Size Decline Of Exploited Fish Populations : Microevolution Or Phenotypic Plasticity?

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Size decline in exploited fish populations: microevolution or phenotypic plasticity? Exploitation of fish stocks tends to be size-selective. The largest individuals are preferentially removed, leading to a decrease in size at maturation and other life history traits within exploited fish stocks. Declining size could represent a genetic change within the population, and so microevolution, or simply a change in the characteristics expressed, a phenotypically plastic response. This debate has remained controversial due to an inability to disentangle the two effects. After reviewing previous literature examining these life history trends, microevolution and phenotypic plasticity do not seem to operate as mutually exclusive mechanisms but…show more content…
Currently, controversy exists over the response controlling this size trend; microevolution or phenotypic plasticity. Microevolution is a genetic change within a species in which size selective harvesting creates an artificial selection pressure. Individuals maturing at a smaller size have more opportunity to reproduce before capture, conveying a higher fitness under exploited conditions7. Phenotypic plasticity states instead that an individual’s genes can produce different phenotypes, observable characteristics, across an environmental gradient8 with no genetic change. Fishing mortality simply reduces population density: individuals can access more food and thus mature at a smaller size9. Unlike microevolution, plasticity is unviable as a long term resolution10. However, the selection pressure of size-selective fishing may cause the loss of the genetic variation required for species to recover and adapt to future scenarios6. As the effects of both responses are challenging to disentangle11, the debate on which is occurring remains controversial. Few studies have conclusively demonstrated a genetic cause12. Methodologies claiming to isolate evolutionary trends support microevolution though plasticity effects have yet to be fully eliminated, while rapid recovery of size when exploitation ceases suggests a plastic response. With fishery yield heavily impacted by life history traits, and size-selective harvesting mandated by minimum
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