7 Ways El Niño and Large Marine Heatwave Could Affect West Coast Marine Species

A large marine heatwave has bathed parts of the West Coast in very warm ocean waters over the past year, breaking temperature records in the Pacific. NOAA has also announced that El Niño has developed in the tropical Pacific and is predicted to intensify to a moderate or strong level this fall. El Niño represents another form of marine warming , though with different drivers and influences. The prolonged period of high temperatures could affect fisheries and marine life in the California Current that have already been buffeted by shifting ocean conditions over the last decade.

One factor may help dampen the impacts, though: The same strong upwelling of cool water along the coast that fuels the West Coast ecosystem with nutrients could help keep some warmer waters at bay, as happened in 2025.

We have seen these back-to-back heat events before. About a decade ago, a major marine heatwave known as "The Blob" began raising ocean temperatures off the West Coast, peaking in 2015. One of the strongest El Niños on record followed in 2015-2016, amplifying ocean warmth-as the current forecast predicts for the coming year. That was a worst-case scenario that drove changes around the world. The Pacific endured a record count of tropical cyclones and the Caribbean Sea and parts of Africa experienced severe droughts. That situation was more extreme than now, with the Blob lasting longer and affecting the entire West Coast compared to the smaller recent marine heatwave. However, research and observations during that unprecedented climatic pileup suggest the kind of changes we may see in the coming months along the West Coast. Though these changes are centered in the Pacific, they have far-reaching impacts.

Here are some of the ways warming water can impact marine life, coastal communities, and economies.

1. Shifting Fisheries

Research found that some commercial West Coast species, such as market squid, may be sensitive to these long-term and episodic changes in ocean temperatures. The shift of market squid north along the West Coast in response to warming from the Blob and subsequent El Niño created new fishing opportunities in Oregon and Washington during the Blob that remained afterward. Squid landings in Oregon rose from none in 2015 to nearly 3 million pounds worth more than $1 million in 2016 and continued to grow rapidly through 2020. This provided new opportunities for purse seine vessels whose opportunities in other fisheries affected by the Blob-such as sardine, Alaska herring, and Alaska salmon-had dwindled. Seafood processors in Oregon scaled up to handle more squid, and Oregon fisheries managers developed their first regulations for the emerging squid fishery. Market squid had been the largest commercial fishery by volume in California, but California landings dropped by more than half from 2014 to 2015. They remain substantially lower than they were prior to the Blob and El Niño.

Meanwhile, tropical species such as whale sharks and hammerhead sharks made northerly appearances off Southern California while fishing vessels caught albacore tuna much closer to shore as far north as Washington. Fishing boats caught a skipjack tuna off the Copper River in Alaska, and surveys turned up an ocean sunfish and thresher shark off southeast Alaska. Pacific bluefin tuna increased in number and size in U.S. waters, exciting recreational anglers and generating new revenue for the charter fleet. This year, Southern California anglers have begun catching dorado and yellowfin tuna much earlier in the year than usual, suggesting these northerly shifts may have begun.

2. Hungry California Sea Lion Pups

Higher sea surface temperatures also affect other fish species, including sardines and anchovy. These fish are high-energy staple foods for California sea lions that breed in Southern California's Channel Islands, but declined with warming ocean temperatures. Sea lions turned to lower quality forage species such as rockfish and squid. Nursing sea lion mothers had to travel farther to find the food their pups needed, forcing pups to fast for longer periods at the rookery. The weight of sea lion pups declined, according to long-term studies in the Channel Islands . In El Niño years, many hungry pups set off on their own in search of food before their usual weaning time. In 2013-2016, as many as 4,000 pups arrived on California beaches, skinny and hungry. These extreme events taxed rehabilitation facilities and prompted NOAA Fisheries to declare an Unusual Mortality Event for the species. Researchers later estimated that an increase of 1 degree Celsius in sea surface temperatures could reduce the growth rate of the sea lion population to zero. A 2-degree rise would reduce the population size by about 7 percent.

3. Harmful Algal Blooms

Warming temperatures can accelerate the growth of the toxic algae Pseudo-nitzschia , which produces domoic acid that can poison humans and wildlife. The Blob drove outbreaks of harmful algae that shut down West Coast crab and other shellfish fisheries. The crab fishing fleet sat idle when they would otherwise be hauling in Dungeness crab, which are holiday traditions for many West Coast families. Warming marine waters, including the Blob and El Niños, may have seeded a region off the coast of Northern California and Southern Oregon with toxic algae, NOAA Fisheries research found. The toxic reservoir may now help fuel future harmful algae blooms with persistent impacts on commercial and recreational fisheries.

4. Tough Times for Salmon

Warming can be harmful to salmon, whether in the freshwater or saltwater chapters of their life cycle. Low snowpack that preceded the Blob combined with atmospheric patterns that blocked cooling winds. A severe California drought also left little cold water in Shasta and other reservoirs. As western rivers warmed to lethal temperatures for salmon, managers had no way to offset the heat. About 95 percent of the eggs spawned by endangered winter-run Chinook salmon in the Sacramento River died in 2015. Current conditions are similar, with record-low snowpack across most of the Western United States, although reservoir storage is much better than it was in 2015.

Young salmon also faced difficulties in the ocean during the Blob and El Niño years, since warmer ocean waters typically lack the high-energy prey juvenile salmon depend on for rapid growth during their first months after entering saltwater. That lack of quality prey reduces their odds of survival, which in turn reduces the chances they will return to rivers and support coastal fisheries as adults 1 to 3 years later. The years following the Blob brought weak salmon returns to many rivers along the West Coast, leading to 2017 closures of salmon fishing along parts of the California and Oregon Coasts. Some salmon stocks, such as Oregon Coast coho, fared better, though, as different stocks rely on different parts of the ocean affected differently by the warming influences.

5. Habitat Compression Raises Whale Entanglement Risk

NOAA scientists recently found a connection between whale entanglements and changes in cool-water areas along the West Coast fed by cold water from the deep ocean. That cold upwelling supplies nutrients to the West Coast ecosystem, attracting anchovies that in turn draw humpback whales hungry for these prey. The same nutrient influx makes it a good place to set crab traps. Warm conditions offshore-driven by marine heatwaves and compounded by El Niño-pressed up against those cool-water corridors along the coast in what is known as "habitat compression." This pushed the whales into the same waters as hundreds of crab traps, increasing their risk of getting entangled in lines to the surface. The new research also showed models can help anticipate changes in habitat compression, providing an early warning system to alert the fishing fleet to increased risks of entanglements.

6. Good Times for Rockfish?

Rockfish were some of the rare winners during the Blob and El Niño years, and could benefit in unusual conditions to come. The bottom-dwelling species had collapsed from overfishing decades before, but stocks had been rebuilding since the early 2000s. Juvenile rockfish boomed over a large area from California to Alaska. Surveys along the West Coast in particular found record numbers of pelagic juveniles of many winter-spawning species in 2015 and 2016. Stock assessments later confirmed strong year classes of young fish for many (but not all) stocks. Although surface waters were warm, subsurface waters were cooler during the Blob-conditions often associated with greater juvenile productivity . However, juvenile abundance has dropped during past El Niño events, such as 1983 and 1998, so the outcome this time remains uncertain and may depend in part on the strength of upwelling and the cool, nutrient-rich water it can provide. Rockfish take decades to reach maturity; researchers are tracking how many of the young rockfish survive to join the population as adults.

7. Seabirds Take a Hit

Research found that more than half of Alaska's population of roughly 8 million common murres disappeared from about 2014 to 2016 , with few signs of recovery afterwards. The decline may have been related to the same impacted food web that reduced survival of salmon in the ocean. Scientists speculated the ecosystem may have changed in fundamental ways that reduced its capacity to support seabirds such as common murres. They suggested the declines of seabirds and other species made the Blob, combined with El Niño, the driver of one of the largest marine mortality events ever recorded in modern times. Other seabird species also suffered: In late 2014, thousands of dead Cassin's auklets covered beaches in the Pacific Northwest.

While past warming events don't guarantee future impacts, the conditions and biological responses we documented during earlier warming episodes can help us anticipate and prepare for what may be coming. El Niño may bring both challenges and opportunities for fisheries on the West Coast and beyond. While some impacts can mainly affect the West Coast, trickle-through effects may reach other U.S. fisheries in ways that affect our seafood supply. Distant subarctic waters and even the Caribbean have exhibited responses to past El Niño events.