The influence of migratory distance on Atlantic salmon Salmo salar population responses to interannual variation in sea surface temperature.

Abstract

As a species, the Atlantic salmon Salmo salar is undergoing a range wide population decline. In the last 40 years alone, wild stocks have specifically declined due to continuing human pressures and global climate change. During the marine life stages, North Atlantic Sea surface temperatures (SST) have specifically impacted stocks, inducing range wide declines in abundance and morphometrics as temperature rises. Recent studies have indicated that SST’s effects on S. salar are more severe at the southernmost ranges, however we lack an explanation for why this may be the case. Acknowledging this trend, we hypothesise that while declines in returning abundance and size are explained by SST rise, the population’s response is moderated by their migration distance. Following, this thesis aims to investigate this hypothesis by examining whether the distance that S. salar migrates during their marine inhabitancy influences their population responses to changes in SST. To address this aim, this thesis includes two critical areas of research vital to the understanding of how migratory distance could influence a populations response to SST rise. 1st a literature review section comprised of two review chapters to outline SST influence on S. salar responses and possible marine migratory routes, and 2nd a quantitative analysis of the impact of migratory distance on population responses. In conclusion, the results document considerable declines and variations between populations across the southern and northern European species range.