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New Study Finds Fishing Erodes Natural Size Variation

06 October 2016

FINLAND - Fishing typically removes the large individuals from the population, this leads to evolutionary shrinking of fish but also erodes natural trait variability in fish stocks.

This was demonstrated in a study where researchers experimentally harvested zebrafish. The loss of natural variability is an alarming observation, as variability facilitates population viability in changing environments.

Intensive and selective removal of large individuals by fishers can act as directional selection force, leading to evolution towards smaller body sizes. Fishing can also reduce size and growth variation among individuals.

Preserving variability is important as a population harbouring variation is less susceptible to changing environments and catastrophic disturbances.

The study, conducted by an international team of researchers, focused on the effect of size-selective harvesting on body size variation.

Zebra fish populations were harvested size-selectively for five generations after which the harvesting was halted for six generations. The researchers found consistent differences in body size variation among differentially harvested zebrafish populations.

“Harvesting large fish led to lower size variation compared to a harvesting strategy where the largest fish were protected,” says Postdoctoral Researcher Silva Uusi-Heikkilä from the University of Turku.

Decreased size variation caused by fishing can have serious consequences for the resilience and recovery of exploited fish stocks. It can negatively affect the population’s ability to buffer environmental changes, decrease the rate of evolutionary rebound and, ultimately slow down recovery from overfishing.

“Sustainable fisheries management should not only manage fish stock abundances but also variability within a stock,” says Uusi-Heikkilä.

The study was conducted in collaboration with the University of Turku (UTU), the University of Helsinki (HY), Åbo Akademi (ÅA) and Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB).

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