Stuart Ludsin | Ohio State University (original) (raw)

Papers by Stuart Ludsin

Acta Zoologica, Jul 15, 2021

Theriogenology, Mar 1, 2023

Animal Reproduction Science, 2020

This study was conducted to compare quality and quantity of sperm collected from sauger (S. canad... more This study was conducted to compare quality and quantity of sperm collected from sauger (S. canadensis) using two collection methods: stripping alone and testicular tissue collection combined with stripping. Sperm were collected from sauger broodstock (n = 20) during the breeding season. Fish were randomly assigned to two sperm collection groups: (1) stripping once or (2) stripping twice before testicular tissue collection for obtaining additional sperm. Sperm motility variables, morphology, total number produced, and fertilization (%) were compared using the two collection methods. Testicular sperm had greater total motility (70.1 ± 2.1% compared with 44.3 ± 5.7%) but there were fewer morphologically normal cells (76.4 ± 1.3% compared with 92.8 ± 1.0%) compared to sperm collected using the stripping procedure. Sperm collection regimen utilizing testicular collections and sperm extractions in combination with stripping resulted in a ∼ten fold increase in total number of motile and morphologically normal sperm (39.5 ± 4.1 × 10 9) compared with the currently utilized two sequential sperm stripping collection procedures alone (3.6 ± 4.1 × 10 9 sperm). In large-scale studies (150,000 eggs), fertilization, using sperm collected from testicular tissues (1.0 × 10 5 motile sperm/egg), was similar to sperm collected with only the stripping procedure (71.2 ± 5.5 %, 81.2 ± 5.5 %, P = 0.265). The results of this study indicate testicular collection combined with sperm extractions allows for collection of sperm of a quantity and quality to maximize fry production and reduce the problems with lack of broodstock availability for sperm collection.

North American Journal of Fisheries Management, Oct 14, 2016

The expected impacts of invasive species are key considerations in selecting policy responses to ... more The expected impacts of invasive species are key considerations in selecting policy responses to potential invasions. But predicting the impacts of invasive species is daunting, particularly in large systems threatened by multiple invasive species, such as North America's Laurentian Great Lakes. We developed and evaluated a scenario-building process that relied on an expert panel to assess possible future impacts of aquatic invasive species on recreational fishing in the Great Lakes. To maximize its usefulness to policy makers, this process was designed to be implemented relatively rapidly and considered a range of species. The expert panel developed plausible, internally consistent invasion scenarios for five aquatic invasive species, along with subjective probabilities of

Fisheries Research, Oct 1, 2020

Demographic and environmental factors can influence the spatial distribution of fish populations,... more Demographic and environmental factors can influence the spatial distribution of fish populations, potentially affecting the timing, location, and magnitude of harvest. Quantifying these relationships can be complicated, if their effects vary spatially over a population's range or are non-additive (i.e., interactive), where one factor mediates the effect of another. Toward understanding the relative influence of demographic and environmental factors on fishery harvest in large freshwater lakes, we used varying-coefficient generalized additive models to explore the existence of non-additive, spatially-dependent effects of adult population size and thermal conditions on recreational harvest patterns of Lake Erie walleye (Sander vitreus) during 2006-2015. We identified nonlinear, additive, and generally positive effects of thermal conditions and adult population size on harvest rates. Their effects were, however, spatially-dependent, the accounting of which can help explain inter-annual and intraannual variation in lake-wide harvest rates. Specifically, harvest rates increased more with increasing cumulative degree days in the eastern portion of the central basin, especially offshore, relative to the rest of the study area. Harvest rates also increased more with increasing walleye population size in the southwest portion of the west basin and the middle of the central basin compared to other study areas. As in marine ecosystems, our findings demonstrate the benefit of using modeling approaches that consider the spatial dependency of harvest rate on demographic and environmental factors to understanding broader harvest dynamics in large lakes. Their use could help managers and policy-makers ensure the sustained use of valued freshwater fish populations amidst demographic and environmental change.

Canadian Journal of Fisheries and Aquatic Sciences, Apr 1, 2013

Techniques that use calcified structures to identify the natal origin of organisms assume that re... more Techniques that use calcified structures to identify the natal origin of organisms assume that reworking of previously deposited material does not occur. While verified for otoliths, this assumption remains unverified for statoliths. Herein, we test the stability of sea lamprey (Petromyzon marinus) statolith microchemistry during metamorphosis. Using laser ablation inductively coupled plasma mass spectrometry, we quantified the concentrations of nine elements in statoliths from sea lamprey larvae (n = 118) and newly metamorphosed (n = 115) individuals that were collected across six tributaries of varying alkalinity in the Laurentian Great Lakes and Lake Champlain basins. In newly metamorphosed individuals from all streams, the portion of the statolith deposited during the larval stage was enriched in rubidium (Rb), strongly suggesting a chemical reworking of statoliths during metamorphosis. As the ability to discriminate among sea lamprey from different streams in the Great Lakes and Lake Champlain mostly relies on premetamorphic levels of Rb, strategies for the use of statoliths to identify the natal origin of sea lamprey parasitic juveniles and spawners (postmetamorphic stages) should take into account the chemical changes associated with metamorphosis. Résumé : Les techniques d'identification de l'origine des organismes vivants à partir de leurs structures calcifiées supposent que les concentrations élémentaires ne soient pas modifiées une fois les éléments déposés dans les structures calcifiées. Bien que vérifiée pour les otolithes, cette supposition n'a pas encore été vérifiée pour les statolithes. Dans la présente étude, nous testons la stabilité microchimique des statolithes de lamproies marines (Petromyzon marinus) au cours de la métamorphose. Nous avons utilisé un spectromètre de masse à plasma induit couplé à l'ablation laser pour mesurer les concentrations de neuf éléments dans les statolithes de larves de lamproies marines (n = 118) et de lamproies marines récemment transformées (n = 115). Les individus ont été collectés dans six tributaires d'alcalinité différente des Grands Lacs Laurentiens et du Lac Champlain. Pour tous les tributaires, les statolithes de lamproies récemment transformées étaient enrichis en rubidium (Rb) dans la portion du statolithe déposée au cours de la phase larvaire, suggérant ainsi une modification chimique des statolithes durant la métamorphose. Etant donné l'importance des concentrations pré-métamorphose en Rb pour discriminer l'origine des lamproies marines dans les Grands Lacs Laurentiens et le Lac Champlain, l'utilisation des statolithes pour identifier l'origine des lamproies juvéniles parasites et des adultes reproducteurs (stades post-métamorphose) nécessite de tenir compte des modifications chimiques liées à la métamorphose.

Fish and Fisheries, Jul 7, 2023

Early life survival is critical to successful replenishment of fish populations, and hypotheses d... more Early life survival is critical to successful replenishment of fish populations, and hypotheses developed under the Growth‐Survival Paradigm (GSP) have guided investigations of controlling processes. The GSP postulates that recruitment depends on growth and mortality rates during early life stages, as well as their duration, after which the mortality declines substantially. The GSP predicts a shift in the frequency distribution of growth histories with age towards faster growth rates relative to the initial population because slow‐growing individuals are subject to high mortality (via starvation and predation). However, mortality data compiled from 387 cases published in 153 studies (1971–2022) showed that the GSP was only supported in 56% of cases. Selection against slow growth occurred in two‐thirds of field studies, leaving a non‐negligible fraction of cases showing either an absence of or inverse growth‐selective survival, suggesting the growth‐survival relationship is more complex than currently considered within the GSP framework. Stochastic simulations allowed us to assess the influence of key intrinsic and extrinsic factors on the characteristics of surviving larvae and identify knowledge gaps on the drivers of variability in growth‐selective survival. We suggest caution when interpreting patterns of growth selection because changes in variance and autocorrelation of individual growth rates among cohorts can invalidate fundamental GSP assumptions. We argue that breakthroughs in recruitment research require a comprehensive, population‐specific characterization of the role of predation and intrinsic factors in driving variability in the distribution and autocorrelation of larval growth rates, and of the life stage corresponding to the endpoint of pre‐recruited life.

Journal of Great Lakes Research, Jun 1, 2023

Zenodo (CERN European Organization for Nuclear Research), Jun 1, 2009

The Great Lakes Fishery Commission was established by the Convention on Great Lakes Fisheries bet... more The Great Lakes Fishery Commission was established by the Convention on Great Lakes Fisheries between Canada and the United States, which was ratified on October 11, 1955. It was organized in April 1956 and assumed its duties as set forth in the Convention on July 1, 1956. The Commission has two major responsibilities: first, develop coordinated programs of research in the Great Lakes, and, on the basis of the findings, recommend measures which will permit the maximum sustained productivity of stocks of fish of common concern; second, formulate and implement a program to eradicate or minimize sea lamprey populations in the Great Lakes.

Canadian Journal of Fisheries and Aquatic Sciences, Jul 1, 2020

Whether bottom hypoxia has long-lasting consequences for pelagic fish populations remains specula... more Whether bottom hypoxia has long-lasting consequences for pelagic fish populations remains speculative for most ecosystems. We explored hypoxia’s influence on two pelagic zooplanktivores in Lake Erie that have different thermal preferences: cold-water rainbow smelt (Osmerus mordax) and warm-water emerald shiners (Notropis atherinoides). To assess acute effects, we combined predictive bioenergetics-based modeling with field collections made across the hypoxic season in central Lake Erie during 2005 and 2007. To assess chronic effects, we related fishery-independent and fishery-dependent catches with hypoxia severity and top predator (walleye, Sander vitreus) abundance during 1986–2014. As our modeling predicted, hypoxia altered rainbow smelt movement and distributions, leading to avoidance of cold, hypoxic bottom waters. In response, diets shifted from benthic to pelagic organisms, and consumption and energetic condition declined. These changes were lacking in emerald shiners. Our long-term analyses showed rainbow smelt abundance and hypoxia to be negatively related and suggested that hypoxia avoidance increases susceptibility to commercial fishing and walleye predation. Collectively, our findings indicate that hypoxia can negatively affect pelagic fish populations over the long term, especially those requiring cold water.

Science of The Total Environment, Dec 1, 2020

General Circulation Model Multiple stressors Species distribution model Trait analysis climate ef... more General Circulation Model Multiple stressors Species distribution model Trait analysis climate effects outweighing those of ACP implementation. Functional trait analysis helped clarify the varied responses among species, indicating that more extreme climate change would reduce available habitat for largebodied, cool-water species with equilibrium life-histories, many of which also are of importance to recreational fishing (e.g., northern pike, smallmouth bass). By contrast, available habitat for warm-water, benthic species with more periodic or opportunistic life-histories (e.g., northern hogsucker, greater redhorse, greenside darter) was predicted to increase. Further, ACP implementation was projected to hasten these shifts, suggesting that efforts to improve water quality could come with costs to other ecosystem services (e.g., recreational fishing opportunities). Collectively, our findings demonstrate the need to consider biological outcomes when developing strategies to mitigate water quality impairment and highlight the value of physical-biological modeling approaches to agricultural and biological conservation planning in a changing climate.

Journal of Great Lakes Research, Feb 1, 2023

Harmful Algae, Feb 1, 2020

With anthropogenic eutrophication and climate change causing an increase in cyanobacterial blooms... more With anthropogenic eutrophication and climate change causing an increase in cyanobacterial blooms worldwide, the need to understand the consequences of these blooms on aquatic ecosystems is paramount. Key questions remain unanswered with respect to how cyanobacteria blooms affect the structure of aquatic food webs, the foraging abilities of higher consumers, and the potential for cyanotoxins (e.g., microcystins [MCs]) to accumulate in fish. Toward addressing these uncertainties, physicochemical attributes, water (for MCs), phytoplankton, zooplankton, and epipelagic and benthic age-0 fish were sampled at 75 sites (44 sites for fish) of varying cyanobacteria concentration (0.1-44 μg/L) in western Lake Erie during the cyanobacteria bloom season, 2013-2014. Sites with high cyanobacteria biomass were characterized by Microcystis spp. (84-100% of biomass), detectible levels of MCs (maximum = 10.8 μg/L), and low water transparency (minimum = 0.25 m). Counter to expectations, strong positive relationships were found between cyanobacteria concentration and the biomass of several herbivorous zooplankton taxa (e.g., Daphnia, Diaphanosoma spp., Bosmina (formerly Eubosmina) coregoni, and Calanoida spp.). Expectations regarding fish were partly supported (e.g., diet selectivity varied across a cyanobacteria gradient) and partly not (e.g., consumption of zooplankton did not differ between bloom and nonbloom sites). These findings show that cyanobacterial blooms can strongly affect the distribution, composition, and interactions of zooplankton and fish, sometimes in surprising ways, highlighting the need to further explore their impact on aquatic food webs.

Scientific Reports, May 10, 2023

Intraspecific interactions within predator populations can affect predator-prey dynamics and comm... more Intraspecific interactions within predator populations can affect predator-prey dynamics and community structure, highlighting the need to better understand how these interactions respond to anthropogenic change. To this end, we used a half-century (1969-2018) of abundance and sizeat-age data from Lake Erie's walleye (Sander vitreus) population to determine how anthropogenic alterations have influenced intraspecific interactions. Before the 1980s, the length-at-age of younger walleye (ages 1 and 2) negatively correlated with older (age 3 +) walleye abundance, signaling a 'density feedback' in which intraspecific competition limited growth. However, after the early 1980s this signal of intraspecific competition disappeared. This decoupling of the density feedback was related to multiple anthropogenic changes, including a larger walleye population resulting from better fisheries management, planned nutrient reductions to improve water quality and transparency, warmer water temperatures, and the proliferation of a non-native fish with novel traits (white perch, Morone americana). We argue that these changes may have reduced competitive interactions by reducing the spatial overlap between older and younger walleye and by introducing novel prey. Our findings illustrate the potential for anthropogenic change to diminish density dependent intraspecific interactions within top predator populations, which has important ramifications for predicting predator dynamics and managing natural resources. Apex predators have been severely impacted by anthropogenic environmental change 1,2 , which can dramatically alter both interspecific and intraspecific interactions 3. Of particular concern are anthropogenic changes to predator 'density feedbacks' 4. These feedbacks are intraspecific interactions that intensify as conspecific density increases, such as competition, aggression, and cannibalism, with subsequent effects on predator population growth or factors that affect growth 4. For example, density feedbacks have been shown to determine body size in fishes 5 , fecundity in birds 6 , mortality in mammals 7 , and the dispersal of predators into new habitats 8. Through these influences on predator growth, reproduction, mortality, and dispersal, density feedbacks can in turn mediate food webs and community structure 9,10 and the ecosystem services generated by predator populations (e.g., wildlife harvest 11). The nature of density feedbacks are often assumed to be fixed within a species (e.g., determined by life-history characteristics 11,12), with environmental change simply altering the number of individuals or the carrying capacity producing a predictable response in the population 9,12,13. However, human-induced environmental change has the potential to alter the intensity of intraspecific interactions such that population growth (or body size, fecundity, mortality, etc.) may no longer respond as expected to changes in population size 14,15 (Fig. 1). For instance, the intensity of intraspecific interactions within a predator population can vary along environmental gradients, with

Scientific Reports, Feb 24, 2021

Complete functional descriptions of the induction sequences of phenotypically plastic traits (per... more Complete functional descriptions of the induction sequences of phenotypically plastic traits (perception to physiological regulation to response to outcome) should help us to clarify how plastic responses develop and operate. Ranid tadpoles express several plastic antipredator traits mediated by the stress hormone corticosterone, but how they influence outcomes remains uncertain. We investigated how predator-induced changes in the tail morphology of wood frog (Rana sylvatica) tadpoles influenced their escape performance over a sequence of time points when attacked by larval dragonflies (Anax junius). Tadpoles were raised with no predator exposure, chemical cues of dragonflies added once per day, or constant exposure to caged dragonflies crossed with no exogenous hormone added (vehicle control only), exogenous corticosterone, or metyrapone (a corticosteroid synthesis inhibitor). During predation trials, we detected no differences after four days, but after eight days, tadpoles exposed to larval dragonflies and exogenous corticosterone had developed deeper tail muscles and exhibited improved escape performance compared to controls. Treatment with metyrapone blocked the development of a deeper tail muscle and resulted in no difference in escape success. Our findings further link the predator-induced physiological stress response of ranid tadpoles to the development of an antipredator tail morphology that confers performance benefits.

Journal of Great Lakes Research, Jun 1, 2023

American Midland Naturalist, 2019

Abstract. Chemical cues are frequently a key source of information to aquatic organisms. Both pre... more Abstract. Chemical cues are frequently a key source of information to aquatic organisms. Both predators (kairomones digestive metabolites) and prey (alarm and damage-released cues) may generate chemical cues during their interactions, and different cue types can have different informational values. How predators and prey use the information from chemical cues to make spatial movement decisions influences both their direct interaction rates and their interactions with other species. We measured the spatial response of predatory larval dragonflies (Anax junius) and predator-naïve green frog (Lithobates clamitans) tadpoles exposed to several types of chemical cues using experimental mesocosms. We found tadpoles only responded with spatial avoidance when exposed to both Anax kairomones and conspecific alarm cues together, whereas Anax did not exhibit consistent spatial responses to any cue type. Our results suggest tadpole prey selectively respond to environmental information from chemical cues (possibly to minimize costly antipredator behavior due to responding to insufficient information or reflecting a need for associative learning). They also show predatory dragonflies may use nonchemical information to make space use decisions (possibly due to inability to detect the same chemical cues as tadpoles).

Aquaculture, Oct 1, 2018

Assisted reproductive technologies (ART) are used to increase fertilization rates in a number of ... more Assisted reproductive technologies (ART) are used to increase fertilization rates in a number of animal species. However, their use with sauger (Sander canadensis), the paternal contributor in the production of the recreationally and economically important saugeye (Sander vitreus × S. canadensis), is limited. State fishery management agencies are periodically unable to meet saugeye production goals due to the inability to collect sufficient numbers of sauger broodstock, as well as a lack of protocols for standardized sperm use during production. Therefore, the need exists to overcome sauger sperm limitation during the saugeye production season using ARTs. Toward this end, we investigated the effect of human chorionic gonadotropin (hCG) on sperm production, determined an efficient sperm-to-egg ratio for fertilization, and validated the use of a densimeter to measure sauger sperm cell concentration for precise sperm addition during fertilization. The effect of hCG on sperm production was evaluated by comparing pre-and post-treatment milt parameters between fish treated with either hCG or saline (control). Treating fish with hCG increased sperm volume relative to saline controls (hCG 0.64 ± 0.19 mL/kg; control: 0.31 ± 0.05 mL/kg). However, sperm cell concentration and total sperm production were unaffected. To determine an efficient sperm-to-egg ratio, fresh milt from several individuals was pooled and used to fertilize walleye eggs at three sperm-to-egg ratios (20,000, 50,000, and 100,000 sperm/egg). The range of sperm-to-egg ratios used in this study did not significantly affect fertilization rates (20,000: 82.67 ± 3.38%, 50,000: 91.33 ± 2.67% and 100,000: 88.67 ± 3.44%). Lastly, by using linear regression to compare densimeter and hemocytometer estimates in serially diluted sperm we were able to accurately estimate hemocytometer estimates (R 2 = 0.96, p < 0.05). In conclusion, our study provides tools and standards that can be implemented by hatchery staff to increase saugeye production efficiency and lay the foundation for using ART for sauger and other fish species.

Journal of Great Lakes Research, Dec 1, 2017

Microcystin (MC) is a cyanobacteria-produced liver toxin that has been found in fish from Lake Er... more Microcystin (MC) is a cyanobacteria-produced liver toxin that has been found in fish from Lake Erie, sometimes in excess of World Health Organization (WHO) guidelines for safe consumption. Even so, few studies have quantified MCs in Lake Erie fishes, and these studies have drawn different conclusions concerning the risk that fish consumption poses to public health. To address this gap in knowledge, we used Enzyme-Linked Immunosorbant Assay (ELISA) to evaluate the MC concentration in muscle tissue from three commonly harvested fish in Lake Erie: walleye (Sander vitreus, n = 29); yellow perch (Perca flavescens, n = 52); and white perch (Morone americana, n = 55), collected during summer 2013. Satellite remote sensing was used to compare MC concentrations in fish tissue to bloom conditions in Lake Erie at the time of harvest. We found a significant difference among mean MC concentrations in walleye (71 ng MC/g wet weight), white perch (37 ng MC/g), and yellow perch (8.1 ng MC/g). In addition, MC levels in white perch appeared to depend on local bloom conditions. While few of the fish collected contained MC in excess of WHO guidelines, our results indicate that more toxic blooms could increase MC in fish to levels that pose a greater risk to public health.

Acta Zoologica, Jul 15, 2021

Theriogenology, Mar 1, 2023

Animal Reproduction Science, 2020

This study was conducted to compare quality and quantity of sperm collected from sauger (S. canad... more This study was conducted to compare quality and quantity of sperm collected from sauger (S. canadensis) using two collection methods: stripping alone and testicular tissue collection combined with stripping. Sperm were collected from sauger broodstock (n = 20) during the breeding season. Fish were randomly assigned to two sperm collection groups: (1) stripping once or (2) stripping twice before testicular tissue collection for obtaining additional sperm. Sperm motility variables, morphology, total number produced, and fertilization (%) were compared using the two collection methods. Testicular sperm had greater total motility (70.1 ± 2.1% compared with 44.3 ± 5.7%) but there were fewer morphologically normal cells (76.4 ± 1.3% compared with 92.8 ± 1.0%) compared to sperm collected using the stripping procedure. Sperm collection regimen utilizing testicular collections and sperm extractions in combination with stripping resulted in a ∼ten fold increase in total number of motile and morphologically normal sperm (39.5 ± 4.1 × 10 9) compared with the currently utilized two sequential sperm stripping collection procedures alone (3.6 ± 4.1 × 10 9 sperm). In large-scale studies (150,000 eggs), fertilization, using sperm collected from testicular tissues (1.0 × 10 5 motile sperm/egg), was similar to sperm collected with only the stripping procedure (71.2 ± 5.5 %, 81.2 ± 5.5 %, P = 0.265). The results of this study indicate testicular collection combined with sperm extractions allows for collection of sperm of a quantity and quality to maximize fry production and reduce the problems with lack of broodstock availability for sperm collection.

North American Journal of Fisheries Management, Oct 14, 2016

The expected impacts of invasive species are key considerations in selecting policy responses to ... more The expected impacts of invasive species are key considerations in selecting policy responses to potential invasions. But predicting the impacts of invasive species is daunting, particularly in large systems threatened by multiple invasive species, such as North America's Laurentian Great Lakes. We developed and evaluated a scenario-building process that relied on an expert panel to assess possible future impacts of aquatic invasive species on recreational fishing in the Great Lakes. To maximize its usefulness to policy makers, this process was designed to be implemented relatively rapidly and considered a range of species. The expert panel developed plausible, internally consistent invasion scenarios for five aquatic invasive species, along with subjective probabilities of

Fisheries Research, Oct 1, 2020

Demographic and environmental factors can influence the spatial distribution of fish populations,... more Demographic and environmental factors can influence the spatial distribution of fish populations, potentially affecting the timing, location, and magnitude of harvest. Quantifying these relationships can be complicated, if their effects vary spatially over a population's range or are non-additive (i.e., interactive), where one factor mediates the effect of another. Toward understanding the relative influence of demographic and environmental factors on fishery harvest in large freshwater lakes, we used varying-coefficient generalized additive models to explore the existence of non-additive, spatially-dependent effects of adult population size and thermal conditions on recreational harvest patterns of Lake Erie walleye (Sander vitreus) during 2006-2015. We identified nonlinear, additive, and generally positive effects of thermal conditions and adult population size on harvest rates. Their effects were, however, spatially-dependent, the accounting of which can help explain inter-annual and intraannual variation in lake-wide harvest rates. Specifically, harvest rates increased more with increasing cumulative degree days in the eastern portion of the central basin, especially offshore, relative to the rest of the study area. Harvest rates also increased more with increasing walleye population size in the southwest portion of the west basin and the middle of the central basin compared to other study areas. As in marine ecosystems, our findings demonstrate the benefit of using modeling approaches that consider the spatial dependency of harvest rate on demographic and environmental factors to understanding broader harvest dynamics in large lakes. Their use could help managers and policy-makers ensure the sustained use of valued freshwater fish populations amidst demographic and environmental change.

Canadian Journal of Fisheries and Aquatic Sciences, Apr 1, 2013

Techniques that use calcified structures to identify the natal origin of organisms assume that re... more Techniques that use calcified structures to identify the natal origin of organisms assume that reworking of previously deposited material does not occur. While verified for otoliths, this assumption remains unverified for statoliths. Herein, we test the stability of sea lamprey (Petromyzon marinus) statolith microchemistry during metamorphosis. Using laser ablation inductively coupled plasma mass spectrometry, we quantified the concentrations of nine elements in statoliths from sea lamprey larvae (n = 118) and newly metamorphosed (n = 115) individuals that were collected across six tributaries of varying alkalinity in the Laurentian Great Lakes and Lake Champlain basins. In newly metamorphosed individuals from all streams, the portion of the statolith deposited during the larval stage was enriched in rubidium (Rb), strongly suggesting a chemical reworking of statoliths during metamorphosis. As the ability to discriminate among sea lamprey from different streams in the Great Lakes and Lake Champlain mostly relies on premetamorphic levels of Rb, strategies for the use of statoliths to identify the natal origin of sea lamprey parasitic juveniles and spawners (postmetamorphic stages) should take into account the chemical changes associated with metamorphosis. Résumé : Les techniques d'identification de l'origine des organismes vivants à partir de leurs structures calcifiées supposent que les concentrations élémentaires ne soient pas modifiées une fois les éléments déposés dans les structures calcifiées. Bien que vérifiée pour les otolithes, cette supposition n'a pas encore été vérifiée pour les statolithes. Dans la présente étude, nous testons la stabilité microchimique des statolithes de lamproies marines (Petromyzon marinus) au cours de la métamorphose. Nous avons utilisé un spectromètre de masse à plasma induit couplé à l'ablation laser pour mesurer les concentrations de neuf éléments dans les statolithes de larves de lamproies marines (n = 118) et de lamproies marines récemment transformées (n = 115). Les individus ont été collectés dans six tributaires d'alcalinité différente des Grands Lacs Laurentiens et du Lac Champlain. Pour tous les tributaires, les statolithes de lamproies récemment transformées étaient enrichis en rubidium (Rb) dans la portion du statolithe déposée au cours de la phase larvaire, suggérant ainsi une modification chimique des statolithes durant la métamorphose. Etant donné l'importance des concentrations pré-métamorphose en Rb pour discriminer l'origine des lamproies marines dans les Grands Lacs Laurentiens et le Lac Champlain, l'utilisation des statolithes pour identifier l'origine des lamproies juvéniles parasites et des adultes reproducteurs (stades post-métamorphose) nécessite de tenir compte des modifications chimiques liées à la métamorphose.

Fish and Fisheries, Jul 7, 2023

Early life survival is critical to successful replenishment of fish populations, and hypotheses d... more Early life survival is critical to successful replenishment of fish populations, and hypotheses developed under the Growth‐Survival Paradigm (GSP) have guided investigations of controlling processes. The GSP postulates that recruitment depends on growth and mortality rates during early life stages, as well as their duration, after which the mortality declines substantially. The GSP predicts a shift in the frequency distribution of growth histories with age towards faster growth rates relative to the initial population because slow‐growing individuals are subject to high mortality (via starvation and predation). However, mortality data compiled from 387 cases published in 153 studies (1971–2022) showed that the GSP was only supported in 56% of cases. Selection against slow growth occurred in two‐thirds of field studies, leaving a non‐negligible fraction of cases showing either an absence of or inverse growth‐selective survival, suggesting the growth‐survival relationship is more complex than currently considered within the GSP framework. Stochastic simulations allowed us to assess the influence of key intrinsic and extrinsic factors on the characteristics of surviving larvae and identify knowledge gaps on the drivers of variability in growth‐selective survival. We suggest caution when interpreting patterns of growth selection because changes in variance and autocorrelation of individual growth rates among cohorts can invalidate fundamental GSP assumptions. We argue that breakthroughs in recruitment research require a comprehensive, population‐specific characterization of the role of predation and intrinsic factors in driving variability in the distribution and autocorrelation of larval growth rates, and of the life stage corresponding to the endpoint of pre‐recruited life.

Journal of Great Lakes Research, Jun 1, 2023

Zenodo (CERN European Organization for Nuclear Research), Jun 1, 2009

The Great Lakes Fishery Commission was established by the Convention on Great Lakes Fisheries bet... more The Great Lakes Fishery Commission was established by the Convention on Great Lakes Fisheries between Canada and the United States, which was ratified on October 11, 1955. It was organized in April 1956 and assumed its duties as set forth in the Convention on July 1, 1956. The Commission has two major responsibilities: first, develop coordinated programs of research in the Great Lakes, and, on the basis of the findings, recommend measures which will permit the maximum sustained productivity of stocks of fish of common concern; second, formulate and implement a program to eradicate or minimize sea lamprey populations in the Great Lakes.

Canadian Journal of Fisheries and Aquatic Sciences, Jul 1, 2020

Whether bottom hypoxia has long-lasting consequences for pelagic fish populations remains specula... more Whether bottom hypoxia has long-lasting consequences for pelagic fish populations remains speculative for most ecosystems. We explored hypoxia’s influence on two pelagic zooplanktivores in Lake Erie that have different thermal preferences: cold-water rainbow smelt (Osmerus mordax) and warm-water emerald shiners (Notropis atherinoides). To assess acute effects, we combined predictive bioenergetics-based modeling with field collections made across the hypoxic season in central Lake Erie during 2005 and 2007. To assess chronic effects, we related fishery-independent and fishery-dependent catches with hypoxia severity and top predator (walleye, Sander vitreus) abundance during 1986–2014. As our modeling predicted, hypoxia altered rainbow smelt movement and distributions, leading to avoidance of cold, hypoxic bottom waters. In response, diets shifted from benthic to pelagic organisms, and consumption and energetic condition declined. These changes were lacking in emerald shiners. Our long-term analyses showed rainbow smelt abundance and hypoxia to be negatively related and suggested that hypoxia avoidance increases susceptibility to commercial fishing and walleye predation. Collectively, our findings indicate that hypoxia can negatively affect pelagic fish populations over the long term, especially those requiring cold water.

Science of The Total Environment, Dec 1, 2020

General Circulation Model Multiple stressors Species distribution model Trait analysis climate ef... more General Circulation Model Multiple stressors Species distribution model Trait analysis climate effects outweighing those of ACP implementation. Functional trait analysis helped clarify the varied responses among species, indicating that more extreme climate change would reduce available habitat for largebodied, cool-water species with equilibrium life-histories, many of which also are of importance to recreational fishing (e.g., northern pike, smallmouth bass). By contrast, available habitat for warm-water, benthic species with more periodic or opportunistic life-histories (e.g., northern hogsucker, greater redhorse, greenside darter) was predicted to increase. Further, ACP implementation was projected to hasten these shifts, suggesting that efforts to improve water quality could come with costs to other ecosystem services (e.g., recreational fishing opportunities). Collectively, our findings demonstrate the need to consider biological outcomes when developing strategies to mitigate water quality impairment and highlight the value of physical-biological modeling approaches to agricultural and biological conservation planning in a changing climate.

Journal of Great Lakes Research, Feb 1, 2023

Harmful Algae, Feb 1, 2020

With anthropogenic eutrophication and climate change causing an increase in cyanobacterial blooms... more With anthropogenic eutrophication and climate change causing an increase in cyanobacterial blooms worldwide, the need to understand the consequences of these blooms on aquatic ecosystems is paramount. Key questions remain unanswered with respect to how cyanobacteria blooms affect the structure of aquatic food webs, the foraging abilities of higher consumers, and the potential for cyanotoxins (e.g., microcystins [MCs]) to accumulate in fish. Toward addressing these uncertainties, physicochemical attributes, water (for MCs), phytoplankton, zooplankton, and epipelagic and benthic age-0 fish were sampled at 75 sites (44 sites for fish) of varying cyanobacteria concentration (0.1-44 μg/L) in western Lake Erie during the cyanobacteria bloom season, 2013-2014. Sites with high cyanobacteria biomass were characterized by Microcystis spp. (84-100% of biomass), detectible levels of MCs (maximum = 10.8 μg/L), and low water transparency (minimum = 0.25 m). Counter to expectations, strong positive relationships were found between cyanobacteria concentration and the biomass of several herbivorous zooplankton taxa (e.g., Daphnia, Diaphanosoma spp., Bosmina (formerly Eubosmina) coregoni, and Calanoida spp.). Expectations regarding fish were partly supported (e.g., diet selectivity varied across a cyanobacteria gradient) and partly not (e.g., consumption of zooplankton did not differ between bloom and nonbloom sites). These findings show that cyanobacterial blooms can strongly affect the distribution, composition, and interactions of zooplankton and fish, sometimes in surprising ways, highlighting the need to further explore their impact on aquatic food webs.

Scientific Reports, May 10, 2023

Intraspecific interactions within predator populations can affect predator-prey dynamics and comm... more Intraspecific interactions within predator populations can affect predator-prey dynamics and community structure, highlighting the need to better understand how these interactions respond to anthropogenic change. To this end, we used a half-century (1969-2018) of abundance and sizeat-age data from Lake Erie's walleye (Sander vitreus) population to determine how anthropogenic alterations have influenced intraspecific interactions. Before the 1980s, the length-at-age of younger walleye (ages 1 and 2) negatively correlated with older (age 3 +) walleye abundance, signaling a 'density feedback' in which intraspecific competition limited growth. However, after the early 1980s this signal of intraspecific competition disappeared. This decoupling of the density feedback was related to multiple anthropogenic changes, including a larger walleye population resulting from better fisheries management, planned nutrient reductions to improve water quality and transparency, warmer water temperatures, and the proliferation of a non-native fish with novel traits (white perch, Morone americana). We argue that these changes may have reduced competitive interactions by reducing the spatial overlap between older and younger walleye and by introducing novel prey. Our findings illustrate the potential for anthropogenic change to diminish density dependent intraspecific interactions within top predator populations, which has important ramifications for predicting predator dynamics and managing natural resources. Apex predators have been severely impacted by anthropogenic environmental change 1,2 , which can dramatically alter both interspecific and intraspecific interactions 3. Of particular concern are anthropogenic changes to predator 'density feedbacks' 4. These feedbacks are intraspecific interactions that intensify as conspecific density increases, such as competition, aggression, and cannibalism, with subsequent effects on predator population growth or factors that affect growth 4. For example, density feedbacks have been shown to determine body size in fishes 5 , fecundity in birds 6 , mortality in mammals 7 , and the dispersal of predators into new habitats 8. Through these influences on predator growth, reproduction, mortality, and dispersal, density feedbacks can in turn mediate food webs and community structure 9,10 and the ecosystem services generated by predator populations (e.g., wildlife harvest 11). The nature of density feedbacks are often assumed to be fixed within a species (e.g., determined by life-history characteristics 11,12), with environmental change simply altering the number of individuals or the carrying capacity producing a predictable response in the population 9,12,13. However, human-induced environmental change has the potential to alter the intensity of intraspecific interactions such that population growth (or body size, fecundity, mortality, etc.) may no longer respond as expected to changes in population size 14,15 (Fig. 1). For instance, the intensity of intraspecific interactions within a predator population can vary along environmental gradients, with

Scientific Reports, Feb 24, 2021

Complete functional descriptions of the induction sequences of phenotypically plastic traits (per... more Complete functional descriptions of the induction sequences of phenotypically plastic traits (perception to physiological regulation to response to outcome) should help us to clarify how plastic responses develop and operate. Ranid tadpoles express several plastic antipredator traits mediated by the stress hormone corticosterone, but how they influence outcomes remains uncertain. We investigated how predator-induced changes in the tail morphology of wood frog (Rana sylvatica) tadpoles influenced their escape performance over a sequence of time points when attacked by larval dragonflies (Anax junius). Tadpoles were raised with no predator exposure, chemical cues of dragonflies added once per day, or constant exposure to caged dragonflies crossed with no exogenous hormone added (vehicle control only), exogenous corticosterone, or metyrapone (a corticosteroid synthesis inhibitor). During predation trials, we detected no differences after four days, but after eight days, tadpoles exposed to larval dragonflies and exogenous corticosterone had developed deeper tail muscles and exhibited improved escape performance compared to controls. Treatment with metyrapone blocked the development of a deeper tail muscle and resulted in no difference in escape success. Our findings further link the predator-induced physiological stress response of ranid tadpoles to the development of an antipredator tail morphology that confers performance benefits.

Journal of Great Lakes Research, Jun 1, 2023

American Midland Naturalist, 2019

Abstract. Chemical cues are frequently a key source of information to aquatic organisms. Both pre... more Abstract. Chemical cues are frequently a key source of information to aquatic organisms. Both predators (kairomones digestive metabolites) and prey (alarm and damage-released cues) may generate chemical cues during their interactions, and different cue types can have different informational values. How predators and prey use the information from chemical cues to make spatial movement decisions influences both their direct interaction rates and their interactions with other species. We measured the spatial response of predatory larval dragonflies (Anax junius) and predator-naïve green frog (Lithobates clamitans) tadpoles exposed to several types of chemical cues using experimental mesocosms. We found tadpoles only responded with spatial avoidance when exposed to both Anax kairomones and conspecific alarm cues together, whereas Anax did not exhibit consistent spatial responses to any cue type. Our results suggest tadpole prey selectively respond to environmental information from chemical cues (possibly to minimize costly antipredator behavior due to responding to insufficient information or reflecting a need for associative learning). They also show predatory dragonflies may use nonchemical information to make space use decisions (possibly due to inability to detect the same chemical cues as tadpoles).

Aquaculture, Oct 1, 2018

Assisted reproductive technologies (ART) are used to increase fertilization rates in a number of ... more Assisted reproductive technologies (ART) are used to increase fertilization rates in a number of animal species. However, their use with sauger (Sander canadensis), the paternal contributor in the production of the recreationally and economically important saugeye (Sander vitreus × S. canadensis), is limited. State fishery management agencies are periodically unable to meet saugeye production goals due to the inability to collect sufficient numbers of sauger broodstock, as well as a lack of protocols for standardized sperm use during production. Therefore, the need exists to overcome sauger sperm limitation during the saugeye production season using ARTs. Toward this end, we investigated the effect of human chorionic gonadotropin (hCG) on sperm production, determined an efficient sperm-to-egg ratio for fertilization, and validated the use of a densimeter to measure sauger sperm cell concentration for precise sperm addition during fertilization. The effect of hCG on sperm production was evaluated by comparing pre-and post-treatment milt parameters between fish treated with either hCG or saline (control). Treating fish with hCG increased sperm volume relative to saline controls (hCG 0.64 ± 0.19 mL/kg; control: 0.31 ± 0.05 mL/kg). However, sperm cell concentration and total sperm production were unaffected. To determine an efficient sperm-to-egg ratio, fresh milt from several individuals was pooled and used to fertilize walleye eggs at three sperm-to-egg ratios (20,000, 50,000, and 100,000 sperm/egg). The range of sperm-to-egg ratios used in this study did not significantly affect fertilization rates (20,000: 82.67 ± 3.38%, 50,000: 91.33 ± 2.67% and 100,000: 88.67 ± 3.44%). Lastly, by using linear regression to compare densimeter and hemocytometer estimates in serially diluted sperm we were able to accurately estimate hemocytometer estimates (R 2 = 0.96, p < 0.05). In conclusion, our study provides tools and standards that can be implemented by hatchery staff to increase saugeye production efficiency and lay the foundation for using ART for sauger and other fish species.

Journal of Great Lakes Research, Dec 1, 2017

Microcystin (MC) is a cyanobacteria-produced liver toxin that has been found in fish from Lake Er... more Microcystin (MC) is a cyanobacteria-produced liver toxin that has been found in fish from Lake Erie, sometimes in excess of World Health Organization (WHO) guidelines for safe consumption. Even so, few studies have quantified MCs in Lake Erie fishes, and these studies have drawn different conclusions concerning the risk that fish consumption poses to public health. To address this gap in knowledge, we used Enzyme-Linked Immunosorbant Assay (ELISA) to evaluate the MC concentration in muscle tissue from three commonly harvested fish in Lake Erie: walleye (Sander vitreus, n = 29); yellow perch (Perca flavescens, n = 52); and white perch (Morone americana, n = 55), collected during summer 2013. Satellite remote sensing was used to compare MC concentrations in fish tissue to bloom conditions in Lake Erie at the time of harvest. We found a significant difference among mean MC concentrations in walleye (71 ng MC/g wet weight), white perch (37 ng MC/g), and yellow perch (8.1 ng MC/g). In addition, MC levels in white perch appeared to depend on local bloom conditions. While few of the fish collected contained MC in excess of WHO guidelines, our results indicate that more toxic blooms could increase MC in fish to levels that pose a greater risk to public health.