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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. Acknowledgements. Great Lakes Fisheries Commission (GLFC) Great Lakes Restoration Initiative (GLRI) - PowerPoint PPT Presentation
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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 (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
Outline
• Laurentian Great Lakes• Ecology in Lake Michigan• My research• Hypothesis testing• Results• Discussion• Implications
Credit: COSEE
Laurentian Great Lakes• Glacial• Colonization• Human influence
– Pollution– Exploitation– Extinctions– Habitats– Climate change– Invasive species
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
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
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)
(g/ha)
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• Diet proportions
SS=1016, DWS=699 RG=552
• Sampled at FF, STB, TR, MSKdepths 69-128m
• WhenJan-May 2009–2010
• Diet Proportions– Used dry weight
proportions time/space effects analyses and diet overlap analyses
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 January 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
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
Results: space GLMs
TIME EFFECTSDay of year (DOY)
TR only
N = nets (fish)SS=22 (468) DWS=19 (238) RG=18 (156)
Alpha set to: SS: 0.05/4 = ≤ 0.012
DWS: 0.05/3 = ≤ 0.017
RG: 0.05/2 = ≤ 0.025
Few effects
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 . .
• 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)
Diets -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 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
Index of fullness Results
• A) = SS B) = DWS• FDW important
• No location effects!
• No temporal effects! (Jan-Apr)
• Max values 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 (> 40 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) Diet proportions 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– further research needs to address DWS recruitment
limitation
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: [email protected]