New UAF Analysis Offers Insight Into Salmon at Sea

A map using information from a new database shows relative abundance of Chinook salmon in the Bering Sea during June and July. A hotspot of abundance appears to correspond with a region of known high productivity along the Bering Sea shelf break. Image by Joe Langan.

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 announced April 15.

According to Joe Langan, who led the study as a post-graduate fellow at UAF, the research is establishing a new quantitative, baseline understanding of salmon distributions and temperature preferences that will allow 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 said. “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, now on the staff of NOAA Fisheries in the midwestern U.S., noted that the study did not 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 via email.

“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 wrote.

“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 tough temperatures were still suitable for salmon in the original area,” he explained.

At the same time, he added, salmon may still occupy an area that is less thermally suitable for them if there is 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 these numerous international studies, while consistently noting the water temperature and location where salmon were caught. The 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 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 about 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.