An experimental study with size-selectively harvested zebrafish that began in 2006 at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries in Berlin, Germany reveals that size-selective harvesting causes changes in key life-history traits, leading to low maximum body size and poor reproductive output.
In her groundbreaking experiment published in Evolutionary Applications, Postdoctoral Researcher Silva Uusi-Heikkilä from the University of Turku mimicked the size-selectivity typical to many fisheries by systematically removing large fish from the experimental fish populations.
After just five generations of harvesting, adult body size shrunk by 7%, which also affected the egg production of the surviving fish. The now-smaller individuals produced fewer and smaller eggs and offspring compared to the large fish that were harvested using a mortality schedule mimicking a maximum-length, rather than a minimum-length, limit regulation. In most fisheries, minimum-length limits are the standard tool, but these standard tools appear to be the most damaging from a Darwinian perspective.
Most significantly, intensive size-selective harvesting also induced genetic changes in the experimentally exploited fish populations.
Small and Shy Fish Are Harder to Capture
Size-selective harvesting also induced changes in fish behaviour. The researchers found that the now- smaller fish were more cautious and less explorative.
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