IT’S THE KIND of sunny spring day that makes a person want to stay in the Pacific Northwest forever. At Twin Beach, on the northern coast of Washington state’s Olympic Peninsula, aquaculturist Mark Tagal sits on the back of his truck, looking out at the Strait of Juan de Fuca. The peaks of Vancouver Island rise up across the water. Tagal’s eyes are on the birds — watching for the moment when they begin to congregate just above the water’s surface — and on the waves, waiting for the tide to rise and show signs of the fish he’s come here to catch.

One by one, others gather at the remote beach. They stand at the shoreline with long-handled nets, hoping to catch surf smelt (Hypomesus pretiosus), a silvery, 8-inch fish that serves as a keystone species in its marine ecosystem in various stages of its life, providing prime forage for salmon, seabirds, raptors, marine and terrestrial mammals, and humans.

Smelt are common in Washington state, where they spawn on different beaches throughout the year. Despite this, scientists know little about them.

Unlike most forage fish — small bait fish that feed on plankton and other microscopic organisms, schooling in large shoals for protection — surf smelt swim all the way up to the high tide line to spawn, leaving their fertilized eggs in the beach sediment as the water recedes. Ranging from Southern California to Alaska, smelt are common in Washington state, where they spawn on different beaches throughout the year. Despite this, scientists know little about them, including how many there are, or whether there are distinct genetic populations. They do know, however, that some populations frequent the east side of Puget Sound, near Seattle, in summer; in winter, they migrate south toward Tacoma; in spring, they move northwest to the Strait of Juan de Fuca, including Twin Beach — which is where Tagal and other fishermen are now waiting for them to push in to spawn.

Donning chest-high waders, Tagal gathers his dip net, his cooler, and his plastic collection vials. Never one to shy away from meeting new people, he strikes up a conversation with another fisherman as they make their way down to the water. They step into the surf, lower their nets into the ocean, and wait to feel the heaviness of the smelt moving in with the waves. There’s never a big crowd out fishing for smelt, likely because there’s no significant commercial market for the fish — which is normally eaten whole, bones and all. The recreational fishery requires no permits, and even on a busy day you might find only 10 to 15 people on the beach. Those who do come, however, prize this fish and form a diverse group comprised of Southeast Asian, Eastern European, Indigenous, and more rural White communities.

Each beach has its own makeup, but everyone at Twin today seems to be having better luck hauling in smelt than Tagal. Finally, he turns to the fisherman he met on the walk in and asks, enthusiastically: Could he please squeeze his fish?

The fisherman chuckles and says yes, and Tagal gets to work finding “ripe” fish by gently squeezing their lower abdomens. If the fish are ready to spawn, their bellies will be distended by the eggs or milt — sperm-containing fluid — in their bodies, and the gametes will flow freely. When that happens, Tagal immediately mixes the eggs and sperm together in the plastic vials. Then, adding a little saltwater, he gives the vials a light shake and pops them into his cooler.

An hour later, Tagal leaves the beach with enough specimens for his research, along with some whole smelt the fisherman gifted him for dinner. In the coming days, he will place these fertilized embryos in specially designed cages on beaches around Puget Sound as part of a pilot project to track the presence of pollution in their habitat.

Tagal and the team he’s working with at the Washington Department of Fish and Wildlife (WDFW) hope that the smelt embryos will reveal how human changes to the fish’s intertidal environment — such as ocean pollution, coastal development, and ecological restoration — affect both smelt and the overall ecosystem that they support.

ON MARCH 24, 1989, the Exxon Valdez oil tanker ran aground in Prince William Sound, Alaska, more than 1,300 miles northwest of Twin Beach. The ship spilled 11 million gallons of crude oil across thousands of kilometers of Alaskan coastline, killing hundreds of thousands of seabirds, thousands of marine mammals including sea otters, harbor seals, and orcas, and hundreds of thousands of salmon and herring — generations of fish that are essential to coastal ecosystems, economies, and cultures across the Pacific Northwest.

In the wake of the disaster, researchers from the National Oceanic and Atmospheric Administration (NOAA) and the United States Geological Survey launched what at the time was the largest environmental impact assessment ever conducted on a marine oil spill, a now decades-long effort that has monitored the impacts on various species found in Prince William Sound. Pacific herring — which, like smelt, are important forage fish — spawned soon after the spill. In the first years following the initial spill, researchers discovered oil-associated liver lesions in adult herring and found that developing herring from areas affected by the spill had twice the mortality rate of those from unoiled sites, with significantly more external physical and chromosomal abnormalities. Even after the most visible signs of the spill had begun to dissipate, the damage continued to proliferate. By 1993, only 25 percent of the expected adults returned to spawn, and the Pacific herring population crashed.

Starting in 2008, a series of toxicology studies helped explain the collapse, revealing that compounds found in crude oil damage herring embryos’ developing hearts, causing sublethal, lifelong defects that impair the health of individual fish (and potentially the larger fishery). In November 2024, the commercial herring fishery reopened for the first time in more than 30 years, though populations remain lower than before the spill.

“What happens to all the fish that didn’t get killed by the oil but are still screwed up?”

While the Exxon Valdez first helped scientists understand the damaging effects of crude oil on developing herring, it was another spill that would provide the opportunity to apply what had been learned as a tool to monitor the health of the underwater environment.

In November 2007, leading into herring spawning season, the Cosco Busan container ship collided with the San Francisco-Oakland Bay Bridge and spilled more than 200,000 liters (53,000 gallons) of heavy fuel oil into the water. Three months after the spill, researchers designed an in situ, or “in place” biomonitoring approach to better understand the impacts of the event on developing herring. Depositing manually fertilized herring embryos in underwater cages, similar to those that Tagal would eventually design for smelt, and collecting them after seven days of exposure to the oil that had washed through the Bay, the team examined the developing larvae using photo- and video-microscopy. They not only confirmed that the oil caused rapid and extensive cardiac damage to the embryos but were also able to show that, while the levels of pollutants present in the water appeared to be below the lethal threshold based on previous laboratory studies, extreme die-off nonetheless occurred because of interactions between the pollutants and sunlight. This proved the value of using the fish embryos as a toxicology monitoring tool, opening up a new avenue to study the health of the nearshore environment.

Since then, research teams have used similar techniques to study the impacts of land-based pollutants, such as urban stormwater runoff and the creosote (wood preservative) used to treat pilings of piers and docks, which contains the same damaging compounds as crude oil. The methods have also been pivotal in guiding restoration projects aimed at removing these pilings.

“When you look at an oil spill,” said Tagal, “you say okay, X amount of oil is going to kill this whole population of fish. That’s horrible, but it’s kind of easy to wrap your head around, you know? But the hard part is, what happens to all the fish that didn’t get killed by the oil but are still screwed up?”

Over the years, herring embryos revealed much more to scientists than the toll of pollution on just one species. But studying herring has limits. Herring spawn only in shallow “nearshore” waters, in places like eelgrass or kelp beds, and their embryos must always be submerged. Surf smelt, on the other hand, ride the high tide all the way onto the beach, and their young embryos cling to small gravel in the “upper intertidal” zone as the water retreats during low tide, and are exposed to air and sunlight. This means that smelt are more susceptible to land-based pollution, such as urban stormwater, sewage overflows, shoreline development projects, and the “bathtub” effect of oil and other spills. Researchers have since adapted herring techniques to study smelt, to better understand the effects of pollution in the upper intertidal — the critically important places where land meets sea and marine and human ecosystems converge.

EIGHT MONTHS PREGNANT, Louisa Harding was situated farther back from the makeshift microscopy station in her basement than she would normally sit. Light filtered in from a large window across the room as Harding, a WDFW research scientist who studies contaminants in fish, drew a dropperful of water and smelt embryos — collected and placed by Tagal along Washington beaches — into her pipette. When Covid-19 shuttered the NOAA lab where she had been doing her microscopy imaging to all but essential personnel, Harding set up a home lab so she could continue her work. With each embryo Harding examined, she was looking for sublethal effects of pollution.

Harding had previously studied herring embryos as part of a research team looking at the impacts of stormwater runoff and had partnered with Tagal to collect the herring gametes and embryos. Smelt provided intriguing new research opportunities, but also new challenges: No one knew exactly how to fertilize or rear smelt embryos in a lab. Nor had the embryos ever been deployed in the field specifically for monitoring contaminants.

“I’m useful to the toxicology guys because I’m able to keep fish alive,” said Tagal, who was immediately attracted to the challenge of working with a novel species like smelt. “We were shooting from the hip,” he said. It took a year just to figure out how to fertilize the eggs. Unlike herring, which still have viable gametes after hours dead on ice, Tagal found that smelt gametes require immediate fertilization. His first success involved an impromptu mixing session in a Pepsi cup on the beach. Then, he had to figure out how to keep the embryos alive.

Smelt embryos depend on being out of the water for part of the day at a “Goldilocks” depth — not too deep in the gravel and coarse sand, not too exposed to air and sun. To recreate the tidal cycle in the lab, Tagal used a metal container of the sort you see piled with lemon wedges at a restaurant, filling it with pea-sized gravel and placing the embryos on top in a small cross-section of PVC pipe. Two tubes controlled the inflow and outflow of water to the gravel, while an electric valve set to a timer simulated the tidal cycle. Amounts of pollutants added to the water changed to mimic shifting concentrations over time — one day after an oil spill, one month, one year, and so on. “When oil hits the beach and sticks to all these rocks,” Tagal explained, “even after years, the amount of oil is going to degrade but, as the tide comes in, it’s going to be in contact with these rocks and get to the eggs.”

When Harding examined these lab-raised smelt embryos, she found that, like herring, their hearts became deformed when exposed to crude oil.

The next challenge was to take this work to the field, keeping embryos alive and in place in their natural intertidal environment. To do this, the team needed a cage that supported normal development, was resistant to predators and vandalism, and was easily assembled, deployed, and retrieved. Unlike herring eggs, which could be suspended in the water column on plastic screens, smelt cages had to sit directly on the beach at the high-tide line. After more trial and error, Tagal designed a DIY-combo of a commercial crab bait trap, PVC pipes, and nylon mesh that they could bury in the beach sediment, allowing water and potential pollutants to pass freely over the developing embryos.

In the field, it was Tagal’s job to find ripe smelt, fertilize the eggs, take the embryos home in a cooler to develop for a few days, then deposit them in the cages at both “clean” and “dirty” study sites around Puget Sound. Ten to 30 days later, depending on the season (smelt take longer to develop in the winter), he’d return after a data logger in the cage notified him that the embryos were ready to hatch, and bring them to Harding for imaging. At her home lab, Harding painstakingly counted the embryos — each hardly bigger than a grain of sand — and tracked developmental milestones like eye formation, pigmentation, and heart function in the embryos across time. And she seemed to appreciate them all. “Smelt are adorable,” Harding said. So are their embryos, she added as she admired a specimen under her microscope. “They have really long necks that make them kind of look like geese.”

“Sometimes the fish can tell us a lot, before we even know what chemical we’re looking for.”

In previous research on herring, scientists found that even brief exposure to pollutants could lead to lifelong heart defects. The heart deformities Harding found in lab-raised smelt embryos suggest that the long-term impacts of pollutants may be similar. The fish may appear normal from the outside. But those cardiac deformities can impede a smelt’s ability to swim, to breathe, and to reproduce, which can hinder predator evasion, finding food, or spawning — which could, in turn, cause population declines. While these impacts may be less obvious than those seen in the immediate wake of major pollution events like the Exxon Valdez, the losses can ripple through the food web, to the seabirds, raptors, and marine mammals that feed on species such as herring and smelt.

“Not a lot of people have heard about surf smelt or thought about forage fish,” Tagal said, “but a lot of people around Puget Sound have an opinion on orcas.”

Tagal and Harding hope the new knowledge they’ve uncovered about smelt development could reveal impacts of coastal development and pollution that may otherwise be difficult to detect through traditional water monitoring. This may be because chemicals like oil and PCBs are more likely to stick to the sediment where smelt embryos are deposited, or because the levels of a toxin are either too low to read or — as in the case of the Cosco Busan — because they aren’t immediately lethal, and obscure the true impact of those pollutants in a real-world environment. “Sometimes the fish can tell us a lot before we even know what chemical we’re looking for,” Harding said.

By listening to the smelt, researchers and regulators might not only track the health of the intertidal zone, but also bring new insights that could guide future management and land-use decisions and environmental remediation work. Perhaps, Tagal mused, regulators could deploy smelt embryos near new construction projects to “correct the mistakes that have been made elsewhere, so that stormwater doesn’t just run directly onto the beach.” Combined with other research — on smelt population genetics, for instance — the new tools might even help illuminate why smelt have declined or vanished from some areas.

ON A WARM July afternoon off Camano Island in Puget Sound, about an hour’s drive north of Seattle, the sky fills with storm clouds and Josh Cousins, a commercial fisherman, scouts the waters for smelt. Cousins, 34, started fishing at age two and has been motoring the waterways of Puget Sound in search of smelt ever since, the last in his family to keep up the trade. His boat, a small 19-footer Glasply with a modified bench for a better view beneath the surface, hardly screams “commercial,” but he is the last smelt fisherman catching large numbers in this area. He knows the waters, tides, and ecology of this region like the back of his hand, and has seen everything from bald eagles to river otters to harbor seals come out to feast on spawning smelt. “You should have been here yesterday!” he says to me as I hop onto the bow of his boat. (It’s a phrase he will repeat on subsequent days.)

The smelt fishery has changed, Cousins tells me as he cruises the shallow waters, perched high on his bench with a cigarette in one hand and a Red Bull in the other. The last two seasons, he says, the smelt have spawned later than they used to. They’ve abandoned certain spawning beaches but have shown up for the first time in other locations. He attributes those changes to the degradation of their spawning habitat. “It’s the bulkheads put in all through Puget Sound destroying smelt spawning beaches, and the clearing of trees that used to shade the beach for smelt eggs.” Harding and Tagal’s research helped reveal other, invisible causes as well: lethal and sublethal levels of pollution that are harming smelt and their shoreline ecosystems.

Cousins has been a willing contributor to their research: When Tagal needed gametes for his embryo cages, he would occasionally reach out to Cousins, waiting at a designated beach while Cousins put his Glasply into position in shallow waters and motored in a semicircle around the schooling smelt, driving them toward land as he dropped his net. At water’s edge, Cousins would kill the engine, leap out of the boat, and single-handedly — though Tagal always offered to help — haul his beach seine toward the shore. The smelt would school closer and closer together with each strenuous pull. Then, Tagal would step inside the net containing the panicked smelt, check them for ripeness, squeeze eggs and milt into his collection vials, and let Cousins get back to his work.

On this summer afternoon, as the storm clouds dissipate, Tagal isn’t here to collect specimens. But Cousins still waits for the smelt to spawn, letting his net sit against the side of his boat as the tide laps up on the beach. Only after the milky cloud has started to dissipate in the water does he bring the fish into his boat with a dip net, as the smelt’s characteristic smell of sliced cucumber permeates the air.

Before long, the early alpenglow will begin to color the glaciers of Mount Baker pink. And even after the sun dips below the horizon, recreational fishermen will dot the beach, standing chest-high in the water with their dip nets, hoping, along with Cousins, that the smelt will continue to return.

The smelt are telling us something important about the health of our coastal environment. Harding and Tagal have learned to listen. In the end, Harding told me, “We have to step back and ask, ‘What are the fish telling us?’”