Abstract
Size-selective harvesting is assumed to alter life histories of exploited fish populations, thereby negatively affecting population productivity, recovery, and yield. However, demonstrating that fisheries-induced phenotypic changes in the wild are at least partly genetically determined has proved notoriously difficult. Moreover, the population-level consequences of fisheries-induced evolution are still being controversially discussed. Using an experimental approach, we found that five generations of size-selective harvesting altered the life histories and behavior, but not the metabolic rate, of wild-origin zebrafish (Danio rerio). Fish adapted to high positively size selective fishing pressure invested more in reproduction, reached a smaller adult body size, and were less explorative and bold. Phenotypic changes seemed subtle but were accompanied by genetic changes in functional loci. Thus, our results provided unambiguous evidence for rapid, harvest-induced phenotypic and evolutionary change when harvesting is intensive and size selective. According to a life-history model, the observed life-history changes elevated population growth rate in harvested conditions, but slowed population recovery under a simulated moratorium. Hence, the evolutionary legacy of size-selective harvesting includes populations that are productive under exploited conditions, but selectively disadvantaged to cope with natural selection pressures that often favor large body size.
Highlights
Human harvest of wild populations is often intense and nonrandom with respect to phenotypes (e.g. Darimont et al 2009)
Much of the current debate around the prevalence of fisheriesinduced evolution (FIE) has centered on whether the observed phenotypic changes are genetic (Jørgensen et al 2007; Kuparinen and Meril€a 2007; Law 2007) and if so, whether these changes matter for population dynamics and management (Hutchings and Fraser 2008; Andersen and Brander 2009; Kuparinen and Hutchings 2012; Laugen et al 2014; Marty et al 2015)
The strength of our experimental study is that it establishes an unambiguous cause-and-effect relationship by showing that (i) size-selective harvesting can lead to genetic and a range of phenotypic changes in contemporary timescales, (ii) a relatively low evolutionary rate, and (iii) seemingly subtle phenotypic changes in individual life-history traits can cumulatively have a strong effect on population growth rate and recovery potential
Summary
Human harvest of wild populations is often intense and nonrandom with respect to phenotypes (e.g. Darimont et al 2009). Through early maturation at small size and/or increased reproductive investment at the expense of postmaturation somatic growth (Stearns 1992) Such phenotypic changes could be magnified when harvesting is intensive and positively size selective (Laugen et al 2014). While early maturation increases the probability that an individual will reproduce before it is harvested, small body size at reproduction may confer fitness costs through a decrease in egg number (fecundity), reduced egg and offspring quality (Walsh et al 2006; Arlinghaus et al 2010; Uusi-Heikkil€a et al 2010), and increased natural mortality (Jørgensen and Fiksen 2010; Audzijonyte et al 2013a; Heino et al 2013; Jørgensen and Holt 2013). Evolutionary changes of body size and related lifehistory traits can have important repercussions for species and community ecology (Peters 1983; de Roos and Persson 2002; Haugen et al 2007), management reference points (Heino et al 2013), and population productivity, recovery speed, and fisheries yield (Law and Grey 1989; Hutchings and Fraser 2008; Conover et al 2009; Laugen et al 2014) and may be of high relevance to contemporary fisheries management (Conover and Munch 2002; Jørgensen et al 2007)
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