Low oxygen levels off the northwest coast raise fears of marine “dead zones”


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Low oxygen levels measured off the coasts of Oregon and Washington raise fears of large “dead zones” that could wipe out crabs and groundfish inside.

The National Oceanic and Atmospheric Administration, or NOAA, announced Wednesday that researchers had detected abnormally low oxygen levels in a large area off the Pacific coast.

Year after year, low oxygen levels from the early 2000s have led researchers to determine that Oregon now has a “hypoxic season” just like it has a fire season – and fire season. he hypoxia this year came on much earlier than usual.

This could have major implications for coastal economies, especially those related to Dungeness crab.

“When it starts very early, we give [oxygen levels] still several months to go down and [the dead zone to] grow in space, ”said Francis Chan, who heads the Cooperative Institute for Marine Resource Studies at Oregon State University.

According to NOAA, dead zones occur when winds pick up in the spring and summer, dragging cold water from the ocean floor to the surface. This contributes to phytoplankton blooms, which later die off and sink to the ocean floor. Bacteria consume oxygen by breaking down plankton.

Sea creatures like crabs that cannot escape from the low oxygen zone are left behind.

“It’s a relatively natural characteristic, but it intensified over time,” Chan said. “We know that at some point [oxygen] becomes too weak and marine life suffocates.

The start of the hypoxic season is marked by the rise of cold bottom waters. The winds initiated this rise this year around March. Chan said they were Oregon’s first ocean observers for 35 years.

Two of the worst hypoxic seasons off the Oregon coast occurred in 2006 and 2018. Crab fishermen have reported removing traps with choked crabs unfit for consumption.

“Unfortunately, this is another year that appears to be a pivotal year for these areas of hypoxia,” said Tim Novotny, communications manager for the Oregon Dungeness Crab Commission.

Hypoxic areas can kill not only 4-year-old crabs – which are often what seafood eaters find on their plates – but younger crabs as well. This can affect crab catches years later, Novotny said.

Researchers, with help from fishermen, are looking for more data to determine the size and intensity of low oxygen areas off the coast this year. Chan spoke to OPB while at sea on a research vessel, collecting additional measurements.

He said more and more people have their eyes on the ocean now, and researchers hope they can map where and when hypoxic areas develop off the coast.

The Oregon Legislature passed a bill this session allocating $ 1.9 million to research and monitor hypoxia and ocean acidification off the coast.

“Any kind of data that comes in is gold, as far as we’re concerned,” Novotny said. “You can’t fight what you don’t know.”

Modeling from the Cooperative Institute for Climate, Ocean and Ecosystem Studies predicts a large hypoxic zone off the northwest coast through the fall of this year.

Copyright 2021 Oregon Public Broadcasting. To learn more, visit Oregon Public Broadcasting.

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