Fisheries-induced evolution of body size and other life history traits: the impact of gear selectivity

Commercial fishing utilizes a variety of gears, all of which are selective with respect to at least some phenotypic characteristics of individuals such as body size or girth. Empirical evidence is mounting that such fishing induces rapid evolutionary changes, with consequences for the size structure and dynamics of the exploited stocks. Here we present the results of life-history models designed to study fisheries-induced evolutionary changes in body size at maturation, growth, and reproduction in a stock fished by different gear types. We examine evolutionary endpoints of, and selection pressures on, three corresponding life-history traits. We show that fishing usually selects for earlier maturation at smaller size, higher reproductive investment, and faster growth. This is especially true for trawl-like gears, which are primarily size-selective and remove large fish. On the other hand, gears that only remove fish within a certain size slot, such as gillnets, can lead to evolutionary bistability and evolution of delayed maturation. Moreover, gears that are also directly selective on behavioral traits influencing growth, such as baited lines, can lead to slower growth. Our results also highlight how the evolutionary effects of fishing are sensitive to changes in mesh size and fishing mortality, commonly regulated in fisheries management. Keywords: life histories, maturation, reproductive investment, growth rate, trawls, gillnets, baited line