Long-term changes in migration timing of adult Atlantic salmon (Salmo salar) at the southern edge of the species distribution

Abstract

The Connecticut River historically represented the southernmost extent of the North American range of Atlantic salmon (Salmo salar), but the native population was extirpated 200 years ago by dam construction. An extensive restoration effort has relied upon stock transfers from more northerly rivers, especially the Penobscot River (Maine). Recent work has shown differences in age structure between donor and derivative populations. Here we focus on a related life-history trait, the timing of the adult migration. We examined 23 years of migration timing data collected at two capture locations in the Connecticut River drainage. We found that both dates of first capture and median capture dates have shifted significantly earlier by about 0.5 days·year–1. To conclude whether this is a consequence of local adaptation or a coast-wide effect, we also quantified changes in migration timing of more northerly stocks (in Maine and Canada). We found that the changes in migration timing were not unique to the Connecticut River stock and instead observed coherent patterns in the shift towards earlier peak migration dates across systems. These consistent shifts are correlated with long-term changes in temperature and flow and may represent a response to global climate change.

Genetic change for earlier migration timing in a pink salmon population

“…This provides evidence of a rapid microevolutionary change in this population that has proved exceptionally elusive in other studies [5,9]. The trend towards earlier migration timing in this population does not appear to be anomalous, because it is replicated in the even-year population that uses the same freshwater habitat, and in other salmonid species and life histories (figures 2 and 3) [23][24][25][26]. Importantly, another recent study that used a modelling approach determined that microevolution for earlier migration timing has occurred in a population of sockeye salmon in the Columbia River [20].…”

Responses of Marine Organisms to Climate Change across Oceans

“…Earlier arrivals (up to 21 days per decade) into river systems have also been observed in Atlantic salmon, Salmo salar, breeding migrations to eastern North America. These shifts are positively correlated with warming temperatures (northern stocks) and river discharge rates (southern stocks), presumably reflecting the different migration patterns, and hence phenological triggers, of salmon populations (Juanes et al, 2004).…”

“…The majority of marine phenological studies come from the north-east Atlantic, across a range of trophic levels from plankton to seabirds, and from Antarctic seabird colonies (Figure 3). Sparser evidence also arises from studies of highly migratory fish such as salmon and tuna (Juanes et al, 2004;Dufour et al, 2010).…”

Managing the Effects of Climate Change: Fishery Management's Greatest Challenge

“…Although Atlantic salmon occur as far south as Northern Spain and Portugal, towards the southern end of the range the populations generally avoid the high water temperatures of the lower reaches of rivers and inshore waters by returning to the river early in the year (and to a lesser extent very late in the year) and ascending to upland areas where water temperatures are lower (Garcia de Leaniz et al 1988, Martinez et al 2001, Juanes et al 2004. Southern Britain and Northern France (Normandy and Brittany) represent the southern limit of the species spawning and rearing in lowland headwaters and tributaries.…”

“…It is noteworthy that all the southern population of salmon in Europe (including those in Northern Spain and South-west France) are currently at well below historic levels, and the southern limit of distribution has moved northwards from the river Douro in Portugal to the river Miño on the border of Portugal and Spain (MacCrimmon & Gots 1979). In North America, a gradual shift to earlier median date of return to the river (about 12 days over the 24-year period from 1978 to 2001) has coincided with the recent period of warming (Juanes et al 2004). …”