Opening the black box: New insights into the role of temperature in the marine distributions of Pacific salmon

Abstract

Pacific salmon (Oncorhynchus spp.) spend much of their life near the ocean surface where climatic and oceanographic conditions affect their habitat and survival. Despite decades of study, critical knowledge gaps persist regarding their ecology and distributions. Consequently, it has been difficult to assess how environmental conditions influence the high‐seas distribution and habitat use of these culturally and socioeconomically important fishes, presenting challenges to fisheries managers trying to evaluate how climate change and fishing activities may impact salmon populations. We used a recently compiled, comprehensive database of historical coastal and high‐seas salmon survey data (1953–2022) in the North Pacific to fit species distribution models that (1) characterize the marine spatial distribution of six species of Oncorhynchus, (2) evaluate species‐specific temperature preferences, and (3) investigate how species' temperature preferences influence distribution. Sea surface temperature, along with seasonal migrations associated with spawning and feeding, significantly affects the distribution of all species, where the warm limits of estimated preferred thermal ranges were more similar than the cold limits. Furthermore, the distributions of some species appear more responsive to temperature than others and recently observed warm conditions have likely impacted realized ranges. These models have expanded our understanding of salmon ocean distributions and thermal niches by providing a unique window into this often unobserved but important part of the life cycle. They also serve as a baseline for future investigations into the mechanisms influencing salmon spatial ecology, responses to climate change, and vulnerability to harvest across the North Pacific.

Pacific salmon in the Canadian Arctic highlight a range‐expansion pathway for sub‐Arctic fishes

“…Indeed, the broader distribution of chum and pink salmon in the Arctic, compared to other species, may stem from their limited reliance on freshwater habitats (Nielsen et al, 2013;Salonius, 1973). However, sockeye salmon catches have also been more common in recent years (Dunmall et al, 2021); this fish is among the most cold-tolerant of Pacific salmon species (Abdul-Aziz et al, 2011;Langan et al, 2024).…”

“…For the Beaufort Sea watch-zone, meanwhile, the first and last day of the year with a mean SST above 2°C, the total number of days with a mean SST above 2°C (which may span days of SSTs below 2°C), the maximum mean SST, and the number of degree-days above a mean SST of 2°C (the sum of positive values obtained by subtracting 2 from each daily mean SST) were calculated for each year and evaluated in the GLM. The 2°C threshold was chosen based upon published estimates of salmon temperature preferences (Abdul-Aziz et al, 2011;Langan et al, 2024), but testing revealed that using alternate choices close to this value did not substantially change the results. The predictive skill of the selected GLM was evaluated by calculating the symmetric mean absolute percentage error for predictions made via leave-one-out cross-validation.…”

“…Analysis was focused on the North American coastal Chukchi and Beaufort seas, which together form the most direct path for Pacific salmon to travel from the Bering Sea to the western Canadian Arctic (Figure 1). Because salmon are highly mobile while at sea and are known to preferentially select marine habitats within their preferred thermal niches (Abdul-Aziz et al, 2011;Beamish, 2018;Langan et al, 2024), we hypothesized that SST along this migratory route would play an important role in modulating the number of salmon that reach the locations targeted by subsistence fishers. Daily SST and sea-ice concentration data on a 0.25° grid for the Chukchi and Beaufort seas were obtained for 2000-2022 from the NOAA Optimum Interpolation Version 2 high resolution dataset (Huang et al, 2021).…”

“…How to cite this article: Dunmall, K. M., Langan, J. A., Cunningham, C. J., Reist, J. D., Melling, H.;(2024). Pacific salmon in the Canadian Arctic highlight a range-expansion pathway for sub-Arctic fishes.…”

Hatcheries to high seas: climate change connections to salmon marine survival

“…We consider this a reasonable assumption because migratory behavior in salmon is inherited (Putman, 2015;Thompson et al, 2020). Ranges of chum salmon thermal habitat used in our analysis were narrower (thermal limits, 4.0-13°C) than previously published estimates, based largely on historical high seas salmon survey data collected before the winter 1976-1977 climate regime shift (preferred spring-summer SST range, 1.3-12.6°C; Langan et al, 2024). The pre-regime shift period was characterized by low ocean productivity, cold winter SSTs in the Gulf of Alaska, and low abundance of salmon populations that overwinter in the Gulf of Alaska, including Japanese chum salmon.…”