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While recent research has shed insight into how bottom hypoxia affects pelagic food webs in coastal marine ecosystems and natural lakes, its effects on man-made lake (reservoir) food webs remains more incomplete. To address this gap, we conducted a study in two midwestern USA reservoirs to examine how the spatial overlap and vertical distributions of dominant zooplanktivores (i.e., pelagic fish, bentho-pelagic Chaoborus spp.) and their prey vary between periods of normoxia and hypoxia. Surprisingly, we found high levels of spatial overlap between zooplankton and both intermediate consumers (pelagic fish and Chaoborus) during both normoxia and hypoxia, though the extent of spatial overlap was higher during hypoxia at night relative to day. As expected, pelagic fish and zooplankton avoided hypoxic waters, and Chaoborus moved from hypoxic waters during the day to the well-oxygenated surface waters at night. Using our findings, we discuss the potential influence of bottom hypoxia and Chaoborus on the function and structure of north-temperate reservoir food webs. Si des travaux de recherche recents ont ameliore la comprehension de l'incidence de l'hypoxie de fond sur les reseaux trophiques pelagiques dans les ecosystemes marins cotiers et les lacs naturels, la comprehension des effets de cette hypoxie sur les reseaux trophiques de lacs artificiels (reservoirs) demeure moins complete. Pour combler cette lacune, nous avons mene une etude dans deux reservoirs du Midwest americain afin d'examiner les variations du chevauchement dans l'espace et de la repartition verticale de zooplanctivores dominants (c.-a-d., poissons pelagiques et benthopelagiques du genre Chaoborus) et de leurs proies entre des periodes de normoxie et d'hypoxie. Etonnement, nous avons releve des degres eleves de chevauchement dans l'espace entre le zooplancton et les deux types de consommateurs intermediaires (poissons pelagiques et Chaoborus) tant durant des conditions de normoxie que d'hypoxie, l'ampleur de ce chevauchement etant toutefois plus grande durant l'hypoxie la nuit que le jour. Comme prevu, les poissons pelagiques et le zooplancton evitent les eaux hypoxiques, et les Chaoborus se deplacent entre des eaux hypoxiques durant le jour et des eaux de surface bien oxygenees la nuit. A la lumiere de nos observations, nous discutons de l'influence potentielle de l'hypoxie de fond et des Chaoborus sur la fonction et la structure des reseaux trophiques de reservoirs de regions nordiques temperees. [Traduit par la Redaction], Introduction Bottom hypoxia ( In general, organisms have been shown to move vertically (up) or horizontally (nearshore) to avoid bottom hypoxia, which in turn could alter their spatial overlap and [...]

Objective: We evaluated the effect of a 381‐mm minimum length limit (MLL) on saugeye (female Walleye Sander vitreus × male Sauger S. canadensis) population and fishery characteristics implemented in Ohio reservoirs in 2011. Methods: Using a before‐after–control‐impact study design (n = 6 control populations and n = 11 impact populations that received the MLL), we compared total CPUE, age‐2+ CPUE, proportional stock density‐harvestable (381‐mm), and length at age 2 (to index growth) determined from standardized gill‐net surveys and saugeye angler effort, catch rate, harvest rate, length of saugeye at harvest, yield, and satisfaction obtained from standardized creel surveys. Result: We found evidence that the 381‐mm MLL led to an increase in age‐2+ CPUE but had no effect on other saugeye population metrics. In the regulation reservoirs, harvest rates declined following MLL implementation. Total length of harvested saugeye did not increase significantly in response to the MLL, and combined with decreased harvest rates, yield was suppressed in the regulation reservoirs relative to the control reservoirs. However, over 90% of anglers reported that they were satisfied with the MLL during creel surveys. Conclusion: Despite marginal influence on saugeye populations and failure to increase yield, anglers supported the MLL. Our results suggest that the effects of harvest regulations may be marginal, and managers should consider the nuances of angler satisfaction in regulation decisions. Impact statementFisheries management agencies commonly use minimum length limits to attempt to improve recreational fisheries; however, robust evaluations of regulation success are often lacking. In saugeye fisheries, minimum length limits minimally affected population size structure and angler yield but still received strong angler support. Fisheries managers should implement rigorous experimental designs in regulation evaluations and consider both biological and social effects of fishery regulations. [ABSTRACT FROM AUTHOR]

ABSTRACT. Municipal water managers use copper sulfate (CuS[O.sub.4]) to control algae, predominantly phytoplankton, in water supply reservoirs. In multiple-purpose upground reservoirs in northwestern Ohio, CuS[O.sub.4] application regimens vary from no [...]

Seasonal degradation of aquatic habitats from hypoxia occurs in numerous freshwater and coastal marine systems and can result in direct mortality or displacement of fish. Yet, fishery landings from these systems are frequently unresponsive to changes in the severity and extent of hypoxia, and population-scale effects have been difficult to measure except in extreme hypoxic conditions with hypoxia-sensitive species. We investigated fine-scale temporal and spatial variability in dissolved oxygen in Lake Erie as it related to fish distribution and catch efficiencies of both active (bottom trawls) and passive (trap nets) fishing gears. Temperature and dissolved oxygen loggers placed near the edge of the hypolimnion exhibited much higher than expected variability. Hypoxic episodes of variable durations were frequently punctuated by periods of normoxia, consistent with high-frequency internal waves. High-resolution interpolations of water quality and hydroacoustic surveys suggest that fish habitat is compressed during hypoxic episodes, resulting in higher fish densities near the edges of hypoxia. At fixed locations with passive commercial fishing gear, catches with the highest values occurred when bottom waters were hypoxic for intermediate proportions of time. Proximity to hypoxia explained significant variation in bottom trawl catches, with higher catch rates near the edge of hypoxia. These results emphasize how hypoxia may elevate catch rates in various types of fishing gears, leading to a lack of association between indices of hypoxia and fishery landings. Increased catch rates of fish at the edges of hypoxia have important implications for stock assessment models that assume catchability is spatially homogeneous. Une degradation saisonniere des habitats aquatiques decoulant de l'hypoxie caracterise de nombreux systemes marins cotiers et d'eau douce et peut entrainer la mortalite directe ou le deplacement de poissons. Cela dit, les debarquements provenant de ces systemes sont bien souvent peu sensibles aux changements de l'intensite et de l'etendue de l'hypoxie, et les effets a l'echelle de la population sont difficiles a mesurer sauf pour les especes sensibles a l'hypoxie dans des conditions d'hypoxie extreme. Nous avons etudie la variabilite temporelle et spatiale a petite echelle de l'oxygene dissous dans le lac Erie et son lien avec la repartition de poissons et l'efficacite d'engins actifs (chaluts de fond) et passifs (filets-pieges). Des enregistreurs de temperature et d'oxygene dissous places pres de la bordure de l'hypolimnion temoignaient d'une variabilite beaucoup plus grande que prevu. Des episodes hypoxiques de duree variable etaient frequemment ponctues de periodes de normoxie, ce qui concorde avec la presence de vagues internes de haute frequence. Des interpolations de haute resolution des resultats de leves hydroacoustiques et de la qualite de l'eau donnent a penser que l'habitat des poissons est comprime durant les periodes hypoxiques, produisant des densites de poissons plus elevees en bordure de zones d'hypoxie. Aux emplacements fixes d'engins de peche commerciale passifs, les plus grandes prises se produisaient quand les eaux de fond etaient hypoxiques pour des proportions de temps intermediaires. La proximite de l'hypoxie explique des variations significatives des prises au chalut de fond, dont des taux de prises plus grands en bordure des zones d'hypoxie. Ces resultats soulignent comment l'hypoxie peut rehausser les taux de prises de divers types d'engins de peche, se traduisant par l'absence de lien entre les indices d'hypoxie et les debarquements. Des taux de prises accrus en bordure de zones hypoxiques ont d'importantes consequences pour les modeles d'evaluation des stocks reposant sur l'hypothese de l'homogeneite spatiale de la capturabilite. [Traduit par la Redaction], Introduction Hypoxia in aquatic systems is a worldwide phenomenon often linked to excessive nutrient loadings from human activities (Diaz 2001; Diaz and Rosenberg 2008). Numerous experimental laboratory and field studies [...]

Fisheries managers commonly use low‐frequency electrofishing to survey Flathead Catfish Pylodictis olivaris and Blue Catfish Ictalurus furcatus populations; however, inconsistent methods prohibit comparisons among studies. Here, we simultaneously sampled Flathead Catfish and Blue Catfish to compare single‐ and chase‐boat low‐frequency electrofishing configurations in five Ohio River navigational pools and inform standard sampling of these catfishes. Our objectives were to (1) compare Flathead Catfish and Blue Catfish CPUE among length categories, (2) evaluate the prevalence of high‐catch samples, and (3) determine the number of 15‐min electrofishing sites needed to achieve predefined precision and catch objectives between single‐ and chase‐boat configurations. The chase‐boat configuration produced greater catches of both Flathead Catfish (mean total CPUE was 44.6 fish/h for the chase‐boat configuration versus 32.8 fish/h for the single‐boat configuration) and Blue Catfish (mean total CPUE of 6.8 fish/h for the chase‐boat configuration versus 2.8 fish/h for the single‐boat configuration). Zero‐inflated negative binomial models revealed that CPUE was greater with the chase boat for both Flathead Catfish and Blue Catfish across substock, stock–quality, and quality and larger length categories. High‐CPUE samples (total CPUE >52 Flathead Catfish/h or >8 Blue Catfish/h) were more likely with the chase‐boat configuration than the single‐boat configuration. We found that a similar number of sites were needed to achieve the precision objective (relative standard error of CPUE <25%) for both configurations for Flathead Catfish; however, to achieve the precision objective for Blue Catfish, more single‐boat sites/pool were needed compared to chase‐boat sites/pool. To achieve the catch objective (capture 100 stock‐length catfish/pool), more single‐boat sites/pool were needed than chase‐boat sites/pool for both species. Our results suggest that using a chase boat better indexes the abundance of Flathead and Blue catfish, particularly when high catches are possible. However, more research is needed to inform the standardization of low‐frequency electrofishing for sampling catfishes in large river systems. [ABSTRACT FROM AUTHOR]

Given the importance of reservoir fisheries and the investments made by fisheries management agencies to create and maintain these fisheries, the loss of reservoir‐stocked fish through downstream emigration warrants action to be taken to understand and prevent it. The factors driving emigration of reservoir fish and the measurable effects of emigration on fish population dynamics are not well understood. In this study, we sought to understand the seasonal emigration patterns of two popular sport fish, saugeye (female Walleye Sander vitreus × male Sauger Sander canadensis) and Muskellunge Esox masquinongy, and determine if their annual declines in abundance were correlated with predicted annual emigration rates. We modeled daily emigration probabilities of saugeye and Muskellunge from PIT tag data collected in the dam spillway of an Ohio reservoir. Using data on discharge from previous years, these models were used to estimate annual emigration rates, which were regressed against historical catch data to test whether emigration explained annual cohort declines. Our models showed that downstream emigration from the reservoir occurred primarily during spring for both species, especially during periods of high reservoir discharge. All saugeye and nearly all Muskellunge emigrants were adults, with 13% of tagged adult saugeye and 17% of tagged adult Muskellunge emigrating. Our models predicted historical annual emigration losses (across all age‐classes) as high as 24% for saugeye and 8.6% for Muskellunge. Furthermore, historical annual emigration rates were negatively related to catch rates for both species. These results illustrate that, depending on flow regime and seasonal effects on fish movements, emigration can have measurable effects on reservoir sport fish populations. As such, it is important to understand the factors driving downstream migration and use this understanding to inform decisions on potential mitigation of emigration as well as fish stocking decisions. [ABSTRACT FROM AUTHOR]

North American fisheries management agencies commit considerable resources to managing reservoir fisheries for Channel Catfish Ictalurus punctatus, which often includes stocking. However, Channel Catfish population characteristics often vary greatly among reservoirs, resulting in variable and unpredictable fishery quality. We sampled Channel Catfish populations in 44 Ohio reservoirs with tandem, baited hoop nets to understand relationships among population characteristics (density, as CPUE from hoop nets; growth, as mean length at age 7; mortality, as total annual mortality from catch‐curve analysis; and size structure, as proportional size distribution), stocking, and the relationships between these characteristics and reservoir size (as surface area), predator density (as Largemouth Bass Micropterus salmoides electrofishing CPUE), and productivity (as chlorophyll‐a concentration). We used multiple linear regression and an information theoretic approach to select the most parsimonious models for explaining observed variation in Channel Catfish density, growth, mortality, and size structure. We found that population density varied greatly among our study reservoirs, and none of our models sufficiently explained variation in density. Reservoir size and the interaction between reservoir size and population density explained the most variation in Channel Catfish growth, but productivity was also important. Small reservoirs (≤101 ha) had low to moderate densities and growth was uniformly slow; however, in larger reservoirs, lower densities resulted in faster growth. Growth increased as productivity increased. Total annual mortality was uniformly low (<0.26) but increased with density. Faster growth led to populations with larger size structures. These outcomes show that the largest Ohio reservoirs (≥406 ha) are the most suitable for supporting populations with fast growth and large size structures. Dense populations (CPUE > 50 Channel Catfish/net set) resulted in slower growth, greater mortality, and poor size structure. Future research to understand natural recruitment in reservoir Channel Catfish populations could be important for explaining variation in density. [ABSTRACT FROM AUTHOR]

Fisheries managers efficiently sample reservoir Channel Catfish Ictalurus punctatus populations with tandem, baited hoop nets. However, catchability (the fraction of a fish stock caught with a defined unit of effort) of Channel Catfish with this gear and the size selectivity of this gear are not fully known. Furthermore, scientists have not identified a standard sampling period that maximizes catches while minimizing variation in catchability. Here, we estimated Channel Catfish population density (number/ha) and catchability with tandem, baited hoop nets using mark–recapture methods in three Ohio reservoirs during May–July 2016–2018. We tested for differences in catchability (1) among reservoirs; (2) among 50‐mm length categories; and (3) by week. We then tested CPUE as an index of density by simulating the sampling of populations with different densities based on observed variation in catchability and estimating the statistical power to detect density differences. We found that total catchability differed among study reservoirs, among length categories, and among sampling events but did not consistently change during the May–July sampling period. Catchability of 50‐mm length categories did not differ among reservoirs. The greatest catchability was observed for 400–649‐mm Channel Catfish. Our power analysis showed that we could detect a large (>2:1 effect sizes) difference in density with 80% power by using 20 or more sample sites. Furthermore, our length‐category‐specific catchability estimates provide information to reduce bias in size structure, growth, and mortality estimates derived from Channel Catfish samples collected with tandem, baited hoop nets. We encourage further development, validation, and application of tandem, baited hoop nets to better understand differences in reservoir Channel Catfish densities and size structures. [ABSTRACT FROM AUTHOR]

Management agencies commonly stock Channel Catfish Ictalurus punctatus as advanced yearlings instead of fingerlings (age 0) to help reduce potential predation mortality despite uncertainty regarding the degree to which predation limits fingerling poststocking survival. To better understand whether fingerling survival during the first 7 d after stocking—when predation risk is likely greatest—could benefit from the presence of alternative prey fish, we conducted an experiment in 0.4‐ha ponds (N = 18; 6 ponds/treatment) that measured fingerling (TL range = 56–186 mm) survival in ponds with predators only (adult Largemouth Bass Micropterus salmoides; mean TL = 327 mm; SE = 21), with predators and alternative prey fishes (Bluegill Lepomis macrochirus and Goldfish Carassius auratus), or with neither (i.e., control ponds). Without alternative prey, fingerling Channel Catfish survival 1 week after stocking was significantly (P < 0.01) lower (89%) than in the ponds with alternative prey (98%) or in the control treatment with no predators (97%). Our experiment also indicated the potential for alternative prey to promote fingerling survival by reducing water clarity, not just by serving as a buffer from predation. Further research, however, is needed to determine the degree to which our findings apply to larger ecosystems and to learn whether stocked fingerlings survive well enough after the initial stocking period to achieve desired management goals. Even so, our results suggest that alternative prey can reduce Largemouth Bass predation mortality on fingerlings immediately after stocking, which could influence Channel Catfish stocking approaches in some managed systems. [ABSTRACT FROM AUTHOR]

Species‐specific target strength (TS)‐to‐length (L) and TS‐to‐weight (W) equations can reduce bias in biomass estimates from hydroacoustic surveys, yet these equations do not exist for most fishes. Equations specific to the Gizzard Shad Dorosoma cepedianum, a wide‐ranging and often highly abundant prey fish in North American reservoirs and rivers, do not exist. Herein, we sought to develop TS–L and TS–W equations for Gizzard Shad by insonifying free‐swimming individuals of known sizes (36–209 mm TL) in a net cage at three transducer frequencies (70, 120, and 200 kHz). We derived TS–size relationships using major‐axis regression (MAR) and least‐squares regression (LSR), comparing our resultant TS–L equations to a commonly used multispecies equation (Love 1971). To determine how our Gizzard Shad‐specific equations affected estimates of prey fish biomass, we conducted mobile hydroacoustic surveys in four small, shallow Midwestern reservoirs and then estimated biomass using each equation. In general, for TS–L equations, MAR produced the highest estimates of biomass, followed by LSR and then the multispecies equation. Similarly, the TS–W equation derived using MAR produced greater biomass estimates than the equation using LSR. Our findings highlight the value of using species‐specific TS–size equations over multispecies equations in ecosystems dominated by a single fish species (e.g., Gizzard Shad in Midwestern reservoirs). They also demonstrate the value of using MAR to develop TS–size equations, owing to its ability to account for fish size measurement error. The use of species‐specific TS–size equations and MAR should lead to robust estimates of biomass in single‐species‐dominated ecosystems, thus benefiting fisheries assessment and decision making. [ABSTRACT FROM AUTHOR]

Rising temperatures caused by climate change are likely to affect cool‐water and warm‐water fishes differently. Yet, forecasts of anticipated temperature effects on fishes of different thermal guilds are lacking, especially in freshwater ecosystems. Towards this end, we used spatially explicit, growth rate potential (GRP) models to project changes in seasonal habitat quality for a warm‐water piscivore (largemouth bass Micropterus salmoides), a cool‐water piscivore (walleye Sander vitreus) and a hybrid piscivore (saugeye S. vitreus × S. canadensis) in two Midwestern reservoirs. We assessed habitat quality for two periods (early and middle 21st century) under two realistic greenhouse gas emission scenarios (a mid‐century emissions peak and a rapid continuous increase in emissions). Largemouth bass were projected to experience enhanced or slightly reduced habitat during all seasons, and throughout the mid‐21st century. By contrast, walleye habitat was projected to decline with anticipated warming, except during the spring in the smaller of our two study reservoirs and during the fall in the larger of our two study reservoirs. Saugeye habitat was projected to either increase modestly or decline slightly during the spring and fall and declines in habitat quality and quantity that were smaller than those for walleye were identified during summer. Collectively, our findings indicate that climate warming will differentially alter habitat suitability for reservoir piscivores, favouring warm‐water species over cool‐water species. We expect these changes in habitat quality to impact the dynamics of reservoir fish populations to varying degrees necessitating the consideration of climate when making future management decisions. [ABSTRACT FROM AUTHOR]

Hypoxia induced by eutrophication and high summer temperatures is common in most Midwestern reservoirs, with uncertain effects on resident fishes. To evaluate the potential influence of low dissolved oxygen (DO) and high‐temperature conditions on habitat quality for three common sport fishes (Largemouth Bass Micropterus salmoides, saugeye [Walleye Sander vitreus × Sauger S. canadensis], and White Crappie Pomoxis annularis), we used spatially explicit bioenergetics models to measure growth rate potential (GRP) in three Ohio reservoirs of varying productivity and size. Dissolved oxygen, temperature, and prey biomass data were collected throughout each study reservoir during August in 2015 or 2016, when temperature and hypoxia levels were expected to be at or near their peak. Growth rate potential was generally low in hypoxic bottom waters and higher in the epilimnion due to prey concentrating above the oxycline. The amount of high‐quality habitat (HQH; i.e., GRP > 0 g/g/d) always declined owing to hypoxia; however, the extent of the decline depended on the modeled species and reservoir. Among species, hypoxia‐induced losses of HQH were small, differing by less than 8% in each reservoir. Among‐reservoir differences in HQH were greater; reductions in HQH ranged from 31.3% to 42.5% among species in the reservoir with the lowest DO (mean ± SE = 2.7 ± 0.04 mg/L) and highest gape‐appropriate prey biomass (5.1 ± 0.07 to 5.3 ± 0.07 g/m3), whereas they varied by 0.3–0.6% in the reservoir with the highest DO (5.1 ± 0.07 mg/L) and lowest gape‐appropriate prey biomass (0.2 ± 0.004 to 0.6 ± 0.01 g/m3). Even so, the reservoir with the lowest mean DO (i.e., greatest hypoxic extent) had the highest mean GRP and percentage HQH owing to high prey biomass. Collectively, our findings indicate that bottom hypoxia can reduce sport fish habitat quality in temperate reservoirs, but high prey biomass may mitigate the negative effect of hypoxia. [ABSTRACT FROM AUTHOR]

Reproductive investment, expressed in terms of fecundity and egg quality produced by individual female fish, varies among populations for many species, reflecting plasticity in life history strategies related to intraspecific density dependence or environmental variability. Fisheries scientists and managers have long sought to understand differences in Largemouth Bass Micropterus salmoides population dynamics, yet basic life history traits, such as variation in reproductive investment, remain largely unknown. We determined the fecundity–weight and ovary energy density–weight relationships (where fecundity indexes egg quantity and ovary energy density indexes egg quality) for Largemouth Bass populations from 19 Ohio reservoirs and examined factors that were correlated with population‐specific differences. We found that both relationships varied among reservoir populations, with some interannual variation in reservoirs sampled in multiple years. We then related fecundity and ovary energy density to (1) population characteristics, including population density (as indexed by standard shoreline boat electrofishing CPUE, fish/h) and growth (as indexed by the growth coefficient k from the von Bertalanffy growth function); and (2) reservoir characteristics, including reservoir size (as surface area) and productivity (as Secchi transparency depth). We found that populations with greater fecundity also exhibited greater ovary energy density, indicating that the quantity and quality of reproductive output were greater in some populations than in others. Populations with high reproductive investment were associated with low Largemouth Bass density, fast growth, large reservoir size, and high productivity (i.e., low Secchi transparency). The among‐population variation in reproductive investment provides evidence of density‐dependent control of fecundity and egg quality. [ABSTRACT FROM AUTHOR]

Fisheries managers implement minimum length limits (MLLs) to improve the size structure of populations of crappie Pomoxis spp. throughout Midwestern and southeastern U.S. reservoirs. The success of these regulations has been mixed, with several implementations resulting in undesirable outcomes, including slow growth and stunting of crappies, and ultimately regulation removal. Consequently, it is unclear whether and where MLLs should be used to improve crappie size structure. Beginning in 2003, Ohio instituted a statewide standard sampling protocol to monitor reservoir crappie populations, and between 2003 and 2010 a 229‐mm MLL was implemented at over 40 reservoirs throughout the state. Using these spatially and temporally extensive crappie population data, we sought to (1) test for the response of crappie population adult abundance, growth, and size structure to the MLL, (2) test whether reservoir surface area and/or productivity mediated this response, and (3) model fisheries outcomes at different reservoir sizes and productivities to predict where application of a MLL would be most appropriate. Using linear mixed‐effects models and an information theoretic approach, we found that crappie population abundances generally increased, whereas growth decreased in small, unproductive reservoirs but increased in large, productive reservoirs. Overall, the MLL failed to produce increases in size structure, except in large reservoirs. Yield‐per‐recruit models predicted a decrease in angler yield in response to a 229‐mm MLL in small reservoirs, whereas in large, productive reservoirs this regulation was predicted to increase angler yield. Consequently, the MLL could improve crappie fisheries in reservoirs larger than 1,000 ha with high productivity (total phosphorus concentrations > 50 μg/L) but could be counterproductive in small, unproductive reservoirs. Finally, our approach highlights the benefits of standard sampling as we were able to integrate data across years and reservoirs to make comparisons on a statewide scale. [ABSTRACT FROM AUTHOR]

Standardized sampling methods can benefit fisheries management by facilitating a comparison of fish abundance estimates within and among ecosystems. Towards developing an improved standardized hydroacoustic method for estimating prey‐fish abundance and target strength in small (surface areas <15 km2), shallow (maximum depths <20 m), freshwater ecosystems (e.g., north‐temperate reservoirs), we evaluated how the incorporation of several recommended hydroacoustic data‐analysis procedures from the Great Lakes Standard Operating Procedures (GLSOP) into an existing hydroacoustic protocol used in north‐temperate reservoirs influenced estimates of prey‐fish abundance. To facilitate our evaluation, we conducted hydroacoustic surveys in four Ohio reservoirs during August 2016 and then compared prey‐fish abundance estimates generated from the existing Ohio Department of Natural Resources, Division of Wildlife reservoir protocol with those that included three GLSOP recommendations separately and in combination. The three recommendations were (1) removal of background noise, (2) use of a lower maximum beam compensation (MBC) setting, and (3) application of the Sawada index (Nv) to identify and replace biased, in situ, cell‐specific target strengths. Our analyses showed that the removal of background noise (−0.1% to 0% change) and application of Nv (−7.8% to 0% change) had little substantive effect. However, decreasing the MBC from 12 to 6 dB significantly reduced prey‐fish abundance estimates (4.1% to 16.1% decrease). When we simultaneously applied all three GLSOP recommendations, estimated prey‐fish abundance consistently decreased (−8.8 to −16.0%) across reservoirs. Collectively, our findings suggest the need for incorporation of several GLSOP data‐analysis procedures into protocols developed for shallow, target‐rich ecosystems, such as Ohio reservoirs. By doing so, more precise estimates of fish abundance can be generated to the benefit of fisheries management. [ABSTRACT FROM AUTHOR]

Understanding the factors that affect water quality and the ecological services provided by freshwater ecosystems is an urgent global environmental issue. Predicting how water quality will respond to global changes not only requires water quality data, but also information about the ecological context of individual water bodies across broad spatial extents. Because lake water quality is usually sampled in limited geographic regions, often for limited time periods, assessing the environmental controls of water quality requires compilation of many data sets across broad regions and across time into an integrated database. LAGOS-NE accomplishes this goal for lakes in the northeastern-most 17 US states. LAGOS-NE contains data for 51 101 lakes and reservoirs larger than 4 ha in 17 lake-rich US states. The database includes 3 data modules for: lake location and physical characteristics for all lakes; ecological context (i.e., the land use, geologic, climatic, and hydrologic setting of lakes) for all lakes; and in situ measurements of lake water quality for a subset of the lakes from the past 3 decades for approximately 2600-12 000 lakes depending on the variable. The database contains approximately 150 000 measures of total phosphorus, 200 000 measures of chlorophyll, and 900 000 measures of Secchi depth. The water quality data were compiled from 87 lake water quality data sets from federal, state, tribal, and non-profit agencies, university researchers, and citizen scientists. This database is one of the largest and most comprehensive databases of its type because it includes both in situ measurements and ecological context data. Because ecological context can be used to study a variety of other questions about lakes, streams, and wetlands, this database can also be used as the foundation for other studies of freshwaters at broad spatial and ecological scales. [ABSTRACT FROM AUTHOR]

Understanding catchability—the fraction of a stock caught by a defined unit of effort—is crucial to using fisheries assessment data to index abundance. We conducted mark–recapture experiments to estimate catchability and evaluate standard boat electrofishing methods for assessing populations of Largemouth BassMicropterus salmoides. We then used a resampling analysis to test for differences in bass CPUE (fish/h and fish/km) between two high-density reservoirs and one low-density reservoir and among surveys within each reservoir. We compared scenarios using surveys conducted only during (1) the standard time period (mid-April to mid-May) and (2) the entire assessment period (early April to mid-June). We considered the percentage of significant differences in CPUE between the high-density and low-density reservoirs to represent statistical power (i.e., the ability to detect a difference in CPUE when a difference actually exists) and the percentage of significant differences in CPUE between surveys in the same reservoir to represent the false-positive rate (i.e., the detection of a difference in CPUE when no difference in density exists). Catchability and CPUE were greatest and least variable during recapture events conducted during the standard period. The mean catchability of sub–stock length Largemouth Bass (150–200 mm) and memorable-length bass (≥510 mm) was significantly less than those for other length categories. Statistical power exceeded 80%, and the false-positive rate was generally less than 10% for sampling during the standard period at as few as six electrofishing sites. When including samples from outside the standard period, power was lower and the false-positive rate was as high as 60%. Power and false-positive rate were similar whether effort was measured in time or distance. Our results emphasize that standardized springtime boat electrofishing assessments validly index Largemouth Bass density and size structure. Received October 7, 2016; accepted February 2, 2017 Published online April 24, 2017 [ABSTRACT FROM AUTHOR]

Hypoxia, low dissolved oxygen (DO) concentrations (<2 mg/L), has been a major issue in Lake Erie for decades. While much emphasis has been placed on biological factors, particularly algal blooms, contributing to hypolimnetic oxygen depletion, there has been little focus on the role of weather. For this study, we monitored water temperature and DO concentrations at sites in the western, central, and Sandusky basins in Lake Erie during June and July 2010-2012. We then compared trends in stratification and DO concentrations to weather patterns during that period. We found that during those three years, there was significant variation in weather patterns, particularly decreased ice coverage and increased storm events in 2012. These weather patterns corresponded to 2012 having the warmest water temperatures, some of the lowest DO concentrations, and a deeper and thinner hypolimnion (especially in the central basin) than the previous years. We found a relationship between weather and hypoxia, providing further evidence for why these basins are susceptible to low DO conditions during summer months. The role of weather in hypoxia is another indication that the lake is vulnerable to effects of climate change and should be considered in management strategies. [ABSTRACT FROM AUTHOR]

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Both abiotic and biotic explanations have been proposed to explain recent recurrent nuisance/harmful algal blooms in the western basin and central basin of Lake Erie. We used two long-term (>10 years) dataseis to test ( 1 ) whether Lake Erie total phytoplankton biomass and cyanobacterial biomass changed over time and (2) whether phytoplankton abundance was influenced by soluble reactive phosphorus or nitrate loading from agriculturally-dominated tributaries (Maumee and Sandusky rivers). We found that whereas total phytoplankton biomass decreased in Lake Erie's western basin from 1970 to 1987, it increased starting in the mid-1990s. Total phytoplankton and cyanobacterial seasonal (May-October) arithmetic mean wet-weight biomasses each significantly increased with increased water-year total soluble reactive phosphorus load from the Maumee River and the sum of soluble reactive phosphorus load from the Maumee and Sandusky rivers, but not for the Sandusky River alone during 1996-2006. During this same time period, neither total phytoplankton nor cyanobacterial biomass was correlated with nitrate load. Consequently, recently increased tributary soluble reactive phosphorus loads from the Maumee River likely contributed greatly to increased western basin and (central basin) cyanobacterial biomass and more frequent occurrence of harmful algal blooms. Managers thus must incorporate the form of and source location from which nutrients are delivered to lakes into their management plans, rather than solely considering total (both in terms of form and amount) nutrient load to the whole lake. Further, future studies need to address the relative contributions of not only external loads, but also sources of internal loading. [ABSTRACT FROM AUTHOR]

Traditionally, each NC member could nominate one or two AFS members, those nominees would be vetted by the NC, and the NC would vote, identifying the top two candidates. The American Fisheries Society Nominating Committee (NC) has a straightforward job. Focused Process: Nominating the Next AFS Second Vice President Candidates: 2021-2022 American Fisheries Society Nominating Committee. [Extracted from the article]

Grand Lake St. Marys, hereafter Grand Lake, is a large shallow reservoir in western Ohio that has become hypereutrophic in recent decades owing to external phosphorus (P) loading. To restore water quality in Grand Lake, managers must decide whether to reduce external P loading from tributaries or continue to reduce internal P loading from sediments using aluminum sulfate additions. To help managers identify the most effective strategies for water quality improvements in Grand Lake, we quantified the reservoir's seasonal P dynamics using tributary and in-reservoir P measurements during 2009–2011. We also tested the short-term effects of reduced external P loading on Grand Lake's water quality using a pond experiment performed at the adjacent St. Marys State Fish Hatchery. The highest P concentrations in Grand Lake (1660, 391, and 311 μg/L in 2009, 2010, and 2011, respectively) occurred in summer when external P loads from tributaries were minimal, suggesting internal P release from sediments was the major source of P to fuel cyanobacterial blooms. Results from our pond experiment showed that decoupling the reservoir from external P loading during summer months does not improve short-term water quality. We conclude that external P loading during winter and spring, coupled with internal P loading from sediments during summer, drive the extremely high P concentrations in summer that support dense cyanobacterial blooms. Long-term improvement in Grand Lake water quality will first require major reductions to the external P loads from tributaries, followed by manipulations to reduce internal P loading from sediments. [ABSTRACT FROM PUBLISHER]

Over-fertilization with phosphorus and carryover copper residual in the sediment from copper sulfate treatment in double-cropped ponds were suspected as the primary causes of low larval percid survival in coolwater aquaculture ponds. Consequently, in this study, we compared saugeye (male sauger Sander canadensis X female walleye S. vitreus) survival, growth, and yield among ponds that were single-cropped with only saugeyes in the spring during the previous two consecutive years (SS ponds) and ponds that were double-cropped (with saugeye culture in the spring and channel catfish Ictalurus punctatus culture in the summer) during the previous two consecutive years (DD ponds). We also compared sediment phosphorus (soluble reactive phosphorus [SRP] and total phosphorus [TP]), sediment copper concentrations, phytoplankton biomass, and zooplankton biomass. Fish survival (number harvested) and fish yield (mass harvested) were significantly lower in DD ponds than in SS ponds in 2001 but were similar in 2002 (a year of wide temperature fluctuation early in the production season). Sediment analyses revealed that DD ponds had significantly lower SRP and TP but higher copper concentrations than did SS ponds. A detailed study done in 2002 revealed that individual length and wet weight of percids were significantly higher in the SS ponds than in DD ponds; phytoplankton biomass was similar in both sets of ponds, while zooplankton biomass was significantly lower in DD ponds. These results suggest that residual materials used in double-cropped channel catfish ponds may negatively affect subsequent years' percid culture. [ABSTRACT FROM AUTHOR]

Maximizing young-of-year (YOY) fish production in an aquaculture setting depends on matching predatory demand with prey availability. With a size-selective YOY fish species (saugeye: Sander vitreus Mitchell females × S. canadense Griffith & Smith males) supplied with natural zooplankton prey ( Bosmina sp. Baird), selective removal of larger individuals may decrease prey fecundity. However, increased nutrient fertilization may also ameliorate the top-down effects of fish predation. We tested these interactions in outdoor earthen production ponds (ca. 4000 m2; n=12) by measuring Bosmina sp. size at first reproduction (SFR), maximum size (MAX) and neonate size (NEO) in ponds that varied in YOY saugeye densities (18–50 saugeye m−3) and also differed in phosphorus maintenance levels (either 20 or 30 μg PO4-P L−1). We found that SFR decreased by 8% [from 0.298 mm±0.007 (mean±1 SE) to 0.275 mm±0.005], MAX decreased by 11% (from 0.367 mm±0.009 to 0.328 mm±0.009) and NEO decreased by 5% (0.198 mm±0.004 to 0.189 mm±0.003) over the range of saugeye densities, and that SFR increased by 4% (from 0.279 mm±0.004 to 0.290 mm±0.003) and MAX increased by 3% (from 0.336 mm±0.004 to 0.347±0.004) with increased fertilization. Further, prey offspring lengths strongly related to mother lengths and lengths differed from early to late in the production season. These results indicate that multiple factors affect prey sizes and emphasize that the removal of large prey individuals by size-selective YOY predators may decrease trophic efficiency, ultimately decreasing fish production. [ABSTRACT FROM AUTHOR]

Using data compiled from candidate statements published in I Fisheries i (see Supporting Information), we found that since 1995, AFS has elected an academic member in nearly 60% of all Second Vice Presidential elections (16 of 27). The American Fisheries Society will soon elect an active and interested member to the role of Second Vice President. The aggregate of private industry, consultants, and self-employed members comprise just less than 20% of members, but only one such member has been elected, about 4% of recent AFS Presidents. [Extracted from the article]

Abstract: Over-fertilization, low dissolved oxygen concentration, high pH, unionized ammonia, fish stocking density, and cannibalism are all possible causes of variations in larval percid survival and growth in earthen ponds. In this study, we examined the phosphorus fertilization effect over three different production years (2001–2003) by comparing fish raising success in ponds fertilized with phosphoric acid to restore phosphate concentrations to 30 μg P l−1 each week with other ponds restored to only 20 μg P l−1 each week, while restoring the inorganic nitrogen level in both sets to 600 μg N l−1 weekly. At the end of the 5–6 wk production period, there were no significant differences between the two treatments in mean fish length, weight, survival, number harvested ha−1, nor total biomass yield ha−1 (P >0.05). Phytoplankton and zooplankton densities were higher in 30 μg P l−1 ponds than in 20 μg P l−1 ponds (P <0.05) in 2001, but not in 2002. Significantly lower Secchi depths and higher pH (P <0.05) were observed in 30 μg P l−1 ponds, while dissolved oxygen and temperature values were similar between treatments, as were soluble reactive phosphorus, total phosphorus, nitrate–nitrogen, and ammonium–nitrogen concentrations (P >0.05). We conclude that weekly fertilization to the levels of 20 μg P l−1 and 600 μg N l−1 provides sufficient prey for larval percids, and it also reduces the risk of extreme pH and low dissolved oxygen that can cause increased fish mortality. [Copyright &y& Elsevier]

1. Recent increases in phytoplankton biomass and the recurrence of cyanobacterial blooms in western Lake Erie, concomitant with a shift from a community dominated by zebra mussels ( Dreissena polymorpha) to one dominated by quagga mussels ( D. bugensis), led us to test for differences in ammonia-nitrogen and phosphate-phosphorus excretion rates of these two species of invasive molluscs. 2. We found significant differences in excretion rate both between size classes within a taxon and between taxa, with zebra mussels generally having greater nutrient excretion rates than quagga mussels. Combining measured excretion rates with measurements of mussel soft-tissue dry weight and shell length, we developed nutrient excretion equations allowing estimation of nutrient excretion by dreissenids. 3. Comparing dreissenid ammonia and phosphate excretion with that of the crustacean zooplankton, we demonstrated that the mussels add to nitrogen and phosphorus remineralisation, shortening nitrogen and phosphorus turnover times, and, importantly, modify the nitrogen and phosphorus cycles in Lake Erie. The increased nutrient flux from dreissenids may facilitate phytoplankton growth and cyanobacterial blooms in well-mixed and/or shallow areas of western Lake Erie. [ABSTRACT FROM AUTHOR]

The inclusion of unwanted targets in hydroacoustic surveys biases estimates of fish abundance. Thus, knowledge of frequency-dependent responses of unwanted targets (e.g., pelagic macroinvertebrates) can help ensure that transducer frequencies are used that minimize this bias. We determined how fish density estimates varied across multiple frequencies when the larval stage of a midge, Chaoborus , was present in the water column. We hypothesized that fish density estimates would increase with increasing transducer frequency, owing to greater backscattering by Chaoborus at higher frequencies than lower ones, which allows it to be included with the backscattering caused by fish. We found that fish density estimates were always greater at higher frequencies (e.g., 120 and 200 kHz) compared to a lower one (70 kHz) in several productive north-temperate reservoirs. Furthermore, pairwise comparisons of total (i.e., fish plus Chaoborus) backscattering showed that significantly more backscattering occurred at higher rather than lower frequencies. We also found that fish density estimates varied between spring and summer, partially owing to inter-seasonal size variation in Chaoborus that influenced its backscattering. Beyond demonstrating why the presence of pelagic macroinvertebrates needs to be considered when estimating fish abundance with hydroacoustics, we provide methods to identify and reduce this bias. [ABSTRACT FROM AUTHOR]

Studies of the temporal dynamics (e.g., dissolved oxygen depletion rate) and the annual areal extent of zones of hypoxia (low oxygen, < 4 mg O2 L-1) and anoxia (no oxygen, < 1 mg L-1) in Lake Erie often focus on the perceived influence of external nutrient load and, in turn, the perceived effects of people on affecting oxygen loss. However, bulk hydrodynamic processes as induced by weather may serve to diminish (e.g., through storm-caused mixing) or amplify (e.g., through water-column stagnation with low storm frequency) the effects of nutrient load on hypolimnetic oxygen loss. Here, I investigated how weather (wind speed) and associated hydrodynamic processes (wave height, water level) affected water column dissolved oxygen concentration (DO) in the Sandusky subbasin of Lake Erie during 2005 and 2006. I measured temperature and DO at 0.5-m intervals with a calibrated multiparameter instrument (YSI Model 6600) at a site in the middle of the Sandusky subbasin on 19 and 17 dates in 2005 and 2006, respectively. Weather and hydrodynamic process data for both years were downloaded from National Oceanic and Atmospheric Administration websites (wind speed and wave height station 45005: http://www.ndbc.noaa.gov; water level station 9063079: http://tidesandcurrents.noaa.gov) and daily means were calculated. Initial water column stratification occurred in late-May following periods of calm, low wave-height weather conditions. Hypolimnetic DO dropped below 1 mg L-1 by late-June in both years. The hypoxic zone maintained its volume under stagnant conditions and expanded and contracted with increased wind speed, wave height, and water level oscillations indicating the importance of weather and hydrodynamic processes on DO dynamics in Lake Erie. [ABSTRACT FROM AUTHOR]

Predators negatively influence prey primarily through decreasing their total abundance. However, size-selective predators may also decrease fecundity through selective removal of large, more fecund individuals. Removal of large individuals may decrease trophic efficiency by decreasing the energy reaching higher trophic levels. Better understanding of the interaction between a size-selective zooplanktivorous fish (young-of-year saugeye, Sander vitreus females x S. canadense males) and its zooplankton prey (Bosmina sp.) in an aquaculture setting is especially important in maximizing fish production. At Hebron State Fish Hatchery, Hebron, Ohio in 2003, we took zooplankton samples (0.5-m diameter, 64 ìm-mesh net tows) during the production season (April-May) in 12 ponds, measured Bosmina sp. individuals (mm) under a microscope (at 50 x) in the laboratory, and calculated neonate size (5th percentile of non-ovigerous females), the size at first reproduction (SFR, 10th percentile of ovigerous females), and maximum size (95th percentile of all measurements) for each pond on each date. Additionally, we calculated a predation index (number of saugeye m-3 produced in each pond) to relate prey size to predator density. We hypothesized that prey size would decrease with increased predation according to the size-efficiency hypothesis. From linear regression analyses (size = response variable, predation index = predictor variable) we found significantly smaller SFR (F1,56 = 8.8, P < 0.01, R² = 0.14) and marginally significantly smaller maximum size (F1,56 = 2.6, P = 0.11, R² = 0.05) with increased predation. These results reveal that size-selective predation may decrease prey size, especially reproductive size, potentially limiting trophic efficiency. [ABSTRACT FROM AUTHOR]

Recurring seasonal hypoxia (low dissolved oxygen DO concentration, < 4 mg O2 L-1) and anoxia (< 1 mg L-1) greatly affects pelagic and benthic biota in Lake Erie's central basin. Here, we report the presence of metalimnetic oxygen maxima (MOM) throughout the Sandusky subbasin, the southwest portion of the central basin during 2005, 2006, and 2007. Using weekly (or more frequent) vertical-profile sampling of water temperature (degrees Celsius) and DO at 0.5-m intervals at seven sites in the Sandusky subbasin during summer (June-August), we found that MOM frequently occurred (in 72 of 135 DO vertical profiles) during 2005-2007. We hypothesized that the shallow depth (mean depth = 13.3 m relative to the central basin mean depth = 18.5 m) and high productivity (as chlorophyll a concentration, Chl a) of the Sandusky subbasin permitted adequate light penetration (as Secchi Disk transparency, SD) facilitating metalimnetic phytoplankton growth. We tested this prediction in 2007 and found that deeper, eastern subbasin sites more frequently had DO profiles with MOM than shallower, western subbasin sites (about 67% of the profiles versus 33% for eastern and western sites, respectively). However, neither Chl a nor SD predicted MOM occurrence (P > 0.05, R² < 0.10). These results reveal that either light penetration or the presence of primary producers is unimportant for MOM occurrence or that our temporal and spatial scales of investigation did not appropriately identify effect scales. Nevertheless, occurrence of MOM in the Sandusky subbasin and possibly the rest of the central basin may ameliorate hypoxic and anoxic conditions. [ABSTRACT FROM AUTHOR]

Many hypotheses have been advanced to explain recurrent algal blooms in the western basin of Lake Erie, including abiotic (e.g., total phosphorus load) and biotic (e.g., dreissenid mussel excretion) explanations. We used two long-term (10 + year) datasets to test whether total phytoplankton biomass and cyanobacterial biomass correlated with soluble reactive phosphorus (SRP) loading from agriculturally-influenced tributaries (Maumee and Sandusky rivers) to the western basin of Lake Erie. We constructed linear regression models to determine if total phytoplankton biomass (and cyanobacterial biomass, individually) increased with recent SRP-load increases. Both total phytoplankton and cyanobacterial seasonal (May-October) average (arithmetic mean) wet-weight biomasses (mg L1) significantly increased with increased water-year total SRP load (metric tons = Mg) for the Maumee River (both total phytoplankton and cyanobacteria biomass vs. SRP load: P = 0.008, R² = 0.56) and the sum of SRP load for the Maumee and Sandusky rivers (total phytoplankton biomass vs. SRP load; P = 0.007, R² = 0.57; cyanobacteria biomass vs. SRP load: P = 0.008, R² = 0.56), but not for the Sandusky River (P > 0.05). However, when using seasonal median total phytoplankton and cyanobacterial biomasses as response variables to remove the influence of bloom events and the Beale Ratio Estimator to account for missing SRP data, only the relationship between median cyanobacterial biomass and Beale-ratio estimated SRP load were significant (P < 0.05). In conclusion, recent increased western basin tributary SRP loads possibly contribute to increases in phytoplankton biomass and more frequent algal blooms, especially cyanobacteria, in the western basin of Lake Erie. [ABSTRACT FROM AUTHOR]

Seasonal degradation of aquatic habitats from hypoxia occurs in numerous freshwater and coastal marine systems and can result in direct mortality or displacement of fish. Yet, fishery landings from these systems are frequently unresponsive to changes in the severity and extent of hypoxia, and population-scale effects have been difficult to measure except in extreme hypoxic conditions with hypoxia-sensitive species. We investigated fine-scale temporal and spatial variability in dissolved oxygen in Lake Erie as it related to fish distribution and catch efficiencies of both active (bottom trawls) and passive (trap nets) fishing gears. Temperature and dissolved oxygen loggers placed near the edge of the hypolimnion exhibited much higher than expected variability. Hypoxic episodes of variable durations were frequently punctuated by periods of normoxia, consistent with high-frequency internal waves. High-resolution interpolations of water quality and hydroacoustic surveys suggest that fish habitat is compressed during hypoxic episodes, resulting in higher fish densities near the edges of hypoxia. At fixed locations with passive commercial fishing gear, catches with the highest values occurred when bottom waters were hypoxic for intermediate proportions of time. Proximity to hypoxia explained significant variation in bottom trawl catches, with higher catch rates near the edge of hypoxia. These results emphasize how hypoxia may elevate catch rates in various types of fishing gears, leading to a lack of association between indices of hypoxia and fishery landings. Increased catch rates of fish at the edges of hypoxia have important implications for stock assessment models that assume catchability is spatially homogeneous. [ABSTRACT FROM AUTHOR]

Abstract: The objective of ecological engineering is to design sustainable ecosystems that integrate human communities and their natural environment for the benefit of both. In this paper, we illustrate how social-ecological modeling can be used as a tool to clarify this objective at a landscape scale for freshwater systems. Coupled social-ecological systems (SESs) are open, dynamic systems subject to both ecological and socioeconomic perturbations. Here we demonstrate the interactive effects of social and technological uncertainties on SES dynamics over time. Additionally, we integrate research on ecosystem stability, social-ecological modeling, and ecological engineering to offer guidance for research at the human-environment interface. Based on a case study of Lake Erie''s Sandusky watershed, we use an integrated human-biophysical model to investigate the influence of two parameters on SES dynamics: (1) regional societal preferences that impact watershed management and (2) technological innovation that alters agricultural nutrient efficiency. Our results illustrate ways in which SES dynamics and optimum management strategies depend on societal preferences within the region, indicating a key area of uncertainty for future investigation. As guidance for SES restoration, our model results also illustrate the conditions under which technological change that increases nutrient efficiency on farms can and cannot create a win-win, or increase both human welfare and SES resistance to eutrophication simultaneously. Using these results, we elucidate the value of ecological engineering and offer guidance for assessments of ecological engineering projects using social-ecological modeling. [Copyright &y& Elsevier]