The impact of fishing‐induced mortality on the evolution of alternative life‐history tactics in brook charr

Abstract

Although contemporary trends indicative of evolutionary change have been detected in the life-history traits of exploited populations, it is not known to what extent fishing influences the evolution of alternative life-history tactics in migratory species such as salmonids. Here, we build a model to predict the evolution of anadromy and residency in an exploited population of brook charr, Salvelinus fontinalis. Our model allows for both phenotypic plasticity and genetic change in the age and size at migration by including migration reaction norms. Using this model, we predict that fishing of anadromous individuals over the course of 100 years causes evolution in the migration reaction norm, resulting in a decrease in average probabilities of migration with increasing harvest rate. Moreover, we show that differences in natural mortalities in freshwater greatly influence the magnitude and rate of evolutionary change. The fishing-induced changes in migration predicted by our model alter population abundances and reproductive output and should be accounted for in the sustainable management of salmonids.

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).…”

Old wine in new bottles: reaction norms in salmonid fishes

“…Montgomery (1983), for example, suggested that increased fishing mortality at sea might increase the frequency of the Atlantic salmon parr reproductive tactic because of the reduced survival of seaward migrants and, presumably, the reduced concomitant fitness associated with anadromy. Notwithstanding Myers et al's (1986) objection, it is logical to conclude that increased mortality among anadromous males at sea would increase the fitness associated with the parr tactic, leading to a shift in the inflection points of the reaction norms to lower growthrate thresholds, as hypothesised by Piché et al (2008) for Atlantic salmon and by Thériault et al (2008) for brook trout (Figure 11a).…”

Impact of Environmental Covariation in Growth and Mortality on Evolving Maturation Reaction Norms

“…Mortality may decrease with size, due to a lower vulnerability of larger individuals to predators, or increase with size, a typical feature of human harvest regimes (e.g., Dunlop et al 2007Dunlop et al , 2009aDunlop et al , 2009bThériault et al 2008;Enberg et al 2009;Jørgensen et al 2009;Okamoto et al 2009). Parental effects may enhance offspring survival through better egg quality or parental care (Trippel 1995;Berkeley et al 2004).…”

“…Accordingly, a maturation reaction norm is the curve in the age-size plane connecting the combinations of age and size at maturation that are expressed by a given genotype for different growth rates in the age-size plane (Stearns and Crandall 1984;Stearns and Koella 1986). The evolution of maturation reaction norms has been the subject of numerous theoretical studies (e.g., Stearns and Koella 1986;Perrin and Rubin 1990;Berrigan and Koella 1994;Day and Rowe 2002;Dunlop et al 2007Dunlop et al , 2009aDunlop et al , 2009bThériault et al 2008;Enberg et al 2009;Jørgensen et al 2009). As the costs and benefits of maturing earlier or later accrue in terms of survival and/or size-dependent fecundity, the rates of somatic growth and mortality are expected to serve as primary determinants of maturation evolution.…”