability to detect early versus late run fish is impossible and would therefore

have no present implications on the commercüal gaspereau fishery of the NW Miramichi.

Wifd Growth

The size (TL) attained by the end of tthe first growing season for wild Miramichi

striped bass was the same in 1996 (mean TL of 115 mm) as it was in 1992 (rnean TL of

114mm) (Robichaud-LeBlanc et al. 1998), bu-t not the same as in other years (Bradford

and Chaput 1998). Pre-winter size of striped bass is highly variable in sorne years for the

Miramichi population (Bradford and Chaput 1998), as welI as other southem populations

(Cooper et al. 1998). Growth of wild youngr-of-the-year striped bass is known to be

affected by abiotic factors such as food abundance (Rutherford et al. 1997), rese~o i r

discharge (Rulifson and Manooch 1990), t ime of spawning (Ulanowicz and Polgar 1980;

McGovern and Olney 1996; Bulak et al. 1997), water temperature (Rutherford and

Houde 1995; Rutherford et al. 1997), and salinity (Secor et al. 2000).

Robichaud-LeBlanc et al. (1998) reparted that growth was most rapid during

sumrner and slowed during autumn for Miramichi striped bass. Their logistic equation

predicted a maximum length of 123.3 mm wittn daily increases of 0.73 mm between June

and October. My results are consistent with ahose of Robichaud-LeBlanc et al. (1998),

predicting a maximum length of 125.7 mm by the end of the growing season in 1996 and

recording a mean observed growth rate of 0.83 mmld by the beginning of September. If

striped bass growth continued into September and October 1996 at a reduced pace, the

mean growth rate would decrease and approximate that reported by (Robichaud-

LeBlanc et al. 1998).

Growth rates reported here for wild Miramichi striped bass appear to be higher

than other populations of striped bass at the south and the center of the species range.

Although growth of hatchery-reared striped bass did not support Conover's (1990)

countergradient variation model, growth rates of wild northern striped bass appear to be

higher than in other southern populations. However, it has been noted in several wild

striped bass populations that growth rates can Vary among years (Bulak et al. 1997) and

within cohorts of the same populations (Rutherford et al. 1997). Bulak et al. (1997)

recorded growth rates of between 0.78 and 0.91 mmld from 1988-1 990 for striped bass

in the Santee-Cooper system which is contradictory to Conover et al. (1997) who

demonstrated that Santee-Cooper fish were the slowest growing of their experimental

design. Daily growth rates for striped bass in Albermarle Sound, N.C., were between

0.70 and 1.10 rnmld for years 1990-92 (Cooper et al. 1998) and cohort-specific growth

rates ranged frorn 0.1 1 to 0.46 rnmld in the Potomac River and between 0.18 to 0.36

mmfd in Upper Chesapeake Bay (Rutherford and Houde 1995). Growth for Miramichi

striped bass in 1996 was similar to Shubenacadie striped bass that achieved a mean

total length of 80 mm by August in 1979 (Dadswell et al. 1984). Magnin and Beaulieu

(1967) reported that striped bass from the St. Lawrence River, Quebec, reached a mean

forklength of 97 mm by September-November.

WiId Miramichi striped bass attained a mean TL of 11 5 mm by November 1, while

TRBH-reared Miramichi and Shubenacadie fish were 119 mm and 129 mm by

September 29, respectively. Growth of both populations of TRBH-reared striped bass

was better than what was observed for wild young-of-the-year collected from the

Miramichi River. If growth of wild striped bass coIlected on November 1, 1996 is

assumed to have ceased for the year, and the logistic equation for TRBH-reared

Miramichi fish is accurate, total length achieved by the end of the first growing season

was 33% higher for hatchery fish. It is Iikely that increased water temperatures and food

levels, and an absence of predators in the hatchery, prornoted growth beyond what was

observed in the wild. These data indicate that growth of young-of-the-year striped bass

is highly dependent on environmental factors.

Increased growth of northern striped bass in hatchery facilities is welcome

information for aquaculturists and fisheries managers. If young-of-the-year were reared

in a hatchery during their first growing season, the larger size that could be attained

would undoubtedly promote suwival after stocking. Managers and assessrnent biologists

are currently exploring this idea with Miramichi young-of-the-year for restocking of the St.

Lawrence River in Québec (G. Chaput, DFO Moncton NB, personal communication).

Miramichi young-of-the-year were removed from the estuary at the end of their first

growing season to be maintained in a hatchery through their first winter. In the spring,

after the O+ bass have survived the problem of size-dependent winter mortality, they will

be stocked when water temperatures warm.

Size at the end of the first çrowing season has been cited as an important

criterion for winter survival of young-of-the-year striped bass in the Miramichi River

(Chaput and Robichaud 1995; Bernier 1996; Robichaud-LeBlanc et al. 1998), the

Hudson River (Hurst and Conover 1998), as well as other closely related species (yellow

and white perch, and srnallmouth bass, Oliver et al. 1979; Johnson and Evans 1990;

Shuter and Post 1990). Data presented here for the Miramichi population suggest that

environmental conditions experienced by the juveniles throughout their first growing

season determine their size by winter. Thus, it appears that summer environmental

conditions rnay ultirnately define recruitment to the adult population. Recruitment of

Chesapeake Bay striped bass has been dernonstrated to be highly correlated to

environmental variables (Rutherford and Houde 1995; Secor and Houde 1995;

Rutherford et al. 1997). One rnight hope that with the trend of increasingly warrn

sumrners in the north (Caissie 2000), environmental conditions conducive for better

young-of-the-year growth will prevail, and the abundance of striped bass at the northern

limit of its range will increase.

Total length of wild YOY from the Miramichi River was not a good indicator of

age in 1996. There are several reasons why this phenornenon occurs. Gear selectivity is

one factor; largest individuals of a given age rnay becorne susceptible to capture, while

the srnallest individuals of the same age may not be susceptible. This may be due to

mesh size of the gear, to ontogenetic changes in behavior associated with development,

or a combination. As fish rnove into shallow areas, they becorne susceptible to beach

seine collection. With growth, they eventually move to deeper portions of the estuary and

out of beach seine collections into waters sampled by trawl. A second factor is that

natural mortality of the largest fish of a given age rnay be different to the srnalier fish at

the same age, thus causing the mean or modal length-at-age to reflect "poor growth".

Finally, each fish is an individual and exhibits a unique growth pattern reflecting a

combination of genetics and micro-environment. Because these biases are always

present, the only mechanism that can accurately estimate growth is to determine the age

of each individua1 fish.

SUMMARY AND CONCLUSIONS

Similar to rnany other daily incrernent validation studies, this work makes the

assumption that periodicity of incrernent formation for laboratory produced fish is

identical to the incrernent periodicity o b s e ~ e d on otoliths from fish produced in the wild.

Regardless of the validation rnethod, some form of human intervention is required, which

rnay or rnay not affect otolith growth.

Age validation for both populations of northern striped bass reared under

hatchery conditions was accomplished by two methods: both by knowing the real age of

the fish and by marks associated with the day of OTC marking. Both techniques

produced identical results, so daily aging using otolith increments can now be applied

universally to al1 wild striped bass throughout its range. With the validation of the daily

increment technique for striped bass in the north cornplete, studies requiring daily ages

of wild young-of-the-year, such as, growth, mortality, birthdate analyses, and recruitrnent

dynamics, can now be accomplished.

Light microscopy techniques accurately aged hatchery reared and wild striped

bass to approximately 1 10 dph- Depending on the tirne of wild fish spawning, daily ages

of young-of-the-year could be obtained throughout the summer until (on average) the

end of August or first of September with relatively rninor expense. The daily aging criteria

established here will rnake it possible to identify different cohorts within the sarne wild

population of northern striped bass. This technique will be especially useful in

understanding the size variability of young-of-the-year that can be obse~ed with

Miramichi striped bass in some years.

The daily aging technique produced mutually consistent results with wild caught

striped bass from the Miramichi River. The expectation that wild striped bass laid down

daily increments was fortified with the observation that birthdates closely coincided with

the adult bycatch in the commercial gaspereau fishery of the NW Miramichi River.

Although both populations of striped bass were reared under identical conditions

at Two Rivers Bass Hatchery, no difference in growth occurred between Shubenacadie

and Miramichi striped bass during their first 1 13 days of life. These results suggest that

growth is highly dependent on abiotic factors and challenges the general application of

Conover's (1 990) countergradient variation hypothesis. Size at age for both of these

northern populations is likely to be the same, so broodstock from either population could

be selected for striped bass production either for the aquaculture industry or stocking

initiatives. Factors other than growth need to be considered before any fish are stocked

to the wild.

Growth of both populations of TRBH-reared striped bass was better than what

was observed for wild young-of-the-year collected from the Miramichi River. Observed

mean growth of wild Miramichi young-of-the-year at the beginning of September was

0.83 mrn/d. Growth appears to be highly dependent on environmental conditions

experienced by young-of-the-year striped bass. Environmental conditions experienced

by young-of-the-year throughout their first growing season may ultimately define

recruitment to the adult population.

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