Juvenile Salmon Face Competition for Food in Northwest Waters

A tagged sablefish. Photo via NOAA Fisheries.

Juvenile sablefish in increasing numbers off the coastal waters from Central Oregon north to northern Washington are competing with juvenile salmon for food, according to NOAA Fisheries research recently published in the journal Marine and Coastal Fisheries.

The report, released Jan. 7, shows the influence of warming ocean temperatures off the West Coast. It matches reports of fishing boats catching smaller sablefish closer to shore.

Researchers said their findings mean that salmon may face new competition from sablefish at a critical time in their life cycle, which is already threatened by climate change.

Adult sablefish live for many years in deep offshore waters along the ocean floor.  Juvenile sablefish, like young salmon, first feed and grow along the highest layers of the water near the surface, which is teeming with life. Sablefish are voracious eaters of much the same food as juvenile salmon, often consuming large prey and lots of it.

“They are around the same size as juvenile salmon, but they can eat bigger prey and much more prey than salmon can at the same size,” Elizabeth Daly, an ecologist with the joint NOAA-Oregon State University Cooperative Institute for Marine Ecosystem and Resources Studies in Newport, Oregon, explained.

Daly is the lead author of a new paper documenting increased competition between the two species, both of which support commercial fisheries off the West Coast. She and her team found no clear evidence of sablefish consuming young salmon, but said that based on the size of their other prey, they certainly could.

Other research has documented a similar influx of juvenile sablefish in waters off Alaska, although the new study did not include Alaska.

Numbers of salmon and their survival rates vary widely from year to year, so it’s difficult to detect a specific impact from sablefish competition on salmon survival. Still, the research suggests that the direct overlap of sablefish in the waters where young salmon first feed may put salmon at a competitive disadvantage, particularly if ocean warming makes food harder to find.

“We now know that prey resources are extremely important for salmon growth and survival during this critical early marine period,” said study co-author Brian Burke, who’s a research scientist at NOAA Fisheries Northwest Fisheries Science Center.

“But unraveling the impact of competition on salmon is extremely difficult,” he added. “This new data helps us understand how species interact in our coastal environment. They also point to potential changes from continued ocean warming due to climate change.”

Juvenile sablefish were most numerous in coastal waters off Oregon and Washington in 2020, which was a boom year for the species. These juvenile sablefish were four times more numerous than sub-yearling Chinook salmon, 32 times more numerous than yearling Chinook salmon and 13 times more numerous than coho salmon.

The sablefish also had considerably more food in their stomachs at the time.

Climate change projections have indicated a rising risk to salmon in the ocean, since higher ocean temperatures often reduce salmon survival. The additional competition from sablefish could make things even rougher.

Sablefish, in contrast, could benefit if the juveniles that have expanded into coastal waters grow into adults that add to the population, the report said.