The potential evolutionary impacts of size selective fishing have recently become focus of a lot of research and controversy (see e.g. Science-debate here). The heart of the controversy appears to be in some critical assumptions central to any evolutionary inference which are particularly hard to verify in the case of wild fish stocks. Namely, in order to talk about evolution, one has to assume (in fact: demonstrate) that observed phenotypic changes are genetically based, rather than environmentally induced (see here why). This is not easy.
If estimating genetic parameters in wild fish populations is difficult, estimation of the other critical parameter central to any evolutionary inference – intensity of selection – should be more straightforward. Yet, little attention has been so far paid on estimating actual selection intensities imposed by different fishing practices.
In an interesting meta-analysis of 73 commercially fished stocks, Hilborn and Minte-Vera compared the intensity of fisheries selection and growth-rates to see if there were any signs that would be consistent with the expectation that size selective harvesting would have reduced growth rates in these fish stocks. They also reviewed the size-selectivity patterns in number of fisheries compared them to those used in laboratory experiments of fisheries induced selection.
The study recovered little evidence for any reduction in growth rates associated with fisheries induced selection. Their results also suggest that the selection intensities on growth rate in the commercial fisheries are actually much less than used in laboratory experiments. On the basis of their simulations, they suggest that given the intensity of selection and size-selectivity patterns in most current fisheries, little evolutionary impacts would be expected.
Is this the last word in this debate? I do not think so – watch and see.
Hilborn R & CV Minte-Vera (2008) Fisheries-induced changes in growth rates in marine fisheries: are they significant? Bulletin of Marine Science 83:95-106.