Salmon in the Arctic and How They Avoid Lethal Low Temperatures

With climate change, scientists and others are interested in the future of Pacific salmon in the Arctic. Chum, pink, sockeye, coho, and chinook salmon have been encountered in the Beaufort Sea, well within Canadian Arctic waters. Chum is the only salmon species regarded as natal to the Mackenzie River watershed, although both pink and chum salmon appear to be natal to Alaska's North Slope rivers. It is not possible to say whether apparent recent increases in the frequency of occurrence of salmonids in the Arctic is an effect of climate change, but it appears there are either increases in the survival of natal fish from the Mackenzie, or in the wandering of non-natal fish to the Mackenzie, or both. We propose three hypotheses to explain how chum salmon survive cold marine winter conditions, and thereby persist in the North American Arctic: (1) Bering Sea Refuge - young salmon migrate to the Bering Sea and Gulf of Alaska where they remain until they are ready to return to spawn; (2) Atlantic Layer Beaufort Refuge - salmon remain in the Beaufort Sea, wintering offshore deep under pack ice; and (3) Freshwater Beaufort Refuge - salmon remain in the Beaufort Sea region, wintering in the brackish, under-ice Mackenzie River plume or in fresh water adjacent to the Beaufort Sea. As a preliminary test of these hypotheses, we examined the strontium-to-calcium ratios (Sr:Ca) of otoliths from chum salmon from the Colville (Alaska's North Slope) and Tanana (Yukon River drainage) rivers. Yukon River chum salmon were assumed to reside in the Gulf of Alaska and the Bering Sea. Otolith Sr:Ca ratios were similar between rivers, implying that fish from each group lived in similar environments, but also exhibited significant fluctuations often associated with migrations between freshwater and marine environments. Age compositions and sizes of adult chum salmon from the upper Mackenzie River watershed did not differ from chum from a Yukon River tributary. We are not able to refute any of our hypotheses, but the most parsimonious explanation is that arctic chum salmon live in the North Pacific for most of their marine life, rather than in the Beaufort Sea region. Because of the long distance to migrate between the mouth of the Mackenzie and the North Pacific Ocean, we suggest salmon may spend their first winter deep within the Beaufort Sea (i.e., a combination of Hypotheses 1 and 2). Additional elemental and isotopic signature measurements will enable a more thorough testing of these hypotheses, allow us to understand how chum salmon survive cold winter conditions, and thereby better predict potential climate change effects on salmon in the Arctic.