Habitat Range Expansion in Atlantic Salmon

The marine migrations of many fish species are now fairly well-understood owing to new technologies such as pop-up satellite tags (PSATs). Anadromous species, including the Atlantic salmon (Salmo salar), have displayed an ability to undertake long migrations to marine feeding grounds and return to their natal rivers. Although these foraging migrations essentially determine the size and survival of individuals and populations, very little is known of the routes taken, the location of primary feeding habitats, or the in-situ behaviour of migrating individuals in real-time. Populations of Atlantic salmon from five river systems in Europe (spread from 51ºN in southern Ireland to 70ºN in northern Norway; n=104 PSATs) exhibited differing migratory routes, but consistently used the polar front as primary foraging habitat. Data provide evidence that salmon travel with oceanic currents and gyres, reaching latitudes as high as 79ºN—which is further north than previously recorded. Some populations appeared to mix at these marine feeding areas, with obvious international fishery management implications. Salmon also made deep dives regularly, descending below 860 m—a feat previously thought impossible. The brief duration of these dives (<30 min) deviates from the traditional habitat-range description of this species, suggesting that salmon are able to adapt very quickly to depths and return to the surface equally as fast. Our results expand the known niche of Atlantic salmon, in terms of habitat range, vertical habitat use, and physical abilities, classifying salmon as one of the countless species that rely on the polar front for survival. As the polar oceans get warmer and current patterns shift, changes in the location and productivity of the polar front are evident. The successful application of our tagging study clearly demonstrates that we can now document the subsequent consequences of environmental change in polar regions from the perspective of fish populations. It is now possible for communication amongst polar stakeholders to begin so that policies aimed at the conservation and management of fisheries, in a rapidly changing but highly important biome, can be constructed and implemented in a timely fashion.