New ecosystem reports by NOAA Fisheries cover the impact of climate change on Alaska’s marine ecosystems in the Gulf of Alaska, Bering Sea and Aleutian Islands, including heatwave periods and sustained warm conditions.
NOAA scientists note that the Gulf of Alaska has been in transition since marine heatwave periods that took place from 2014 through 2016 and again in 2019, with some marine populations decreasing and others increasing.
The year 2021 was the second consecutive year without such conditions. Mixed trends were noted in the prey base in the Gulf, with the abundance of zooplankton that provides food for fish, whales and other marine life either below average or average overall. The abundance of forage fish, including herring and age-one Pollock, was higher than in previous years. Groundfish predators such as Pacific cod, arrowtooth flounder and Pacific halibut were in reduced numbers, while sablefish biomass has been increasing. Salmon harvests also rose from lows in 2020, mostly driven by increased numbers of pink salmon.
The Bering Sea has seen cumulative impacts of sustained warm conditions since 2014. The Aleutians Islands meanwhile have experienced sustained warm conditions since 2013, resulting in the combined biomass of Pacific Ocean perch and northern rockfish rising to become the dominant pelagic foragers. Fall 2020 sea-ice formation was delayed by warm ocean temperatures and there was variable sea ice thickness due to winds across the northern and southern regions.
The NOAA reports said cumulative years of sustained warm conditions likely have played a role in declines in snow crab and Bristol Bay red king crab abundance, as well as Yukon-Kuskokwim salmon runs and seabird colony failures. Still the Bristol Bay sockeye run proved the largest since 1963.
In the Aleutians, sea-surface temperatures were near average over much of the year. Still the western and central Aleutians saw record high temperatures in August through September within the satellite time series starting in 2003. At Unalaska island, toxins in blue mussels were above the regulatory level; in 2021 they were 75 times that level, the report said.
Relatively high total mercury concentration was observed in 25% of Steller sea lion pups sampled to date in the western and central Aleutians. Research also showed that phthalates, a chemical used to make plastics more durable, was found in seabirds throughout the Aleutians.
Multi-year patterns observed across the Aleutians include an increased abundance of Eastern Kamchatka pink salmon in odd years. There were above-average water temperatures, weaker eddies and lower flow through the passes and also below-average abundance of large diatoms and biomass of mesozooplankton.
Also noted by researchers—how much the groundfish pelagic foraging guild continues to be dominated by rockfish. The combined biomass of Pacific Ocean perch and northern rockfish is higher than Atka mackerel and walleye Pollock combined.
The report said potential cumulative effects include lower productivity across the system, with increased bioenergetic needs for fish, faster growth rates for zooplankton, increased competition for prey and changes in prey=field timing, availability, quality and composition.