Impact of naturally spawning captive-bred Atlantic salmon on wild populations:depressed recruitment and increased risk of climate-mediated extinction

摘要

The assessment report of the 4th International Panel on Climate Change confirms that global warming isstrongly affecting biological systems and that 20-30% of species risk extinction from projected futureincreases in temperature. It is essential that any measures taken to conserve individual species andtheir constituent populations against climate-mediated declines are appropriate. The release of captivebred animals to augment wild populations is a widespread management strategy for many species buthas proven controversial. Using a regression model based on a 37-year study of wild and sea ranchedAtlantic salmon (Salmo salar) spawning together in the wild, we show that the escape of captive bredanimals into the wild can substantially depress recruitment and more specifically disrupt the capacityof natural populations to adapt to higher winter water temperatures associated with climate variability.We speculate the mechanisms underlying this seasonal response and suggest ,that an explanation basedon bio-energetic processes with physiological responses synchronized by photoperiod is plausible.Furthermore, we predict, by running the model forward using projected future climate scenarios, thatthese cultured fish substantially increase the risk of extinction for the studied population within 20generations. In contrast, we show that positive outcomes to climate change are possible if captive bredanimals are prevented from breeding in the wild. Rather than imposing an additional genetic load onwild populations by releasing maladapted captive bred animals, we propose that conservation effortsshould focus on optimizing conditions for adaptation to occur by reducing exploitation and protectingcritical habitats. Our findings are likely to hold true for most poikilothermic species where captivebreeding programmes are used in population management.