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Dead zones, a ‘horseman’ of climate change, could suffocate crabs in the West, scientists say

Oregon State University scientists and students conduct research to track hypoxia in the Pacific Ocean off the Oregon coast. (Francis Chan/Oregon State University)

As the Pacific Ocean’s cool waters hugged Oregon’s rugged shore, Nick Edwards, a seasoned commercial fisherman, could not believe his eyes. Stretching over at least 100 yards, he said, were the carcasses of hundreds of Dungeness crabs piled in the sands of a beach south of Cape Perpetua.

The remains of what Edwards deemed “the crème de la crème of seafood” — also one of the state’s most prized fisheries — are the most visible byproduct of a process that usually goes unnoticed by most beach-dwellers: hypoxia, or the emergence of swaths of low-oxygen zones in marine waters.

Hypoxic areas in Oregon, researchers found, have surfaced every summer since they were first recorded in 2002 — leading scientists to determine a recurring “hypoxic season,” akin to wildfire and hurricane ones.

However, climate change has exacerbated its effect, said Francis Chan, the director of the Cooperative Institute for Marine Resources Studies at Oregon State University, resulting in increasingly frequent and extensive hypoxic areas that can morph into “dead zones,” where the total lack of oxygen kills off species that cannot swim away, much like the Dungeness crabs.

“It’s one of the horsemen of climate change in the sea,” Chan said. “And that’s because the water that we get is lower in dissolved oxygen than it used to be.”

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Such is the case this year that an NOAA-sponsored scientific cruise found a large hypoxic area growing off the coast of northern Washington and through Oregon, just six miles from the shore. Its onset came prematurely, with oxygen levels dropping as early as April. With months left until the temperature cools, both experts and fishermen worry it will turn into a vast dead zone, ballooning over its currently detected 7,700-square-mile range.

“We’re still trying to figure out how large this is going to be because the major impact occurs in late August, early September,” said Richard Feely, senior scientist at the Pacific Marine Environmental Laboratory of the National Oceanic and Atmospheric Administration.Right now, we’re anticipating there could be impacts on crabs and fish that live at the bottom.”

As the hypoxic area inches closer to the areas where fisheries operate, it has forged a partnership between scientists and fishermen — as both wish to understand its underlying causes and future effects.

This phenomenon is in part spurred by natural events. During the spring and summer, strong winds push the bottom waters onshore, providing a flood of nutrients that “feed phytoplankton productivity,” Feely said. When these marine creatures die, they sink to the bottom and decay — a process that consumes oxygen and, in turn, causes hypoxia.

Experts are increasingly worried about low-oxygen waters off the coast of Washington and Oregon potentially becoming large "dead zones.” (Video: The Washington Post)

The problem comes when a changing climate is thrown in the mix. As carbon dioxide is released into the atmosphere, the ocean becomes “a sink,” Feely said, and absorbs the emissions. The result is water acidification, which can cause the shells and skeletons of some marine creatures to dissolve.

This occurrence paired up with hypoxia becomes a “double whammy from the atmosphere and the ocean” that the Oregon and Washington coast is particularly sensitive to, Feely said.

Rising temperatures are another point of concern exacerbating hypoxia, said Chan. “When the surface ocean is really warm, it acts as a blanket that suffocates and keeps the interior of the ocean from refreshing, taking a breath of oxygen,” he said.

Though these climate events have strengthened since the turn of the millennium, their effects are often hard to pinpoint. “With other events, if you look outside your window, you can see a drought or a wildfire,” Chan said. “But the ocean, it’s really hard to know because it’s changing. That’s why it’s important to have more eyes on the ocean, and it takes not only scientists but our fishermen, too.”

Commercial fishermen have been fundamental to the understanding of hypoxia since the beginning, Chan said. In fact, it was a crabber’s call detailing dead crabs and octopuses crawling over the fishing lines that inspired his research.

Chan’s team has joined efforts with a crew of Dungeness crabbers to measure oxygen levels in the chilly waters. He developed a smart sensor that is placed in crab pods — the data collected can then help scientists learn more about the changing ocean and tell fishermen where hypoxia may be affecting their catch.

“The partnership between commercial fishermen and these researchers is the easy solution to getting that data,” said Aaron Ashdown, a second-generation Oregon fisherman. “We’re out there, if not every day, so we get to see things that most other people don’t get to see.”

The impacts of dead zones and hypoxic regions in Oregon’s Dungeness crab industry are still largely unknown.

This year has not provided the same bountiful catch as previous years. With a little more than 12 million pounds of crab caught, the season is less than the 17 million pound decade average, and well bellow the over 20 million pounds of the past three years, according to Tim Novotny, the Oregon Dungeness Crab Commission’s spokesman.

Yet the cyclical nature of the crab season combined with other factors that can naturally affect fishing challenge determinations, said Novotny.

Still, with hypoxia presenting both a short-term and long-term problem, Novotny said the industry is hoping to adapt.

“It’s concerning because if we’re starting to see it earlier, then we’re starting to see it impact more of the catch, more of the landings for that particular season,” he said. And if that’s a trend that is going to continue, we need to know about it. The more data we can get from research, the better we are to be prepared and dealing with these sorts of events.”