First posted August 3, 2017 For additional information, contact: Director, Great Lakes Science Center U.S. Geological Survey 1451 Green Rd. Ann Arbor, MI 48105 Great Lakes fishery managers have the opportunity and have expressed interest in reestablishing a native forage base in the Great Lakes consisting of various forms and species within the genus Coregonus. This report summarizes the proceedings of a workshop focused on a subset of the genus, and the term "coregonines" is used to refer to several species of deepwater ciscoes (also known as "chubs") and the one more pelagic-oriented cisco species (Coregonus artedi, also known as "lake herring"). As the principal conservation agency for the United States Government, the Department of Interior has unique and significant authorities and capacities to support a coregonine reestablishment program in the Great Lakes. To identify and discuss key uncertainties associated with such a program and develop a coordinated approach, the U.S. Geological Survey (USGS) and the U.S. Fish and Wildlife Service (FWS), the principal Department of the Interior bureaus to address Great Lakes fishery issues, held the first of a series of workshops on coregonine science in Ann Arbor, Michigan, on October 11–13, 2016. Workshop objectives were to identify (1) perceived key uncertainties associated with coregonine restoration in the Great Lakes and (2) DOI capacities for addressing these key uncertainties.

Understanding differences in zooplankton abundance depends on comparing similar data. Scientists employ numerous methods to collect and count freshwater zooplankton, potentially leading to difficulties when comparing studies. As scant information concerning specific biases exists, we quantified how (1) net mesh size and (2) counting techniques influence zooplankton size and abundance estimates. We compared mesh sizes by collecting zooplankton with four vertically hauled nets differing only in mesh size. We examined mesh‐size effects on filtration efficiency across a suspended sediment gradient by comparing the known (quantified with a flowmeter) and assumed (from site depth) sample volumes. Finally, eight samples were counted with each of four methods to compare estimates of zooplankton abundance among techniques that differ in the minimum number of individuals counted. We found that only 64‐µm mesh nets effectively capture small‐bodied zooplankton (small cladocerans, copepod nauplii, and rotifers, mean size = 0.13−0.30 mm) whereas all nets effectively collected larger‐bodied zooplankton (mean size > 0.48 mm). All three > 100 µm‐mesh nets were > 90% efficient, regardless of suspended solids abundance. In contrast, the 64‐µm mesh net was at best 60% efficient; hence, actual volume sampled must be determined to avoid underestimation. We found counting‐method‐specific shortcomings, particularly for those in which few individuals were counted. We recommend, then, that a moderate number of individuals are counted for many finely resolved taxonomic categories or many individuals are counted for fewer, broader taxonomic categories. Consequently, to directly compare zooplankton densities between studies, scientists need a clear understanding of field collection and laboratory enumeration methods.

We quantified thiamine in eggs of Lake Erie walleye to determine if differences exist between spawning stocks within the Maumee and Sandusky rivers, both of which drain into the Western Basin. In spring 2004, eggs of walleye were collected in the Maumee River at three occasions (early, peak and late of the spawning run) and in the Sandusky River during the spawning run. After collection, eggs were fertilized with a known amount of milt, incubated and embryo survival was determined at the pigmented eyed stage. Thiamine and its derivatives were analyzed using high performance liquid chromatography. Thiamine pyrophosphate (TPP) was the most abundant form of vitamin B1 present in eggs (60–95% of the total vitamin B1 concentration). Total thiamine concentrations in walleye eggs from the Maumee and Sandusky rivers at the peak of the spawning run averaged 6.1 ± 1.6 nmol g−1 and 5.0 ± 2.9 nmol g−1, respectively. Our results also indicated that Maumee River stock survival to the eyed stage embryo declined as the spawning season progressed (72%, 59% and 37% in the early, middle and late of spawning run, respectively) as well as the total thiamine and TPP concentrations. At the peak of the spawning run, survival to the eyed stage embryo did not differ significantly between stocks 59% versus 65% in the Maumee and Sandusky rivers, respectively, and thiamine concentrations were not significantly different between sites.

Mr. Chairman and members of the committee, my name is Roy Stein. I am the Vice-Chair of the Great Lakes Fishery Commission. I am also a professor in the Department of Evolution, Ecology, and Organismal Biology at The Ohio State University. On behalf of my Great Lakes Fishery Commission colleagues, I am pleased to be here today to discuss the Great Lakes fishery and to outline some challenges ahead for restoration of this invaluable resource. I commend Senator Voinovich for holding this hearing on the shores of the Great Lakes. The lakes require care and attention and we appreciate all you have done to help protect them for today and for future generations.

We parameterized and evaluated a bioenergetics model for saugeye (walleye Sander vitreus x sauger S. canadensis) by using laboratory experiments in an effort to improve predictions of prey consumption. First, we measured daily prey consumption rate and growth of age-0 and age-1 saugeyes fed two daily rations (ad libitum and 50% of maximum) at five temperatures ranging from 10 degrees C to 28 degrees C. Additional experiments quantified routine respiration rates and waste losses for three ages of saugeye (ages 0, 1, and 2) at five temperatures ranging from 10 degrees C to 28 degrees C. Mean daily rates of prey consumption (g.g(-1).d(-1)) by saugeyes increased from 10 degrees C to 25 degrees C, declining at 28 degrees C. Respiration rates (gO(2).g(-1).d(-1)) increased over the entire range of water temperatures. Waste losses were minor for saugeyes as egestion averaged 3.5% of consumed energy and energy lost via excretion was 4.5% of assimilated energy. We evaluated the accuracy of bioenergetics model predictions of saugeye prey consumption using daily prey consumption and corresponding growth data from our first set of experiments. Model estimates of prey consumption rates (g.g(-1).d(-1)) closely followed observed trends, providing reasonable estimates of cumulative prey consumption across temperature and fish size. The saugeye model provided improved estimates of consumption compared with a model published for walleyes (Kitchell et al. 1977), especially when water temperatures were in excess of 25 degrees C. The differences we observed in predictive performance between the two models resulted from higher thermal optima for saugeyes compared with walleyes, and waste constants for saugeyes were two to three times lower than those calculated from the walleye model. These differences may largely be responsible for the walleye model's overestimation of consumption. Saugeye thermal optima are warmer than those of either parent species, and saugeye is better suited for warm, productive midwestern U. S. reservoirs. The saugeye model developed herein will improve the ability of managers to more accurately predict the consumptive demand of in situ saugeye populations and better tailor stocking rates to match available prey biomass.

In Ohio reservoirs, a perceived excess of available gizzard shad Dorosoma cepedianum prey and poor recruitment of stocked walleyes Sander vitreus during the 1970s resulted in research to develop and expand a program to stock saugeyes (walleye X sauger S. canadensis), a hybrid better suited for shallow, productive, and turbid reservoirs with short water-residence times. Development of successful production techniques increased saugeye stocking from fewer than 1.2 million to 6-10 million fingerlings (28-42 mm) per year during 1980 through 1990, presenting the challenge of determining stocking rates suited to available prey. To improve Sander spp. stocking practices, we assessed prey supply by quantifying fish biomass in Ohio reservoirs using acoustic technology. Fish biomass varied from 10 to 897 kg/ha as estimated by 53 acoustic surveys conducted on 16 reservoirs during 1999-2006. Among 15 variables associated with reservoir productivity, 84% of the variability in fish biomass was explained by watershed area, trophic state, reservoir area, and reservoir volume; watershed area plus trophic state explained 77% of this variability. Dominance of fish prey smaller than 160 mm, which represented more than 80% of fishes sampled in acoustic surveys, revealed that reservoir fish biomass largely reflected the upper limit of prey fish biomass morphologically available to age-1 and older Sander spp. Gizzard shad represented more than 50% of the fishes captured in 92% of gill-netting surveys conducted in conjunction with acoustic surveys. Unexpectedly, reservoirs with extensive prey biomass occasionally had poor recruitment for Sander spp., and these reservoirs often were stocked at lower rates than ones with better recruitment. Fisheries managers in Ohio can improve stocking practices by using acoustic surveys to predict reservoir capacity for stocked sport fish based on reservoir attributes, then applying these results to details of reservoir-specific recruitment of stocked fishes and their consumptive demand. Refining this supply and demand approach will require continual progress in understanding reservoir ecosystems and their watersheds.

The movement of fish from onstream impoundments into connected streams and rivers has traditionally been overlooked in fish stocking decisions but is critical to the ultimate impact of stocking riverine species into reservoirs. Hybrid saugeyes (female walleye Sander vitreus x male sauger S. canadensis) stocked into Deer Creek Reservoir, Ohio, readily move from the reservoir to the tailwater below. Downstream movement of these saugeyes from the tailwater may have consequences for native prey species and parental stocks downstream. We used fixed-station radiotelemetry to quantify the temporal movement patterns of 203 reservoir-stocked saugeyes from the tailwater of the reservoir, the stream flowing from the tailwater, and the river into which the stream flowed. From October 1998 through July 2000, most (75%) saugeyes never left the tailwater, and those that left returned 75% of the time. Overall, saugeyes spent 90% of their time in the tailwater, 7-8% of their time downstream in small streams, and 2-3% of their time farther downstream in the Scioto River (45 km downstream). No radio-tagged saugeyes moved to the Ohio River (155 km downstream). The probability of downstream movement generally increased with increasing flow and when dissolved oxygen dropped to lethal levels in summer. The probability of movement was highest in winter and spring, when it was probably related to spawning, and low in summer (except when dissolved oxygen was low) and fall. The patterns of movement seemed to reflect the relative suitability of tailwater over stream habitat. The predominant use of and return to tailwater habitat after downstream movement limited overall stream and river residence time. Although the daily movement probability for an individual was low, when we apply these rates to all of the stocked saugeyes in the Ohio River drainage, we cannot safely conclude that only small numbers move from reservoir tailwaters to downstream river systems. We recommend that managers refrain from stocking systems for which there are concerns about native species in connected drainages.

The fish communities in the Laurentian Great Lakes have been dramatically altered through overfishing, habitat destruction, contaminants, and invasive species, specifically the alewife Alosa pseudoharengus and the sea lamprey Petromyzon marinus. By the mid-20th century, populations of lake trout Salvelinus namaycush, lake whitefish Coregonus dupeaformis, and burbot Lota lota were decimated, multiple species of deepwater ciscoes Coregonus spp. had become extinct, and the invasive alewife comprised the bulk of the remaining biomass. Commercial, recreational, and tribal Fisheries had collapsed. With significant reductions in contaminant and nutrient loading, stream restoration, and a successful sea lamprey control program came opportunities for rehabilitation. Cooperatively, federal, provincial, and state Fisheries management agencies initiated stocking programs to restore native species and to introduce Pacific salmonids Oncorhynchus spp. as a biocontrol for alewife, as well as for recreational angling. Lake Superior and the warmwater communities in Lake Erie have been rehabilitated. Lake whitefish and burbot populations have increased throughout Lakes Superior, Michigan, and Huron; self-sustaining take trout populations are becoming established in Georgian Bay, Lake Huron. Nevertheless, the rehabilitation of lake trout populations in Lakes Erie, Michigan, and Ontario has been unsuccessful. Recent invasions by dreissinid mussels, large zooplankton species, and round gobies Neogobius melanostomus have greatly altered lower trophic levels. During the rehabilitation process, commercial, recreational, and tribal harvests have continued to be economically viable. In this paper, we describe a consensus-building process surrounding the nature of decision making within the context of fishery management, the science-based rationale for stocking and harvest, and the "lessons learned" from the application of these processes.

Although effects of land use/cover on nutrient concentrations in aquatic systems are well known, half or more of the variation in nutrient concentration remains unexplained by land use/cover alone. Hydrogeomorphic (HGM) landscape features can explain much remaining variation and influence food web interactions. To explore complex linkages among land use/cover, HGM features, reservoir productivity, and food webs, we sampled 11 Ohio reservoirs, ranging broadly in agricultural catchment land use/cover, for 3 years. We hypothesized that HGM features mediate the bottom‐up effects of land use/cover on reservoir productivity, chlorophyll a, zooplankton, and recruitment of gizzard shad, an omnivorous fish species common throughout southeastern U.S. reservoirs and capable of exerting strong effects on food web and nutrient dynamics. We tested specific hypotheses using a model selection approach. Percent variation explained was highest for total nitrogen (R2 = 0.92), moderately high for total phosphorus, chlorophyll a, and rotifer biomass (R2 = 0.57 to 0.67), relatively low for crustacean zooplankton biomass and larval gizzard shad hatch abundance (R2 = 0.43 and 0.42), and high for larval gizzard shad survivor abundance (R2 = 0.79). The trophic status models included agricultural land use/cover and an HGM predictor, whereas the zooplankton models had few HGM predictors. The larval gizzard shad models had the highest complexity, including more than one HGM feature and food web components. We demonstrate the importance of integrating land use/cover, HGM features, and food web interactions to investigate critical interactions and feedbacks among physical, chemical, and biological components of linked land‐water ecosystems.

In this study, an outdoor pool experiment was used to evaluate the effect of prey resources during 4 months before spawning on the gonadal investments of male and female white crappie Pomoxis annularis, a popular freshwater sportfish that exhibits erratic recruitment. Fish were assigned one of three feeding treatments: starved, fed once every 5 days (intermediate) or fed daily (high). All measurements of male testes (i.e. wet mass, energy density and spermatocrit) were similar across treatments. Conversely, high‐fed females produced larger ovaries than those of intermediate‐fed and starved fish, and invested more energy in their ovaries than starved fish. Compared to pre‐experiment fish, starved and intermediate‐fed females appeared to increase their ovary size by relying on liver energy stores (‘capital’ spawning). Conversely, high‐fed females increased liver and gonad mass, implying an ‘income’‐spawning strategy (where gonads are built from recently acquired energy). Fecundity did not differ among treatments, but high‐fed fish built larger eggs than those starved. Females rarely ‘skipped’ spawning opportunities when prey resources were low, as only 8% of starved females and 8% of intermediate‐fed females lacked vitellogenic eggs. These results suggest that limited prey resources during the months before spawning can limit ovary production, which, in turn, can limit reproductive success of white crappies.

Gizzard shad (Dorosoma cepedianum) population characteristics vary with lake productivity, competing with and providing prey for sport fishes. Because age-0 gizzard shad (>30 mm total length) are facultative detritivores, they can link benthic energy, carbon, and nutrients to pelagic food webs. To determine how age-0 gizzard shad success varies along a detritus-quality gradient, we completed a 15-day laboratory experiment in which age-0 gizzard shad fed lake sediment and starved gizzard shad both suffered-high mortality, whereas fish fed zooplankton grew and survived well. This suggested that detritus alone is insufficient to ensure gizzard shad growth and survival. When sediment quality was high in outdoor mesocosms, density-dependent factors led to rapid growth only at low fish density and high-quality sediments; however, survival generally increased with sediment quality, regardless of gizzard shad density. In four small reservoirs, annual growth of gizzard shad increased with sediment quality. Collectively, our findings suggest that detritus quality ultimately can contribute to regulation of community and ecosystem productivity, mediated by its influence on gizzard shad biomass available for trophic transfer to gape-limited predators (i.e., piscivorous fish). This role of gizzard shad can link higher trophic levels in aquatic food webs to allochthonous detritus subsidies from the surrounding watershed.

Lake Erie's food web has been dramatically modified by exotic species. Both exotic dreissenid mussels and the round goby Neogobius melanastomus have shifted the food web from a pelagic-based to a benthic-based one, potentially creating a new pathway for contaminant transfer to top predators. Before the invasion of round gobies, few predators of dreissenids occurred in Lake Erie, allowing contaminants to be confined to these benthic organisms. The invasion of the round goby has produced a new pathway through which these contaminants can enter the food web. To characterize heavy-metal transfer through this new food web and to assess risk to humans, water, surficial sediment, dreissenid, round goby, and smallmouth bass Micropterus dolomieui samples were collected at three sites during summers, 2002 and 2003, and analyzed for total lead (Pb), total mercury (Hg), and methyl mercury (MeHg). In addition, we compared smallmouth bass Pb and Hg concentrations to those measured in 1993/1994, before round gobies were prevalent. Pb biodiminished and MeHg biomagnified through the food web to smallmouth bass; patterns were similar among our three sites. Total Pb concentrations in smallmouth bass were higher before the incorporation of round gobies into their diet. We attributed this decline to changes in food web structure, changes in contaminant burdens in prey, or declines in sediment Pb concentrations in Lake Erie. By comparison, Hg concentrations in smallmouth bass changed little, before and after the round goby invasion, possibly due to a shift in diet that increased growth. Despite a decline in sediment Hg concentrations in Lake Erie, smallmouth bass continued to accumulate Hg at historical rates possibly because of their high consumption rates of benthivorous round gobies. As smallmouth bass continue to consume round gobies during their lives, their Hg concentrations may well continue to increase, potentially increasing the risk of Hg contamination to humans.

Animals can be important in nutrient cycling in particular ecosystems, but few studies have examined how this importance varies along environmental gradients. In this study we quantified the nutrient cycling role of an abundant detritivorous fish species, the gizzard shad (Dorosoma cepedianum), in reservoir ecosystems along a gradient of ecosystem productivity. Gizzard shad feed mostly on sediment detritus and excrete sediment-derived nutrients into the water column, thereby mediating a cross-habitat translocation of nutrients to phytoplankton. We quantified nitrogen and phosphorus cycling (excretion) rates of gizzard shad, as well as nutrient demand by phytoplankton, in seven lakes over a four-year period (16 lake-years). The lakes span a gradient of watershed land use (the relative amounts of land used for agriculture vs. forest) and productivity. As the watersheds of these lakes became increasingly dominated by agricultural land, primary production rates, lake trophic state indicators (total phosphorus and chlorophyll concentrations), and nutrient flux through gizzard shad populations all increased. Nutrient cycling by gizzard shad supported a substantial proportion of primary production in these ecosystems, and this proportion increased as watershed agriculture (and ecosystem productivity) increased. In the four productive lakes with agricultural watersheds (>78% agricultural land), gizzard shad supported on average 51% of phytoplankton primary production (range 27-67%). In contrast, in the three relatively unproductive lakes in forested or mixed-land-use watersheds (>47% forest, <52% agricultural land), gizzard shad supported 18% of primary production (range 14-23%). Thus, along a gradient of forested to agricultural landscapes, both watershed nutrient inputs and nutrient translocation by gizzard shad increase, but our data indicate that the importance of nutrient translocation by gizzard shad increases more rapidly. Our results therefore support the hypothesis that watersheds and gizzard shad jointly regulate primary production in reservoir ecosystems.

Stock-recruit models typically use only spawning stock size as a predictor of recruitment to a fishery. In this paper, however, we used spawning stock size as well as larval density and key environmental variables to predict recruitment of white crappies Pomoxis annularis and black crappies P. nigromaculatus, a genus notorious for variable recruitment. We sampled adults and recruits from 11 Ohio reservoirs and larvae from 9 reservoirs during 1998-2001. We sampled chlorophyll as an index of reservoir productivity and obtained daily estimates of water elevation to determine the impact of hydrology on recruitment. Akaike's information criterion (AIC) revealed that Ricker and Beverton-Holt stock-recruit models that included chlorophyll best explained the variation in larval density and age-2 recruits. Specifically, spawning stock catch per effort (CPE) and chlorophyll explained 63-64% of the variation in larval density. In turn, larval density and chlorophyll explained 43-49% of the variation in age-2 recruit CPE. Finally, spawning stock CPE and chlorophyll were the best predictors of recruit CPE (i.e., 74-86%). Although larval density and recruitment increased with chlorophyll, neither was related to seasonal water elevation. Also, the AIC generally did not distinguish between Ricker and Beverton-Holt models. From these relationships, we concluded that crappie recruitment can be limited by spawning stock CPE and larval production when spawning stock sizes are low (i.e., CPE < 5 crappies/net-night). At higher levels of spawning stock sizes, spawning stock CPE and recruitment were less clearly related. To predict recruitment in Ohio reservoirs, managers should assess spawning stock CPE with trap nets and estimate chlorophyll concentrations. To increase crappie recruitment in reservoirs where recruitment is consistently poor, managers should use regulations to increase spawning stock size, which, in turn, should increase larval production and recruits to the fishery.

Community structure and species composition may be strongly influenced by predator-prey interactions resulting from and leading to episodes of population abundance or scarcity. We quantified diets of stocked saugeyes (female walleye Sander vitreus X male sauger S. canadensis) and estimated biomass of their primary prey, gizzard shad Dorosoma cepedianum, in three Ohio reservoirs at quarterly intervals during July 2002-July 2003 to determine whether saugeye consumptive demand could exceed the supply of available gizzard shad prey, resulting in a shift to alternative prey. We incorporated water temperature and saugeye diet composition, growth, and mortality into walleye bioenergetics models, which allowed us to compare estimated prey-specific consumption rates by saugeyes with gizzard shad standing stocks estimated with acoustics. Spring and summer were critical seasons. During spring, gizzard shad biomass was low, saugeye consumptive demand was low, and saugeyes consumed primarily alternative prey. During summer, when age-0 gizzard shad became available as prey, saugeyes consumed similar proportions of gizzard shad and alternative prey. Saugeye cumulative consumptive demand in summer was high and approached the gizzard shad standing stock. However, during fall and winter, gizzard shad supply was adequate to support high (fall) or declining (winter) saugeye consumptive demand. Across reservoirs and seasons, saugeyes consumed alternative prey to varying degrees, primarily sunfishes Lepomis spp., yellow perch Perca flavescens, logperch Percina caprodes, and minnows Pimephales spp. Seasonal asynchrony between saugeye consumptive demand and gizzard shad biomass during spring and summer indicated that a saugeye population with high survival, growth, and consumptive demand will opportunistically increase use of prey other than gizzard shad. The manner in which saugeye predation quantitatively influences these prey species could not be assessed. However, overexploitation of gizzard shad prey appears to be unlikely at current saugeye population sizes, particularly considering the opportunistic use of alternative prey and the high reproductive potential of gizzard shad.

For an increasing number of species, maternal characteristics have been correlated with the characteristics of their eggs or larvae at the individual level. Documenting these maternal effects at the population level, however, is uncommon. For white crappies Pomoxis annularis, we evaluated whether individual maternal effects on eggs existed and then explored whether incorporating maternal effects explained additional variation in recruitment, a population-level response. Individual egg quality (measured as ovary energy density) increased with maternal length among individuals from seven Ohio reservoirs in 1999 and three in 2000. Among these same individuals, egg quality increased with maternal condition factor (measured as residual wet mass for a given length) in 1999 but not in 2000. In 2000 we estimated somatic energy density, an improved measure of condition; egg quality increased with somatic energy density, but somatic energy density was also strongly correlated with maternal length. Hence, we could not determine whether maternal length or condition was the primary factor influencing white crappie egg quality. Across seven populations, the relative population fecundity (i.e., stock size) of the 1999 year-class was unable to explain the variation in recruitment to age 2 (Ricker model r(2) = 0.04 and Beverton and Holt model r(2) = 0.02). Mean ovary energy density (i.e., egg quality), however, was unable to explain additional recruitment variability in either model. Hence, we documented evidence of maternal effects on individual ovaries but not on population-level recruitment. Nonetheless, we recommend that future studies seeking to understand white crappie recruitment continue to consider maternal effects as a potential factor, especially those studies that may have greater sample sizes at the population level and, in turn, a greater probability of documenting a population-level effect.

We studied how storms, angling, and nest predation during angling affected smallmouth bass (Micropterus dolomieu) nest survival in the Bass Islands, Lake Erie, Ohio, USA. Increasing angler effort and introduction of an exotic nest predator, round goby (Neogobious melanostomus), have raised concerns about smallmouth bass recruitment in Lake Erie. We surveyed smallmouth bass nests and calculated daily survival rates for nests assigned to different angling treatments: control, angling without predation, or angling with predation treatments. Only 30% of control nests were successful compared with 11% of angling without predation and 14% of angling with predation treatments. We used the Mayfield method and maximum likelihood models in the program MARK to estimate the survival rates for nests of different treatments and exposed to different numbers of storms. Although nest predators consumed about 35% of broods during angling, daily nest survival rates of both angling treatments were similar. Angling reduced nest survival compared with controls by approximately 5%. Storms reduced both nest success and daily survival. The best model predicting daily nest survival included the added effects of angling treatment and number of storms. Thus, whereas storms and angling affected smallmouth bass nest survival, nest predation during angling did not.