Aleutian waters warmest in more than a century; cod most vulnerable

The waters off the Aleutian Islands registered the warmest winter temperatures last year in over a century, part of a decade-long period of warming, according to a report issued by the National Oceanic and Atmospheric Administration.

The record-high temperatures in the western and central Aleutians moderated later in 2023 but warmer-than-normal conditions persisted for the rest of the year throughout the waters around the 1,100-mile chain extending from southwestern Alaska, according to the 2023 NOAA Fisheries Ecosystem Status report for the region.

The Aleutians report is one of three annual ecosystem status reports issued by NOAA Fisheries for marine areas of Alaska. The reports, compiled by large teams of scientists, were released in December and presented to the North Pacific Fishery Management Council, the panel that sets regulated commercial fishing in federal waters off Alaska.

The annual reports provide snapshots of current conditions and clues about future conditions in a warming climate, information needed to manage fish harvests and other activities, NOAA Fisheries said in a statement.

“Warming at rates four times faster than the rest of the ocean, Alaska’s Arctic ecosystems are a bellwether for climate change. Now more than ever having ecosystem and climate-related data and information is essential to support adaptive resource management and resilient commercial, recreational and subsistence fisheries, and rural and coastal communities,” Robert Foy, director of NOAA’s Alaska Fisheries Science Center, said in the statement.

The Bering Sea and other marine waters off Alaska produce more than half of the nation’s commercially harvested seafood.

In the Aleutians, the fish most vulnerable to the warm condition are Pacific cod, according to the Aleutian ecosystem status report. There are several reasons for that, NOAA Fisheries biologist Ivonne Ortiz told the council in her presentation of the report.

“Pacific cod has a very narrow range of temperatures for the eggs to hatch,” Ortiz said. That range, from 3 degrees to 6 degrees, has been exceeded in the waters, she said.

Higher temperatures also increase Pacific cod’s energy needs, Ortiz said. “The cost of living is higher, the cost of growing, feeding, pooping, having sex, swimming around is higher, so they need to either consume prey that has higher caloric content or consume more prey to make up for that,” she said. But high-quality food for Pacific cod is less available in the Aleutian region, she said.

Also vulnerable and sensitive to higher temperatures are Atka mackerel, an important species for commercial harvests, according to the ecosystem status report. But pink salmon originating from eastern Kamchatka, on the Russian side of the ocean, appear to be thriving, with the third-highest population on record, the report said.

With warming temperatures come higher risks of algal toxins, and the past year’s record provides evidence of the association. Mussels found in June at Sand Point, Unalaska, False Point and Akutan, communities in the eastern Aleutians or at the western tip of the Alaska Peninsula, had levels of paralytic shellfish toxins that were 47 times the amount deemed safe for human consumption, according to the Aleutians ecosystem status report.

The Bering Sea and Gulf of Alaska are recovering from extreme marine heatwaves that struck in recent years, according to the ecosystem status reports issued for those regions. Temperatures there have returned to more normal levels, but the unprecedented heat waves have lingering effects, according to the reports.

The Bering Sea remains warmer than the long-term average, though it has cooled since the heatwaves, NOAA Fisheries biologist Elizabeth Siddon told the North Pacific Fishery Management Council in her presentation of the report.

“It has cooled but is not cool,” she said.

Ecosystem conditions there are mixed, complex and in some cases not easily explained, Siddon said.

On the negative side, some crab stocks have continued to decline, forcing disruptive harvest closures, according to the report for that marine region. In the northern part of the Bering Sea, jellyfish — a less-nutritious prey for other fish in the food web and a competitor with groundfish for food — are proliferating.

In the southern part of the eastern Bering Sea, there has been continuation of a decade-long slide in production of high-quality plankton that is the base of the food chains. This year, the concentration hit the lowest levels in several years in that part of the Bering Sea, Siddon said. Conversely, there was a continuation of a trend to high levels of coccolithophores, a type of phytoplankton that are considered poor quality food for the food web, she said.

On the positive side, according to the Bering Sea ecosystem report, were some increases in juvenile chinook and chum salmon found in the northern region, hinting at possible improvement for Western Alaska salmon runs that collapsed in recent years.

There was improved reproduction success for some seabirds, a result that follows years of successive bird die-offs, the report said.

In the Gulf of Alaska, where the marine heat waves caused Pacific cod stocks to crash so drastically that harvests there were canceled in recent years, there is a continuing pattern of low populations of cod, as well as low population halibut and arrowtooth flounder, according to that region’s ecosystem status report. But populations of sablefish and perch, both commercially important species, continue to increase, according to the report.

Since larvae and juvenile groundfish are the most sensitive to changes in water temperature, warming seas could potentially harm the larvae of cod, pollock and northern rock sole, NOAA Fisheries biologist Bridget Ferriss told the council.

“That could harm future years’ stocks,” she said. Some adults could be vulnerable, too, because warming would diminish quality and fat levels of zooplankton.

The Alaska Beacon is an independent, donor-funded news organization.


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