Ecological and evolutionary consequences of size‐selective harvesting: how much do we know?

Abstract

Size-selective harvesting, where the large individuals of a particular species are preferentially taken, is common in both marine and terrestrial habitats. Preferential removal of larger individuals of a species has been shown to have a negative effect on its demography, life history and ecology, and empirical studies are increasingly documenting such impacts. But determining whether the observed changes represent evolutionary response or phenotypic plasticity remains a challenge. In addition, the problem is not recognized in most management plans for fish and marine invertebrates that still mandate a minimum size restriction. We use examples from both aquatic and terrestrial habitats to illustrate some of the biological consequences of size-selective harvesting and discuss possible future directions of research as well as changes in management policy needed to mitigate its negative biological impacts.

Fisheries-induced disruptive selection

“…Harvesting a stock's large individuals, as happens through many widely adopted fishing policies (Table 2), increases the directional selection pressure toward early maturation, as recurrently highlighted by earlier studies (e.g., Law 356 1979; Law and Grey 1989;Abrams and Rowe 1996). Moreover, when harvesting is adaptive, a fishery behaves similar to an optimally foraging predator that maximizes its intake rate (e.g., Egas et al 2005): this tends to increase the mortality of 358 large individuals, as these are more profitable to harvest (Fenberg and Roy, 2008;Darimont et al, 2009 has targeted large individuals of Northern pike for four decades (Carlson et al, 2007;Edeline et al, 2009). Size-selective 362 gill nets were also used for catching striped bass in Maryland during 1950s (Mansueti, 1961); size-selective harvesting of British Columbia pink salmon has been recorded since 1950 (McAllister andPeterman, 1992).…”

“…These results imply that fisheries-induced disruptive selection is readily caused by commonly used fishing policies, 230 namely those targeting large adult and mature individuals while protecting juveniles and immature individuals (Fenberg and Roy, 2008;Darimont et al, 2009). By contrast, scenarios (a) to (c) cannot occur for six of the ten studied fish-232 ing policies: this applies to the only-juvenile, only-small, juvenile-or-small, only-immature, only-immature-and-small, and only-mature-and-small fishing policies.…”

Understanding and monitoring the consequences of human impacts on intraspecific variation

“…Instead, the most obvious effect of harvesting and domestication is typically altered selection. For instance, hunting and fishing practices can inadvertently result in selection for a smaller body size and earlier maturation (Coltman et al., 2003; Law & Salick, 2005; Swain et al., 2007), which can negatively influence survival, resilience, and recovery (Fenberg & Roy, 2008). Like harvesting, domestication (e.g., crop maturity and fish hatcheries) can alter selection and lead to evolutionary changes that alter productivity (Denison, 2012).…”

Human-induced evolution caused by unnatural selection through harvest of wild animals

“…Handford et al (25) stated that management was ''seriously deficient in [its failure] to take into account the possibility of adaptive genetic change in exploited stocks of fish. '' In the last few years, such concerns about capture fisheries for a variety of species have escalated (4,(26)(27)(28). Nevertheless, in large part because direct evidence for fisheries-induced evolution in specific cases remains elusive (17), fishery management almost nowhere yet incorporates evolutionary considerations: Fisheries are managed on the basis of demographic considerations alone-primarily adult abundance.…”