A new analysis of high seas salmon surveys is enhancing the understanding of salmon ecology, adding details about where various species congregate in the North Pacific Ocean and their different temperature tolerances.
The project, led by researchers at the University of Alaska Fairbanks (UAF), integrates numerous international salmon studies from the North Pacific dating back to the 1950s. Although many individual reports were published by nations and agencies that funded those efforts, these were never fully compiled into an overarching database or analysed comprehensively at this scale.
UAF said this new research effort builds upon the extensive and valuable past body of work on the marine component of the salmon life cycle.
Together, the data represent a trove of more than 44,000 high seas survey gear hauls across the North Pacific, netting over 14 million salmon. The ocean-based data also provide a contrast from the bulk of salmon research, which tends to focus on river habitat.
"This is a portion of the salmon life cycle that arguably gets overlooked, at least in terms of the grand investment in salmon research," said Curry Cunningham, an assistant professor at UAF's College of Fisheries and Ocean Sciences. "As someone who always wondered where all these fish went when they left Bristol Bay, seeing that pattern come to life was so satisfying."
Although methods and data varied among the studies, they consistently noted the water temperature and location where salmon were caught. That data allowed the research team to create maps with significantly greater detail showing the areas that various salmon species occupy while at sea.
For example, the maps 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 through passes into the Bering Sea outside Bristol Bay throughout the spring and summer.
The study also produced 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 lived in the middle of those ranges.
Cunningham said those 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.
The focus of the dataset is from the 1950s to the 1990s, and the research required gathering forgotten reports from varying sources.
The project was funded by the National Oceanic and Atmospheric Administration's Office of Law Enforcement, which hopes to use information about where salmon are concentrated at sea to help curb illegal fishing. The centralised database will be housed by the North Pacific Anadromous Fish Commission and made publicly available.
