Perch Stocks Research Articles

Status of the fish stocks and fisheries of the main commercial fish species of Lake Ladoga in the XXI century

In the 21st century, there has been decrease in stocks and catches of aquatic biological resources in Lake Ladoga as well as a change in the structure of the fish population in the Lake, primarily due to changes in the trophic capacity of the reservoir. Smelt dominates in the commercial catches. Stocks and catches of autumn-spawning whitefish and lakecisco show obvious downward trend. Biological and commercial indicators of the pike-perch population are at a low level. Stocks of bream, roach and perch are in good condition.

Dynamics of catches and state of stocks the European perch Perca fluviatilis in rivers in the middle Ob basin (in the Tomsk region)

European perch Perca fluviatilis Linnaeus, 1758 — is a mediumsized representative of the Percidae. It distributed in lowland rivers, lakes and artificial reservoirs, as well as in desalinated coastal areas of the seas of Northern Eurasia, with the exception of the Far East and the coast of the Arctic Ocean. This species is numerous almost everywhere. It is one of the main objects of industrial and amateur fishing. In the Middle Ob basin, a significant part of the life cycle of perch is associated with the floodplain system. There is, during the spring flood, its spawning and subsequent feeding of juveniles and producers take place. Therefore, the regulation of the Ob’s flow by the Novosibirsk hydroelectric power station dam served as one of the important factors that had a negative impact on the state of its reserves. Thus, within the Tomsk region, commercial catches of perch before the regulation of the Ob flow (1946–1961) averaged 354 tons per year, and after regulation (during the period of stable fishing pressure, in 1960–1985) — 157 tons. In recent years (2018–2022), the catch of perch has increased slightly and, according to official fisheries statistics, amounts to 211 tons per year, providing 5.9% of the total fish production in the region. Currently, the reserves of perch are in a relatively stable state, the estimated indicators of its biomass in rivers within the Tomsk region in recent years range from 1190.9 to 2277.5 tons, with an average number of 10.6 million pieces. The development of the perch’ reserves is satisfactory, averaging 94.2% of the recommended catch. Amateur fishermen do not have a significant impact on the state of perch stocks.

Conflicting perspectives on ecosystem conservation in a cultivated floodplain: The role of science and the challenge of pluralism in decision‐making in Lac Saint‐Pierre (Quebec, Canada)

AbstractBy generating and explaining facts, science holds an important role in environmental policy decision‐making. However, scientific knowledge is often framed as objective and neutral in policy debates, which can be challenged by stakeholders who have a different view of the issue. To counter this situation, we propose a novel scientific approach to analyze problems that are highly contested and seem difficult to resolve, that is, wicked problems. Our study combined post‐normal science and environmental justice perspectives to shed light on a wicked problem—the largely unsuccessful efforts to rehabilitate yellow perch stocks in Lac Saint‐Pierre (LSP), Quebec, Canada. The combination of these two perspectives allows us to investigate the causes of the decrease of yellow perch stocks and the social and institutional barriers to rehabilitation—which can only be overcome if the injustice perceived by different stakeholders is overcome. Our study presents an approach that addresses uncertainties, integrates various knowledge forms, reassesses decision‐making procedures, and highlights inequalities within a specified territory. The research also underlines the importance of the qualitative dimension in the development of knowledge and the need to address equity in the development of environmental policies.

Sea Surface Temperature Affects the Reproductive Biology of Female Pearl Perch (Glaucosoma scapulare Macleay, 1881) in Queensland, Australia

Pearl perch (Glaucosoma scapulare) are endemic to the east coast of Australia and have a long history of exploitation. Recent stock assessments indicate that the current rate of fishing mortality is unsustainable in the long term. To better inform the management of the pearl perch stock and to address gaps in our understanding of their reproductive biology, we investigated patterns in gonad development and estimated length- and age-at-maturity and batch fecundity from females collected from southern and central Queensland waters between 2018 and 2022. The mean gonadosomatic index (GSI) varied both temporally and spatially, with maxima in the austral autumn in southern Queensland and in summer in central Queensland, coinciding with sea surface temperatures between 25.26 and 26.32°C. The length- and age-at-maturity of females were 353 mm (fork length, FL) and 4.42 years, respectively, and batch fecundity (B) was correlated to FL such that Ln(B) = 2.45 × Ln(FL) + 3.90. Our results will inform a management strategy to recover the stock to acceptable levels of exploitation.

Content and complexity of stakeholders’ mental models of socio-ecological systems

Stakeholders' interactions with environmental resources are influenced by their mental models of the socio-ecological system of the environmental resource. Individual differences in such mental models are particularly important to identify, as diverse mental models may be associated with different behaviour or policy preferences and affect collaborative conservation efforts. In the present work, we explore stakeholders' mental models of a socio-ecological system and assess content and complexity differences across fishing experience levels, migration status, and regions. We mapped Tanzanian fishers' (N = 185) mental models of the drivers of the Nile perch stock fluctuation at Lake Victoria. The findings show that (1) fishers’ mental models were complex and diverse, (2) mental models focused on the causal influence of destructive fishing activities, (3) mental model complexity, but not content, varied across regions, and (4) fishing experience and migration status were not consistently related to mental model complexity or content. These results have important implications for environmental resource management at Lake Victoria.

Ice fishing reveals size structure but not abundance of Eurasian perch in small boreal lakes

AbstractManagement of inland recreational fisheries would benefit from stock abundance and size structure data. Feasibly standardised angling methods such as ice fishing could produce representative catch‐per‐unit‐effort (CPUE) information on the abundance of different‐sized fish in small lakes. Here, we first used standard Nordic multimesh gillnets to obtain number‐per‐unit‐effort (NPUE), biomass‐per‐unit‐effort (BPUE) and size structure data on Eurasian perch (Perca fluviatilis) stocks in 11 small boreal lakes in summer. Second, the same lakes were ice‐fished by voluntary anglers using a pre‐defined, loosely standardised protocol to obtain angling‐based NPUE, BPUE, and length frequency distributions. Effects of environmental variables such as water oxygen concentration and light penetration on angling catch rates were controlled statistically. Neither perch Nordic gillnet NPUE nor BPUE corresponded to ice‐fishing CPUEs. However, the length distribution of the catch did not differ between methods. Our results imply that traditional ice fishing applying natural baits is relatively unselective for fish size and could produce valid length‐based indicators for management purposes while angling CPUE was poorly related to Nordic gillnet CPUE.

Assessment of Four Major Fish Species Stocks in the Lithuanian and Russian Parts of Curonian Lagoon (SE Baltic Sea) Using CMSY Method

Fisheries in the Curonian Lagoon (1584 km2 coastal lagoon in South-East Baltic) can be classified as artisanal, small-scale, multi-species, and multi-gear. Such types of fisheries are characterised as data-poor and require appropriate investigation methods. We used CMSY (version CMSY_2019_9f. R) to assess maximum sustainable yield (MSY) and related indicators for freshwater bream, roach, pike-perch, and European perch. A decline in pike-perch and roach was identified, while the stocks of freshwater bream and European perch were sustained. As the CMSY model does not consider the impact of environmental factors, the decline in roach stock may be attributed to the increase in salinity rather than to overfishing. In the case of freshwater bream and pike-perch, the method cannot consider the increase of the percentage of small-sized fishes in catches due to the allowance of low-selectivity gears in the fishery. Additionally, in the case of the pike-perch, the model does not take into account the interannual fluctuations in the stock-recruitment system. The assessment of the European perch stock can be considered to be good. However, the accuracy of CMSY is limited, and it should be used for fisheries management only in combination with other methods.

Assessment of behavioural and physiological traits as indicators of suitability for European perch aquaculture

Domestication and selective breeding can mitigate current bottlenecks in European perch aquaculture. Monitoring the condition and stress tolerance of European perch stocks from different recirculating aquaculture systems is of general interest to set the baseline values of promising candidates for further breeding processes. We recorded morphometric, behavioural (critical swimming speed, activity, aggressiveness, propensity to approach a novel object), and physiological parameters (plasma cortisol, glucose, ion concentrations, enzyme activity levels) after stress induction across four European perch stocks obtained from different aquaculture facilities in France (I and II), Denmark, and Hungary. The European perch stock from Denmark revealed the population with the most pronounced activity pattern. This was reflected by the highest relative swimming speed and a high percentage of bold-exploratory behaviour, which coincides with increased aggressive interactions within this stock. Additionally, we detected a higher tolerance to adverse environmental challenges in the perch stock from Denmark compared with the stocks from France and Hungary. The observed characteristics suggest that the stock from Denmark has a higher potential in the future framework of selective-breeding assessment. Further in-depth research is required to elucidate which traits and genetic as well as epigenetic components accelerate the domestication processes of European perch aquaculture and promote selective breeding processes.

How knowledge acquisition shapes system understanding in small-scale fisheries

Within socio-ecological systems, actors’ interaction with the system may differ greatly, which is likely to result in differences in system understanding. The current work investigated this assumption in the Nile perch fishery at Lake Victoria. Specifically, a survey on Nile perch stock level and the drivers behind stock fluctuations was conducted with 225 participants with formally versus informally acquired knowledge across Kenya, Tanzania, and Uganda. Whereas most participants agreed that the stock has declined, several differences in system understanding were found between types of knowledge acquisition. Specifically, participants with informally acquired knowledge focused on examples of fewer drivers related to tangible human activities (e.g., the use of illegal fishing gear), whilst participants with formally acquired knowledge used more abstract and a larger variety of drivers related to the presence of humans (e.g., overpopulation). These findings confirm that the type of knowledge acquisition affects system understanding in small-scale fisheries and highlights the importance of assessing system understanding of various actors for successful resource management.

Cormorant (Phalacrocorax carbo) predation on a coastal perch (Perca fluviatilis) population: estimated effects based on PIT tag mark-recapture experiment

Abstract The number of cormorants has rapidly increased in the northernmost Baltic Sea. In 2018, 50 km × 50 km ICES catch rectangle 55H1 had 3140 breeding pairs. To estimate the predation effect of cormorants on perch populations, we Passive Integrated Tags tagged 1977 perch and 9.9% of tags were found. The median instantaneous cormorant-induced mortality during the breeding time, with consumption by non-breeding individuals, was estimated at 0.23 and at 0.35 during the whole residing period. We estimated with a yeild-per-recruit model that the long-term maximum loss of perch yield of tagged sub-population would be at 80% probability interval 32–67%, and when extended to the entire 55H1, 10–33%, respectively. The cormorants’ share of the >2-year-old perch biomass and production would be 8%, while that of other natural mortality would be 63% and that of fishing 29% in 55H1. The yield-per-recruit-results should be interpreted as an estimate of maximum cormorant effect because the dependence of predation rate on prey density was not accounted for, and density-dependence of growth, mortality, and reproduction of perch could partly compensate the loss. The results indicate that high density of cormorants can reduce the perch stocks and catches locally.

Genetic characterization of selected populations of European perch, Perca fluviatilis (Actinopterygii: Perciformes: Percidae), in the waters of north-western Poland with recommendations for fishing and stocking policies

Background. European perch, Perca fluviatilis Linnaeus, 1758, is a predatory freshwater fish present also in the coastal waters of the Baltic Sea. The available catch data indicate that the population profile of this species is disrupted, and the condition of the population is not stable. The aim of this study was to determine the diversity and genetic structure of and assess phylogenetic links and gene flow between selected perch populations originating from various types of reservoirs in northern Poland. Materials and methods. A total of 392 perch were collected from selected bodies of water in north-western Poland and the fin samples were preserved in 96% ethanol or stored for short periods at –20°C. Genomic DNA was isolated, while for further mitochondrial DNA analysis, a 1081-bp fragment of the control region was amplified. Amplification products were sequenced and subjected to restriction analysis (PCR-RFLP) in order to determine the genetic diversity of the control region of mtDNA. The obtained sequences were analyzed using bioinformatics tools, and phylogenetic trees were generated to determine the degree of diversity between individuals in selected perch stocks. Results. Seven haplotypes were identified. Ten polymorphic sites were defined, and the degree of genetic diversity between selected haplotypes was determined. Based on the distribution of perch haplotypes, stocks from Pomeranian Bay (haplotypes F, D), the Szczecin Lagoon (haplotypes D, F, H), and the more homogeneous stocks from Pomeranian Bay (haplotypes F, D) and the Kamieński Lagoon (D, F) can be distinguished. Analysis of phylogenetic relations allowed identifying stocks with the most conserved genome, similar to the standard perch genome, and stocks that have become more genetically distant, probably due to the diversity of the inhabited ecosystems or natural hybridization observed in this species. Conclusion. European perch inhabiting waters of north-western Poland is a species with high plasticity, without isolated stocks or populations that can be clearly distinguished on a genetic basis. It does, however, have a tendency for mitochondrial genomic modifications, which is likely due to the broad spectrum of ecosystems inhabited by the species. Due to the homogeneity of the perch populations from the Szczecin Lagoon, the Kamieński Lagoon, and Lake Myśliborskie, they should be used for the restoration of populations in water bodies in which their genetic structure is severely disrupted. For the same reason, the policy of perch catches should be modified. The authors suggest increasing the protected size to 20 cm and limiting the catches of the species as by-catch by modifying fishing tools, including the introduction of a seasonal prohibition of tools that might eliminate individuals of 15–16 cm in length from natural waters in their spawning period.

Зміни основних біологічних показників та живлення окуня звичайного (Perca fluviatilis linnaeus, 1758) в умовах спеціального товарного рибного господарства

Зміни основних біологічних показників та живлення окуня звичайного (Perca fluviatilis linnaeus, 1758) в умовах спеціального товарного рибного господарства

Yellow perch genetic structure and habitat use among connected habitats in eastern Lake Michigan.

Maintenance of genetic and phenotypic diversity is widely recognized as an important conservation priority, yet managers often lack basic information about spatial patterns of population structure and its relationship with habitat heterogeneity and species movement within it. To address this knowledge gap, we focused on the economically and ecologically prominent yellow perch (Perca flavescens). In the Lake Michigan basin, yellow perch reside in nearshore Lake Michigan, including drowned river mouths (DRMs)—protected, lake‐like habitats that link tributaries to Lake Michigan. The goal of this study was to examine the extent that population structure is associated with Great Lakes connected habitats (i.e., DRMs) in a mobile fish species using yellow perch as a model. Specifically, we tested whether DRMs and eastern Lake Michigan constitute distinct genetic stocks of yellow perch, and if so, whether those stocks migrate between the two connected habitats throughout the year. To do so, we genotyped yellow perch at 14 microsatellite loci collected from 10 DRMs in both deep and littoral habitats during spring, summer, and autumn and two nearshore sites in Lake Michigan (spring and autumn) during 2015–2016 and supplemented our sampling with fish collected in 2013. We found that yellow perch from littoral‐DRM habitats were genetically distinct from fish captured in nearshore Lake Michigan. Our data also suggested that Lake Michigan yellow perch likely use deep‐DRM habitats during autumn. Further, we found genetic structuring among DRMs. These patterns support hypotheses of fishery managers that yellow perch seasonally migrate to and from Lake Michigan, yet, interestingly, these fish do not appear to interbreed with littoral fish despite occupying the same DRM. We recommend that fisheries managers account for this complex population structure and movement when setting fishing regulations and assessing the effects of harvest in Lake Michigan.

Maximum salinity tolerance and osmoregulatory capabilities of European perch Perca fluviatilis populations originating from different salinity habitats.

Although considered a stenohaline freshwater species, European perch (Perca fluviatilis) inhabit brackish waters. The present study determined the maximum salinity tolerance and osmoregulatory capability on individuals originating from brackish water and from freshwater populations. The fish were acclimated for 3 weeks to salinities of 0, 10, 12.5, 15, 17.5 and 20 after an initial stepwise increase to the target salinity. The maximum salinity tolerance was determined as the test salinity below which the fish could not acclimate and lost equilibrium. Blood plasma osmolality was measured if the fish had not lost equilibrium after the acclimation period. The maximum salinity tolerance was 17.5 for brackish water European perch and 10 for fresh water European perch. The high salinity tolerance of the brackish water European perch was caused by their ability to both hyper- and hypo-osmoregulate, whereas the freshwater originating fish could only hyper-osmoregulate. The results showed that maximum salinity tolerances and osmoregulatory capabilities depends on the origin habitat salinity. Due to genetic differentiation between European perch populations in brackish and fresh water, the possibility of brackish water European perch being a subspecies of European perch is discussed, yet vital knowledge concerning heritability of salinity tolerance traits is still missing. Regardless of species status, within-species plasticity in the ability to cope with varying salinities have substantial ecological and conservation implications and underlines the need for managing brackish water and freshwater European perch stocks separately.

Growth, mortality and recruitment of Nile perch (Lates niloticus) in Lake Victoria, Kenya

AbstractThis study investigated the growth, mortality and recruitment of Lates niloticus in Lake Victoria basis on length–frequency data collected during the period 2014‐2015. The asymptotic length (L∞) had a value of 124 cm TL, growth curvature (K) of 0.22 year−1, total mortality (Z) of 0.96 year−1, a natural mortality (M) of 0.42 year−1, a fishing mortality (F) of 0.54 year−1, an exploitation rate (E) of 0.57 and a growth performance index () of 3.53. Logistic selection model showed that 50% of fish of 46.09 cm TL encountering the gear are retained. There were two peak recruitment periods, a minor one in March and a major one in July, accounting for 12.04% and 22.04%, respectively, of the total fish catch. The Beverton and Holt's relative yield‐per‐recruit model indicated the indices for sustainable yields are 0.32 for optimum sustainable yield (E0.5), 0.60 for maximum sustainable yield (Emax) and 0.51 for economic yield (E0.1). Compared to previous findings, there is a great decline in the sizes of Nile perch stocks in Lake Victoria. Thus, managing the fishery requires strict adherence to the slot size of 50–85 cm TL, and restrictions on illegal gear and methods, by the devolved governments through monitoring, control and surveillance in liaison with the Beach Management Units (BMUs).

Sex-based trade-offs among growth, mortality, and maturation in Great Lakes yellow perch stocks

Trade-offs among growth, mortality, and reproduction form the basis of life history theory but may vary among populations owing to local ecological conditions. We examined life history trade-offs driving variation in maturation among 13 yellow perch (Perca flavescens) stocks in the Great Lakes using sex-specific age and length at 50% maturity (A50 and L50, respectively) and probabilistic maturation reaction norm midpoints (Lp50,a). Both sexes exhibited positive correlations between growth and mortality, and faster-growing stocks were mature at younger ages but larger sizes. Male and female A50 and L50 were positively correlated among stocks, but Lp50,a estimates were negatively correlated among stocks, indicating stocks that matured at large sizes for a given age in females matured at smaller age-specific sizes in males. Female Lp50,a estimates were negatively related to growth and mortality, while male Lp50,a estimates were positively related to growth. These results suggest that (i) sex-based life history trade-offs sometimes act to differentially structure maturation schedules in males and females and (ii) males may be less responsive to changes in mortality than females.

Ecosystem change and decadal variation in stock–recruitment relationships of Lake Erie yellow perch (Perca flavescens)

Abstract Fish stock–recruitment relationships (SRRs) may vary in response to ecosystem change, increasing uncertainty for fisheries management. We defined three periods between 1975 and 2015 over which Lake Erie, a Laurentian Great Lake, underwent significant ecosystem changes: before zebra mussel (Dreissena polymorpha) establishment, after zebra mussel establishment and before re-eutrophication, and after re-eutrophication. To examine the extent to which SRRs of Lake Erie yellow perch (Perca flavescens) also varied over these periods, we compared the performance of Baseline (constant recruitment), Ricker (constant SRR), Periodic Ricker (different SRRs among three periods) and Random-walk Ricker (annually varying SRRs) models fitted to data for yellow perch stocks corresponding to three lake basins. Periodic and Random-walk Ricker models performed better for stocks in the western and eastern basins, but the Baseline model performed best in the central basin. Annual variation in the SRRs coincided with the timing of zebra mussel establishment and re-eutrophication in the shallower western basin, but not in the deeper eastern basin, where quagga mussels (Dreissena bugensis) established later and conditions are less eutrophic. These results underscore that temporally and spatially varying SRRs associated with ecosystem change should be taken into account in models of fish population dynamics.

Genetic discrimination of brackish and freshwater populations of Eurasian perch (Perca fluviatilis L.) in the Baltic Sea drainage: implications for fish forensics

Over recent years a growing number of studies suggest that both unregulated and illegal fishing can lead to the unsustainable exploitation of populations or species. For developing biologically sound management and conservation actions and to effectively fight against the illegal fish trade, it is crucial to understand the spatial and temporal patterns of genetic diversity of commercially important fish species. In this study we characterized for the first time the population structure of Eurasian perch at both freshwater (Lake Peipus) and Baltic Sea locations, representing important targets of commercial perch fisheries in Estonia. We also evaluated the effectiveness of individual and group-based assignment tests to identify the genetic origin of fish at different geographic scales. Results of our study showed low genetic divergence among sample sites, which resulted in a low self-assignment accuracy of individual fish to their sampling locations (mean 36.7%). However, the assignment accuracy at the regional level was considerably higher (Baltic Sea: 84.9%; Lake Peipus 88.0%). When assuming an unmixed origin of the group of individuals, it was possible to identify the brackish and freshwater origin of perch with very high confidence (log10 LR>3) if the sample size exceeded 15-20 individuals. Our study demonstrates the power of highly variable genetic markers to distinguish between the two commercially most important Eurasian perch stocks in Estonia and the usefulness of assignment tests to successfully identify the genetic origin of fish. We expect that the developed microsatellite-based reference database together with the described analytical framework provides an important tool to more efficiently combat against illegal fishing and fish trade.

Genetic characterization and relatedness of wild and farmed Eurasian perch (Perca fluviatilis): Possible implications for aquaculture practices

Aquaculture of the Eurasian perch, Perca fluviatilis, in recirculating systems has emerged over the past decades to become a significant way of diversification for inland areas in Europe. The development of such a production relies partly on the improvement of growth performance (i.e., reducing production costs), which requires suitable genetic management of broodstocks and the development of selective breeding programs. In this context, the present study was undertaken assessing for the first time the genetic diversity of farmed stocks of perch. Twelve microsatellite loci were used to investigate the genetic diversity of nine farmed stocks (547 individuals) from two perch farms located in France and their supposedly wild founder population from Lake Geneva (394 individuals). First, the wild population displayed the lowest genetic diversity and differed genetically from all farmed populations except one, XB2. Second, genetic diversity did not decrease between farmed breeders and their potential offspring. However, in the three groups of broodstock-offspring the number of alleles decreased by 10%, 21%, and 15%, respectively. In addition, effective population size decreased in all offspring groups. A family structuring was also observed among broodstocks and their offspring, with an unequal family contribution being suspected. In the absence of parental information, these results attest to the utility of genetic tools to evaluate genetic diversity and the necessity of a monitoring program to maintain genetic variability among farmed perch. Genetic variability among farmed stocks appears to be sufficient for perch production to be sustainable and selective breeding programs to be developed.

Rapidly shifting maturation schedules following reduced commercial harvest in a freshwater fish.

Size-selective harvest of fish stocks can lead to maturation at smaller sizes and younger ages, which may depress stock productivity and recovery. Such changes in maturation may be very slow to reverse, even following complete fisheries closures. We evaluated temporal trends in maturation of five Great Lakes stocks of yellow perch (Perca flavescens Mitchill) using indices that attempt to disentangle plastic and evolutionary changes in maturation: age at 50% maturity and probabilistic maturation reaction norms (PMRNs). Four populations were fished commercially throughout the time series, while the Lake Michigan fishery was closed following a stock collapse. We documented rapid increases in PMRNs of the Lake Michigan stock coincident with the commercial fishery closure. Saginaw Bay and Lake Huron PMRNs also increased following reduced harvest, while Lake Erie populations were continuously fished and showed little change. The rapid response of maturation may have been enhanced by the short generation time of yellow perch and potential gene flow between northern and southern Lake Michigan, in addition to potential reverse adaptation following the fishing moratorium. These results suggest that some fish stocks may retain the ability to recover from fisheries-induced life history shifts following fishing moratoria.