Fisheries-induced life-history evolution in anadromous stocks
Atlantic salmon and other salmonid species are threatened by anthropogenic disruptions, including overfishing, habitat degradation and fragmentation, and global shifts in climate. Given the economic and cultural importance of these species, different policy measures have been taken to accomplish their conservation and sustainable exploitation. In particular, high-seas salmon fisheries were prohibited in the 1990s, with catches thenceforth allowed only during the spawning migration. The resultant shifts in mortality regimes have likely impacted the evolution of life-history traits in Atlantic salmon. For instance, the timing of the habitat switch from the early juvenile habitat in rivers to the prematuration years in the ocean is subject to natural selection. In the ocean, salmonids experience increased food availability that elevates the energy they can allocate to growth and energy reserves. An early habitat switch thus enables high energy reserves and consequently raises fecundity. However, small-sized salmon face elevated mortality from predation in the ocean. Conversely, a late habitat switch increases body size and consequently reduces predation risk after migrating to the ocean. I will investigate the effects of fishing on this fecundity-survival tradeoff, to predict fisheries-induced life-history evolution under different mortality regimes, including those before and after the prohibition of high-seas salmon fisheries. For this purpose, I will use an adaptive-dynamics approach in conjunction with physiologically structured population models. The results of this research will contribute to understanding the effects of fishing mortality and conservation policy on the evolution of anadromous species such as Atlantic salmon, which is key for their conservation and sustainable exploitation.