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Pikeperch (Sander lucioperca Linnaeus, 1758) is a wide-ranged percid predator fish characterised by a great ecological value in the Eurasian freshwater and brackish ecosystems. It is also one of the most famous fish species of Lake Balaton (Hungary), where a unique (genetically separated) pikeperch stock lives. However, until now, no detailed information was available about the pikeperch population genetic structure in Lake Balaton. In the present study, the population genetic structure of the pikeperch assemblages in the lake was revealed by using microsatellite markers. Commercial fishery and angler catch data going back more than 100 years verified that the pikeperch has always been a key element of Lake Balaton's fish stock utilization. Results of genetic data analyses showed that the pikeperch in the Lake Balaton forms a metapopulation system, in which only the westward stocks show certain separation. Moreover, it seems that the exploitation and mass fish kills that happened in the 1960s and 1970s may have had only a slight impact on the population genetic structure of Balaton pikeperch stocks. The information about genetic features and utilization changes of pikeperch stocks can help to develop area-specific management plans and ensure the long-term survival of this carnivore fish species characteristic of Lake Balaton. [ABSTRACT FROM AUTHOR]

Pikeperch is a valuable object of fisheries around the world. Accordingly, the cultivation of this species under controlled conditions is a promising direction of aquaculture development. However, the technology of its cultivation needs improvement, as there are currently certain difficulties, especially at the early stages of ontogenesis, when a transition to artificial nutrition occurs and high mortality rates are observed. Therefore, we carried out a study the results of which suggest that natural spawning allows obtaining high-quality fish seeds. Weight of pikeperch during one growing season reaches 50 g that facilitates wintering and contributes to high rates of yield from it. The experiment was carried out on age-4--6 females and age-3-5 males, selected according to their outer appearance. The average individual body weight of the females was 2.4 kg and such of males was 2.0 kg. At the same time, females were characterized by a more slender body and a higher body weight than the males, but these differences were insignificant. According to the results of work with the brood fish, 810.7 kg of juvenile pikeperch were harvested from spawning ponds. They were characterized by the average body weight ranging 2.41 g to 2.50 g and the Fulton's condition factor measuring 3.5. The industrial fecundity of females based on the output of 3-week-old fry amounted to the average of 43.5 thousand ind. per female. According to the test catches, the highest body weight was observed in young-of-the-years, grown at the stocking density of 2.5 thousand ind./m2 (second experimental group). They also had the highest rate of daily weight gain, exceeding such in the other experimental groups, 18.2% in the first and 2.7% in the second, with the stocking densities of 1.5 thousand ind./m² and 2.0 thousand ind./m², respectively. In general, the dynamics of daily weigh gain in all experimental groups was progressing, measuring 0.05-0.10 g in the first 50 days of cultivation and 0.20-1.04 in the following days (from the middle to the end of the experiment). The absolute and relative weight gains confirm the obtained results. In particular, the minimum values of the absolute weight gain of pikeperch were recorded in the first half of the experiment. However, the relative increase did not have a clear trend in the experimental groups. In the first experimental group, a clear peak (32.5-39.0%) of the weigh gain was observed on days 67-85 of cultivation with a decline (29.1-15.3%) starting from day 99 until the end of the growing season. At the same time, similar growth peaks were not recorded in the second and third experimental groups. By contrast, there was a decline on day 67, increasing to 30% on day 71, and further having a tendency to decrease until the end of the season. The highest individual weight and absolute weigh gain were recorded in the second and third experimental groups, where the maximum fish productivity was achieved from 1 m2, being 61.2 and 78.8 kg, respectively. At the same time, the survival rate, which is important for aquaculture conditions, was lower in these two groups than such in the first experimental group, 1.6% and 1.4%, respectively. Thus, the results of our study can help in ensuring the availability of high-quality pikeperch seeds, which in turn would be positive for both the consumer market of fish products and the state of native fish populations. [ABSTRACT FROM AUTHOR]

Pikeperch (Sander lucioperca) is a European fresh and brackish water piscivorous fish, important as a key predator and a valuable fisheries species. Despite concerns that some stocks are depleting due to overfishing and environmental changes, stock assessments are implemented sporadically. We provide an overview of data collection and population assessments currently used for nine pikeperch stocks across six European countries and apply a unified assessment framework (Bayesian surplus production models) to evaluate population status and trends. Our results show that three stocks, including two in the Baltic Sea, are strongly depleted, with estimated biomasses considerably lower than the biomass at maximum sustainable yield (B MSY). Other stocks are close to their estimated B MSY. Further, recent population trends suggest that only one stock (Kvädöfjärden) is increasing, whereas three (Curonian Lagoon, Lipno, Galtfjärden) are rapidly declining. In most cases the stocks with a favorable status or signs of recovery were also those for which strong management strategies have been implemented. Importantly, although most stocks are strongly targeted by recreational fishing, estimates of recreational catch are highly uncertain. We highlight an urgent need to improve pikeperch scientific monitoring and assessment of recreational catches. • One third of pikeperch stocks assessed were depleted below MSY. • Stocks with favorable status reflected their strong management strategies. • Cessation of commercial fishing did not necessarily promote recovery. • Bayesian surplus production modeling (JABBA) effectively revealed stock trends. • Recreational fishing is important for most stocks but catches usually remain unknown. [ABSTRACT FROM AUTHOR]

Angler trip success and catch rates are dependent upon a fishes' vulnerability to angling. Angling vulnerability can be influenced by angler-specific attributes (i.e., bait choice, lure size, use of a guide), and individual fish traits (i.e., boldness, aggression, stress responsiveness, and memory retention). The mechanisms that function in a fishes' angling vulnerability, and contribute to catch rate, are likely correlated with environmental factors however, the influence of environmental factors on angling vulnerability are not well understood. We used the long-term (1946 –present) compulsory creel dataset from Escanaba Lake, WI, USA to test for interactions between angling vulnerability (i.e., angler trip success and catch rates) and environmental factors to better understand these dynamics in recreational fisheries. Our objective was to test for the influence of angler associated variables and environmental factors on open water angler trip success (i.e., catch ≥ one fish) and catch rate of walleye Sander vitreus and muskellunge Esox masquinongy during 2003–2015 using a hurdle model approach. Fishing trip success and catch rates for both species were most strongly influenced by angler-related variables (i.e., guide status, bait type, the proportion of the fish population previously caught). Environmental factors associated with lower light intensity (i.e., diel period, mean daily solar radiation, solar-Julian day interaction) had a positive influence on walleye vulnerability. Lower air temperatures and lunar position (moon overhead or underfoot) and phase (gibbous' and full moon) also had a positive effect on walleye angling. Muskellunge trip success and catch rate were positively influenced by light metrics (i.e., diel period and mean daily solar radiation) and increased with air temperature. Lunar variables (position and phase), as well as wind speed and direction also influenced muskellunge angling vulnerability. A better understanding of the influence of environmental factors on angling vulnerability is an important component of fisheries management as management goals focus on balancing fish populations and creating satisfactory catch rates to enhance the angling experience. Our results suggest that angler-specific variables, light, temperature, lunar, and weather conditions influenced species-specific angling vulnerability for walleye and muskellunge. [ABSTRACT FROM AUTHOR]

Fragmentation of river systems by dams can have substantial genetic impacts on fish populations. However, genetic structure can exist naturally at small scales through processes other than isolation by physical barriers. We sampled individuals from five native fish species with varying life histories above and below a dam in the lower Boardman River, Michigan, USA, and used RADseq to investigate processes influencing genetic structure in this system. Species assessed were white sucker Catostomus commersonii, yellow perch Perca flavescens, walleye Sander vitreus, smallmouth bass Micropterus dolomieu, and rock bass Ambloplites rupestris. We detected significant differentiation within each species, but patterns of population structure varied substantially. Interestingly, genetic structure did not appear to be solely the result of fragmentation by the dam. While genetic structure in yellow perch and walleye generally coincided with "above dam" and "below dam" sampling locations, samples from our other three species did not. Specifically, samples from rock bass, smallmouth bass, and, to a much lesser extent, white sucker, aligned with a putative Great Lakes (GL) group that contained mostly individuals sampled below the dam and a putative Boardman River (BR) group that contained individuals sampled both above and below the dam, with some evidence of admixture among groups. We hypothesize that the GL and BR groups formed prior to dam construction and our samples largely represent a mixed stock that was sampled sympatrically outside of the spawning season. Support for this hypothesis is especially strong in smallmouth bass, where GL fish were 151 mm smaller than BR fish on average, suggesting a potential ontogenetic habitat shift of young GL fish into the lower river for feeding and/or refuge. Our study illuminates the complex dynamics shaping genetic structure in fragmented river systems and indicates that conclusions drawn for a single species cannot be generalized. [ABSTRACT FROM AUTHOR]

• Allometric trophic network model built for boreal Lake Oulujärvi. • No clear trophic cascades from pikeperch to phytoplankton. • Fishing and pikeperch had both direct and indirect effects in the food web. • Fishing and pikeperch together had synergistic negative effects on vendace and smelt. • Fishing and pikeperch together reduced whitefish, but less than expected. Fish communities face changes in environmental conditions and fishing that affects the abundances and structures of the populations. Before 1960s there were abundant stocks of both pikeperch (Stizostedion lucioperca) and whitefish (Coregonus lavaretus) in Lake Oulujärvi, but in 1960s–1970s the stock of pikeperch declined to very low levels while whitefish stock remained abundant. Due to massive re-introductions, pikeperch recovered since 1999 and is again common while whitefish stock has declined. To understand the ecosystem-level changes observed along the recovery of the pikeperch stock, we constructed a food web model capturing the two most recent states of pikeperch abundance in Lake Oulujärvi. We used Allometric Trophic Network (ATN) model to simulate the pelagic food web in the presence and absence of pikeperch and in the presence and absence of fishing. To parametrize ATN model based on body masses and food web interactions, we used data collections of fish cohort analyses, fish individuals, fish stomach contents, zooplankton, and phytoplankton in Lake Oulujärvi. Pikeperch decreased the biomasses of its planktivorous prey. Fishing truncated the age distribution of planktivorous fish. Pikeperch and fishing had synergistic negative effects on vendace (Coregonus albula) and smelt (Osmerus eperlanus) percentages of fish biomass, and antagonistic negative effect on whitefish and brown trout (Salmo trutta) percentages of fish biomass. Mysis relicta, Chaoborus flavicans, Leptodora and other predatory zooplankton, and Cyclopoida zooplankton guilds increased with fishing and pikeperch. Fishing, and pikeperch in the presence of fishing, increased biomass of Crustacean zooplankton guild. There were marked differences between the ATN model simulations and empirically observed time series of fish stock abundances suggesting that the observed changes are partially caused by environmental or fishing-related factors that were not included in the model. [ABSTRACT FROM AUTHOR]

Pike-perch is a very active predatory fish in its natural environment, but extremely sensitive in aquaculture units. Usually, the frequent manipulations may cause many losses in the fish farms, especially during artificial or controlled reproduction. This paper presents the obtained results at S.C.D.P. Nucet, in 2018-2020 period, regarding the pikeperch controlled reproduction in ponds units. The fish were divided into three experimental variants, in triplicate: V1- controlled reproduction, without hormonal induction, V2-controlled reproduction with hormonal induction (carp pituitary), V3 -controlled reproduction, with hormonal induction (synthetic analogue hormone-Nerestin 5A). Each variant used 5 females and 5 males with an average body weight of 2 kg/fish. The best technological indicators were registered in V3 variant, which was based on hormonal induction with Nerestin 5A hormone (88-92% eggs fertilization rate, 71-78% eggs hatching rate, about 2.7 million 7-8 days larvae). The smallest brood stock losses were recorded in V1 variant (without hormonal induction). [ABSTRACT FROM AUTHOR]

Recruitment declines of walleye, Sander vitreus (Mitchill), observed in some northern Wisconsin lakes have resulted in management actions to evaluate and rehabilitate populations. An effective index for estimating relative abundance of yearling walleye is required. The objectives herein were : (a) to evaluate the relationship between yearling walleye electrofishing CPUE and density in northern Wisconsin lakes; (b) to test for the influence of lake‐specific factors on electrofishing catchability of yearling walleye; and (c) to develop an index whereby electrofishing CPUE can be used to quantify yearling walleye relative abundance. Yearling density was significantly positively related to electrofishing CPUE on a long‐term dataset from Escanaba Lake as well as a dataset including several lakes combined. Electrofishing catchability of yearling walleye was negatively related to lake‐surface area but was not related to other lake‐specific variables. This index can provide an efficient method to continue monitoring natural recruitment and also to evaluate survival of stocked walleye. [ABSTRACT FROM AUTHOR]

Many aquatic ecosystems are experiencing multiple anthropogenic stressors that threaten their ability to support ecologically and economically important fish species. Two of the most ubiquitous stressors are climate change and non‐point source nutrient pollution.Agricultural conservation practices (ACPs, i.e. farming practices that reduce runoff, prevent erosion, and curb excessive nutrient loading) offer a potential means to mitigate the negative effects of non‐point source pollution on fish populations. However, our understanding of how ACP implementation amidst a changing climate will affect fish production in large ecosystems that receive substantial upstream sediment and nutrient inputs remains incomplete.Towards this end, we explored how anticipated climate change and the implementation of realistic ACPs might alter the recruitment dynamics of three fish populations (native walleye Sander vitreus and yellow perch Perca flavescens and invasive white perch Morone americana) in the highly productive, dynamic west basin of Lake Erie. We projected future (2020–2065) recruitment under different combinations of anticipated climate change (n = 2 levels) and ACP implementation (n = 4 levels) in the western Lake Erie catchment using predictive biological models driven by forecasted winter severity, spring warming rate, and Maumee River total phosphorus loads that were generated from linked climate, catchment‐hydrology, and agricultural‐practice‐simulation models.In general, our models projected reduced walleye and yellow perch recruitment whereas invasive white perch recruitment was projected to remain stable or increase relative to the recent past. Our modelling also suggests the potential for trade‐offs, as ACP implementation was projected to reduce yellow perch recruitment with anticipated climate change.Overall, our study presents a useful modelling framework to forecast fish recruitment in Lake Erie and elsewhere, as well as offering projections and new avenues of research that could help resource management agencies and policy‐makers develop adaptive and resilient management strategies in the face of anticipated climate and land‐management change. [ABSTRACT FROM AUTHOR]

The reproductive status of walleye (Sander vitreus) and lake whitefish (Coregonus clupeaformis) is largely unstudied in the northern extent of their ranges. Tathlina Lake and Kakisa Lake are large, shallow lakes in the Northwest Territories, Canada, supporting important commercial and subsistence fisheries for these species while being threatened by climate change. Fish were sampled in both lakes across multiple years in the spring and autumn to assess differences in reproductive status in the pre- and post-spawning periods for both species. Condition factor (K), gonadosomatic index (GSI), liversomatic index (LSI), and fecundity were calculated, and plasma samples were also taken from each fish to determine levels of reproductive hormones, specifically 17β-estradiol in females, and 11-ketotestosterone in males. Significant temporal (intra- and interannual) and spatial (between lakes) variation was found for both species and both sexes for all metrics. Expected differences in hormones and indices of reproductive success between pre- and post- spawning periods were demonstrated. When compared with previously published data, a latitudinal gradient for LSI, GSI and fecundity was evident for walleye, but not for lake whitefish. The differences in the reproductive biology of lake whitefish and walleye in these two neighbouring lakes highlights limitations in the use of a reference lake approach in biomonitoring studies. The data in this study can be used and expanded upon to provide information for the sustainable management of these fish stocks for the future. [ABSTRACT FROM AUTHOR]

The pikeperch (Sander lucioperca L.) possesses great potential for diversifying European aquaculture. However, studies on the genetic risk of stocking natural waters with farmed individuals of this species have been limited. Even the effect of pond culture on the genetic composition of stocks with natural-origin has not yet been determined. Our study aimed to compare the genetic variability of a wild living pikeperch population, a pond cultured broodstock (originating from the wild population) and its offspring generation. We also aimed to detect the potential signs of selection using three different methods. By analyzing the molecular data with 14 microsatellite markers, we illustrated that the impact of pond culture on the genetic diversity of fish stocks is similar to hatchery rearing due to its diversity reducing effect caused by using lower effective population sizes. Although the heterozygosity was similar in all populations (Ho = 0.68-0.71), the average number of alleles and allelic richness were significantly lower in the pond cultured stocks (NA = 7.5 and 6; AR = 7.5 and 5.9) compared to the wild population (NA = 11.00, AR = 10.47). Despite the semi-natural conditions of the present study, we detected changing selection pressure in one of the 14 microsatellite markers. [ABSTRACT FROM AUTHOR]

How spawning stock size, environmental conditions and recruitment relate to each other is an essential question in understanding population dynamics of exploited fish stocks. We estimated the recruitment of Eurasian perch (Perca fluviatilis), one of the most important species in coastal fisheries in northern Baltic Sea, and examined the factors that determine perch recruitment success. We hypothesized that perch spawning population biomass and summer water temperature would increase perch recruitment, with potential density dependence, while the effect of the population size of pikeperch (Sander lucioperca) would be negative. Different forms of general stock–recruitment functions, with and without density dependence, and with and without water temperature and pikeperch population size as environmental factors were fitted to long-term (1981–2014) stock assessment data of perch and pikeperch in the Archipelago Sea, southwestern coast of Finland. Perch spawning stock biomass (ages 5–14), water temperature in June–July and pikeperch stock size (ages ≥ 1) at spawning year best explained variation in perch recruitment. The results supported the predictions: perch recruitment increased with spawning stock in density-dependent manner, pikeperch effect on perch recruitment was negative and summer temperature effect was positive suggesting environmentally affected competitive interaction between these two percids. [ABSTRACT FROM AUTHOR]

Walleyes Sander vitreus are an important sport fish found throughout the northern Great Plains of North America. Periods of increased precipitation across the Great Plains can result in new or expanded lakes that contain unexploited fish populations. We assessed angler exploitation of a previously unexploited walleye population to estimate exploitation rates, subsequent changes in walleye abundance, and changes in angler behavior. This research provides an opportunity to add to the limited body of information concerning walleye exploitation and exploitation of unexploited populations. Hazeldon Lake, South Dakota contained an unexploited walleye population and was opened to angling on 15 July 2006. Initial exploitation was high, estimates exceeded 16% after two days and 75% after 16 days. Anglers harvested an estimated 6868 walleyes during 15 July - 31 August 2006; this harvest represented 79% of the pre-opener population estimate of 8661. The 2007 spring population estimate was 2436 fish and represented a 72% decline from the 2006 estimate. Gill net catch per unit effort (CPUE) averaged 30.0 fish net−1 prior to fishing in 2006; the 2007 CPUE was 76% lower at 7.2 fish net−1. A lack of recruitment resulted in no substantial increases in relative abundance from 2007-2017. Fishing pressure was high when the lake first opened to fishing. However, the number of anglers and exploitation rates declined once walleye catch and harvest rates dropped off. Our results suggest that walleye populations in new or expanded waters located in the northern Great Plains can be extremely vulnerable to angling but when catch rates drop off few anglers will continue to fish a given water; instead moving to other waters potentially having higher walleye catch rates. [ABSTRACT FROM AUTHOR]

Understanding stock composition is critical for sustainable management of mixed-stock fisheries. When natural markers routinely used for stock discrimination fail, alternative techniques are required. We investigated the feasibility of using acoustic telemetry to estimate spawning population contributions to a mixed-stock fishery using Lake Erie's summer walleye (Sander vitreus) recreational fishery as a case study. Postrelease survival was estimated after tagging and used to inform simulations to evaluate how contribution estimates could be affected by survival, sample size, and expected population contributions. Walleye experienced low short-term survival after tagging, but showed higher survival after 100 days, likely allowing fish to return to spawning areas the following spring. Based on simulations, accuracy and precision of population composition increased with an increase in the number of tagged fish released, and both appeared to stabilize when ≥200 tagged fish were released. Results supported the feasibility of using acoustic telemetry to estimate spawning population contributions to mixed-stock fisheries in Lake Erie. [ABSTRACT FROM AUTHOR]

Global climate change has been altering freshwater ecosystems by impacting many ecological processes, including individual fish growth. Predictions of responses of local fish populations to future environmental change can draw inferences from past long-term biochronological data. In this study, we reconstructed individual growth pattern of one of the most valuable predatory species in European inland waters, pikeperch (Stizostedion lucioperca), using back-calculated length from their otoliths. Samples were collected at the Lipno reservoir (Czech Republic) between 2008 and 2020. We used linear mixed-effects models to investigate how individual state and environmental conditions affect the somatic growth of the local pikeperch population. We found that individual growth rates increased with temperature and tended to be higher when chlorophyll- a concentration was higher, and water transparency was lower. This suggests the species will likely benefit from the warmer waters predicted in future climate scenarios. However, the decreasing nutrient loading associated with efforts to curb eutrophication in Central Europe may offset these benefits. Together, these results provide a better understanding of how multiple environmental factors, directly and indirectly, influence the somatic growth of pikeperch in long term. [Display omitted] • A time-series of pikeperch growth was reconstructed using otoliths. • Pikeperch growth benefits from an increased mean annual temperature (14–18 °C). • Pikeperch growth benefits from increased eutrophication levels (Chl- a 9–25 µg/L). • Pikeperch growth benefits from a decrease in water transparency (2.1–1.5 m). [ABSTRACT FROM AUTHOR]

Abstract: The collection of Walleye Sander vitreus eggs to meet stocking needs is an essential part of Walleye management for many state and provincial agencies. The stress of capture, holding, and stripping gametes from wild broodstock can potentially lead to Walleye mortality. In waters < 1,200 ha, high levels of mortality could alter population size structure and affect angler success, future egg collections, and survival of stocked Walleyes. We quantified short‐term (i.e., 5 d) mortality of female Walleyes during artificial spawning operations during 2015 to 2017 in four eastern South Dakota natural lakes (Swan Lake in 2015, Long Lake in 2016, and Antelope Lake and Reid Lake in 2017). Each year 25 female Walleyes were stripped of their eggs and 25 additional female Walleyes were included as reference fish. No Walleyes died in 2015, four fish that were stripped of eggs at Long Lake died in 2016, and one stripped of eggs at Reid Lake died in 2017. Overall short‐term mortality was low (5 of 73 fish, 6.8%) during the study. No reference fish expired during the 3 years. Contusions were apparent on ovaries of both egg‐stripped and reference fish. We believe that if fisheries personnel follow standard artificial spawning procedures for Walleye the amount of mortality will be low and should not impact populations of mature female Walleyes. [ABSTRACT FROM AUTHOR]

Abstract: Bag and size limits are commonly used in recreational fisheries management, but these regulations are often treated as separate management tools. This effectively overlooks how bag and size limits can be simultaneously used to achieve multiple management outcomes (e.g., reduce exploitation, prevent overfishing, maximize angler acceptance, etc.). Our objectives were to combine data‐limited stock assessment methods with an angler catch simulation and a yield‐per‐recruit model to assess the effectiveness of bag and size limits to decrease exploitation rates and improve the spawning potential ratio (SPR). We then applied these methods to the Kipawa Lake Walleye Sander vitreus fishery that has experienced overfishing and poor fishing quality. Using data‐limited assessment methods, the exploitation rate was estimated at 0.45 (95% CI = 0.32–0.59) and the population was overfished (mean SPR = 0.06; 95% CI = 0.02–0.13). Bag limits significantly reduced total harvest when extremely restrictive (i.e., reduced to one fish per angler from the current limit of six), but changes in bag limits alone were not sufficient to prevent overharvest because SPR remained below 0.35. Size limits could be used to prevent overharvest with narrow harvest slots (up to a 14‐cm slot range with a minimum harvestable size greater than 32 cm) or large minimum size limits (>52 cm) at the current bag limit of six. When bag limits were reduced to one or two fish per day, harvest windows could be 3–13 cm larger and minimum length limits could be 3–12 cm lower to prevent overharvest. This analysis outlines a relatively simple and effective method that can be applied using data commonly collected in annual agency surveys to predict which regulatory combinations can be used to prevent overharvest, reduce exploitation rates, and maximize angler satisfaction and acceptance of regulations. Finally, the data and model code are included in the Supplement and can be easily applied to other data limited fisheries. [ABSTRACT FROM AUTHOR]

Abstract: Quantile regression is a method of estimating fish weight at length for alternate portions of a probability distribution, but it is an approach that has not received much attention in fisheries literature. Quantile regression can provide estimates of any quantile of weight at length without bias (including the 75th quantile, which was often the focus of standard weight [Ws] equations), and this is more advantageous than previously defined Ws equations derived from linear or quadratic regression methods. The goal of this study was to demonstrate the utility of quantile regression as a tool to assess fish weight at length at various portions of the probability distribution without bias using Walleye Sander vitreus as a case study. Quantile regression models at the 75th quantile were developed for three randomly selected Walleye populations from Georgia and South Dakota and compared with a large (N = 33,589) reference population. Bootstrap resampling procedures indicated that only one population from the state of Georgia had an intercept and slope similar to the reference population. For the one population that had similar intercept and slope to the reference population, predictions of weight at various lengths still fell below the 95% CIs for predicted weights of the reference population, suggesting that slight differences in intercepts and slopes in allometric relationships can result in predicted weights that still differ at some lengths. Predicted weights of Walleye derived from the 10th, 25th, 50th, 75th, and 90th quantiles were used to demonstrate how individuals and populations may be compared at different management targets. Overall, this study demonstrates the relative ease with which quantile regression may be used to compare fish body condition between populations without bias. [ABSTRACT FROM AUTHOR]

Pikeperch Sander lucioperca is an endemic species present in many rivers and lakes of Eurasian regions and also distributed in the Caspian Sea basin. This species was caught by commercial fishermen in the south part of the Caspian Sea, with the highest annual record of 4167 tons in 1931, but due to over-fishing and destruction of natural spawning areas, wild populations have completely collapsed. In order to cope with this marked decline of pikeperch stocks, the Iranian Fisheries Organization developed the artificial propagation and rearing activities for stock rehabilitation. Currently, breeders are caught from natural environments for artificial propagation with or without hormonal induction in order to produce annually millions of fingerlings for releasing into the rivers of the Caspian Sea. Although aquaculture of pikeperch is still in the phase of research and development, some carp farmers are now interested to use it for biological control of undesirable species in earthen ponds. In recent years, total annual fish landings of pikeperch in the southern part of the Caspian Sea increased to 100-300 tons, because of Iranian restocking program. However, more studies are still necessary to successfully achieve pikeperch domestication and to produce a specific formulated feed for this species, with the ultimate goal that pikeperch be adopted by Iranian commercial fish farmers. [ABSTRACT FROM AUTHOR]

The influence of model complexity on integrated tagging and catch-at-age analysis (ITCAAN) parameter estimation is poorly understood for populations exhibiting natal homing. We investigated ITCAAN performance under varying levels of movement, degree of similarity in population productivities, data quality, spatial complexity in parameterization, and whether natural mortality and (or) reporting rates were fixed at actual values, estimated, or misspecified. Dynamics of four populations with natal homing that intermixed during periods of harvest were simulated based on Lake Erie walleye ( Sander vitreus). Our results suggest, when high-quality tagging data are available, ITCAAN models are able to simultaneously estimate movement rates, natural mortality, and tag reporting rates, though accuracy and precision of model estimates will decrease with greater model complexity and fewer tags released. Additionally, ITCAAN models may have difficulty estimating individual population abundances under certain movement rates when population productivities are vastly different. ITCAAN models that estimate natural mortality and reporting rates may perform best with similar sized populations and when data are available to assist the estimation of reporting rates. [ABSTRACT FROM AUTHOR]

Aquaculture plays an important role in supplying the fresh fish. However its production is dominated by only few long-established species that in turn limit the variety of available products in the market. Therefore, new fish species need to be properly introduced to create a diversification in the current market. In order to achieve this goal, it is important to know, understand and characterize their quality features so they can be addressed to local and global markets. Sensory, compositional, instrumental texture parameters and somatic properties of five emerging fish species, namely wreckfish, greater amberjack, grey mullet, meagre, and pikeperch, were examined for characterization purposes. Sensory references were specifically developed for the training of the assessors, both from a qualitative and quantitative perspective. Twenty two sensory descriptors were used for describing the samples. Several differences were observed among the measured parameters. Somatic measures revealed the filleting yield to be the most important of them. Regarding the compositional parameters, fat content was among the most relevant discriminating aspect between species, while hardness was among the most differentiating ones when dealing with texture. Greater amberjack was described with sour flavor, pikeperch was associated to an earthy flavor and grey mullet was characterized by bitter flavor. Sensory firmness was clearly distinctive for wreckfish, while meagre related to juicy texture. The analysis of the relationship between all parameters provided important correlations, especially those related to texture parameters, fat content, laminar structure and teeth adherence. The species in this study exhibited a wide range of physicochemical and sensory characteristics that show their potential for being further exploited when designing new products. [ABSTRACT FROM AUTHOR]

Fish populations that exhibit movement patterns present challenges to fishery management. In the Inland Waterway in Michigan’s northern Lower Peninsula, monitoring WalleyeSander vitreuspopulation dynamics and harvest management is difficult because of seasonal intermixing among interconnected lakes. In addition, the presence of tribal subsistence fishing and recreational angling fisheries that occur during different discrete time periods adds complexity to understanding harvest management performance. We used stochastic simulation to determine the influence of movement and harvest dynamics on the performance of harvest management targets for Walleye in our study system. After accounting for postspawn movement and harvest dynamics, our results indicated that population-specific exploitation rates on average did not exceed the target rates (u= 0.35) that are mandated in the waterway. We did, however, determine that some areas are at risk because they experienced population-specific exploitation rates that surpassed the target. We also determined that the interplay between movement and uncertain population and harvest dynamics will likely determine the ability of management to meet currently accepted harvest targets on average over time, as well as the risk of exceeding harvest targets each year. Our findings are broadly applicable for mobile species inhabiting lake chains and highlight that it is critical for managers to gain an understanding of movement as well as harvest dynamics, because both are imperative for understanding how these dynamics influence harvest management performance. As such, we recommend that managers of Walleye populations in other waterways implement tagging studies and harvest monitoring programs to gain an understanding of movement rates and harvest dynamics. An understanding of movement and harvest dynamics along with the stochastic simulation framework we used provides a better understanding of complex system dynamics and leads to informed harvest management decisions. Received July 30, 2016; accepted January 6, 2017 Published online March 31, 2017 [ABSTRACT FROM AUTHOR]

Offspring size determines offspring survival rates; thus, understanding factors influencing offspring size variability could elucidate variation in population dynamics. Offspring size variation is influenced through multigenerational adaptation to local environments and within-lifetime plastic responses to environmental variability and maternal effects among individuals. Moreover, offspring size variation may represent trade-offs in energy allocation within individuals that influence lifetime reproductive success. However, the mechanisms whereby environmental conditions influence offspring size, e.g., via inducing adaptive and plastic variation in population-scale maternal effects, remain poorly understood. We evaluated intra-specific variation in maternal effects, egg size, and intra-individual egg size variation in six populations of walleye ( Sander vitreus) and related among- and within-population patterns to thermal conditions. Egg size was conserved within populations and negatively related to long-term thermal conditions among populations, while maternal effect strengths were positively related to thermal conditions, suggesting that populations inhabiting warmer environments adapted to produce smaller eggs but stronger maternal effects. Within a population, egg size was positively related to colder winters, suggesting cold winters may alter egg size through effects on maternal condition or as an adaptive maternal effect to improve offspring survival. Intra-individual egg size variation varied little among populations or with female size, but declined with increasing summer and decreasing winter temperatures. Our result suggests that environmental conditions could impact not only short-term offspring production but also spur adaptive changes in offspring phenotypes. Thus, it is necessary to account for adaptive responses to predict population dynamics under environmental changes. [ABSTRACT FROM AUTHOR]

Reproductive habitats are vital for sustaining fish populations, but their location and relative natal contributions are often unknown or poorly understood. We used otolith microchemistry to examine natal origins of WalleyesSander vitreusin Missouri River reservoirs (i.e., Lake Oahe, Lake Sharpe, Lake Francis Case, and Lewis and Clark Lake) in North Dakota and South Dakota. Water Sr:Ca and Ba:Ca were spatially heterogeneous and temporally consistent in all impoundments. Otolith Sr:Ca and Ba:Ca from age-0 Walleyes permitted the reclassification of fish to known natal habitats (i.e., tributary, embayment, main stem) and individual sites with 87% and 75% accuracy, respectively. Natal contributions were highest in tributaries, particularly those in Lake Oahe, where 32% of all adults and 77% of Lake Oahe adults hatched. Embayments and main-stem environments had high natal contributions (67–78%) in Lakes Sharpe and Francis Case and Lewis and Clark Lake, where tributaries are less abundant. Our research demonstrates the utility of otolith microchemistry for measuring habitat- and site-specific natal contributions and provides further information that can be used in managing Walleyes in Missouri River reservoirs, particularly for broodstock collection, habitat protection and restoration, and harvest regulations. Received April 17, 2015; accepted December 11, 2015 Published online March 30, 2016 [ABSTRACT FROM AUTHOR]

Saginaw Bay WalleyesSander vitreuscontribute to fisheries throughout Lake Huron including a recreational fishery and by-kill stemming from the state-licensed commercial fishery in the bay. Two critical uncertain states of nature exist concerning the true magnitude (catchability) of the by-kill and the future of AlewivesAlosa pseudoharengusin Lake Huron, the latter being a strong determinant of Walleye recruitment. After consulting with fishery managers, a stochastic simulation model was developed and used to evaluate management options for the recreational fishery in the form of a decision analysis and the value of information for improved estimates of by-kill magnitude. Decision analysis sought to identify the maximum sustainable recreational harvest. Sustainable harvest was defined as the average across 250 stochastic simulations for each management option considered while penalizing any simulation year with a value of zero if sustainability criteria were exceeded. Decision analysis indicated that sustainable harvest would be maximized if recreational fishing mortality were increased 50% from recent levels. Realizing this potential, however, would require more intensive management to ensure that desired levels of fishing mortality occurred. Choices by managers for allocating surplus harvest are a matter of policy, but concerns over maintaining predation pressure on Alewives to suppress their resurgence may be reasons to manage conservatively by electing instead to maintain a higher predator abundance. The value of information analysis revealed that the improvement in the recreational fishery warrants investment in further research on the uncertainty over by-kill catchability. Received June 25, 2015; accepted November 20, 2015 Published online March 31, 2016 [ABSTRACT FROM AUTHOR]

Fish often exhibit complex movement patterns, and quantification of these patterns is critical for understanding many facets of fisheries ecology and management. In this study, we estimated movement and fishing mortality rates for exploited walleye ( Sander vitreus) populations in a lake-chain system in northern Michigan. We developed a state-space model to estimate lake-specific movement and fishery parameters and fit models to observed angler tag return data using Bayesian estimation and inference procedures. Informative prior distributions for lake-specific spawning-site fidelity, fishing mortality, and system-wide tag reporting rates were developed using auxiliary data to aid model-fitting. Our results indicated that postspawn movement among lakes was asymmetrical and ranged from approximately 1% to 42% per year, with the largest outmigration occurring from the Black River, which was primarily used by adult fish during the spawning season. Instantaneous fishing mortality rates differed among lakes and ranged from 0.16 to 0.27, with the highest rate coming from one of the smaller and uppermost lakes in the system. The approach developed provides a flexible framework that incorporates seasonal behavioral ecology (i.e., spawning-site fidelity) in estimation of movement for a mobile fish species that will ultimately provide information to aid research and management for spatially structured fish populations. [ABSTRACT FROM AUTHOR]

Walleye Sander vitreus are native to central North American freshwater habitats. Introductions within and outside their native range have occurred in all of the lower 48 states. These stockings have occurred due to the increasing popularity of this species, leading to the demand surpassing the supply. Despite the popularity of this species for anglers, and extensive research on the distribution, life history, population dynamics, culture, and stocking strategies, there is disparate information on first year survival of stocked populations. The objective of this study was to test for associations between biotic and abiotic variables for recruitment of age-0 fish in the fall. We tested for the influence of the number of stocking events, moronid stocking density, spring/summer warming rate, and spring/summer maximum discharge on electrofishing catch rates in the fall of age-0 walleye. We used a hierarchical generalized linear model with the Poisson distribution to evaluate these relationships. Parameters of the model were estimated using Bayesian inference. Our model suggested the number of stocking events, moronid stocking density, and maximum discharge/rainfall were the most important factors influencing walleye recruitment. Fall catch rates of age-0 walleye were positively related to stocking events, negatively related to moronid stocking density, and negatively related to maximum discharge/rainfall. However, these relationships were not concordant across all reservoirs. Further, variability we observed across reservoirs support the conclusion that walleye populations must be managed at individual reservoirs. This study will assist managers locally and regionally to determine stocking strategies for walleye to improve recruitment in midwestern reservoirs. [ABSTRACT FROM AUTHOR]

The effectiveness of stocking hatchery-reared WalleyesSander vitreusto supplement native populations in large, open systems like the Great Lakes has not been thoroughly evaluated. I quantified recent contributions of stocked Walleye fingerlings to populations in Little Bay de Noc (LBDN) and Big Bay de Noc (BBDN) in northern Green Bay, Lake Michigan. Oxytetracycline-marked Walleye fingerlings were stocked in June, and late summer gill-net and night-time boat electrofishing surveys were used to index Walleye year-class abundance and collect juvenile Walleyes for hatchery mark evaluation. For the 2004–2009 year-classes, 76% of the age-0 to age-3 Walleyes examined from LBDN were of wild origin and 62% in BBDN were naturally reproduced fish. Survey catch rates of juvenile Walleyes were similar for stocked and nonstocked year-classes. Assessment catch rates of age-1 and age-2 Walleyes differed significantly by location, with average catch rates in LBDN often being ten times higher than those in BBDN. Age-0 Walleyes persisted to older ages and were well-represented at numerous sampling locations in LBDN, but few age-1 and older Walleyes were caught in BBDN. The differences in growth between hatchery-reared and wild Walleyes were minor compared with the differences between bays. Based on stocking records and creel estimates available since 1985, the harvest rate of Walleyes was not significantly correlated to the numbers of Walleyes stocked 4–6 years earlier in LBDN or BBDN. Despite low stocking rates, stocked fish likely provided some contribution (though not a statistically significant one) to Walleye year-classes and the sport fishery in LBDN, but their contribution in BBDN was less apparent. Managers should weigh the trade-offs of supplemental stocking in Great Lakes waters when considering requests for hatchery Walleyes in smaller lakes and rivers, especially when stocking resources are limited. Received February 20, 2014; accepted April 17, 2015 [ABSTRACT FROM PUBLISHER]

Understanding variability in fish production, biomass, production/biomass ( P/ B) ratios, and their relationship to exploitation is central to fisheries sustainability. At Escanaba Lake, Wisconsin, USA, data from a compulsory creel census (1965-2009) were combined with survey data on fish populations to test for empirical relationships between annual production and exploitation rates of walleye ( Sander vitreus). Empirical estimates of walleye production were relatively high and temporally variable in Escanaba Lake. Annual production, biomass, and P/ B ratios ranges were 2.4-11.3 kg·ha−1·year−1, 9.1-49.4 kg·ha−1, and 0.15-0.30 year−1, respectively. Walleye production rates were significantly and positively correlated with adult (i.e., age 3+) walleye density - the core metric used to manage walleye populations in the Ceded Territory of Wisconsin. However, adult walleye density correlated best with ages 4-6 production. Annual exploitation based on the percentage of individuals removed from the population was linearly related to annual exploitation based on the percentage of production removed. On average, 100% of annual production was harvested at ∼20% annual exploitation of individuals; thus, higher sustained exploitation rates would deplete walleye biomass in Escanaba Lake over time. A sustainable annual exploitation rate of 20% annually is lower than the 35% limit reference point currently used for walleye management in the Ceded Territory of Wisconsin. Nevertheless, our estimate is strongly concordant with two recent and independent modeling efforts addressing this same topic. We suggest empirical estimates of fish production are a vastly underutilized tool for better understanding sustainable exploitation rates in walleye populations and, likely, fisheries in general. [ABSTRACT FROM AUTHOR]

Movement of WalleyesSander vitreusamong reaches in a large, fragmented river was assessed by employing a combination of tagging, telemetry, and genetic analyses. Our objective was to determine whether the existing dams in the Ottawa River, Canada, were impeding Walleye movement among river reaches. Movement was predicted to be greater among contiguous, unimpounded reaches in comparison with impounded reaches. In total, 1,586 Walleyes were tagged in five river reaches, and 35 Walleyes were tracked by radiotelemetry in three river reaches. Genetic analyses (linkage disequilibrium, genetic divergence and diversity, effective population size, genetic structuring, bottlenecks, and migration rates) were conducted on 221 Walleyes from seven river reaches by genotyping at six microsatellite loci. Based on both tag returns (return rate = 12.1%) and telemetry data, there was limited movement among river reaches whether impounded or unimpounded, and movement was predominately upstream. Genetic analyses identified population structuring, with three genetic groupings occurring within the river. There was also evidence of genetic isolation in an upper reach of the river, indicating potential residual effects of a bottleneck or genetic drift. Our results suggest that existing dams may not act as significant barriers to Walleye movement in the Ottawa River, but limited movements appear to maintain genetic diversity and minimize genetic drift. Consequently, maintaining the genetic attributes of Walleye stocks in segmented rivers may require some level of fish passage. Received July 9, 2012; accepted January 16, 2015 [ABSTRACT FROM PUBLISHER]

Walleye ( Sander vitreus) populations are cyclic because of biotic and abiotic factors, and wind activity, wave energy, and water levels may be influential given walleye spawn close to shore. We installed an anemometer and tridirectional velocimeter on a spawning reef in Big Crooked Lake, Wisconsin, in 2005 to determine wind-wave relationships and wave energy exceedance of critical velocities of both egg (affecting transport) and substrates (affecting abrasion or burial). To evaluate egg movement, we delineated egg locations at adhesive, postspawn, and black-eyed stages and surveyed on-shore for stranded eggs. We monitored water level with a staff gauge. Wind and wave velocities were significantly ( p < 0.01) correlated, and wave velocities were significantly higher ( p < 0.01) nearshore (2.0 m) than further from shore (4.6 m). Mean nearshore wave velocities were often sufficient to initiate movement of nonadhesive eggs (45% of records) and fine sand (39%) during egg incubation. Surveys indicated waves moved eggs closer to shore and some onto shore. Water level fluctuations (range = 2.4 cm) likely did not strand or desiccate eggs. We documented that wind and wave activity transports eggs and substrates and should be considered a critical factor in annual walleye egg survival and year-class strength. [ABSTRACT FROM AUTHOR]

Fish migration in large freshwater lacustrine systems such as the Laurentian Great Lakes is not well understood. The walleye (Sander vitreus) is an economically and ecologically important native fish species throughout the Great Lakes. In Lake Huron walleye has recently undergone a population expansion as a result of recovery of the primary stock, stemming from changing food web dynamics. During 2011 and 2012, we used acoustic telemetry to document the timing and spatial scale of walleye migration in Lake Huron and Saginaw Bay. Spawning walleye (n = 199) collected from a tributary of Saginaw Bay were implanted with acoustic tags and their migrations were documented using acoustic receivers (n = 140) deployed throughout U.S. nearshore waters of Lake Huron. Three migration pathways were described using multistate mark-recapture models. Models were evaluated using the Akaike Information Criterion. Fish sex did not influence migratory behavior but did affect migration rate and walleye were detected on all acoustic receiver lines. Most (95%) tagged fish migrated downstream from the riverine tagging and release location to Saginaw Bay, and 37% of these fish emigrated from Saginaw Bay into Lake Huron. Remarkably, 8% of walleye that emigrated from Saginaw Bay were detected at the acoustic receiver line located farthest from the release location more than 350 km away. Most (64%) walleye returned to the Saginaw River in 2012, presumably for spawning. Our findings reveal that fish from this stock use virtually the entirety of U.S. nearshore waters of Lake Huron. [ABSTRACT FROM AUTHOR]

From 2006 to 2009, 18,712 fish were tagged and released in 45 tagging events using nonreward and high-reward T-bar anchor tags to estimate the rate of exploitation (u) by anglers in various Idaho fisheries. In total, 3,100 nonreward tags and 592 high-reward tags were reported by anglers. Annualuwas adjusted for tag loss, tagging mortality, and angler tag reporting rate. Tag loss, estimated by double-tagging a subsample of fish, varied greatly among species; tag loss was lowest for Yellow PerchPerca flavescens(1.1% in year 1 and 4.5% in year 2) and crappiesPomoxisspp. (2.9% and 4.8%) and was highest for Largemouth BassMicropterus salmoides(14.8% and 30.3%), WalleyesSander vitreus(11.4% and 43.2%), and Smallmouth BassM. dolomieu(10.5% and 41.6%). Short-term (7–33-d) mortality averaged about 1% for both hatchery and wild fish. The nonreward-tag reporting rate averaged 54.5% across all species and years. Adjusteduaveraged 19.4% (range = 2.0–44.3%) and was generally highest for crappies (mean = 28.7%) and Smallmouth Bass (22.0%) and lowest for wild trout (9.5%). Estimates of total annual mortality (A), based on the difference in tag returns between years 1 and 2, were plausible for some species but were unusually high for other species, especially Smallmouth Bass and wild trout. The implausibility of some estimates ofAprobably resulted from a combination of factors, including the reduced vulnerability of larger, older fish to angling, which would have caused a reduction in tag returns in year 2, likely due to a shift in fish behavior or habitat preference as tagged fish grew in size. Our results demonstrate the utility of using the high-reward tagging method to estimateufor fisheries under a variety of circumstances, but fisheries managers should use caution in attempting to simultaneously estimateAfrom the tag returns. Received December 23, 2013; accepted July 21, 2014 [ABSTRACT FROM AUTHOR]

Fish stocking (artificial supplementation) has been used to augment populations and angling opportunities. However, genetic composition and adaptations of native fish populations may be affected, raising management concerns. From 1995 to 2000, the New York State Department of Environmental Conservation stocked WalleyeSander vitreusfry and fingerlings from the Maumee River (western Lake Erie) into Cattaraugus Creek (eastern Lake Erie). We analyzed nuclear microsatellite (sat) DNA and mitochondrial DNA (mtDNA) variation in Cattaraugus Creek Walleyes for comparisons between prestocking and poststocking groups, among annual spawning runs (1998–2011), among age cohorts, and between sexes. Results for genetic differentiation (indexFST) were not significant between prestocking and poststocking groups (sat:FST= 0.003; mtDNA:FST< 0.001), and the two groups did not resemble stocked Maumee River fingerlings (sat:FST= 0.003–0.012; mtDNA:FST= 0.076–0.090). Tests for differentiation were not significant among annual spawning runs (sat:FST= <0.001–0.007; mtDNA:FST= <0.001–0.049), among age cohorts (sat:FST= <0.001–0.006; mtDNA:FST= <0.001–0.097), or between sexes (sat:FST< 0.001; mtDNA:FST< 0.001). Genetic diversity levels were high and consistent (sat: observed heterozygosity [mean ± SE] = 0.71 ± 0.04; mtDNA: haplotype diversity = 0.79 ± 0.01). Thus, despite stocking, the genetic signature of the native spawning run remained distinctive. However, the genetic composition of the local wild population and the stocking source should be assessed prior to any future supplementation plans. Received December 6, 2013; accepted June 12, 2014 [ABSTRACT FROM AUTHOR]

The maintenance of genetic integrity is an important goal of fisheries management, yet little is known regarding the effects of management actions (e.g., stocking, harvest regulations) on the genetic diversity of many important fish species. Furthermore, relationships between population characteristics and genetic diversity remain poorly understood. We examined relationships among population demographics (abundance, recruitment, sex ratio, and mean age of the breeding population), stocking intensity, and genetic characteristics (heterozygosity, effective number of alleles, allelic richness, Wright's inbreeding coefficient, effective population size [Ne], meand2[a measure of inbreeding], mean relatedness, and pairwise population ΦSTestimates) for 15 populations of WalleyeSander vitreusin northern Wisconsin. We also tested for potential demographic and genetic influences on Walleye body condition and early growth. Combinations of demographic variables explained 47.1–79.8% of the variation in genetic diversity. Skewed sex ratios contributed to a reduction inNeand subsequent increases in genetic drift and relatedness among individuals within populations; these factors were correlated to reductions in allelic richness and early growth rate. Levels of inbreeding were negatively related to both age-0 abundance and mean age, suggestingNewas influenced by recruitment and generational overlap. A negative relationship between the effective number of alleles and body condition suggests stocking affected underlying genetic diversity of recipient populations and the overall productivity of the population. These relationships may result from poor performance of stocked fish, outbreeding depression, or density-dependent factors. An isolation-by-distance pattern of genetic diversity was apparent in nonstocked populations, but was disrupted in stocked populations, suggesting that stocking affected genetic structure. Overall, demographic factors were related to genetic diversity and stocking appeared to alter allelic frequencies and the genetic structure of Walleye populations in Wisconsin, possibly resulting in disruption of local adaptation. Received September 4, 2013; accepted November 19, 2013 [ABSTRACT FROM AUTHOR]

The influence of water levels on population characteristics of yellow perch, Perca flavescens (Mitchill), and walleye, Sander vitreus (Mitchill), was evaluated across a range of glacial lakes in north-eastern South Dakota, USA. Results showed that natural variation in water levels had an important influence on frequently measured fish population characteristics. Yellow perch abundance was significantly ( P < 0.10) greater during elevated water levels. Yellow perch size structure, as indexed by the proportional size distribution of quality- and preferred-length fish ( PSD and PSD-P), was significantly greater during low-water years, as was walleye PSD. Mean relative weight of walleye increased significantly during high-water periods. The dynamic and unpredictable nature of water-level fluctuations in glacial lakes ultimately adds complexity to management of these systems. [ABSTRACT FROM AUTHOR]

Late summer sampling of pelagic age-0 year fish communities in five Czech reservoirs and one Dutch reservoir revealed extremely small age-0 year pikeperch Sander lucioperca (mean 24 mm standard length, LS, minimum 13 mm LS) alongside more normal-sized S. lucioperca that are found at the end of the first growing season (mean 50 mm LS), resulting in two clearly size-separated cohorts. Reference to such small age-0 year S. lucioperca in lakes or reservoirs at this time of year and in such large numbers are almost absent the scientific literature, and the presence of these small S. lucioperca is contradictory to the common understanding of the reproductive biology of this species. This overlooked phenomenon may have a major effect on the population dynamics of this valuable species because of size-dependent winter mortality. [ABSTRACT FROM AUTHOR]

Rates of tag loss should be estimated and accounted for when using mark–recapture surveys and angler tag returns to estimate fish population abundance and exploitation rates. WalleyesSander vitreussampled during April 2010 spawning assessments conducted in the Winnebago system, Wisconsin, were marked with anchor tags and upper caudal fin clips to estimate tag loss rates during three time intervals: 0–11 d posttagging, 0–90 d posttagging, and 1 year posttagging. Tag loss was negligible (<0.5%) within the first 11 d but increased to 4.7% within the first 90 d and to 21.9% after 1 year. After we corrected for the tag loss occurring within the first 90 d, estimates of population abundance decreased 4.3% for females and 4.4% for males, while estimates of exploitation increased 4.9% for both sexes. Accounting for 21.9% annual tag loss led to more severe decreases in the estimates of population abundance (20.0% for females and 21.2% for males) and increases in the estimates of exploitation (28.0% for both sexes) than not accounting for any tag loss. Higher exploitation rates resulted in higher estimates of fishing mortality and lower estimates of natural mortality. When used in yield-per-recruit models, the estimated natural mortality rates derived from exploitation rates that accounted for tag loss resulted in higher yields through the implementation of larger minimum length limits to maximize yield. We recommend that managers evaluate the effectiveness of their tagging operations by estimating tag loss and assessing the potential impacts of quantified loss on management metrics. We also caution against the application of population models without an accurate estimate of tag loss and the associated impacts on estimates of population abundance and exploitation and, in turn, fishing and natural mortality rates. Received May 22, 2013; accepted June 11, 2013 [ABSTRACT FROM PUBLISHER]

Walleye ( Sander vitreus) is an important sport fish throughout much of North America, and walleye populations support valuable commercial fisheries in certain lakes as well. Using a corrected algorithm for balancing the energy budget, we reevaluated the performance of the Wisconsin bioenergetics model for walleye in the laboratory. Walleyes were fed rainbow smelt ( Osmerus mordax) in four laboratory tanks each day during a 126-day experiment. Feeding rates ranged from 1.4 to 1.7 % of walleye body weight per day. Based on a statistical comparison of bioenergetics model predictions of monthly consumption with observed monthly consumption, we concluded that the bioenergetics model estimated food consumption by walleye without any significant bias. Similarly, based on a statistical comparison of bioenergetics model predictions of weight at the end of the monthly test period with observed weight, we concluded that the bioenergetics model predicted walleye growth without any detectable bias. In addition, the bioenergetics model predictions of cumulative consumption over the 126-day experiment differed from observed cumulative consumption by less than 10 %. Although additional laboratory and field testing will be needed to fully evaluate model performance, based on our laboratory results, the Wisconsin bioenergetics model for walleye appears to be providing unbiased predictions of food consumption. [ABSTRACT FROM AUTHOR]

Predation events during ontogeny may have long-term consequences for fish population abundance and variability. We used a stage-based matrix model to evaluate WalleyeSander vitreusand Brown TroutSalmo truttapredation on Chinook SalmonOncorhynchus tshawytschaparr of the Muskegon River stock and the relative influence of parr predation on the long-term population dynamics and recruitment of Chinook Salmon in Lake Michigan. The model predicted the number of Chinook Salmon individuals in each stage (fry, smolts, and lake age 0 [recruits] through lake age 4) and forecasted population trajectories based on demographic data (e.g., survival, growth, and fecundity). The relative influence of parr predation was compared with influences of environmental stochasticity in the egg stage and AlewifeAlosa pseudoharengusabundance (prey for lake-stage salmon) on Chinook Salmon fecundity, recruitment, and population growth. To simulate environmental stochasticity and the influence of Alewife abundance, we varied Chinook Salmon stage-specific survival rates, growth rates, maturity schedule, and carrying capacity. Relative to a baseline recruitment scenario, removal of stocked Brown Trout resulted in a significant increase in parr survival and long-term Chinook Salmon abundance. Walleye predation on parr had little apparent influence on Chinook Salmon population dynamics. Predation on parr during out-migration was positively correlated with variation in Chinook Salmon population stability and was negatively correlated with population growth, suggesting that Brown Trout have a significant negative effect on Chinook Salmon recruitment and long-term population stability. The negative effects of variation in egg survival rates and Alewife abundance on Chinook Salmon recruitment and population growth rates were similar to the negative effects from parr predation scenarios. Our study suggests that management decisions to promote Great Lakes Chinook Salmon populations may require evaluation of trout stocking practices in nursery habitats. Received October 9, 2012; accepted April 15, 2013 [ABSTRACT FROM AUTHOR]

Walleye ( Sander vitreus) in Lake Erie is a valuable and migratory species that spawns in tributaries. We used hydroacoustic sampling, gill net sampling, and Bayesian state-space modeling to estimate the spawning stock abundance, characterize size and sex structure, and explore environmental factors cuing migration of walleye in the Maumee River for 2011 and 2012. We estimated the spawning stock abundance to be between 431 000 and 1 446 000 individuals in 2011 and between 386 400 and 857 200 individuals in 2012 (95% Bayesian credible intervals). A back-calculation from a concurrent larval fish study produced an estimate of 78 000 to 237 000 spawners for 2011. The sex ratio was skewed towards males early in the spawning season but approached 1:1 later, and larger individuals entered the river earlier in the season than smaller individuals. Walleye migration was greater during low river discharge and intermediate temperatures. Our approach to estimating absolute abundance and uncertainty as well as characterization of the spawning stock could improve assessment and management of this species, and our methodology is applicable to other diadromous populations. [ABSTRACT FROM AUTHOR]

Populations existing in formerly glaciated areas often display composite historical and contemporary patterns of genetic structure. For Canadian freshwater fishes, population genetic structure is largely reflective of dispersal from glacial refugia and isolation within drainage basins across a range of scales. Enhancement of sport fisheries via hatchery stocking programs and other means has the potential to alter signatures of natural evolutionary processes. Using 11 microsatellite loci genotyped from 2182 individuals, we analyzed the genetic structure of 46 inland lake walleye (Sander vitreus) populations spanning five major drainage basins within the province of Ontario, Canada. Population genetic analyses coupled with genotype assignment allowed us to: 1) characterize broad- and fine-scale genetic structure among Ontario walleye populations; and 2) determine if the observed population divergence is primarily due to natural or historical processes, or recent anthropogenic events. The partitioning of genetic variation revealed higher genetic divergence among lakes than among drainage basins or proposed ancestries—indicative of relatively high isolation among lakes, study-wide. Walleye genotypes were clustered into three major groups, likely reflective of Missourian, Mississippian, and Atlantic glacial refugial ancestry. Despite detectable genetic signatures indicative of anthropogenic influences, province-wide spatial genetic structure remains consistent with the hypothesis of dispersal from distinct glacial refugia and subsequent isolation of lakes within primary drainage basins. Our results provide a novel example of minimal impacts from fishery enhancement to the broad-scale genetic structure of inland fish populations. [ABSTRACT FROM PUBLISHER]

Understanding the dynamics of angling effort and how fish populations are affected by angler effort is an important and often unappreciated component of fisheries management. Our objective was to determine the extent to which angling-induced mortality limits walleyeSander vitreuspopulation density in northern Wisconsin lakes. We developed a simulation model to evaluate the effects on long-term equilibrium walleye population density caused by effort limitations, density-dependent angling effort, and angling regulations. Equilibrium density was limited by angling effort when effort was held constant but was generally lower when effort was density dependent. Equilibrium density ranged from 3.46 to 21.79 adults/ha when effort was density dependent, similar to the observed median density in lakes sustained by natural reproduction (8.7 adults/ha). Median equilibrium density was 23.3 adults/ha when effort was zero. Equilibrium density was higher when harvest was regulated by a minimum length limit as opposed to no length limit and with no postrelease mortality than with postrelease mortality. Population collapse was more likely and equilibrium density was lower when the population density and effort/ha relationship was strongest. Because the observed relationship between adult walleye population density and effort/ha was weaker, we conclude that open-access walleye fisheries in northern Wisconsin are generally self-regulating. However, populations likely persist at lower population densities than would be expected if angling effort were limited to lower levels than those currently observed. Our results are intuitive; however, they suggest that density increases may be on the order of 100% when effort is severely restricted compared with open-access fisheries with unlimited effort. Other fish species may experience different expected density increases with restricted angler effort depending on a number of factors, but our results suggest that population density changes can be dramatic and that similar modeling exercises may be useful to managers of other fish species if increasing density is of interest. Received December 19, 2011; accepted June 13, 2012 [ABSTRACT FROM PUBLISHER]

Kim, S. T. 2012. A review of the Sea of Okhotsk ecosystem response to the climate with special emphasis on fish populations. – ICES Journal of Marine Science, 69: .This article provides a brief review of climatic, oceanographic, and biological changes in the Sea of Okhotsk in recent decades. The Sea of Okhotsk is distinguished by its high biological productivity and its significant impact on the Pacific Ocean through water exchanges. Long-term temperature data have shown periodic cooling and warming of the Sea that in turn have resulted in changes to its biological communities. In the 1980s, a generally warm period, the Sea of Okhotsk had abundant fish, primarily large stocks of gadoids, especially walleye pollock. The second half of the 1990s was a transitional period when the marine ecosystem was being restructured. In particular, by the mid-1990s, the total biomass of fish in the Sea of Okhotsk had decreased significantly. In the early 2000s, the situation reached a critical level, but by the end of that decade, there was a renewed warming and an increase in the abundance of walleye pollock. [ABSTRACT FROM PUBLISHER]