Evolutionary impacts of fishing on life history of exploited fish stocks: A meta-analysis

Industrial-scale fishing has imposed heavy, sustained mortality on many marine fish species for decades.  Although impacts of fishing on population size are well-known, the size-selectivity of most fishing can also impose strong evolutionary selection on life history characteristics.  We used meta-analysis of published data to ask whether fishing has changed age and size at maturity of exploited stocks.  We collected data on age (A50) and length (L50) at which 50% of the population reached maturity, from the beginning and end of the available time series from each stock, assuming that these represent periods of lower and higher fishing intensity respectively.  We obtained data from 83 finfish stocks, representing 23 species in 11 families, with an average interval of ~25 years of fishing between estimates.  Overall, fishing strongly and significantly reduced both A50 (-28%) and L50 (-18%). The effect on L50 increased significantly with duration of fishing, representing an average decline of 1.4% per year and explaining 23% of the variation in L50 among stocks.  The effect of fishing on A50 was unimodally related to generation time: effect size was negatively related to generation time in the range of 1-7 years, but positively related to generation time from 7-13 years.  The most parsimonious explanation for our results is that size-selective fishing mortality has produced genetically based evolutionary declines in age and size at maturity in many exploited fish stocks.  These evolutionary changes may be difficult to reverse and have important implications for fishery management and stock rebuilding strategies.