A new analysis of multiple international high seas salmon surveys, led by the University of Alaska Fairbanks (UAF), is building on an extensive body of work on the marine component of the salmon life cycle, the university said in mid-April.
According to Joe Langan, who led the study as a post-graduate fellow at UAF, the research is establishing a baseline from which to view salmon distributions and temperature preferences, allowing other researchers to have a better foundation from which to build and answer more detailed questions.
“The goal was to generate a baseline, quantitative understanding of the broad-scale, average distribution patterns of salmon species across the North Pacific,” Langan stated. “While past efforts have produced schematic representations of salmon distributions as well as estimates of thermal preferences, we feel that our model-based approach represents a step forward in describing these patterns by applying robust statistical models to a large historical dataset.”
Langan, who’s now based in the Midwest with NOAA Fisheries, noted that the study didn’t answer questions about whether salmon are moving to specific areas in pursuit of their traditional or new prey.
“We suggest that the most thermally suitable habitats for salmon at sea may be moving northward, but that does not necessarily mean that the salmon are,” Langan told Fishermen’s News in email responses to questions about the study.
“Where salmon go at sea is determined by a complex interaction of a number of factors, including temperature, prey distribution, population-specific migration patterns, life stage and other physical factors,” he said.
“It could be that a given prey species has different temperature tolerances than salmon and moves in response to warming. In such a case, salmon may follow the prey to a new area even though temperatures were still suitable for salmon in the original area,” he continued.
At the same time, he added, salmon still may occupy an area that is less thermally suitable for them if there’s enough food there.
The analysis was conducted on a trove of over 44,000 high-seas survey gear hauls across the North Pacific, netting over 14 million salmon. The ocean-based data provided researchers with a contrast from the bulk of salmon research, which tends to focus on river habitat.
Methods and data varied in the numerous international studies, while consistently noting the water temperature and location where salmon were caught. That data allowed researchers to create maps with unprecedented detail showing areas occupied by various salmon species while at sea.
Study maps, for example, highlight a hotspot for Chinook salmon gathering in the Bering Sea. They chart a path that maturing sockeye tend to take from the North Pacific and Gulf of Alaska toward the Alaska Peninsula, traveling though passes into the Bering Sea outside Bristol Bay during the spring and summer months.
The study also offered more evidence that cold-water tolerance varies significantly among salmon species.
Sockeye and chum salmon were commonly found in temperatures down to just a few degrees above freezing, while coho and steelhead were absent from the coldest areas. Chinook and pink salmon were found living in the middle of these temperature ranges.
These tendencies are likely to influence which species will be most capable of shifting to colder waters as their traditional ranges are warmed by climate change, Curry Cunningham, an assistant professor at UAF’s College of Fisheries and Ocean Sciences, said.
The bulk of the dataset is from the 1950s through the 1990s and the research required digging up forgotten reports from varying sources.
Retired researcher Skip McKinnell, of the Department of Fisheries and Oceans Canada, participated in some of the earlier surveys, helping to compile and standardize many of the older reports. “It was more of a search-and-rescue mission rather than convincing anyone to provide their data,” Langan said.
The project was funded by the National Oceanic and Atmospheric Administration’s Office of Law Enforcement. The centralized database is to be housed by the North Pacific Anadromous Fish Commission in Vancouver, British Columbia, where it will be available to the public.