Marine heat waves in the northeast Pacific Ocean in 2015, 2016, 2017, and 2019 have resulted in low marine survival for many salmon populations. Unfortunately, marine heat waves are becoming more frequent and more intense. Because larger, healthier fish are more likely to survive in the ocean, researchers are working to understand how freshwater management actions will improve young salmon survival in the ocean.
Impacts from poor ocean conditions take years to affect the number of returning adult fish. The delay varies by species based on their life cycles in freshwater and the ocean. On average, Chinook salmon have a 4- to 5-year delay and steelhead trout have a 1- to 2-year delay. Poor ocean conditions during the past 8 years (particularly between 2015-2017) mean that returns of most species were low in recent years but should start to improve after 2022 with better ocean conditions.
Dangers to Young Fish from Predators
During their complex life cycles, salmon occupy numerous habitats and face challenges during each of them. During their downstream migration from freshwater to the ocean, salmon and steelhead smolts from the upper Columbia River migrate more than 500 miles and pass seven to nine dams and reservoirs. In recent years, birds have eaten young migrating fish in such large numbers that they are identified as a factor limiting recovery of imperiled salmon populations. Upper Columbia River steelhead appear particularly susceptible to predation by Caspian terns, double-crested cormorants, and gulls. Birds have caused more than 50 percent of the smolt deaths, making them the largest killer of these young migrating fish.
Danger to Adults from Sea Lions and Seals
Adult salmon also face increased predation as they enter freshwater to return to spawning grounds. In the past decade, increasing numbers of sea lions below Bonneville Dam have been killing more salmon. Studies indicate that 22 percent of the salmon returning to the Columbia River early in the spring, including Methow spring Chinook, are being eaten by sea lions, the largest amount of predation in recent years. Eleven percent of intermediate arriving populations, including Entiat and Wenatchee spring Chinook, also are being eaten by sea lions. Sea lions are being hazed and removed at Bonneville Dam to reduce predation pressure on adult salmon and steelhead.
Visit the Salmon Data Hub for more of the data behind the indicator charts and graphs used throughout this site.