Scientists from Australia and Canada have found that fishing constitutes a human-driven evolutionary pressure that selects against fast-growing, bold fishes.
The study by Peter Biro and John Post, which was published in a recent issue of the Proceedings of the National Academy of Sciences, examined the possibility that faster-growing fishes may be more vulnerable to fishing because of greater appetite and correspondingly greater feeding-related activity rates and boldness that could increase encounters with fishing gear and vulnerability to it.
The authors artificially stocked two lakes in British Columbia with rainbow trout (Oncorhynchus mykiss), and then proceeded to simulate an intensive commercial gillnet fishery on the lake by using established experimental gillnet protocols (consisting of two sinking gillnet gangs set out per lake).
The authors found that that fast-growing fish genotypes were caught at three times the rate of the slow-growing genotypes in the two lakes, with about half of fast-growing individuals caught compared with one third of slow-growing individuals overall.
The authors attribute the higher harvest of the fast-growing individuals to their more active and bolder behaviour, which renders them more vulnerable to capture; as a result, they speculate that the evolution of slower-growing, shyer fish may be an attribute of all commercially harvested fish populations (given that growth rate and behavioural attributes are heritable traits in fishes).
Given that the results observed by the authors were independent of body size, they conclude that ...commonly used minimum size-limits will not prevent overexploitation of fast-growing genotypes and individuals because of size independent growth-rate selection by fishing.
For more information, see the paper: Biro, PA and JR Post (2008) Rapid depletion of genotypes with fast growth and bold personality traits from harvested fish populations. Proceedings of the National Academy of Sciences 105, pp. 2919"2922.