Even as the Gulf of Alaska concludes a second consecutive non-marine heatwave year, with average ocean temperatures on the surface and at depth, impacts of four years of marine heatwave period are continuing to impact the Gulf ecosystem.
And now the 2021 Gulf ecosystem status report on the Gulf predicts a cool phase in 2022 that might shed light on how persistent the impacts of the heatwaves of 2014-2016 and 2019 will continue to be.
Researchers said that even with average to cooler ocean temperatures they can’t automatically predict higher abundance of large copepods, an important food source for some species.
NOAA Fisheries on Tuesday, Dec. 21, released its 2021 ecosystem status reports for the Gulf of Alaska, Eastern Bering Sea and Aleutian Islands, compilations of input from its own research team and the work of many contributors from fishing, coastal and Alaska Native communities, academic researchers, the state of Alaska and other federal agencies.
Report observations ranged from abundance or declining abundance of zooplankton to toxic substances found in mussels, Steller sea lion pups and seabirds in the Aleutians.
The aim of these reports is to provide a collaborative approach to inform fisheries management, including abundance trends of various fisheries and the condition of certain species at various stages of life, and an assessment of survival rates for the young of many species from larval fish to sea lion and fur seal pups.
Reports on these three ecosystems also integrate date from multi-year trends to place current year observations in a broader context, NOAA researchers said.
In the Gulf of Alaska researchers note mixed trends in prey abundance, with zooplankton at below average to average abundance and forage fish at above average abundance. Researchers found reduced abundance of groundfish apex predators, including Pacific cod, arrowtooth flounder and Pacific halibut, while adult salmon returns improved from the low numbers in 2020, with an abundance of pink salmon.
Herring spawning stock biomass continues to increase, supporting fish eating species including sablefish, the rising population of humpback whales in Glacier Bay and murres and gulls.
Collaborators noted that juvenile Pollock, a common prey species, were in high abundance, while juvenile salmon in Icy Strait were, on average, in lower abundance. Other prey species, including Tanner crab and shrimp around Kodiak, continue to increase in abundance.
Predation pressure from major groundfish predators including reduced populations of Pacific cod, Pacific halibut, and arrowtooth flounder remained lower, but was increased with sablefish. This lower pressure from those three species may enable other species to boost their abundance, but may also reflect lower system productivity and prey availability, the report said.
The report also said there is evidence of the large population of pink salmon impacting the food web in the western Gulf. This was apparent through reduced abundance of large copepods, which are pink salmon prey, increased biomass of large diatoms and the reduced reproductive success of black-legged kittwakes, who compete with pink salmon for large copepods, the report said.
Species populations that remain reduced in the Gulf include capelin, a small forage fish, as well as common murres, Prince William Sound humpback whales and some groundfish species, including Pacific cod. Some groundfish species, the study notes, continue to be skinnier than average. Possible explanations for such trends include the cumulative effects of and variable recovery times from the warm period across species at different stages of their development. Another explanation could be the continued lower productivity of the marine ecosystem in species composition of zooplankton communities.
Lower abundance of large copepods was observed around Kodiak Island. Closer to the central Gulf, the Seward Line survey observed average to above average spring abundance of large calanoid copepods in association with a large spring phytoplankton bloom.
Researchers said this productivity was not reflected in higher trophic levels as planktivorous seabirds had below average reproductive success in this region, but that above-average copepod abundance was observed in southeast Alaska inside waters. Eastern Gulf shelf conditions may have been less productive, given the below-average reproductive success of planktivorous seabirds in that area.
The Eastern Bering Sea, meanwhile, has been in a persistent warm phase since about 2014, with sea surface temperature higher than average from 1985 through 2014.
Temperatures near the seafloor in northern Bering Sea coastal waters were very warm with a small area of cold water, called a cold pool, to the southwest of St, Lawrence Island.
Those cumulative years of sustained warm conditions likely played a role in the decline of snow crab and Bristol Bay red king crab abundance as well as declines in salmon runs in the Yukon and Kuskokwim rivers and the failure of seabird colonies, the report said.
In the Aleutian Islands, in general, sea surface temperatures were near average over much of the year, but the western and central Aleutians saw record high temperatures in August and September within the satellite time series starting in 2003, the report said.
The time series is for visual data translated into temperature data, with this temperature data being the highest temperatures in this region since at least 2003.
Toxic substances were also observed in blue mussels at 75 times the regulatory level in 2021, and relatively high total mercury concentration was found in 25 percent of the Steller sea lion pups sampled to date in the western and central Aleutians. Researchers also found phthalates, a type of plastics derived contaminant, in seabirds across the Aleutians, with the highest concentrations in crested auklets, who are diving plankton-feeders.