Changes in Northwest Atlantic Arctic and Subarctic conditions and the growth response of Atlantic salmon

There has been a systematic change in the weight at age of Atlantic salmon (Salmo salar L.) in the Northwest Atlantic that is related to climate variability. This relationship emerged from analyses of broad-scale measures of ocean surface thermal habitat, which shows that expansion of the area bounding 4-8°C is associated with greater growth. To further elucidate the effect of the environment on salmon growth, time-series of sea surface temperature (SST), sea ice coverage, chlorophyll concentration, net primary production and zooplankton abundance were examined temporally and spatially in relation to changes in weight of salmon. SST data and zooplankton data were extracted from in situ analyses, whereas sea ice and chlorophyll- based measures of productivity were collected with satellite sensors. Salmon growth was found to be unrelated to productivity at the base of the food chain but highly associated with thermal regime during winter and spring. Warming conditions during specific segments of the salmon life cycle have been associated with poor adult recruitment; yet warming during others is beneficial to salmon growth and is assumed to increase reproductive output of spawning fish. Despite these positive influences, climate change will continue to erode the viability of salmon populations whilst the negative effects of warming on survivorship outweigh the benefits of any increase in reproductive output related to growth.