2023 Ocean Conditions: Where and when salmon migrate determines their ocean experience, growth, and survival; freshwater management can help marine survival

Understanding how ocean conditions affect salmon, especially as the climate warms, is a priority of the Council’s Columbia River Basin Fish and Wildlife Program. Its measures support monitoring ocean conditions and river restoration work to determine the management actions that could bring the greatest benefits to fish. The data collected is one of the strategy performance indicators in the Council’s Program Tracker.

At its March meeting, Brian Burke, research fish biologist with the National Oceanic and Atmospheric Administration, gave an update on 2023 ocean conditions for salmon and steelhead and explained how actions taken in freshwater can improve survival in the ocean. See presentation and video.

“A lot of people in the region use lifecycle models to understand salmon and create effective management decisions,” said Burke. “They’re great in that they link all of the habitats in the life stages that salmon go through.”

According to Burke, one of the things that becomes very clear when you compare habitats is that survival in the ocean is particularly poor, averaging only about 1 percent for Chinook or steelhead, which is low compared to other habitats.

“Salmon are particularly sensitive to changes in the ocean ecosystem,” said Burke. “To make matters worse, we know that climate change is going to be impacting all the habitats that salmon rely on. It will be really important to understand how they will be affected and what the options are to mitigate that effect.”

Where Salmon Go in the Ocean Matters

There are three main migration patterns that juveniles take when they first enter the ocean. The first is to travel north along the coast. Spring Chinook salmon are a classic example; they can reach Alaska within a few weeks to a couple of months. It’s a very direct and speedy path.

The second pattern is to stay in coastal waters without venturing very far out. Fall Chinook salmon and some populations of coho salmon exhibit this behavior. They can remain local off of Oregon and Washington for that first summer and winter, and even for their entire time in the ocean.

The third pattern is to not stay along the coast at all but to enter the main Pacific Ocean directly, and steelhead are a classic example of this. They stay along the coastline for a very short time, making them difficult to catch since they move so quickly out to sea.

Adult fish tend to mirror those patterns on their return to the rivers. But there are differences within species.

“The ocean is dynamic and highly variable; because fish are going to different places, their experiences can be different. Where and when they go in the ocean determines their growth rates and survival, which can be highly variable among stocks,” noted Burke.

2023 Ocean Conditions

Last year’s conditions will influence adults returning this year and next year. In general, the ocean was warm in 2023, which has been the case for a decade or more.

While conditions were better earlier in the year, they worsened later in the summer as temperatures rose.

“Much of the North Pacific is warmer than average, and unfortunately, it’s only going to get worse in the summer,” said Burke.

Burke noted that there is some cooling along the equator, so El Niño is diminishing and we’re moving into La Niña conditions. While La Niña is usually connected to good salmon conditions, overall global warming is causing marine heat waves to be much worse—bigger and more frequent. And the expectation is that the size and duration of these marine heat waves will continue to grow.

For 2022 and 2023, while signals were mixed, it resulted in average conditions for salmon.

Other Factors of Influence

One of the factors contributing to the good start to 2023 was the upwelling that occurred early in the year. Upwelling—when deeper, cold, nutrient-rich water rises to the surface—kept warm water offshore so fish along the coastline could experience favorable conditions before it got warmer in the summer.

“The reason cold water and warm water are important is because of their impact on the ecosystem,” noted Burke. “It can influence things like competitor species and prey species.”

“The fish can handle the temperature changes just fine; warm water might not burn them to death, but it might starve them if their food sources are affected. And it could bring in a whole suite of predators. It’s the ecosystem effects of these temperature shifts that’s important,” said Burke.

“We may have entered a new era of ecosystem dynamics for salmon.”

Freshwater Experience Can Affect Salmon Survival in the Ocean

One encouraging means to strengthen survival in the ocean is how we manage their freshwater experience, referred to as carryover effects, where one period can influence later periods.

Fish released from hatcheries at different body sizes or times of year can experience different survival rates in the ocean.

“Size depends on where they came from and which hatchery they came from. Management actions influence size and growth rates in the ocean—that’s a lever we have some control over through actions we’re already taking.”

Habitat restoration can also influence fish growth in freshwater, which may result in improved ocean survival.

“We can optimize some freshwater management actions to influence marine survival; the size of fish caught in the ocean depends on their experiences in fresh water,” said Burke.

Looking Ahead

Burke’s research and monitoring data have shown how much ocean conditions can vary by location in the ocean or across seasons and years. The current “stoplight” chart of ocean conditions describes in a general sense the suite of indicators that can influence salmon and steelhead growth and survival. To understand conditions affecting a particular stock, it would be necessary to develop a stock-specific indicator using data from the specific areas of the ocean inhabited by that stock. Burke noted that while stock-specific indicators would be better for forecasting, it’s not feasible to develop them at this time, given staffing and funding levels.

Coming up, critical ocean research and monitoring topics will be discussed at the next Ocean and Plume Science and Management Forum on April 4.

For more information, see the National Oceanic and Atmospheric Administration’s Integrated Ecosystem Assessments.