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

1. Assessing diet overlap and potential recruitment limitation of prey by native and invasive benthivores in offshore Lake Michigan. Justin G. Mychek-Londer and David (Bo) Bunnell

2. Acknowledgements • Great Lakes Fisheries Commission (GLFC) • Great Lakes Restoration Initiative (GLRI) • 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

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

4. Laurentian Great Lakes • Glacial • Colonization • Human influence • Pollution • Exploitation • Extinctions • Habitats • Climate change • Invasive species Credit: COSEE Credit: COSEE

6. Non-natives • Engineering: Canal systems • Sea lamprey • Alewife • Introductions • Brown trout • Rainbow trout • Smelt • Alewife control • Chinook salmon • Coho salmon

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

9. Lake Michigan coregonid complex • Prior to 1936 six named deepwater ciscoes • Commercial Fishery • Restoration

10. WHITE = extinct, extirpated • BLACK = present day • RED = extirpated, restoration consideration

12. Ballasts: Ponto-caspian invertebrates 1995 2000 2005 • Bythotrephes spp. • Zebra mussels • Quagga mussels Quagga mussels • Quagga effects • -Inshore and offshore • -Span LMichigan basin • -Estimates in trillions • -Establish in sediments • -Dreissenid biomass > prey fish

13. 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

15. Native invertebrate preyfish food • Diporeia • Mysis • Copepods

16. Lake-wide biomass of prey fish in 2008 Lake-wide biomass of prey fish time series 2008: 94% decline from the peak in 1989 Prey fish biomass has never been lower GLFC objective: 500-800 kt of planktivore biomass At 25 kt = 5% of objective at best

17. Slimy sculpin (Cottuscognatus) 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

18. Age-0 bloater (< 120 mm) • Coregonushoyi • Better lake trout food • Sex ratio, survivial bottleneck • 30 year cycle hypothesis • Planktivore • Max length ~ 275 mm, 12 YO Adult bloater (> 120 mm)

19. Round goby Deepwater sculpin(Myoxocephalusthompsonii) USGS long term trawl data by species X-axis = year Y-axis = Mean g/ha

20. 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: • RGnew 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)

21. (g/ha)

22. Hypotheses about benthivore diets • Within species prey specific diet proportions will vary significantly across time and sampling locations • Between sculpins diet overlap should be high, while between goby and sculpins overlap should be moderate • All 3 benthic predators eat bloater eggs - SS eat the most, most frequently

23. Methods • Diet proportions SS=1016, DWS=699 RG=552 • Sampled at FF, STB, TR, MSK depths 69-128m • When Jan-May 2009–2010 • Diet Proportions • Used dry weight proportions time/space effects analyses and diet overlap analyses

24. 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 January only • Space • Location (port): all samples

25. Schoener’s and Morista’s • 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).

26. 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 DWS SS RG

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

28. Results: space GLMs • 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 • Many effects

29. TIME EFFECTS Day of year (DOY) TRonly • N = nets (fish) SS=22 (468) DWS=19 (238) RG=18 (156) • Alpha set to: SS: 0.05/4 = ≤ 0.012 DWS: 0.05/3 = ≤ 0.017 RG: 0.05/2 = ≤ 0.025 Few effects

30. 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

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

32. Results: Hypothesis two, overlap • Values: 0 = no overlap 1 = perfect overlap ≥ 0.6 = overlap possible competition

33. NMS supports diet overlap

34. RESULTS: Egg Genetics • 85 bloater eggs • February- May • All four ports • Eyed eggs • 19 @April 17-20 • 14 @ May 1, 18 • 31 eggs in FF in APR • 26 individual SS • Apr 17, 20th • 66% consumed by SS 34% by DWS • RG ate minimal eggs 0 0 0 Eyed bloater egg eaten by slimy sculpin 0 0 0 0

35. 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

36. 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

37. 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)

39. Approach • Population Level • Daily Consumption • Individual sculpin prey specific daily consumption • Index of fullness and • daily ration • Gastric evacuation rate (GEVAC) • Diets - • now we know • Bloater Eggs Eaten • Bloater Eggs Produced

40. GEVAC using live sculpins

41. 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

42. GEVAC results • Slimy sculpin • No variation • by temperature (panel a) • or prey type (panel b) • Very slow: temps

43. GEVAC results • Deepwater sculpin • No variation by temperature

44. Index of fullness • Used additional fish from our diet samples • 1) Dry fish in a drying tin • 2) Separately dry each fishes 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

45. Index of fullness Results • A) = SS B) = DWS • FDW important • No location effects! • No temporal effects! (Jan-Apr) • Max values HIGHER THAN • !?

46. 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

47. 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 (> 40 mm) • Bloater: numbers + fecundity = total bloater egg production

48. Consumption modeling • Population Level • Daily Consumption • Individual Prey Specific Daily Consumption • Individual Average Meal Size • (Daily Ration) • Gastric Evacuation Rate • Diet • Bloater Eggs Eaten • Bloater Eggs Produced

49. Initial lakewide consumption modeling results for year 2010, done in 2010 • Bloater egg production consumed = 40.7% • Sensitivity analysis = 20-130*%

50. A closer, more recent look however….