November 08, 2023
El Niño, translated as “Little Boy” in Spanish, is a Pacific Ocean phenomenon that can cause plenty of grief for Pacific Northwest steelhead and other salmonids soon. This year’s El Niño is shaping up to be moderate to strong based on the best indicator–the temperature of ocean surface in the equatorial Pacific region from the International Dateline to the coast of South America. Emily Becker with the University of Miami/Cooperative Institute for Marine and Atmospheric Studies wrote in the ENSO blog: “Forecasters give this event a high chance of qualifying as a strong event, based on our climate prediction model predictions and the current conditions.”
What is the El Niño and How Does This Impact Our Weather
El Niño begins far, far away from steelhead country, starting as an unusually warm ocean temperature in the Equatorial Pacific during summer or fall. The dynamic between ocean temperature and the atmosphere–an oscillation of the ocean-atmosphere system along the equator known as El Niño/Southern Oscillation (ENSO), is known to us as El Niño. The warmer than average water in the eastern Pacific weakens air movements, slowing the trade winds and upper-level winds. The jet stream extends farther eastward and shifts southward during El Niño winters. The Pacific storms that usually soak the Pacific Northwest blanket California and the southern United States instead resulting in drier conditions in steelhead country.
Close to the West Coast, the ocean warms due to changes in the wind and ocean currents that come from El Niño. Because the east-to-west trade winds slacken during El Niño events, the tropical ocean adjusts by creating and sending upper level ocean waves, known as Kelvin waves, from the eastern Pacific towards the South American coast. After these waves strike the coast, the resultant wave undulates poleward into the Gulf of Alaska, thereby warming and stratifying waters along the Pacific Northwest coast.
How Does El Nino Affect Steelhead
El Niño creates some real challenges for the already imperiled steelhead of the Pacific Northwest. The 10-year average numbers of returning steelhead over Bonneville Dam on the Columbia River, returning to watersheds from the Deschutes River to the upper reaches of Idaho, has trended down since the boom years of the first decade of the 2000s. The historically low steelhead return in 2021 resulted in steelhead angling closures up and down the Columbia River system. While the steelhead return numbers rebounded more recently, the numbers of steelhead, including wild steelhead, are still below the already-stunted ten-year average.
So many of the steelhead rivers of the Pacific Northwest, particularly the interior Northwest, are fed from the snowpack, either directly or through reservoirs. Because an El Niño results in lower snowpack in the mountains, expect lower-than-normal stream and river flows–less water for steelhead to migrate through, spawn in, and return to the ocean. In addition, lower river flows mean higher stream temperatures and degradation of conditions for spawning, rearing, and migration. That said, Northern California is actually more likely to experience cooler and wetter winter and spring conditions that may be more favorable to Northern California runs. However, Dr. Nate Mantua, a climate scientist at the NOAA/NMFS Southwest Fisheries Science Center where he focuses on studies of anadromous fish including steelhead and salmon, cautions “the warming of the California Current System that often comes with El Niño is typically bad for all West Coast salmon, including those in California.”
The thermal stratification caused by an El Niño does not spell good things for steelhead. The normal upwelling of cool waters from the bottom of the Pacific that cools the surface waters and lifts plankton from the bottom disappears. The food chain suffers as the bottom of the food pyramid diminishes.
When steelhead are in the ocean, there are El Niño caused issues. Dr. Laurie Weitkamp, a Research Fisheries Biologist with NOAA at its Northwest Fisheries Science Center, explains: “…It’s not just that the water is warmer than normal, but it’s also very low nutrient. The reason it’s warm is that it’s not mixing. These nutrients aren’t coming to the surface.”
“There is a real reduction in the prey base that steelhead depend upon,” added Gary Marston, the Wild Steelhead Initiative Science Advisor for Trout Unlimited. The steelhead diet shifts to other less nutritious foods. For example, diets shift from squid and herring, and the energy-dense northern copepods to southern copepods that don’t have the higher fat content. The lipid-rich planktons that are typical of ocean waters off the Northwest are replaced by less nutritious southern species.
Predators from the south are found in northern waters during El Niño periods, driven either by abnormal currents or migrating with the warmer water. Predatory fishes such as mackerel and hake come into the shallows and prey on juvenile steelhead. These predatory fish also compete with the older and larger steelhead for the more limited food sources. Mantua wrote “the reduced food supply can cause other predators like seabirds and marine mammals to eat more salmon and more of the available food for salmon and steelhead.”
El Niño’s influence on the North Pacific climate is strongest from October to March, and the effects can last well into the spring. This means that El Niño will often impact growth and survival rates for salmon and steelhead smolts after they enter the ocean, as most enter during the spring.
Once in the salt, steelhead, unlike other anadromous salmonids, move offshore quickly after entering the salt. Steelhead are the long-distance voyagers of the salmon world.
“When we do a survey in May off of the Washington and Oregon coast, we catch a few steelhead,” Weitkamp commented. “When we come back in June, we don’t catch a single steelhead. Steelhead fin their way straight out into the open Pacific, well off of the continental shelf.” They are found as far west as the western North Pacific, as close as 200 miles off the Kamchatka peninsula in Russia.
“Because steelhead are found over such a vast range of the North Pacific and into the Bering Sea, different fish have very different experiences with the same El Niño,” Mantua said.
“We have these anomalous blob events out in the Pacific, which are really affecting more open Pacific area that steelhead are inhabiting,” Marston said. These are “marine heatwaves,” impacting the North Pacific. Mantua reports that “marine heatwaves in the past 10 years have had widespread negative impacts on ocean productivity for many West Coast steelhead populations by degrading their food supply, both directly by changing the quantity and quality of steelhead prey, and by boosting the abundance of pink salmon that appear to be competing with steelhead.”
Weitkamp also advises that steelhead “stay super shallow, even in the top 3 feet of water. It’s surprising how surface oriented they are out in the ocean.” She recounts a NOAA high seas survey with five ships. Four trawlers set out nets, but there was inevitable net sag of 3 to 6 feet below the surface between the buoys that held the nets. The trawlers didn’t catch a single steelhead. However, one other ship used gill nets with cork across the top and no sag.
“The difference was really staggering” in how many steelhead were caught using the gill nets, Weitkamp recalled. Because steelhead stay so shallow while in the Pacific, marine heatwaves are problematic.
Considerations For Fisheries Managers
While steelhead have proven their resiliency for millions of years through climate events and changes, it remains imperative that fisheries managers be forward thinking in their approaches to managing steelhead in their respective states.
“It is incumbent upon managers to properly and conservatively manage steelhead fisheries,” John McMillan, the Science Director of The Conservation Angler, advised.
“We have these limited windows of just a handful of fish over the escapement goal,” Marston added. “It’s a really tight window to manage regimes as they’re currently set.” Fisheries managers should plan for abundance, plan for greater numbers of wild fish numbers above the escapement goals and thereby manage for future fish return uncertainty.
A key to steelhead productivity is maintaining a large degree of life history diversity that can help steelhead adapt to these changing conditions. McMillan thinks getting as many wild fish onto the spawning grounds in the best condition possible is key.
“These fish are like evolutionary lottery tickets. We don’t know which individuals will be the most successful in the new conditions,” he said. But some of them will be and those are the genes we want steelhead to pass on.
As an example, a key element to steelhead and salmon migration up the Columbia River and its tributaries is cold water refugia. Oregon designates cold water refuges and prohibits angling in the plume of cold water. However, not all states provide the same level of protection. The Executive Director for The Conservation Angler, David Moskowitz, advises: “…With climate change impacts increasing, the Columbia will be impassible to migratory salmon as soon as 2040 without action.”
Something that gives us hope, is that all of the biologists say steelhead have survived for millions of years by adapting to a changing climate, and we should see this continue.
Glenn Zinkus is an outdoor writer and photographer from Oregon. More of Glenn’s work is at www.glennzinkusoutdoors.com.