Posts Tagged low-oxygen zones

Oct 7 2017

Coastal Researchers, Fishermen Worried About More Frequent Low Oxygen Zones

Olympic Coast National Marine Sanctuary research team members, Kathy Hough and LTJG Alisha Friel, recover sensors deployed seasonally off the coast of Washington from the research vessel Tatoosh in July 2017. — S. Maenner / NOAA


Scientists in Oregon and Washington are noticing a disruptive ocean phenomenon is becoming more frequent and extreme. It involves a suffocating ribbon of low oxygen seawater over our continental shelf.

The technical term is hypoxia, sometimes called “dead zones,” It’s an unwelcome variation on normal upwelling of cold, nutrient rich water from the deep ocean. When the dissolved oxygen drops too low, it drives away fish and can suffocate bottom dwellers such as crabs and sea worms who can’t scurry away fast enough.

It seemed to marine ecologist Francis Chan like this is happening most every summer lately. So the Oregon State University researcher looked back as far as coastal oxygen readings go—to about 1950—to see if it’s always been this way.

“The ocean starting in 2000 really looked different from the ocean we had between the 1950s and 1990s,” Chan said.

Chan said climate change could affect oxygen levels via disrupted circulation and ocean warming. 
 A September storm flushed away this year’s low oxygen zone by churning Northwest coastal waters. But Chan described the severity of the low oxygen readings recorded this summer as among the worst ever observed locally.

“It’s very much a patchy ribbon,” he said from his post in Newport, Oregon. Marine surveys and fixed instruments recorded notably low oxygen values from south of Yachats up past Newport.

Ten oceanographic moorings deployed by the Olympic Coast National Marine Sanctuary also found very low (hypoxic) oxygen values between Cape Elizabeth and Cape Flattery, Washington, this summer.

“This is not a happy year for organisms out on the coast,” said Jenny Waddell, the marine sanctuary’s research coordinator.

Waddell added that at least one sensor dipped into anoxic conditions, “where there’s literally no oxygen.”

“We had indications of a relatively persistent hypoxia event along the Quinault Reservation coastline,” wrote marine scientist Joe Schumacker of the Quinault Department of Fisheries in an email Friday. “Dead fish and shellfish at various locations and times beginning near the end of July and extending through most of August.”

More frequent and severe near-shore hypoxia concerns fishermen and crabbers. Commercial harvesters face reduced catches and economic losses when crabs suffocate and fish and prawns flee the oxygen-starved waters.

One of the tip-offs to OSU researchers of the onset of low oxygen conditions this summer was when Oregon Department of Fish and Wildlife biologists monitoring crab populations noticed crabs dying from lack of oxygen in a research trap. Other observers noted crabs leaving the ocean to seek more oxygenated waters in coastal estuaries and bays.

Earlier this year, researchers and fishery advocates found a receptive ear at the Oregon Legislature when they presented their concerns about silent changes in the ocean. Legislators approved the creation of a new council to be co-chaired by the state Fish and Wildlife director and an OSU leader.

The council is tasked with recommending and coordinating a long-term strategy to address hypoxia as well as ocean acidification.

Originally published:

Mar 17 2015

NW scientists discover Pacific fish surviving dead zones

10516983-mmmainSome species of Pacific Ocean rockfish have been found to survive in low-oxygen dead zones off the West Coast, while other species struggle significantly, researchers in Oregon and Washington reported in a recent study. (Cindy, Oregon Coast Aquarium)

GRANTS PASS — Scientists say they have found that some fish can survive in low-oxygen dead zones that are expanding in deep waters off the West Coast as the climate changes.

While the overall number and kinds of fish in those zones are declining, some species appear able to ride it out, according to a study published this month in the journal Fisheries Oceanography.

The study focused on catches from 2008 through 2010 of four species of deepwater groundfish — Dover sole, petrale sole, spotted ratfish and greenstriped rockfish.

Catches of ratfish and petrale sole both declined in low-oxygen areas, while catches of greenstriped rockfish and Dover sole showed no changes. Dover sole are well-known for being adapted to low oxygen, but greenstriped rockfish are not.

Oregon State University oceanographer Jack Barth, a co-author, says commercial fishermen will likely start taking oxygen levels into account as they decide where to tow their nets.

“It’s rearranging that ocean geography,” Barth said of the low-oxygen conditions. “If you go out to a spot where you’ve always gone before commercial fishing, and you don’t catch what you expect, is it because the oxygen has gone low and things moved someplace else?”

Dead zones were first noticed off Oregon in 2002, where they peaked in 2006, and have since spread to Washington and California waters.

Some, such as where the Mississippi River flows into the Gulf of Mexico, are caused by agricultural runoff. On the West Coast, scientists have demonstrated they are triggered by climate change.

North winds cause the ocean to turn over, drawing cold low-oxygen water up from the depths. Conditions get worse as tiny plants, known as phytoplankton, are drawn to the surface, where sunshine triggers a population explosion. As they die, they sink and use up more oxygen as they decompose.

Underwater videos have shown crabs and other slow-moving bottom-dwellers in shallow waters die, but scientists from NOAA Fisheries Service and Oregon State wanted to know what happened to fish.

NOAA Fisheries was already chartering fishing trawlers to do annual surveys of groundfish populations off the West Coast. They equipped the nets with oxygen sensors.

Lead study author Aimee Keller, a fisheries biologist for the NOAA Fisheries Service’s Northwest Fisheries Science Center in Seattle, said scientists ultimately want to see whether fish forced out of preferred habitats grow more slowly, are less successful reproducing, and whether other species adapted to low-oxygen conditions move in.

The next step, she said, is to expand the surveys to include more commercially important species.

Tim Essington, professor of fisheries at the University of Washington, was not part of the study but said it was significant for covering a large geographic area, and was consistent with what has been seen in estuaries. He added he expects fish to congregate along the edges of low-oxygen zones, where predators will be able to feed on less active fish inside the zone.

NOAA oceanographer Bill Peterson, who was not part of the study, said there was no doubt that low-oxygen waters were expanding, but it was a slow process that would take decades to be felt.

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