Ocean Indicators We’re Tracking for El Niño’s Arrival on the West Coast

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Has El Niño reached the West Coast?

You might think it has. After all, the ocean off Southern and Central California is unusually warm. But that is from a recent marine heatwave predates the current El Niño. Much of the Pacific Coast is experiencing relatively normal conditions while still awaiting the impacts of what could be a very strong El Niño.

In June, NOAA's National Weather Service declared that El Niño had developed. That finding, however, is based on ocean temperatures from the tropical Pacific Ocean, near the Equator, which warm ahead of El Niño's impact on the Americas.

While eastern tropical Pacific temperatures have already risen more than 2°C (about 3.6°F) above normal, El Niño-related warming along the West Coast typically lags that increase by a few months. NOAA Fisheries scientists are tracking West Coast conditions as part of our Integrated Ecosystem Assessment. Here are some of the changes in ocean conditions and marine life that typically signal the arrival of El Niño's influence along the West Coast.

Ocean Conditions

Coastal Sea Level

During El Niño, winds that typically blow westward along the Equator weaken and periodically reverse in "westerly wind bursts." These wind bursts set off oceanic Kelvin waves that travel east along the Equator. After reaching Central and South America, the waves travel north as "coastal trapped waves" along the North American coast. This creates a link between the tropics and the United States known as an oceanic teleconnection. These waves travel underwater, but produce relatively small changes in sea level (approximately 15 cm or 6 inches) that are measurable at tide gages along the coast and from satellites. Kelvin waves originating along the Equator this spring and summer first reached California in June. However, their impacts on the West Coast will likely be minor compared to this fall and winter, said Nate Mantua, a research scientist with NOAA's Southwest Fisheries Science Center based in Santa Cruz, California.

Water Temperature

As these Kelvin waves move north along the coast, they deepen the thermocline -an underwater boundary at which temperatures drop rapidly at greater depths. Additionally, an atmospheric teleconnection allows El Niño conditions in the tropics to modify atmospheric pressure patterns over the North Pacific. This atmospheric influence can weaken or reverse winds that normally drive upwelling of cold, nutrient-rich water along the coast. The oceanic teleconnection is particularly impactful off Southern California, while the atmospheric teleconnection is more important off the Pacific Northwest, said Michael Jacox, a research oceanographer with NOAA's Southwest Fisheries Science Center and Physical Sciences Laboratory. Both of these teleconnections drive surface ocean warming. Together they are likely to produce unusually high temperatures that are prominent in a nearshore band extending from Baja California to Alaska.

Biological Indicators

Shifting Distribution of Fish

Migratory fish favoring warm waters are known to increase in abundance off the West Coast with El Niño. They often gain attention as one of the most visible indicators of warmer conditions. However, these species-such as dorado, striped marlin, and yellowfin tuna-have already extended their ranges north along the West Coast as marine heatwaves have warmed coastal waters without El Niño. That means they are no longer a good indicator of El Niño. A striped marlin caught in August off Washington set a new state record. Market squid, one of the West Coast's biggest commercial fisheries, typically move north in warm conditions. The fishing fleet follows the squid along the Oregon and Washington coasts. An extended warm period from 2014 to 2018 began with a large marine heatwave known as The Blob and concluded with El Niño. Scientists at NOAA Fisheries and Scripps Institution of Oceanography documented 36 unusual species off California during that time, most associated with warm waters. They included species such as blue marlin and giant manta ray. Fourteen species such as wahoo and whitenose shark were spotted in the California Current for the first time on record.

Red Crabs

Pelagic red crabs, also known as tuna crabs because they are a favorite prey of tuna, are common off Baja California. But at times they show up on the beaches of Southern California, Monterey Bay, and even as far north as the Pacific Northwest. Previous research linked these sightings to anomalous ocean currents flowing north, often (though not always) associated with El Niño. Red crabs have been reported off the West Coast in recent months, but not in the numbers often seen during warmer periods. So any unusual currents associated with El Niño do not seem to have set in-not yet, anyway.

Seabirds

Researchers track seabird populations along the West Coast because many seabirds depend on marine species as prey. Their growth and abundance reflect changes in the makeup of the prey. Initial indications suggest continued poor conditions for pelicans and Brandt's cormorants. Many seabirds in the California Current, which encompasses the West Coast, experienced declines during the 2015-2016 El Niño. In the Farallon Islands off the San Francisco Bay, the impact was not as great as in prior El Niños. The number of birds attempting to breed and their breeding success were both reduced during, and chicks took longer to grow and fledged at lower weights. On the Oregon Coast, common murres experienced complete reproductive failure in 2015 and 2016, with few eggs incubated long enough to hatch chicks.

Species Richness

Scientists have regularly measured and sampled the ocean off Newport, Oregon, along the Newport Hydrological Line for 30 years. They track changes year-round, in and out of El Niño periods. They have long observed that changes in the species of tiny marine crustaceans called copepods reflect changes in the ocean, specifically the "source waters" influencing the West Coast. Colder northern waters from the subarctic bring different species of copepods than warmer subtropical southern waters. The changes observed off Newport during previous El Niño events have all been a little different. Those differences depend on the strength and longevity of the warming at the equator, as well as the current background ocean conditions off Oregon, said Jennifer Fisher, a faculty research assistant with NOAA's Northwest Fisheries Science Center and Oregon State University's Cooperative Institute for Ecosystem and Marine Resources Studies in Newport who specializes in copepod indicators. What is consistent with each El Niño is an increase in "species richness," the diversity of copepod species compared to their abundance, she said. Greater species richness indicates a more distant water source, a common signal during El Niño. Researchers in Newport include copepod species richness in their overview of ocean condition trends that can affect juvenile salmon survival and subsequent adult salmon returns. Greater copepod species richness reflects the warmer conditions associated with El Niño. These conditions are usually unfavorable for salmon because the copepods have less lipids that fuel the food chain and help young salmon grow when they first reach the ocean.