Jan Dierking

Fisheries-induced evolution refers to genetic changes in fish populations that are induced by the exploitation of fish stocks. Any harvesting of natural populations, including fishing, selects for certain traits in a population (Jorgensen et al. 2007). Size-selectivity of fisheries in particular, leads to a situation where fish that start to reproduce early (i.e., at low size or age) are more likely to have offspring than fish that reproduce late. In addition, though not falling directly under the term fisheries-induced evolution, fishing imposed declines in population size can lead to declines in genetic diversity. Such harvesting-induced changes in mean population traits are inevitable when the traits selected for have a heritable basis, as is almost invariably the case in life-history parameters. It is thus not surprising that more and more case-studies suggest that evolutionary changes take place in harvested fish populations, with potentially dramatic ecological and economic consequences. Interestingly, cases of fisheries-induced evolution have also provided some of the most convincing examples of rapid evolution, i.e., evolution on the time-scale of a few generations , thus stressing that humans may now be the biggest evolutionary force on earth (Palumbi 2001). My proposed work has two specific aims: Aim I is to arrive at a more general understanding of the role and effect size of factors that promote or restrain fisheries-induced evolutionary changes. For this purpose, I propose to conduct a meta-analysis based on published datasets providing direct or indirect evidence for and against fisheries-induced evolution (see details below). Aim II is to specifically assess fisheries-induced trends in maturation reaction norms in the Eastern Baltic cod stock (ICES sub-division 25). I will do so by analyzing the 25-year Baltic cod data-series of the IFM-GEOMAR and the Danish Technical University Institute of Aquatic Resources (DTU Aqua) in the context of environmental and fishery datasets for the same fishing grounds.