Abstract
Over the recent years, growing number of studies suggests that intensive size‐selective fishing can cause evolutionary changes in life‐history traits in the harvested population, which can have drastic negative effects on populations, ecosystems and fisheries. However, most studies to date have overlooked the potential role of immigration of fish with different phenotypes as an alternative plausible mechanism behind observed phenotypic trends. Here, we investigated the evolutionary consequences of intensive fishing simultaneously at phenotypic and molecular level in Eurasian perch (Perca fluviatilis L.) population in the Baltic Sea over a 24‐year period. We detected marked changes in size‐ and age‐distributions and increase in juvenile growth rate. We also observed reduction of age at sexual maturity in males that has frequently been considered to support the hypothesis of fisheries‐induced evolution. However, combined individual‐based life‐history and genetic analyses indicated increased immigration of foreign individuals with different life‐history patterns as an alternative mechanism behind the observed phenotypic change. This study demonstrates the value of combining genetic and phenotypic analyses and suggests that replacement or breakdown of locally adapted gene complexes may play important role in impeding the recovery of fish populations.
Highlights
Fishing causes substantial mortality in commercially exploited fish stocks, often exceeding the level of natural mortality (Stokes and Law 2000; Jørgensen et al 2007; Law 2007)
Based on combined individual-based life-history and genetic analysis, the findings of this study provide empirical evidence that temporal phenotypic trends can arise from increased immigration of foreign individuals with different life-history patterns
The results of the present study are in accord with recent findings in Atlantic cod, demonstrating that fishing can differentially target genetically and phenotypically distinct components of a population, leading to phenotypic changes associated with a change in the population composition (Arnason et al 2009; Jakobsdottir et al 2011)
Summary
Fishing causes substantial mortality in commercially exploited fish stocks, often exceeding the level of natural mortality (Stokes and Law 2000; Jørgensen et al 2007; Law 2007). Despite various management strategies aimed at reducing fishing pressure, only few populations show signs of recovery in abundance (Stockwell et al 2003; Hutchings and Reynolds 2004). This suggests that exploitation, and subsequent population recovery, is not simple processes decreasing or increasing biomass, but several environmental, ecological and genetic mechanisms can be involved, such as habitat alterations, shifts in species interactions and changes in population genetic composition as well as the evolution of life-history traits (Hutchings 2005; Enberg et al 2009; Swain 2011; Kuparinen and Hutchings 2012). Little remains known about the genetic consequences of harvesting, partly because temporal investigations that simultaneously evaluate phenotypic and molecular changes are very scarce (Arnason et al 2009; Jakobsdottir et al 2011)
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