Chinook salmon. (Photo: NOAA)
2015’s ocean conditions may cause poor juvenile chinook salmon return
Tuesday, March 21, 2017, 01:50 (GMT + 9)
Researchers from Oregon State University (OSU) and the National Oceanic and Atmospheric Administration (NOAA) forecast this year there will be a slightly below-average run of spring chinook salmon on the Columbia River.
These predictions are based on the fact that ocean conditions were historically bad in the spring of 2015, when migrating yearling fish that will comprise the bulk of this spring’s adult chinook salmon run first went out to sea.
Besides, Pacific Decadal Oscillation values – which reflect warm and cold sea surface temperatures – suggest it was one of the warmest nearshore oceans encountered by migrating chinook salmon dating back to at least 1900.
Researchers believe that the lack of food for the salmon in 2015 may have resulted in significant mortality that will show in this year’s run of Columbia River springers.
“When juvenile salmon first enter the ocean, it is a critical time for them. They are adjusting to a saltwater environment, they have to eat to survive, and they have to avoid becoming prey themselves. When we sampled juvenile salmon in May and June of 2015, the fish were much smaller and thinner than usual, and many of them had empty stomachs. There just wasn’t anything for them to eat,” pointed out lead author Elizabeth Daly, a senior faculty research assistant with the Cooperative Institute for Marine Resource Studies, jointly operated by OSU and NOAA out of the Hatfield Marine Science Center in Newport.
The researcher explained that when the oceanic waters off Oregon and Washington are cold, young salmon primarily feed on readily available fish prey such as Pacific sand lance and smelts, which triggers their growth spurt. When waters are warmer, there is less food available, and they primarily eat juvenile anchovies and rockfish, which are less-desirable prey than cold-water species.
By the time the juvenile chinook salmon migrated to the ocean in spring in 2015, the larval anchovies and rockfish had all but disappeared – making even backup food sources for the salmon scarce.
The researchers theorize that these larval fish died off because they themselves had little to eat. Long-time NOAA biologist Bill Peterson told Daly and her colleagues that the Pacific Ocean off the Northwest coast in early 2015 was devoid of cold-water, lipid-rich copepods, a key element in the food chain. In 2015, it was so warm offshore that virtually no lipid-rich copepods were to be found.
“During warm years, there is typically less upwelling that brings cold, nutrient-rich water to the surface,” said Richard Brodeur, a biologist with the NOAA Northwest Fisheries Science Center and co-author on the study. “Salmon populations may be able to handle one year of warm temperatures and sparse food. But two or three years in a row could be disastrous.”
“For the first time, we found that the salmon were eating juvenile sardines in 2016 – a new prey for them,” Daly noted. “Sardines were spawning off the central Oregon coast for one of the first times because of the warm water. We don’t know the long-term impact this will have on salmon. Hopefully, it can become a new food source for them if waters remain warm.”
As this year’s run of spring chinook salmon unfolds on the Columbia River, Daly and her colleagues will be watching to see if the numbers of adult fish returning align with predictions of a poor return based on 2015 ocean conditions, prey availability, and juvenile fish size.
Photo Courtesy of FIS Member National Oceanic and Atmospheric Administration NOAA/NMFS