Comparing rates of contemporary evolution in life-history traits for exploited fish stocks

Trait evolution over time periods spanning generations, not millennia, is increasingly observed to be above the natural baseline in populations experiencing human-induced perturbations. We investigated the relative speed of trait change by comparing rates of evolution in haldanes and darwins for size at maturation as measured by probabilistic maturation reaction norm midpoints for fish stocks from the Pacific Ocean, North Atlantic, Barents Sea, eastern Baltic Sea, and the North Sea. Rates in haldanes for 23 stocks ranged from -2.2 to 0.9 and from 0.5 to 153 in kilodarwins for 26 stocks. The highest rates of evolution corresponded to the most heavily exploited stocks; rates slowed after moratoria were introduced. The estimated rates in fish life-history characteristics were comparable to other examples of human-induced evolution and faster than naturally induced rates. Stocks with high growth showed slower evolutionary change, even under high mortality, suggesting that compensatory somatic growth can slow the rate of trait evolution. Regardless of whether trait changes are due to exploitation or environmental factors, the costs of ignoring trait evolution are high. Management strategies should be based upon precautionary principles; therefore, the effect of changing traits must be integrated into the fisheries assessment process.