Justin G. Mychek-Londer and David (Bo) Bunnell

Assessing diet overlap and potential recruitment limitation of prey by native

and invasive benthivores in offshore Lake Michigan.

Acknowledgements• Great Lakes Fisheries Commission

• USGS Great Lakes Science Center

• My Advisors: Bo Bunnell, James Diana

• Vincent Belill, John French III, Melissa Kostich, Kevin Keeler, Mark Rogers, Lynn Ogilvie, Betsy Puchala, Linda Begnoche, Steven Pothoven, Chuck Madenjian, Bruce Davis, Dave Bennion, Greg Jacobs, Timothy DeSorcie, Barbara Diana, Scott Nelson, Jean Adams, Jeff Holuszko, Solomon David, and others I’ve forgotten.

• The Crew of the RV Grayling Ed Perry and Jim Paige

• Susie Q Commercial Fishery in Two Rivers, WI

• School of Natural Resources at The University of Michigan, Ann Arbor

Outline

• Laurentian Great Lakes• Ecology in Lake Michigan• My research• Hypothesis testing• Results• Discussion• Implications

Credit: COSEE

E.P.A., Population growth since 1900

Laurentian Great Lakes• Glacial• Colonization• Human influence

– Pollution– Exploitation– Extinctions– Habitats– Climate change– Invasive species

Thunder Bay Sanctuary Research Collection

Credit: COSEE

Non-natives• Engineering: Canal systems

• Sea lamprey• Alewife

• Introductions• Brown trout • Rainbow trout• Smelt• Alewife control

– Chinook salmon– Coho salmon

Lake Michigan

• Within US territory• Inshore and offshore• Extinctions, extirpations • Recent environmental change• Offshore Ponto-caspian invaders• Offshore native aquatic species

• Prior to 1936 six named deepwater ciscoes

• Commercial Fishery• Restoration

Lake Michigan coregonid complex

Coregonids Superior Michigan Huron Erie Ontario

hoyi (bloater) X X X Xreighardi (shortnose) Xzenithicus (shortjaw) X X X Xjohannae (deepwater) Xkiyi X X X Xnigripinnis (blackfin) X X X

WHITE = extinct, extirpated BLACK = present day RED = extirpated, restoration consideration

•Quagga effects-Inshore and offshore-Span LMichigan basin-Estimates in trillions-Establish in sediments-Dreissenid biomass > prey fish

Quagga mussels

20001995 2005Ballasts: Ponto-caspian invertebrates

• Bythotrephes spp.• Zebra mussels• Quagga mussels

•Bytho effects-Daphinds -Competition with fish-Sportfishing line entanglement-Spikes in stomachs-Copepod influence

•Zebra effects-Inshore-Benthification-Filtering-Hard substrate

http://www.freep.com/VideoNetwork/1178696489001/Quagga-mussels-blanket-Lake-Michigan

Ballasts: Round goby

• First found in St. Clair River (D. Jude, 1990)• Now in all Great Lakes• Benthic, wide diet

– larger (>60 mm) molluscivores• May outcompete natives for food and space• May bioaccumulate toxins• Concerns about impacts• Migrate offshore in winterhttp://www.youtube.com/watch?v=eWt_uffYZ4M

Native invertebrate preyfish food

• Diporeia• Mysis• Copepods

1 9 7 3 1 9 8 0 1 9 8 7 1 9 9 4 2 0 0 1 2 0 0 8

Year

0

5 0

1 0 0

1 5 0

2 0 0

2 5 0

3 0 0

3 5 0

4 0 0

4 5 0

5 0 0

Lake

-wid

e bi

omas

s (k

t)

Bloater

Slimy s c ulpin

Deepw ater s c ulpinRainbow s melt

Ro u n d g o b y

N ines pine s tic klebac k

Alew ife

Lake-wide biomass of prey fish time series

Prey fish biomass has never been lower

2008: 94% decline from the peak in 1989

GLFC objective: 500-800 kt of planktivore

biomass

At 25 kt = 5% of objective at best

Deepwater sculpin5.23 kt

Slimy sculpin2.75 kt

Bloater3.33 k t

Rainbow smelt0.89 kt

Nines pine s tick leback0.50 k t

Alewife8.27 k t

Round goby4.65 k t

Lake-wide biomass of prey fish in 2008

Slimy sculpin (Cottus cognatus)

Since 1990, general Increasing trend •Benthic

•No swim bladders•Highly developed sensory•Polygnous nest guarding males•Live 7-9 years TL ~125mm•Other studies have addressed egg predation

19731977

19811985

19891993

19972001

20052009

0200400600800

100012001400160018002000

Adult bloater (> 120 mm)Year

Num

eric

den

sity

(#/h

a)

0

500

1000

1500

2000

2500

3000

Year

Num

eric

den

sity

(#/h

a)

0

200

400

600

800

1000

Age-0 bloater (< 120 mm)

Coregonus hoyi• Better lake trout food

• Sex ratio, survivial bottleneck • 30 year cycle hypothesis

• Planktivore • Max length ~ 275 mm, 12 YO

1973

1977

1981

1985

1989

1993

1997

2001

2005

2009

0

5000

10000

15000

20000

25000

0

1000

2000

3000

Deepwater sculpin(Myoxocephalus thompsonii)

Round goby

USGS long term trawl

data by species

X-axis = yearY-axis =

Mean g/ha

Diet, Distribution•Diporeia, Mysis – Most important for SS and DWS

• SS: copepods, eggs, cladocerans, diverse, adaptable

• DWS: fish eggs, copepods, less diverse• RG: bivalve oriented, diverse in Great Lakes

•Distribution in deepwater benthic zones:• RG new to system: Expected in Lake Michigan in

winter based on Lake Erie• SS and DWS depth segregation, SS 60-83, DWS

past 90m (Madenjian and Bunnell, 2008)

Quagga mussels

20001995 2005• RG predation on smallmouth bass eggs in

Lake Erie (Steinhart et al. 2005)

• Great Lakes SS and DWS consistently demonstrate fish eggs as a component of diets (e.g. Jacoby 1953; O’brien et al. 2009)

• Egg consumption by Lake MIchigan goby and slimy sculpin may limit recovery of lake trout (Chotkowski and Marsden 1999)

Why diets? • Food web

change• Competition• Egg

predation

Nalepa et al. 2009

(g/ha)

• Exclusionary aggressiveness and recruitment failure in mottled sculpin caused by

round goby (Janssen and Jude 2001)

• Slimy sculpin and round goby perform equally well in sensing prey in the dark

• Aggressive behavior by goby can exclude natives from food and space (Bergstrom and Mensinger 2009)

Hypotheses about benthivore diets

1) Within species prey specific diet proportions will vary significantly across time and sampling locations

2) Between sculpins diet overlap should be high, while between goby and sculpins overlap should be moderate

3) All 3 benthic predators eat bloater eggs- SS eat the most, most frequently

SLIMY SCULPIN DIETS

MONTH

TR FF STB MSK2009 2010 2009 2010 2009 2010 2009 2010

JANUARY X X FEBRUARY X X

MARCH X X APRIL X X X X X X MAY X X X

DEEPWATER SCULPIN DIETS

MONTH

TR FF STB MSK2009 2010 2009 2010 2009 2010 2009 2010

JANUARY X X FEBRUARY X X

MARCH X X XAPRIL X X X X X XMAY X X X XJUNE X

ROUND GOBY DIETS

MONTH

TR FF STB MSK2009 2010 2009 2010 2009 2010 2009 2010

JANUARY X X FEBRUARY X X

MARCH X X APRIL X X X X X X MAY X X

Methods• Who

SS=1016, DWS=699 RG=552

• Where FF, STB, TR, MSKdepths 69-128m

• WhenJan-May 2009–2010

• Diet Proportions– Used in

time/space effects analyses and diet overlap analyses

Slimy sculpin SS

Deepwater sculpin DWS

Round goby RG David J. Jude

Diet proportions by dry weight:

1) Individual fish

2) 12 categorical prey typesReduced from ~ 95 prey species

3) Individuals in nets combinednets became sampling unit

Analysis Hypothesis 1: time and space effectsGeneral linear models (GLM)• Individual models built for single predator and single prey:• Prey categories selected: accounted for > 88% of each

predators overall diet proportions

• Sampling unit: Nets weighted by the number of fish within a net

• Time– Day of year (DOY): TR only

• Space– Location (port): all samples

Analysis: Hypothesis two, OverlapTested overlap between species within each port

• Schoener’s = 1 – 0.5(Σ│pxi - pyi│)

• pxi proportion of food category i used by species x• pyi is the proportion of food category i used by species y

•C = Morista’s: overlap between species j and k•pij = proportion resource i of total resources used by species j •pik = proportion resource i of total resources used by species k•nij = # of individuals of species j using resource category i •nik = # of individuals of species k that use resource category i•Nj and Nk = the total number of individuals of each species in the sample (Morista, 1959).

Schoener’s and Morista’s

DNA analysis of fish eggs• Hypothesis 3: Bloater eggs• DNA analysis on viable fish eggs• 10 analyzed per sample• Known DNA

– Bloater, SS, DWS, RG BloaterDWS SS

RG

Results: For all fish sampled

SS N=1016DWS N=799RG N=552

Spaceprey factor

predator

SS DWS RG

mysisdepth 0.347 0.071 0.061port <0.001 <0.001 <0.001year 0.331 0.870 0.004

diporeiadepth 0.039 0.024 .port <0.001 <0.001 .year 0.760 0.240 .

fish eggsdepth . 0.201 .port . 0.017 .year . 0.477 .

limnocaldepth 0.041 . .port <0.001 . .year 0.017 . .

senecdepth 0.188 . .port 0.015 . .year 0.418 . .

bivaldepth . . 0.148port . . 0.074year . . <0.001

chironomidsdepth 0.079 . .port 0.059 . .year 0.079 . .

ostradepth . . 0.051port . . 0.016year . . 0.069

Timeprey factor

predator

SS DWS RG

Mysisdepth 0.010 0.023 0.114

doy 0.179 0.042 0.516year 0.158 0.191 0.506

diporeiadepth 0.320 0.004 .

doy 0.164 0.032 .year 0.561 0.961 .

fish eggsdepth . 0.237 .

doy . 0.936 .year . 0.271 .

limnocaldepth 0.191 . .

doy 0.195 . .year 0.155 . .

bivaldepth . . 0.621

doy . . 0.131year . . 0.038

chironomidsdepth 0.842 . .

doy 0.019 . .year 0.198 . .

Day of year (DOY) TR only

N = nets (fish)SS=22 (468) DWS=19 (238) RG=18 (156)

Alpha set to: SS: 0.05/4 = ≤ 0.012DWS: 0.05/3 = ≤ 0.017 RG: 0.05/2 = ≤ 0.025

Ports: all samples

N = Nets (Fish)SS = 45 (1016)DWS = 40 (699)RG = 36 (552)

Alpha significance SS ≤ 0.010 DWS ≤ 0.017 RG ≤ 0.017

Results: Hypothesis 1 Time, space GLMs

• Schoener’s = overlap between SS and DWS = 0.62• Morista’s = overlap between sculpins = 0.70• No overlap between goby and sculpins (0.41 vs. SS; 0.36 vs. DWS

• Schoener’s: overlap between SS and DWS 0.62 • Morista’s = no overlap between sculpins• No overlap between RG, sculpins using either index

Results: Hypothesis two, overlap• Values:

0 = no overlap1 = perfect overlap≥ 0.6 = overlap

possible competition

Overlap analysis using Schoener's

port species SS DWS

FFSS X X

DWS 0.62 XRG 0.41 0.36

TRSS X X

DWS 0.38 XRG 0.12 0.11

STBSS X X

DWS 0.62 XRG 0.19 0.15

NMS supports diet overlap

RESULTS: Egg Genetics

• 85 bloater eggs• February- May• All four ports• Eyed eggs

19 @April 17-2014 @ May 1, 18

• 31 eggs in FF in APR26 individual SSApr 17, 20th

• 66% consumed by SS 34% by DWS

• RG ate minimal eggs

00

0

0

0

0

0

Eyed bloater egg eaten by slimy sculpin

Summary for benthivore diets

• Hypothesis 1) space vs. time, within species– Diets did not vary through time – Diets differed across ports for all species

• Hypothesis 2) Diet overlap – Diet overlap did occur between sculpins– Goby diets did not overlap with any sculpin species

• Hypothesis 3) Bloater eggs– Most were consumed by slimy sculpin - true– DWS – also ate bloater eggs – true

Worth noting on diets:• Space vs. time

– Cover more space

• Without Diporeia– SS diets became broad– DWS turned almost completely to Mysis

• High egg cannibalism– Species coexistence

• RG impacts offshore on sculpin diets– minimal, perhaps minimal in offshore foodweb

Part II• Determination of: – Gastric evacuation - digestion– Index of fullness – how much food in a sculpin stomach – Daily ration

• Use these estimates, empirical data and diet data to model– How many bloater eggs eaten in one day, by one slimy

sculpin

• Scale up from an individual sculpin to: – to population and lakewide levels of annual bloater egg

predation by sculpin

• Input data into recruitment models to determine if sculpins eat enough bloater eggs to limit bloater recruitment interannually – Can be done for other prey types hypothetically (i.e., Diporeia)

Approach

Individual sculpin prey specific daily consumption

Index of fullness anddaily ration

Gastric evacuation

rate (GEVAC)

DietNow we

know

Population Level Daily

Consumption

Bloater Eggs Eaten

Bloater Eggs Produced

•

GEVAC using live sculpins

GEVAC • Digestion rate

• Two main hypotheses: – Vary by temperature– Vary by prey type

• Methods: – Fed known quantity of food w/known dry-weight

– After 30 min, leftover food removed

– Digest in chamber for 24, 48, 72, 120, 168 Hours

– Euthanize, remove stomach, dry undigested prey

– Quantify %dry-weight remaining → digestion rate

GEVAC results• Slimy sculpin

• No variation – by temperature (panel a)– or prey type (panel b)

– Very slow:temps

• Deepwater sculpin

– No variation by temperature

GEVAC results

Index of fullness• Used additional fish from our diet samples

– 1) Dry fish– 2) Separately dry stomach contents

• Index of fullness– Definition: Dry weight of an individual fishes stomach contents divided by

the dry weight of everything else making up the rest of the fish– Ratio, used in other studies– Larger fish, expect a lower ratio

• Three hypotheses for index of fullness– 1) Vary within species according to date sampled– 2) Vary within species according to location in Lake Michigan sampled– 3) Would be lower than when measured in 1976, due to ecological change

Index of fullness Results

• A) = SS B) = DWS• FDW important

• No location effects!

• No temporal effects!

• HIGHER THAN 1976 !?

Daily Ration• a fish consumes grams of food per day per a unit of fish size

• Regression to determine daily ration = (h-1) FDW

– Where: • S = index of fullness regression equations (herein)• 24 h = 24 hours in one day• r = GEVAC rate (herein)• FDW = fish dry weight (this is explanatory variable)

• Mean daily ration = 32 mg dry weight across all samples• Apply diet proportions to this daily ration weight

– Gives weight of bloater eggs eaten by single sculpin in one day

Population level daily consumption

• USGS Trawl data = numbers of SS and bloater per hectare

• GIS: total hectares (in depth strata 5 to 115m)

• (SS/ha x #ha) = slimy population

• Daily ration of bloater eggs in individual SS diets by total SS population (> 36 mm)

• Bloater: numbers + fecundity = total bloater egg production

Individual Prey Specific

Daily Consumption

Individual Average

Meal Size (Daily

Ration)

Gastric Evacuation

RateDiet

Population Level Daily

Consumption

Bloater Eggs Eaten

Bloater Eggs Produced

Consumption modeling

Initial lakewide consumption modeling results for year 2010, done in 2010

• Bloater egg production consumed = 40.7%• Sensitivity analysis = 20-130*%

A closer, more recent look however….

Likewisedoes not

seem to fit

Take homes

1) Diets did not vary across time, but did vary across space

2) Overlap between sculpins, none between goby and sculpins

3) Gastric evacuation was slow, not affected by temps, prey type

4) Without Diporeia, slimy sculpin diets diversified, whereas deepwater sculpin consumed almost entirely one prey, Mysis

Take homes

5) Despite present differential site based availability, and steep declines in Diporeia abundance since 1976, index of fullness was similar across locations, and mostly higher in 2009-2010

6) Bloater and deepwater sculpin eggs were found in sculpin diets in high numbers, but this may not limit bloater recruitment

7) Restoration Reintroduction of bloater into Lake Ontario may succeed if sculpins

truly control recruitment of bloater through egg predation in Lake Michigan because slimy sculpin lakewide biomass in Lake Ontario is currently at low levels, and deepwater sculpin exists only marginally

Thanks