ORIGINAL ARTICLE: Sizeselective fishing gear and life history evolution in the Northeast Arctic cod

Exploitation of living resources can lead to evolutionary changes in harvested populations of plants (Law and Salick 2005) and mammals (Coltman et al. 2003), but because of the grand scale of commercial fishing most examples come from fish. The reviews by e.g. Jørgensen et al. (2007), Kuparinen and Merilä (2007), Fenberg and Roy (2008), Hutchings and Fraser (2008), and Sharpe and Hendry (2009) list phenotypic evidence of morphology and life history traits that changed over time in wild populations. Because these changes cannot be totally explained by environmental factors, part of the change is thought to represent contemporary evolution. The rates of change are furthermore rapid, and in general comparable to those observed in breeding programs (Reznick and Ghalambor 2001; Jørgensen et al. 2007). In a comparative study of anthropogenic causes for contemporary evolution, harvesting was found to result in quicker evolutionary change than other human influences (Darimont et al. 2009). Heritable changes in a number of behavioral and life history traits have also been observed in populations harvested experimentally (Conover and Munch 2002; Walsh et al. 2006; Biro and Post 2008). The problem of fishing-induced evolution requires attention because it might be widespread, as most commercially harvested fish stocks experience intense exploitation rates, with fishing mortality being up to four times higher than the natural mortality (Mertz and Myers 1998). In general, theoretical models predict less of an evolutionary response to harvesting if fishing mortality is lower (Law and Grey 1989; Ernande et al. 2004; Brown et al. 2008). This prediction is supported also by fisheries data, for example in Pink salmon where phenotypic change that could not be explained by environment was slower in regions with lower fishing mortality or less selective gear [Ricker 1981; see also the meta-analysis by Sharpe and Hendry (2009)].