PACIFIC OCEAN — Commercial fishing, always an uncertain business, may become more tenuous on the West Coast due to spreading areas where there isn’t enough oxygen to support important fish species.

In recent years, few fisheries were more complicated or had a more questionable future than the West Coast groundfish trawl fishery in the waters off the Oregon, Washington and California coasts. Many of the species had been overfished for years and the fishery was declared a federal disaster in 2000.

But through the efforts of fishermen and a drastic overhaul of how the fishery was managed, the fishery bounced back. Last year, it even obtained Marine Stewardship Council (MSC) certification for 13 species, signifying that the fishery met the MSC’s standards for sustainable fishing.

And yet, changes are once again on the horizon — changes that cannot be appealed or debated with, changes that could be difficult to chart or even understand until they have already swept through.

A study by scientists with NOAA Fisheries’ Northwest Fisheries Science Center and Oregon State published this year looks at low-oxygen “dead zones” that first began appearing off the Oregon coast in the early 2000s. Thousands of bottom-dwelling crabs died in those suffocating conditions.

And these low-oxygen areas are spreading. They have been documented closer to shore and now off Washington and California. With climate change, this is expected to continue.

In such conditions, some species will thrive, but others will not. In waters that area already losing productivity, according to recent reports to the Pacific Fishery Management Council, what it could all mean for commercial fishermen based near the mouth of the Columbia River and the fish they hunt — in particular, the deep-dwelling species in the groundfish fishery — remains to be seen.

The deep waters off the West Coast already have naturally low oxygen levels, but as these conditions spread, they have raised pressing questions.

In the early 2000s after the massive die off of bottom-dwelling crabs near the Oregon coast, many people wondered what it could mean for fish. Specifically, what did it mean for the species people fish for?

“We didn’t really know the impacts on fish. We couldn’t see them,” said Oregon State University oceanographer Jack Barth. He is one of the authors of a recent study “Occurrence of demersal fishes in relation to near-bottom oxygen levels within the California Curren large marine ecosystem” published in Fisheries Oceanography this year that looked at low-oxygen areas on the West Coast and their affect on fish populations.

Low-oxygen waters occur off the West Coast in two ways, Barth said.

First, there is a regular wind-driven upwelling that brings nutrients to the surface, fueling blooms of phytoplankton. When the phytoplankton die, they sink to the bottom and their decay consumes oxygen, leaving what scientists term “hypoxic conditions,” or conditions where oxygen levels are low enough to adversely affect marine organisms.

Second, there is the eastward movement of deep, oxygen-poor water that laps up against the West Coast.

“Numerous factors control oxygen concentrations of near bottom water, including when a water mass was last in contact with the atmosphere, oxygen concentration at that point of contact, the rate of oxygen consumption as well as various biological and oceanographic features,” wrote Barth and the other authors of the study.

Every year, NOAA’s Northwest Fisheries Science Center conducts West Coast trawl surveys to access stocks. The information gathered on these trips recently fueled a massive data collection, OceanAdapt, which looked at how species have shifted over time in response to changing ocean temperatures. And they were shifting, in predictable and unpredictable ways.

Barth and the other researchers looking at low-oxygen waters took advantage of the trawl surveys to send oxygen sensors down with the trawl nets. They wanted to determine which species were present in areas with different oxygen concentrations.

Like OceanAdapt, they too found changes.

Petrale sole, one of the 13 species that is MSC-certified in the West Coast groundfish IFQ trawl fishery, appeared to be the most sensitive to changes in oxygen levels — along with spotted ratfish. The presence of both fish declined sharply in areas where there was less oxygen.

However, dover sole proved to be adaptable. According to NOAA, the fish is among the few fish species that can reduce its oxygen consumption to very low concentrations. Greenstriped rockfish also seemed to be unaffected by dissolved oxygen levels.

More questions

The lead researcher behind the OceanAdapt project, Rutgers University professor Malin Pinsky said these climate change-related shifts have big implications.

As fish species shift, traditional fishing grounds will also have to shift, he said.

“You might have fishermen crossing state lines, you might have negotiations between states,” he said in an interview last December.

Many states already have such arrangements, but, he added, “It gets even more complicated when you have populations of fish crossing [national] boundaries… you have to rapidly come up with how we are going to share the benefits of what used to be a resource controlled by one country.”

It’s a discussion that could be coming, in one form or another, to the West Coast limited-entry groundfish fishery fleet as a result of changing oxygen concentrations in the waters off Oregon and Washington. Trawl survey vessels have been carrying oxygen sensors on all of their tows since 2009, and research is ongoing. But a recent report to the Pacific Fishing Management Council points to lower productivity in general in the California Current ecosystems, from Washington to California.

Climate-related changes such as shifting temperatures (warmer in certain areas, colder in others), ocean acidification and shifts in oxygen levels are herding species in different ways.

“We are in some ways entering a situation we haven’t seen before,” said Cisco Werner, director of the Southwest Fisheries Science Center in La Jolla, Calif. “That makes it all the more important to look at how these conditions affect the entire ecosystem because different components and different species may be affected differently.”