NOAA Fisheries: Warming Ocean Should Focus Attention on Freshwater Actions To Improve Salmon Survival
- March 11, 2021
- John Harrison
Water in the North Pacific Ocean is cool, for now, and for salmon and steelhead from the Columbia River Basin that’s good news. But the long-term outlook is not so encouraging, and so it is time to take actions to address the impacts on fish in an environment that is increasingly warming, driven by climate change. And despite long-held assumptions that the ocean is an inscrutable and increasingly hostile environment for cold-water fish like salmon, there are things that can be done to give fish a better chance of survival, Brian Burke, a research scientist at the NOAA Fisheries Northwest Fisheries Science Center, told the Council at its March meeting.
When considering the current and future state of the ocean environment, there is good and bad news but, Burke said, “we’ll take the good with the bad; ocean conditions have not been great, and they will get a lot worse with climate change, but there are some good spots, too, and we need to take advantage of them.”
Currently, the Pacific Decadal Oscillation (PDO), a measure of sea-surface temperatures, is in a cool phase, and has been for a couple of years – what scientists call a negative phase. “That’s important and good,” Burke said. “A negative PDO tends to be associated with periods when salmon in the ocean do really good.” The cool phase also brings the northern-ocean variety of copepods, which are oily and nutritious food for fish, south to waters off the Washington and Oregon coasts. Another indicator, an index of El Nino/La Nina ocean water warming near the Equator, also is in a cool – La Nina – phase currently, and that also is good for salmon and steelhead, Burke said. A third index, which measures marine heat waves, also is favorable for Columbia River fish at the moment, although marine heat waves are expected to become more frequent and last longer in the future. A recent big marine heat wave lasted from 2014-2016 and was devastating for cold-water species in the ocean. That heat wave was nicknamed “The Blob” for its appearance on ocean-temperature maps as an angry red mass. Burke said that despite the other optimistic conditions, warmer water is expected to return this year by late summer.
“So things are not looking good in the future, even though right now we are in a period of average conditions,” he said.
To learn more about ocean conditions, NOAA is conducting monitoring and research on several fronts, including biweekly sampling of plankton, seabirds, and marine mammals off the Oregon and Washington coasts, surveys to determine the abundance of juvenile salmon and steelhead, and other small fish, and experiments involving new and emerging technologies to track fish through their environment.
Research in 2020 had mixed results – good copepod mass and average numbers of coho salmon, but also below-average numbers of Chinook. “There is a lot of uncertainty about how to interpret mixed-signal years,” he said. Another complicating factor is the lack of knowledge about the impact of predators in the ocean – fish-eating birds, marine mammals. NOAA’s estimates for salmon and steelhead returns to the Columbia River in 2021 are mixed – below-average numbers of spring Chinook, an average number of fall Chinook, and lot more coho than in recent years. Average ocean temperatures are anticipated to rise over time, and that is not good news for cold-water fish.
A recent NOAA Fisheries study looked at the marine survival of Chinook under different climate scenarios. “In our life-cycle modeling, we have to make certain assumptions including levels of climate change and management actions in freshwater,” Burke said. Not all climate-change impacts are negative. For example, climate change is likely to cause earlier snow melt and therefore create longer periods of warmer temperatures for juvenile fish to rear and grow before migrating to the ocean, he said. But overall, he said, warmer water will not be good for juvenile fish migration to the ocean, and the long-term outlook is grim.
“We are expecting up to a 90 percent survival decline in the marine stage of life,” he said. “So we cannot continue putting off doing something about it – it is a problem right now, and will grow over the next 10-15 years.”
But again, it’s not all doom and gloom. There are things that can be done.
“Marine survival is related to both timing of entry to the ocean and fish size, which we have some control over by modifying hatchery operations,” he said. “So the idea that there is nothing we can do about ocean survival is just not true. We do have some control.”
Actions in freshwater to improve marine survival include restoring and improving spawning and rearing habitat for wild fish, controlling predators like fish-eating birds and marine mammals– actions that already are being taken and could be accelerated – and improving survival of juvenile fish in the estuary by improving management of prey species and predators.