Heavy fishing and other anthropogenic influences can have profound impact on a species’ resilience to harvesting. Besides the decrease of the census and effective population size, strong declines in mature adults and recruiting individuals may lead to almost irreversible genetic changes in life-history traits. Here, we investigated the evolution of genetic diversity and effective population size in the heavily exploited sole (Solea solea), through the analysis of historical DNA from a collection of 1379 sole (Solea solea) otoliths dating back from 1957. Despite documented shifts in life-history traits, neutral genetic diversity inferred from 11 microsatellite markers showed a remarkable stability over a period of 50 years of heavy fishing. Using simulations and corrections for fisheries induced demographic variation, both point and temporal estimates of effective population size (Ne) were always higher than 1000, suggesting that despite the severe census size decrease over a 50 year period of harvesting, genetic drift is probably not strong enough to significantly decrease the neutral diversity of this species in the North Sea. However the ratio of effective population size to the census size (Ne/Nc) was very small (10-5), suggesting that overall only few adults contribute to the next generation. The high Ne level together with the low Ne/Nc ratio is most likely caused by a combination of an equalized reproductive output of younger cohorts, a decrease in generation time and a large variance in reproductive success typical for marine species. Because strong evolutionary changes in age and size at first maturation have been observed for sole, changes in adaptive genetic variation should be further monitored to detect the evolutionary consequences of human-induced selection.

OtolithGenotypes_bySamplingyear_11lociGenepop input: Otolith genotypes (11 loci) grouped by sampling year:1950s (‘NS50’; sampling years 1957-1959), 1960s (‘NS60’; sampling years 1966-1967),1970s (‘NS70’, sampling years 1971-1974), 1980s (NS80, sampling years 1984-1985-1987) and 1995 (NS95) (For details on age composition of the samples, see Supporting Information Table S2). In addition, contemporary samples were collected in 2007 during research surveys off the Thames (THA07), on the Norfolk Banks (NOR07) and off the Belgian Coast (BEL07)YEARFINAL_11LOC.popOtolithGenotypes_byCohorts_11lociGenepop input file. Otolith genotypes (11 loci),grouped by cohort (year-class). Pops are cohorts.Genotypes_BYCOHORTS.POP