Update on Sparkling Lake predators, smelt,

and crayfish densities

B.M. Roth, C.L. Hein, S.A. Lischka

T.R. Hrabik, M.J. Vander Zanden, N. Mercado-Silva

J.J. Magnuson, S.R. Carpenter, J.F. Kitchell

Eradication Gameplan: Smelt

• Remove adults during spawning run with fyke nets

• Increase predation by stocking walleye (and muskies)

Eradication Gameplan: Rusty crayfish

• Intensively trap adults

• Increase predation on juveniles

John Magnuson

Adult Smelt Removal

0

50

100

150

200250

300

350

400

450

4/22 4/23 4/24 4/25 4/26 4/27 4/28 4/29 4/30 5/1 5/2 5/3 5/4

Date

Ma

ss

of

Sm

elt

Ca

ug

ht

(kg

) 2003

2002: 375kg : 1800kg

Average Daily Temperature from Sparkling

Lake 3/11 to 6/1 (Courtesy of NTL-LTER)

–Smelt spawn immediately after ice out (Water temp = 4.4 C) (Becker 1983)

0

2

4

6

8

10

12

14

16

90 100 110 120 130

Julian Day

Te

mp

era

ture

2002

2003

Smelt spawning temp

Mortality Sources

• Smelt– Us

• Counting

– Walleye• Bioenergetics

– Smallmouth bass• Bioenergetics

• Crayfish– Katie

• Counting

– Smallmouth bass• Bioenergetics

– Rock bass• Bioenergetics

Smelt and Crayfish Mortality

0

100000

200000

300000

400000

500000

2001 2002 2003

Num

ber

of C

rayf

ish

Rem

oved

Katiesmallmouth bassrock bass

0

100000

200000

300000

400000

2001 2002 2003

Num

ber

of S

mel

t R

emov

ed Us

walleye

smallmouth

Crayfish

Smelt

Size Distributions of Rusty Crayfish in Sparkling Lake

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

10 20 30 40 50 60

Carapace Length (mm)

Pe

rce

nt

of

To

tal S

am

ple

Predators

Ambient

Traps

Smelt and Crayfish Mortality

Crayfish

Smelt

0

100000

200000

300000

400000

2001 2002 2003

Bio

ma

ss o

f Sm

elt

Re

mo

ved

(kg

)

Us

walleye

smallmouth

0

200

400

600

800

1000

2001 2002 2003

Bio

ma

ss

of

Cra

yfi

sh

Re

mo

ve

d (

kg

)

Katiesmallmouth bassrock bass

• Specific ecosystem responses to:

– Fishery regulation changes

– Exploitation

– Increased predation

Multiple Working Hypotheses

– Fishery regulation changes (Predators)• Increase in number and size structure

– Exploitation • Overall decrease in exotic populations/density (crayfish and

smelt)• Decreased ambient carapace length (crayfish)• Increased production and/or survivorship of juveniles

(crayfish)

– Increased predation (smelt and crayfish)• Alternate prey become more prevalent in predator diets• Implications for predator growth?

Predator Population Estimates

• 2001: – All three species: Continuous Schnabel mark-

recapture estimates during summer only

• 2002: – Walleye: Spring mark, continuous mark-recap during

summer– RB & SMB: summer mark-recap only

• 2003– Walleye & RB: Spring mark, continuous mark-

recapture during summer– SMB: summer mark-recap only

Predator Population Estimates

0

1000

2000

3000

4000

5000

6000

2001 2002 2003

N

rock basssmallmouth basswalleye

Response of Exotics to Exploitation

– Decreased population or density (smelt and crayfish)

– Decreased ambient carapace length– Increased production and survivorship of

juveniles– More macrophytes and snails

• Sampled 6 lakes in 2002 and 2003– Early July– Late August

• Variables measured:– Total crayfish density

• YOY crayfish• Crayfish >10mm carapace length

– Lengths• All crayfish >10mm carapace length

2002 2003

All collection done on cobble substrate ONLY (France 1985)

Use Crayfish Density as a Proxy

Density of crayfish >10mm actually went up on cobble substrate!!

0

5

10

15

20

25

To

tal

Cra

yfis

h D

ensi

ty

Arrowhead

Birch

Round

Sparkling

Trout

W.Rice

(#/

m2

)

Jul2002

Jul2003

Aug2002

Aug2003

Smelt Population Estimates

• 2001: 770,000

• 2002: 423,000

• 2003: ???,???

Response of Exotics to Exploitation

– Decreased population– Decreased ambient carapace length (crayfish)– Increased production and survivorship of

juveniles (crayfish)– More macrophytes and snails

Crayfish Size Distribution in Sparkling Lake

No apparent change!!

0

0.05

0.1

0.15

0.2P

erce

nt

of

Sam

ple 2002 July

2003 July

0

0.05

0.1

0.15

0.2

5 10 15 20 25 30 35 40 45

Carapace Length (mm)

Per

cen

t o

f S

amp

le

2002 August

2003 August

Increased Production of Juveniles (July Samples)

0

50

100

150

200

250

2001 2002 2003 2004

Year

Den

sity

(#/

m2) Arrowhead

Birch

Round

Sparkling

Trout

W.Rice

Sparkling had the largest density decrease among lakes sampled

Decreased Juvenile Mortality??

0102030405060708090

100

2001 2002 2003 2004

Year

Per

cen

t Ju

ven

ile

Mo

rtal

ity

Arrowhead

Birch

Round

Sparkling

Trout

W.Rice

YOY mortality was higher in 2002 than in 2003

• Increased predation– Alternate prey become more prevalent in

predator diets (smelt and crayfish)– Implications for predator growth?

Smallmouth bass

Rock bass

0%

20%

40%

60%

80%

100%

2001 2002 2003Year

Per

cen

t o

f D

iet

Dry

Wei

gh

t0%

20%

40%

60%

80%

100%

2001 2002 2003

Per

cen

t o

f D

iet

Dry

Wei

gh

t

Walleye

0%

20%

40%

60%

80%

100%

2001 2002 2003

Year

Per

cen

t o

f D

iet

Dry

W

eig

ht

Smallmouth bass

Walleye

0%

20%

40%

60%

80%

100%

2001 2002 2003P

erce

nt

of

Die

t D

ry W

eig

ht

0%

20%

40%

60%

80%

100%

2001 2002 2003Year

Pe

rce

nt

of

Die

t D

ry

We

igh

t

Smallmouth bass

Walleye

0

0.2

0.4

0.6

0.8

1

smelt mimic shiner other fish

Prey Type

Pe

rce

nt

of

Ide

nti

fie

d F

ish

200120022003

0

0.2

0.4

0.6

0.8

1

smelt mimic shiner other fish

Prey Type

Pe

rce

nt

of

Ide

nti

fie

d F

ish

200120022003

• Increased predation– Alternate prey become more prevalent in

predator diets (smelt and crayfish)– Implications for predator growth?

• Residuals of length-weight regression line grouped by year

Relative Body Condition of Sparkling Lake Predators

Year (+1999)

0 1 2 3 4 5Res

idu

als

of

Len

gth

-Wei

gh

t R

egre

ssio

n

-0.04

-0.02

0.00

0.02

0.04

Two-way ANOVA, p < 0.001 Bonferroni post-hoc test for pairwise mean differences

a a b bac b ac ca b b a

smallmouth bassrock basswalleye

More to Come..

• How will crayfish densities, growth, and reproduction respond to continued exploitation?

• Are smelt going to pull off a year class?

• Will trends continue?– Predator growth– Diet shifts

Acknowledgments

• NSF-Biocomplexity, NTL-LTER

• Steve Gilbert, WDNR• Greg Sass, Michele

Woodford, Scott Van Egeren

• Gretchen Anderson, Adam Ray, Ellen Feingold, Andrea Fowler, Patrick Hermann, Laura Kessler

Two Regimes

Introduction

Good initial production

Macrophytes Decline

Adult Densities Rapidly Increase

YOY predators decline

Cobble substrate

Rapid Establishment

High YOY density

Mucky, weedy substrate

Slow Establishment

Poor initial production

Adult Densities Stay Low

Macrophytes Remain

YOY predators remain high

Low YOY density

???

0

50000

100000

150000

200000

250000

300000

2001 2002 2003

Year

Nu

mb

er o

f C

rayf

ish

Co

nsu

med

rock bass

smallmouth bass

0

50000

100000

150000

200000

250000

300000

2001 2002 2003

Year

Nu

mb

er o

f S

mel

t C

on

sum

ed

smallmouth

walleye

Crayfish Consumption

Smelt Consumption

No Data

Add Predators..

Pre-removal Post-removalwith Stocking