Maturation trends indicative of rapid evolution preceded the collapse of northern cod

Abstract

Northern cod, comprising populations of Atlantic cod (Gadus morhua) off southern Labrador and eastern Newfoundland, supported major fisheries for hundreds of years. But in the late 1980s and early 1990s, northern cod underwent one of the worst collapses in the history of fisheries. The Canadian government closed the directed fishing for northern cod in July 1992, but even after a decade-long offshore moratorium, population sizes remain historically low. Here we show that, up until the moratorium, the life history of northern cod continually shifted towards maturation at earlier ages and smaller sizes. Because confounding effects of mortality changes and growth-mediated phenotypic plasticity are accounted for in our analyses, this finding strongly suggests fisheries-induced evolution of maturation patterns in the direction predicted by theory. We propose that fisheries managers could use the method described here as a tool to provide warning signals about changes in life history before more overt evidence of population decline becomes manifest.

Plasticity of European flounder life history patterns discloses alternatives to catadromy

“…Currently, it appears that management of these fisheries cannot rely either on a single country or general European Union policy because the plasticity of flounder life histories varied markedly among proximate estuaries. This type of policy can induce selective fishing mortality on individuals that use 1 particular migratory tactic, with unpredictable consequences for flounder genetic diversity and stock structure (Olsen et al 2004, Thériault et al 2008. At the local scale, sustainable management of flounder stocks is contingent on both connectivity among coastal, brackish and freshwater habitats, which in dam-regulated ecosystems depends on maintaining water discharge below critical levels (Morais et al 2009), while from a metapopulation perspective, it is important to understand the roles of spatial heterogeneity in population structure and connectivity (Smedbol et al 2002).…”

Size‐selective fishing and the potential for fisheries‐induced evolution in lake whitefish

“…Thus, fishing mortality, which can target a large range of ages and sizes, is expected to be an important selection factor on life histories in exploited fish populations, leading to evolutionary changes in growth rate, size and age thresholds for maturation, and fecundity (Dunlop, Enberg, Jørgensen, & Heino, 2009; Heino, Pauli, & Dieckmann, 2015; Jørgensen et al., 2007; Kuparinen & Merilä, 2007). Indeed, evidence has emerged that fishing mortality of stocks, both marine and freshwater, can be sufficiently high for evolutionary changes in life history traits to occur at trackable, ecological timescales (Edeline et al., 2007; Heino et al., 2015; Jørgensen et al., 2007; Nusslé, Bornand, & Wedekind, 2009; Olsen et al., 2004). Further, the direction and intensity of fisheries‐induced selection are expected to depend on which sizes are targeted, either through size or gear restrictions (Dunlop, Heino, & Dieckmann, 2009; Hutchings, 2009; Jørgensen, Ernande, & Fiksen, 2009; Wang & Höök, 2009).…”

The overfishing debate: an eco-evolutionary perspective

“…The picture on the right-hand side is scaled to show the magnitude of this size shift. Although phenotypic plasticity and changes in population age structure reflect components of the overall size reduction, evolutionary contributions have been substantial [12]. Reproduced, with permission, from The Rooms Provincial Archives Division of Newfoundland and Labrador (http://www.therooms.ca/).…”

“…(eric.palkovacs@duke.edu). 12 continue to depress harvestable biomass even after demographic sustainability has been achieved [6].…”