Stock-catch analysis of carp recreational fisheries in Czech reservoirs: Insights into fish survival, and impact of extreme events

In culture-based fisheries, managers strive for high stocking efficiency, the ratio between the total weight of caught and stocked fish. Here we present a new time series approach to examine the dependence of reported anglers. catches on stocking and external events, using data on carp ('Cyprinus carpio' L.) from 14 reservoirs in the Czech Republic. Average stocking efficiency varied between 0.25 and 2.2, with values close to unity in most reservoirs. The lowest efficiencies occurred in three reservoirs receiving cold hypoxic water from a large upstream reservoir, while the highest efficiencis were found in two shallow, highly productive reservoirs. Analyses further indicate that stocked carp are typically caught during the year of release or the year after; but also that the mean time lag- between stocking and capture increases with reservoir area. External events can be important: major floods in the years 2002 and 2006 were in many cases followed by large, up to 10-fold, increases in catches in subsequent years; we attribute the surplus catch to carp washed down from upstream aquaculture and river stretches. In contrast, the "Velvet REvolution" (demise of the communist regime in 1989) had no discernible effect on catches in subsequent years. In conclusion, the proposed method can simultaneously estimate the likely mean survival time of stocked carp and identify the impact of major environmental and societal events on recreational fisheries. The approach thus sheds light on the performance of current stocking practices at individual reservoirs, and could be used to monitor and improve stocking strategies and management of culture-based recreational fisheries

An evolutionary explanation of female‐biased sexual size dimorphism in North Sea plaice, Pleuronectes platessa L.

Sexual size dimorphism (SSD) is caused by differences in selection pressures and life-history trade-offs faced by males and females. Proximate causes of SSD may involve sex-specific mortality, energy acquisition, and energy expenditure for maintenance, reproductive tissues, and reproductive behavior. Using a quantitative, individual-based, eco-genetic model parameterized for North Sea plaice, we explore the importance of these mechanisms for female-biased SSD, under which males are smaller and reach sexual maturity earlier than females (common among fish, but also arising in arthropods and mammals). We consider two mechanisms potentially serving as ultimate causes: (a) Male investments in male reproductive behavior might evolve to detract energy resources that would otherwise be available for somatic growth, and (b) diminishing returns on male reproductive investments might evolve to reduce energy acquisition. In general, both of these can bring about smaller male body sizes. We report the following findings. First, higher investments in male reproductive behavior alone cannot explain the North Sea plaice SSD. This is because such higher reproductive investments require increased energy acquisition, which would cause a delay in maturation, leading to male-biased SSD contrary to observations. When accounting for the observed differential (lower) male mortality, maturation is postponed even further, leading to even larger males. Second, diminishing returns on male reproductive investments alone can qualitatively account for the North Sea plaice SSD, even though the quantitative match is imperfect. Third, both mechanisms can be reconciled with, and thus provide a mechanistic basis for, the previously advanced Ghiselin-Reiss hypothesis, according to which smaller males will evolve if their reproductive success is dominated by scramble competition for fertilizing females, as males would consequently invest more in reproduction than growth, potentially implying lower survival rates, and thus relaxing male-male competition. Fourth, a good quantitative fit with the North Sea plaice SSD is achieved by combining both mechanisms while accounting for sex-specific costs males incur during their spawning season. Fifth, evolution caused by fishing is likely to have modified the North Sea plaice SSD

Fishing-induced evolution of growth: Concepts, mechanisms and the empirical evidence

The interest in fishing-induced life-history evolution has been growing in the last decade, in part because of the increasing number of studies suggesting evolutionary changes in life-history traits, and the potential ecological and economic consequences these changes may have. Among the traits that could evolve in response to fishing, growth has lately received attention. However, critical reading of the literature on growth evolution in fish reveals conceptual confusion about the nature of growth itself as an evolving trait, and about the different ways fishing can affect growth and size-at-age of fish, both on ecological and on evolutionary time-scales. It is important to separate the advantages of being big and the costs of growing to a large size, particularly when studying life-history evolution. In this review, we explore the selection pressures on growth and the resultant evolution of growth from a mechanistic viewpoint. We define important concepts and outline the processes that must be accounted for before observed phenotypic changes can be ascribed to growth evolution. When listing traits that could be traded-off with growth rate, we group the mechanisms into those affecting resource acquisition and those governing resource allocation. We summarize potential effects of fishing on traits related to growth and discuss methods for detecting evolution of growth. We also challenge the prevailing expectation that fishing-induced evolution should always lead to slower growth

2007 Report of the ICES Study Group on Fisheries-Induced Adaptive Change (SGFIAC)

There is a growing body of scientific evidence indicating that fisheries can cause evolutionary responses over time periods as short as 1020 years, in particular in traits such as the onset of maturation. As these changes will most likely result in a reduction of the productivity of a fish stock, management objectives and (precautionary) reference points for sustainable exploitation need to be re-defined, and new objectives and reference points for managing fisheries-induced evolution need to be developed. Current knowledge allows for two generalisations. First, reducing harvest rates will almost always slow the rate and extent of fisheries-induced evolution in most life-history traits. Second, raising a stock's minimum size limit for exploitation well above the size range over which maturation occurs will slow down the rate of evolution in its maturation schedule. To go beyond these generic insights, "Evolutionary Impact Assessments" (EvoIAs) are proposed to quantify the effects of management measures, through the evolutionary response of specific stocks, on the utility functions defined by managers. The Study Group on Fisheries Induced Adaptive Change [SGFIAC] proposes to further develop this framework in dialogue with fisheries scientists and managers, with the aim of integrating the effects of fisheries-induced evolution into fisheries management advice. Developing EvoIAs in the context of suitable case studies is considered to be the most efficient way for making progress

Interactions entre espèces dans le contexte des changements climatiques : liens entre les effets cinétiques de la température sur les individus et la dynamique des communautés

International audienceHuman-induced climate change, dominated by warming trends, poses a major threat to global biodiversity and ecosystem functioning. Species interactions relay the direct and indirect effects of climate warming on individuals to communities, and detailed understanding across these levels is crucial to predict ecological consequences of climate change. We provide a conceptual framework that links temperature effects on insect physiology and behaviour to altered species interactions and community dynamics. We highlight key features of this framework with recent studies investigating the impacts of warming climate on insects and other ectotherms and identify methodological, taxonomic and geographic biases. While the effects of increased constant temperatures are now well understood, future studies should focus on temperature variation, interactions with other stressors and cross-system comparisons

Stock-catch analysis of carp recreational fisheries in Czech reservoirs: Insights into fish survival, water body productivity and impact of extreme events

In culture-based fisheries, managers strive for high stocking efficiency, the ratio between the total weight of caught and stocked fish. Here we present a new time series approach to examine the dependence of reported anglers' catches on stocking and external events, using data on carp (Cyprinus carpio L.) from 14 reservoirs in the Czech Republic. Average stocking efficiency varied between 0.25 and 2.2, with values close to unity in most reservoirs. The lowest efficiencies occurred in three reservoirs receiving cold hypoxic water from a large upstream reservoir, while the highest efficiencies were found in two shallow, highly productive reservoirs. Analyses further indicate that stocked carp are typically caught during the year of release or the year after; but also that the mean time lag between stocking and capture increases with reservoir area. External events can be important: major floods in the years 2002 and 2006 were in many cases followed by large, up to 10-fold, increases in catches in subsequent years; we attribute the surplus catch to carp washed down from upstream aquaculture and river stretches. In contrast, the "Velvet Revolution" (demise of the communist regime in 1989) had no discernible effect on catches in likely mean survival time of stocked carp and identify the impact of major environmental and societal events on recreational fisheries. The approach thus sheds light on the performance of current stocking practices at individual reservoirs, and could be used to monitor and improve stocking strategies and management of culture-based recreational fisheries

Temperature and prey density jointly influence trophic and non-trophic interactions in multiple predator communities

International audienceEnvironmental changes such as global warming can affect ecological communities by altering individual life histories and species interactions. Recent studies focusing on the consequences of environmental change on species interactions highlighted the need for a wider, multi-species context including both trophic and non-trophic interactions (e.g. predator interference). However, the effects of biotic and abiotic factors on trophic and non-trophic interactions remain largely unexplored. To fill this gap, we combined laboratory experiments and functional response modelling to investigate how temperature and prey density influence trophic and non-trophic interactions in multiple predator communities. The system under study consisted of predatory dragonfly larvae (Aeshna cyanea) and omnivorous marbled crayfish (Procambarus virginalis) preying on common carp fry (Cyprinus carpio). We estimated the functional response of each predator in single-predator experiments and used this information to disentangle the trophic and non-trophic interactions and their dependence on environmental conditions in multiple predator trials. We found that consumer identity, prey density, and temperature all affect the magnitude of trophic and non-trophic interactions. Non-trophic interactions mostly decreased predator feeding rates, corroborating previous observations that interference prevails in aquatic communities. Moreover, trophic interactions depended primarily on the environmental variables whereas non-trophic interactions depended mainly on consumer identity. Our results indicate that non-trophic interactions among true predators and omnivores can be substantial and that biotic and abiotic conditions further modify the magnitude and direction of these interactions, which can affect food web dynamics and stability