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S04: Great Lakes Trophic Structure: Innovations and ongoing studies of predatory fishes [clear filter]
Monday, January 28

1:20pm EST

(SYMPOSIA-04) Toward Examining Climate Effects on Yellow Perch Recruitment: How Do Lake Erie Larval Yellow Perch Diets Vary Within a Year?
AUTHORS: Luke A. Bobay, L. Zoe Almeida, Elizabeth A. Marschall, Stuart A. Ludsin – The Ohio State University

ABSTRACT: A full understanding of how climate change affects the recruitment process of fish is lacking for most populations. The possibility exists that altered temperature and precipitation patterns could interact with other factors (e.g., photoperiod) to reduce the availability of zooplankton prey to pre-recruited individuals. If preferred prey sizes or taxa are unavailable during critical periods of development (e.g., larval stage), foraging success, growth, and survival might decline. As a first step toward understanding how climate variation influences larval yellow perch (Perca flavescens) success in Lake Erie, we processed the diets of larvae captured during spring 2017 from several nearshore areas of the western basin. While we expected average zooplankton prey size in the diet to increase with yellow perch size, we were uncertain as to how availability of prey of different sizes and taxa would affect which prey types are consumed. We also did not know if larval yellow perch require a specific size or type of prey during early life, when their ability to catch large, fast prey is limited. Preliminary analyses indicate that the biomass of yellow perch diets varied both through time and between sites (Date: ?<sup>2</sup><sub>4,428</sub>= 114.3, p < 0.001, Site: ?<sup>2</sup><sub>3,428</sub>= 22.7, p < 0.001), with no obvious effect of fish size (Length: ?<sup>2</sup><sub>1,428</sub>= 0.04, p = 0.84). Interestingly, we found that some small prey items (e.g., small Cyclopoida) were primarily consumed by small yellow perch larvae (5 – 9 mm), whereas other small taxa (e.g., Bosmina) were primarily consumed by larger larvae (13 – 18 mm). Future analyses should reveal if these differences in consumption between larvae of different size are due to prey availability or a preference for specific taxonomic groups. Ultimately, these results will direct our impending inter-annual examination of larval yellow perch diets in relation to environmental conditions.

Monday January 28, 2019 1:20pm - 1:40pm EST

1:40pm EST

(SYMPOSIA-04) Lake Huron Prey Fish Community Affects Saginaw Bay Predator/Prey Dynamics and Management Implications
AUTHORS: David G. Fielder, Michigan Department of Natural Resources

ABSTRACT: Saginaw Bay historically supported large Walleye and Yellow Perch populations and fisheries. Walleye diet from 1989 to 2002 was dominated by Clupeids (Gizzard Shad and Alewives). Alewives from the main basin of Lake Huron used the bay for spawning and nursery grounds. Alewives disappeared from most of the lake as a result of a profound foodweb paradigm change in 2003. Walleye diet in the bay has become more diverse with age-0 Yellow Perch now comprising a major component. Yellow Perch have exhibited good reproductive success but mortality between age-0 and age-1 is now routinely upwards of 95%, resulting in failed recruitment to the larger population. It appears that Saginaw Bay’s predator/prey dynamics depend on a predation buffer from main basin pelagic planktivores with Cisco historically playing that role. With Alewives largely extirpated and Cisco not recovered, a broken linkage may exist resulting in suppressed Yellow Perch population and fisheries. Fishery managers are commencing a Cisco restoration initiative in Central Lake Huron partly in hopes of addressing this situation.   

Monday January 28, 2019 1:40pm - 2:00pm EST

2:00pm EST

(CANCELLED) (SYMPOSIA-04) Food Web Interactions Among Walleyes, Lake Whitefish, and Yellow Perch in Green Bay
AUTHORS: Daniel Isermann, Lucas Koenig, Daniel Dembkowski – Wisconsin Cooperative Fishery Research Unit; Iyob Tsehaye, Wisconsin Department of Natural Resources; Wesley Larson, USGS-Wisconsin Cooperative Fishery Research Unit; Scott Hansen, Steve Hogler; Tammie Paoli – Wisconsin Department of Natural Resources; Troy Zorn, Michigan Department of Natural Resources

ABSTRACT: Green Bay supports important fisheries for walleyes, lake whitefish, and yellow perch and these species likely interact in a variety of ways. A better understanding of these interactions is needed to guide management decisions. Specifically, there are concerns that high walleye abundance could negatively influence abundance of yellow perch and lake whitefish, primarily through predation. However, the prevalence of round gobies within the ecosystem may provide a predation buffer for yellow perch and lake whitefish. Moreover, the lake whitefish population in and around Green Bay is comprised of multiple genetic stocks. Consequently, if walleye predation on lake whitefish varies across time and space, this predation could affect certain whitefish stocks to a greater degree than others. To help address some of these uncertainties, our research objectives are to determine if: 1) lake whitefish and yellow perch represent important prey for walleyes in Green Bay; 2) diets of these three species vary spatially and temporally and if diet overlap among species is evident; 3) the extent of walleye predation is sufficiently high to influence recruitment potential of lake whitefish and yellow perch and 4) extent of walleye predation varies among individual stocks of lake whitefish. We are integrating an intensive assessment of diet composition for all three species with bioenergetic modeling and genetic stock identification to address our objectives. We will discuss the innovative experimental framework we are using to address these objectives and provide preliminary results of our diet analyses.

Monday January 28, 2019 2:00pm - 2:20pm EST

2:20pm EST

(SYMPOSIA-04) Spatial Patterns and Temporal Trends of Predator Diets in Lake Huron
AUTHORS: Katie Kierczynski, Michigan State University; Brian Roth, Michigan State University; Ed Roseman, USGS Great Lakes Science Center; Robin DeBruyne, University of Toledo/USGS Great Lakes Science Center

ABSTRACT: Lake Huron has undergone dramatic changes in the past few decades. Introductions of non-native species have drastically altered the food web and nutrient pathways. In the mid-2000s, alewife collapsed closely followed by Chinook salmon. Since then, some native prey species (e.g. bloaters) and some invasive species (e.g. round goby) have increased in abundance. Populations of native predators walleye and lake trout have also increased substantially, but there are now questions regarding the sustainability of current predator populations as well as uncertainty regarding connections among food web members given changes in prey populations and shifts in productivity. Predator diets can be used as evidence that could shed light on the sustainability of the food web. However, the last angler-caught predator diet study in Lake Huron was conducted between 2009 and 2011 (Roseman et al. 2014). That study demonstrated increased reliance on round goby for lake trout and walleye, but Chinook salmon continued to be dependent on alewife despite their exceptionally low abundance. The goals of the present study are to investigate how predator-prey relationships have changed since the 2009-2011 study and to determine spatial patterns and temporal trends in diet composition. We hypothesize that a) consumption of round goby will have increased for native predators, b) consumption of bloaters will have increased for all predator species, c) Chinook salmon will continue to be dependent on alewife, and d) diets will be heterogeneous across space and time. This data will give managers a more thorough understanding of predator-prey interactions in Lake Huron, and will be used to update models used by managers to evaluate the sustainability of current predator levels and stocking strategies.

Monday January 28, 2019 2:20pm - 2:40pm EST

2:40pm EST

(CANCELLED) (SYMPOSIA-04) Reevaluation of Wild Juvenile Lake Trout Spatial Distribution and Diets in Lake Huron (2008 - 2017)
AUTHORS: Taaja R. Tucker, University of Toledo; Edward F. Roseman, Stephen C. Riley, Timothy P. O’Brien, Darryl W. Hondorp, Dustin A. Bowser, Scott A. Jackson – US Geological Survey

ABSTRACT: Rehabilitation efforts of lake trout (Salvelinus namaycush) in Lake Huron have resulted in increased recruitment and capture of young wild lake trout in annual bottom trawl surveys conducted by the U.S. Geological Survey. To better understand the spatial distribution and food habits of wild juvenile lake trout, we performed diet analyses on 311 of 343 fish captured in bottom trawls at six ports in Lake Huron during October/November 2008–2017. Lake trout ranged in size from 27 to 371 mm, representing approximately three age classes. Most of the fish (83%) were captured at 46–64 m depths at the two northernmost ports, typically below the thermocline. Mysis diluviana was the most prevalent diet item, found in 222 of 299 fish with non-empty stomachs (74%), followed by Bythotrephes longimanus (31%), and round goby (Neogobius melanostomus; 11%). Young-of-year lake trout (Mysis and Daphnia, while larger lake trout converted to mostly fish-based diets at age 2+. Compared to a previous diet analysis of young Lake Huron lake trout from 2004–2006, fish in the current study consumed more unique prey items (12 vs. 6) and fish species, although many of the lake trout in the current study were larger than those analyzed in the past (74–120 mm). While the variety of taxa consumed by young lake trout has increased since the last study period, the most commonly observed prey items after Mysis were nonnative taxa. Mysis remain an important early food for lake trout in Lake Huron.

Monday January 28, 2019 2:40pm - 3:00pm EST

3:20pm EST

(SYMPOSIA-04) Diet Complexity of Lake Michigan Salmonids
AUTHORS: Benjamin Leonhardt, Purdue University; Benjamin Turschak, Michigan Department of Natural Resources; Austin Happel, Colorado State University; Sergiusz Czesny, University of Illinois, Illinois Natural History Survey; Harvey Boostma, University of Wisconsin-Milwaukee; Jacques Rinchard, SUNY-Brockport; Matt Kornis, U.S. Fish and Wildlife Service; Charles Bronte, U.S. Fish and Wildlife Service; Tomas Höök, Purdue University, Illinois-Indiana Sea Grant

ABSTRACT: Documenting trophic relationships in aquatic ecosystems can facilitate understanding of not only system processes, but also the potential responses of food webs to stressors.  In Lake Michigan, the introduction of invasive species (e.g., zebra mussel, Dreissena polymorpha; quagga mussel, Dreissena bugensis; round goby, Neogobius melanostomus) and reduced nutrient loading has resulted in changes in nutrient dynamics and community composition over the past two decades. As a result, abundances of many forage fish have declined, including alewife (Alosa pseudoharengus) which have historically supported the five dominant salmonid species of Lake Michigan (brown trout, Salmo trutta; Chinook salmon, Oncorhynchus tshawytscha; Coho salmon, Oncorhynchus kisutch; lake trout, Salvelinus namaycush; rainbow trout, Oncorhynchus mykiss). With these ecosystem changes, there is uncertainty as to the extent of how different species of salmonids will transition to alternative prey items (e.g., round goby). We investigated the diet complexity of Lake Michigan salmonids by evaluating stomach content composition, diet diversity, and lengths of alewife consumed. Stomachs collected in 2015 and 2016 in Lake Michigan revealed that Chinook salmon almost exclusively consumed alewife and had a lower diet diversity compared to the other four species, which consumed round goby (brown trout and lake trout), aquatic invertebrates (Coho salmon), and terrestrial invertebrates (rainbow trout) in addition to alewife. Additionally, salmonid species appeared to consume the entire size range of alewife that were available to them despite year to year changes in alewife length availability. Due to their reliance on alewife, it is likely that Chinook salmon may be more negatively impacted than other salmonid species if patterns of alewife decline continue in Lake Michigan.

Monday January 28, 2019 3:20pm - 3:40pm EST

3:40pm EST

(SYMPOSIA-04) Diet and Niche Overlap of Lake Michigan Piscivorous Fishes as Revealed by Stable Isotopes
AUTHORS: Ben Turschak, Michigan Department of Natural Resources; Harvey Bootma, UW-Milwaukee; Chuck Bronte, U.S. Fish and Wildlife Service; Sergiusz Czesny, University of Illinois; Tomas Hook, Purdue; Matt Kornis, U.S. Fish and Wildlife Service; Ben Leonhardt, Purdue; Jacques Rinchard, SUNY-Brockport

ABSTRACT: In the past several decades, the Lake Michigan ecosystem has experienced significant changes at all levels of the food web including major declines in pelagic forage fish biomass. To some degree, loss of pelagic forage has been offset by the invasion of the benthic Round Goby. Several piscivorous species including Lake Trout, Brown Trout, and Burbot have taken advantage of this novel prey source while others such as Chinook and Coho Salmon continue to rely on Alewives and other pelagic forage.  We explored the trophic structure, diet, and potential for niche overlap of Lake Michigan piscivores from 2014-2016 using stable C and N isotopes. To estimate diet proportions among species, Bayesian mixing models were used. Region and year were used as fixed effects with total length as a continuous covariate. Isotopic niche overlap was assessed by fitting Bayesian ellipses to the data and measuring overlap among species. Regional and interannual variability in trophic structure and diet with corresponding changes in niche overlap were observed. Greatest niche overlap corresponded with dependence on Alewife whereas predators that took advantage of other prey sources including Round Goby, and terrestrial invertebrates exhibited lower probability of niche overlap. Degree of overlap also appeared to decrease corresponding to availability of alternative prey sources or reduced alewife abundance.

Monday January 28, 2019 3:40pm - 4:00pm EST

4:00pm EST

(SYMPOSIA-04) Lake Trout: Not a Picky Eater. Dietary Flexibility and Perseverance
AUTHORS: Dan Traynor, Shawn Sitar – Michigan Department of Natural Resources Marquette Fisheries Research Station; Ji He, Michigan Department of Natural Resources Alpena Fisheries Research Station

ABSTRACT: Lake trout are the dominant piscivore in the upper Great Lakes and are a major focus in fisheries management.  Lake populations underwent catastrophic collapses in the middle of the 20th century but have recovered in Lake Superior due to diligent management actions.  Recently, lake trout recovery has improved in Lake Huron and there are indications that Lake Michigan may be following suit.  Although controls on fishing, sea lamprey suppression, and stocking of hatchery fish were instrumental in lake trout recovery, we pose that dietary flexibility also contributed to its success.  We analyzed the diet of a broad size range of lean and siscowet lake trout from spring and summer gill net surveys conducted in southern Lake Superior and western Lake Huron during 2005-2016.  In addition to categorizing prey items by taxa, we grouped prey items by habitat types to further describe dietary flexibility.  We found that lake trout diet compositions were diverse in both lakes Superior and Huron. Generally, the diet of leans and siscowets in Lake Superior were similar.  We observed ontogenetic diet shifts in both lean and siscowet lake trout with small fish feeding predominantly in the benthos expanding to the pelagic zone as fish grew larger.  Progress in lake trout recovery in Lake Huron coincides with collapses in alewife abundance and declines in Chinook Salmon populations.  We pose that lake trout success in rapidly changing ecosystems is partly due to its high dietary flexibility and declines in Great Lakes Chinook salmon are due to its strong reliance on pelagic prey such as alewife.

Monday January 28, 2019 4:00pm - 4:20pm EST

4:20pm EST

(SYMPOSIA-04) Energy Pathways to Prey Fishes Across a Productivity Gradient: A Case-study in the Laurentian Great Lakes
AUTHORS: Anne Scofield, Paris Collingsworth, Tomas Höök – Purdue University; David Bunnell, USGS Great Lakes Science Center; Aaron Fisk, University of Windsor Great Lakes Institute for Environmental Research; Tim Johnson, Ontario Ministry of Natural Resources; Brian Weidel, USGS Lake Ontario Biological Station

ABSTRACT: Natural stable isotope ratios of nitrogen (d<sup>15</sup>N) and carbon (d<sup>13</sup>C) have proven to be valuable tools for identifying basal energy sources for fish production and describing trophic complexity, but cross-lake comparisons of stable isotope data are often limited by challenges associated with standardizing study design and isotopic baselines. Over the past decade, a great number of resources have been invested to generate stable isotope data for the lower food web and prey fishes across all five of the Great Lakes through the bi-national Cooperative Science and Monitoring Initiative (CSMI), providing opportunities for robust cross-lake comparisons. In this study, we investigate differences in nearshore subsidies and trophic transfer efficiencies to prey fish across the productivity gradient observed in the Great Lakes, which range from eutrophic (western Lake Erie) to ultra-oligotrophic (e.g., Lake Superior). Using rainbow smelt as a case study, we examine the basal carbon sources and trophic positions of prey fish in the offshore regions of the five lakes. We also consider how differences in the densities on non-native species, such as dreissenid mussels, may affect resource distribution and energy flow to fishes. Quantifying how trophic structures in lakes differ across a productivity gradient can help elucidate the consequences of human actions such as nutrient management programs, fish stocking, and non-native species introductions.

Monday January 28, 2019 4:20pm - 4:40pm EST

4:40pm EST

(CANCELLED) (SYMPOSIA-04) Density and Biomass of Drifting Macroinvertebrates in the Upper St. Marys River: A Comparison of the Power Canal and Main Rapids
AUTHORS: Tristan Tackman (Student); Dr. Ashely Moerke (Professor/Undergraduate Advisor); Jake Larsen (Graduate) – School of Natural Resources and Environment, Lake Superior State University

ABSTRACT: The St. Marys River is the only outflow of Lake Superior and feeds both Lake Michigan and Lake Huron. The river itself rears a majority of these lakes’ sports fishes by providing ample spawning grounds; these young fish rely on small macroinvertebrates for most of their growth in early years. The objective of this study was to quantify and compare the supply of drifting invertebrates from the main rapids and the hydropower canal in an effort to understand key food sources available for fishes in the river.  To do so, two larval drift nets were set overnight in the rapids and canal to collect drifting invertebrates during the months of May and June 2016.  For each date biomass was calculated asash free dry weight and density was calculated as number of invertebrates per 100m<sup>3</sup>. Densities were the highest for Hydropsychidae and Mysidae at both sites, andcomprised 18% (the remanding 82% being non-dominant taxa) and 9.5% in the rapids and 26.7% and 8.9% in the canal site. Although Mysidaedensities were higher than other taxa, Hydropsychidae contributed more biomass to the system in both sites during May and June of 2016. Additionally, total drift densities were 2.4 times higher in the canal site than the rapids, suggesting that the canal is a better source of invertebrates to the St. Marys River. The canal is likely drawing water from more offshore areas in Lake Superior, which may explain the higher numbers of drifting Mysids in the canal site compared to the rapids.

Monday January 28, 2019 4:40pm - 5:00pm EST