The waters off Alaska’s Aleutian Islands registered the warmest winter temperatures 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 the year 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 earlier this month 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.

‘Cooled, but not cool’

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 heatwaves 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 the decline that forced 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 heatwaves 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.

On the lookout for El Nino effects

The spring warming that is expected with the ongoing El Nino weather pattern could further jar the Gulf of Alaska, NOAA Fisheries biologist Bridget Ferriss said in her presentation to the council.

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. “These wouldn’t be the fish that we’re fishing on next year,” she said. However, that could harm future years’ stocks, she said. Some adults could be vulnerable, too, because warming would diminish quality and fat levels of zooplankton, she said.

Potentially vulnerable adult fish like pollock won’t necessarily be fewer in number, but their bodies might be changed, Ferriss said. “We might just see skinnier fish next year as they have a little bit of a poorer zooplankton prey base to feed upon,” she said.

Potentially benefiting from El Nino-driven warmth are sablefish, which have thrived in recent years, along with arrowtooth flounder, southern rock sole and halibut larvae, Ferriss said.

Marine heatwaves have profound effects, research has shown.

A new study details how the unusually warm conditions in the Bering Sea in 2018 – a year with the least amount of winter sea ice since records began in 1850 – altered the phytoplankton populations that make up the base of the food web.

Normally, spring sunlight stimulates algal growth on the underside of sea ice, and the algae continues to bloom as the ice melts. That phytoplankton later drops to the seafloor, serving as food for bottom-dwelling species that are part of what is classified as the benthic zone. But when ice is missing, the spring phytoplankton bloom occurs in open water, nourishing marine creatures swimming closer to the sea surface, considered the pelagic zone, but not reaching the benthic zone at the bottom.

Benthic species include clams and snails, which in turn are eaten by mammals like walruses and seals. Pelagic species include salmon, pollock and herring and fish-eating seabirds.

The new study, by scientists with NOAA, the University of Washington and other institutions, tracks the different Bering Sea spring blooms that occurred from 1998 to 2018. It found that while the timing of spring blooms did not shift over that period, the characteristics of the blooms did change.

If the pattern of warm years intensifies, the shift in spring phytoplankton blooms will continue to favor the pelagic species, even in the northern reaches of the Bering Sea, the study authors said.

• Yereth Rosen came to Alaska in 1987 to work for the Anchorage Times. She has reported for Reuters, for the Alaska Dispatch News, for Arctic Today and for other organizations. She covers environmental issues, energy, climate change, natural resources, economic and business news, health, science and Arctic concerns. This story originally appeared at alaskabeacon.com. Alaska Beacon, an affiliate of States Newsroom, is an independent, nonpartisan news organization focused on connecting Alaskans to their state government.