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

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

CoregonidsSuperiorMichiganHuronErieOntario hoyi (bloater) XXXX reighardi (shortnose) X zenithicus (shortjaw) XXXX johannae (deepwater) X kiyi XXXX nigripinnis (blackfin) XXX 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 Ballasts: 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 /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 winter

Native invertebrate preyfish food Diporeia Mysis Copepods

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: kt of planktivore biomass At 25 kt = 5% of objective at best 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

Adult bloater (> 120 mm) 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

Deepwater sculpin (Myoxocephalus thompsonii) Round goby USGS long term trawl data by species X-axis = year Y-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 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 (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 TRFFSTBMSK JANUARYXX FEBRUARYXX MARCHXX APRILXXXXXX MAY X XX DEEPWATER SCULPIN DIETS MONTH TRFFSTBMSK JANUARYXX FEBRUARYXX MARCHXX X APRILX XXXXX MAY XXXX JUNE X ROUND GOBY DIETS MONTH TRFFSTBMSK JANUARYXX FEBRUARYXX MARCHXX APRILXXXXXX MAY X X Methods Who SS=1016, DWS=699 RG=552 Where FF, STB, TR, MSK depths m When Jan-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 types Reduced from ~ 95 prey species 3) Individuals in nets combined nets became sampling unit

Analysis Hypothesis 1: time and space effects General 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, Overlap Tested 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 Bloater DWSSS RG

Results: For all fish sampled SS N=1016 DWS N=799 RG N=552

Space preyfactor predator SSDWSRG mysis depth port<0.001 year diporeia depth port< year fish eggs depth port year limnocal depth port< year senec depth port year bival depth port year..<0.001 chironomids depth port year ostra depth port year Time preyfactor predator SSDWSRG Mysis depth doy year diporeia depth doy year fish eggs depth doy year limnocal depth doy year bival depth doy year chironomids depth doy year 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 = ≤ DWS: 0.05/3 = ≤ RG: 0.05/2 = ≤ Ports: all samples  N = Nets (Fish) SS = 45 (1016) DWS = 40 (699) RG = 36 (552) Alpha significance SS ≤ DWS ≤ RG ≤ 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 overlap 1 = perfect overlap ≥ 0.6 = overlap possible competition Overlap analysis using Schoener's portspeciesSSDWS FF SSXX DWS0.62X RG TR SSXX DWS0.38X RG STB SSXX DWS0.62X RG

NMS supports diet overlap

RESULTS: Egg Genetics 85 bloater eggs February- May All four ports Eyed eggs May 1, eggs in FF in APR 26 individual SS Apr 17, 20 th 66% consumed by SS 34% by DWS RG ate minimal eggs 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 and daily ration Gastric evacuation rate (GEVAC) Diet Now 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

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 Rate Diet 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 = *%

A closer, more recent look however….

Likewise does 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 ) 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