Ecosystem Assessment (pdf)
Bridget Ferriss, Resource Ecology and Fisheries Management Division, Alaska Fisheries Science Center,
National Marine Fisheries Service, NOAA
Last updated: November 2022
This assessment reflects the recognition that the western and eastern GOA ecosystems (divided at 147°W) have substantial differences. The GOA is characterized by topographical complexity, includ- ing islands, deep sea mounts, a continental shelf interrupted by large gullies, and varied and massive coastline features such as Cook Inlet, Prince William Sound, Copper River, and Cross Sound, which bring both freshwater and nutrients into the GOA. The topographical complexity leads to ecological complexity, such that species richness and diversity differ from the western to eastern GOA. Thus, local effects of ecosystem drivers may swamp basin-wide signals. With this in mind, we present report cards and assessments of current ecosystem state for the western and eastern GOA ecoregions separately to highlight inherent differences.
During 2022, operational impacts due to COVID-19 had a negligible effect on information used in this report, due in large-part to effective mitigation strategies put in place to protect the health and safety of field research personnel and communities.
The Status of the Gulf of Alaska 2022
The Gulf of Alaska (GOA) shelf marine ecosystem continues an ongoing transition from a marine com- munity responding to previous marine heatwaves (2014–2016 and 2019), to one potentially characterized by cooler ocean temperatures. This year was the most consistently productive year since the last year dominated by marine heatwave conditions (2019). The productivity was consistent spatially, across the GOA, and across numerous ecosystem metrics. Despite the generally productive year, some concerns persist around thermal and foraging conditions for adult groundfish along the shelf edge and upper slope. There are additional concerns regarding the potential impact of warm, summer and fall, ocean surface temperatures on juvenile groundfish overwinter survival in 2023. This year (2022) was an ‘off’ year in the alternating GOA schedule of NOAA’s bottom trawl, summer acoustic, and spring ecosystem (EcoFOCI) surveys, limiting available information related to groundfish ecosystem conditions, especially in the western GOA.
Western Gulf of Alaska Shelf 2022
The western GOA experienced a third consecutive year of non-persistent marine heatwave conditions, and experienced a mixture of cooler and warmer than average conditions throughout the year. Cooler winter and early spring surface temperatures coincided with a productive start to the year (Temperature Synthesis, p.36). Summer and fall temperatures (as of November 1) were above average, at surface and at depth (Temperature Synthesis, p.36). Warming in the second half of the year has the potential to negatively impact growth and lipid storage for groundfish, especially important for survival of juveniles entering their first winter. Surface temperatures are predicted to be cooler than average in the upcoming winter (2023, Bond, p.34).
The winter and spring ocean temperatures were cooler than average, coinciding with generally average to above-average forage conditions, with the exception of zooplankton around the Semidi Islands. Moving from west to east within the western GOA, zooplankton biomass was potentially below average southwest of Kodiak, as indicated by parakeet auklet reproductive success on the Semidi Islands (Seabird Synthesis, p.124). Spring biomasses of copepods and euphausiids were close to the survey average (1998-2022) along the shelf, offshore of Seward (Hopcroft, p.70). These generally favorable prey conditions east of Kodiak were reflected in average to above-average planktivorous seabird reproduction (observed in colonies on E. Amatuli and Middleton Islands, Seabird Synthesis, p.124). Forage fish appeared relatively abundant and available to predators across the western GOA, based on above-average reproductive success in fish-eating seabirds (at the Semidi Islands, Middleton Island, and mixed trends on Amatuli Island, Seabird Synthesis, p.124). Seabird chicks on Middleton Island were fed a variety of herring, sandlance, age-0 sablefish, and other forage fish (but low levels of capelin), reflecting the presence of key forage species in the adult foraging range (Hatch, p.86). Fish-eating and zooplankton-eating seabirds were also observed in higher densities above the middle shelf of the Seward Line in 2022. This expansion follows a period of concentration in the nearshore regions after the 2014-2016 and 2019 marine heatwave periods, and indicates greater forage opportunities across the shelf (Seabird Synthesis, p.124).
Longer-lived species at higher trophic levels may still be impacted by marine heatwave impacts. The endangered western distinct population segment of Steller sea lions have experienced declines of non-pup counts in the GOA regions from 2017-2021, likely associated with the 2014–2016 marine heatwave in the GOA (Sweeney, p.144). This decline follows an increasing trend since the early 2000’s. Potential mechanisms for this decline include reduced prey availability (walleye pollock and Pacific cod are key prey species), and reduced reproductive success and juvenile survival.
The frequency and intensity of harmful algal blooms were minimal this year, and appear not to have increased in response to the warmer-than-average summer temperatures (Farrugia, p.149).
Eastern Gulf of Alaska Shelf 2022
The eastern GOA shelf had similar trends in thermal conditions and productivity at lower trophic levels as the western GOA. The region experienced a cooler-than-average winter and early spring. Summer and fall temperatures (as of November 1) were above average at the surface (Temperature Synthesis, p.36), including a brief but widespread marine heatwave in July and a more prolonged marine heatwave period through the month of October (and continuing as of November 1). Warm summer and fall ocean temperatures can negatively impact growth and lipid storage for overwinter survival of groundfish, especially juveniles entering their first winter.
The cooler winter and spring ocean temperatures coincided with an above-average zooplankton and for- age fish prey base. Total zooplankton density in Icy Strait (driven by calanoid copepods and euphausiids) was greater than one standard deviation above average (Fergusson, p.72). These positive zooplankton forage conditions were reflected on the shelf, offshore from Sitka, by above-average reproductive success of zooplankton-eating seabirds on St. Lazaria Island (Seabird Synthesis, p.124). Reproductive success of fish-eating seabirds at the same location was also above average, presumably reflecting the availability of nutritious forage fish (Seabird Synthesis, p.124). Herring populations in Sitka Sound and Cross Sound continue to be relatively abundant (supported by a strong 2016 year class) (Hebert, p.91), and numerous young sablefish cohorts appear to be in the GOA system, including age-0’s that appeared in Middleton Island seabird chick diets and presumably traveling from eastern GOA nursery habitat to within foraging range of the Middleton Island seabirds (Goethel et al., 2022, Hatch, p.86). Some metrics of forage fish in the eastern GOA are below average, including eulachon population estimates (Pochardt, p.95) and some juvenile salmon CPUE and smolt productivity in southeast Alaska (Strasburger, p.103, Vulstek, p.109).
Commercial harvest of salmon in southeastern Alaska has been below average (1997–2022) since 2017 (sockeye and Chinook salmon), 2018 (coho and pink salmon), and 2019 (chum salmon) (Strasburger, p.103). Juvenile salmon CPUE from Icy Strait, southeastern Alaska, have been consistently below or near average for all species since 2016 (Chinook salmon), 2017 (chum, pink, and sockeye salmon) and 2018 (coho salmon) (Strasburger, p.103). Explanations of these low indicators of juvenile salmon abundance vary by species and life history, but reflect a combination of spawner abundance (pink salmon), marine survival (chum), and freshwater and early marine survival (Chinook, sockeye, and coho salmon). Average fork length and energy densities of these juvenile salmon were all at or above average in 2022, with the exception of chum salmon, reflecting foraging success (Fergusson, p.105).
Marine mammals are experiencing continued impacts of the 2014–2016 and 2019 marine heatwaves. The eastern distinct population segment of Steller sea lions (removed from the threatened listing under the Endangered Species Act in 2013) have experienced declines of non-pup and pup counts in the GOA regions from 2017–2021, likely associated with the 2014–206 marine heatwave (Sweeney, p.144). Potential mechanisms for this decline include adult movement out of the region, reduced prey availability (walleye pollock and Pacific cod are key prey species) and reduced reproductive success and juvenile survival. Glacier Bay, humpback whale calf production declined since 2020 and 2021, and the 2019–2022 crude birth rate has not recovered to the pre-2014 mean. Humpback whales in Prince William Sound are not considered to have returned to pre-2014 levels, although 2022 encounter rates of humpback whales increased from recent years. The decline in Prince William Sound humpback whales is surprising given the return of Prince William Sound herring biomass, a key prey species, to pre-marine heatwave levels.
The frequency and intensity of harmful algal blooms was minimal this year, and appear not to have increased in response to the warmer-than-average summer temperatures (Farrugia, p.149). Invasive green crabs were detected in Alaska for the first time in July, 2022 (Ferriss, p.22). They are known to expand their range northward in summers following warm winters, so their potential range expansion will be important to monitor if warm temperatures persist in the eastern GOA. However, surface temperatures are predicted to be cooler than average in the winter (2023, Bond, p.34).
GOA Shelf/Upper Slope 2022
The GOA shelf edge and upper slope demersal/benthic habitat is an area characterized by limited ecosys- tem data, but includes some indicators of increased concern. This is habitat for numerous managed groundfish species, including sablefish, rockfish (e.g., shortraker rockfish, rougheye/blackspotted rock- fish, thornyhead rockfish, Pacific Ocean perch), and flatfish (deepwater flatfish complex, including Dover sole). A number of these species migrate onto the shelf to spawn (e.g., sablefish, POP) and others are capable of changing depths in response to environmental conditions (Yang et al., 2019), so their ability to mitigate unfavorable habitat and forage conditions may be greater than some shelf groundfish. However, given the data-poor aspect of this habitat, it is important to highlight declining trends in relevant indicators when they arise. For example, temperatures around 250 m depth, along the shelf edge, have been consistently above average since 2016 (Temperature Synthesis, p.36). Also, structural epifauna (primarily sponges), which are important habitat for rockfish, have experienced a multi-year decline in the western GOA (Whithouse, p.172 and AFSC bottom trawl survey CPUE, Palsson, 2021). In addition, adult female sablefish had below-average condition in 2022, potentially indicating that they experienced challenging forage conditions, despite their characterization as opportunistic predators. We have no data on biomass trends on benthic infaunal prey (polychaetes and clams) or invertebrates on or near the bottom (amphipods and other small crustaceans, shrimp, and brittlestars), which are primary prey for numerous flatfish in this region.
The Gulf of Alaska: Multi-Year Trends
The upcoming winter is predicted to be a third consecutive La Niña, which, coupled with a negative Pacific Decadal Oscillation (PDO) and non-persistent marine heatwave conditions, has been associated with a three year period of cooling on the GOA shelf. A triple La Niña would be the third such event to occur in the past 50 years, yet there are numerous reasons to assume the ecological response to the current period will not follow past trends. Differences include: (1) the current La Niña period beginning in warm ocean thermal conditions throughout the water column, following the 2014–2016 and 2019 cumulative marine heatwave period, (2) a marine community in transition from that warm period,(3) the documented weakening of relationships between various climate indices and GOA community responses due in part to a weak Aleutian Low (Litzow et al., 2018), and (4) the continued long-term warming of the GOA (Thoman, p.32) shifting the definition of warming and cooling as they relate to species’ temperature thresholds and responses.
Previous triple La Niña periods occurred from 1973–1976 and from 1998–2001. The PDO shifted from a previous cool regime (negative index) to a warm regime (positive index) in 1977, which, along with a strong Aleutian low, induced a regime shift from a GOA community dominated by flatfish and crustaceans (as well as increased seabird and Steller sea lion populations) to one dominated by gadids and rockfish (Chavez, 2003; Mueter and Norcross, 2000; Anderson and Piatt, 1999). The second triple La Niña (1998–2001) was characterized as a cool thermal period in the GOA, with a suite of more temporary community responses, including strong 1999 year classes of walleye pollock and Pacific cod, increased shrimp biomass, and increased presence of capelin in seabird diets (Boldt, 2005; Hatch, 2013). The past two La Niña/ negative PDO years (2020, 2021) have coincided with ocean temperatures cooling from initial warmer-than-average thermal conditions throughout the GOA shelf water column to approximately average temperatures, with extended cooler-than-average temperatures for the first half of 2022. Given the residual heat in the system, the productive, cooler-water affiliated communities, as observed in the 1998–2001 period, took multiple years to materialize in the current period, or still remain elusive. For example, localized large phytoplankton blooms were observed in 2021 and 2022 but not consistently across the GOA (Strom, p.60 and Gann, p.57). Zooplankton productivity has remained patchy across the GOA, but has been the most spatially consistent and highest biomass in 2022 (Hopcroft, p.70, Fergusson, p.72, and Kimmel, p.65). Capelin populations remain relatively low (Hatch, p.86), and there are mixed trends in the productivity of certain groundfish species (e.g., Pacific cod has not yet recovered, Hulson et al., 2022).
If the PDO remains negative in upcoming years, and if there is an absence of persistent marine heatwaves, the GOA could remain in a cooler state, but would not be expected to return to the same ecological community as the pre-70’s regime shift. A return to that period is unlikely as there are more than two potential states of the GOA marine system, and there have been multiple ecological and oceanographic shifts, and climate-induced changes since then. However, recently-observed trends may indicate the direction in which the GOA marine community is transitioning. Total apex biomass of groundfish remains low (as of 2021, Whitehouse, 2021) and groundfish surplus production metrics indicate potentially lower productivity (as of 2019) (Mueter, p.187). GOA groundfish biomass remains dominated by arrowtooth flounder, walleye pollock, Pacific Ocean perch, and increasingly sablefish. However, the composition of this group is shifting. Pacific cod has not recovered from the severe decline during the marine heatwave period and arrowtooth flounder has been declining since 2008, while Pacific Ocean perch has steadily increased over many years and sablefish has been increasing since 2016. Other isolated indicators that show differences potentially reflective of community transitions include: (1) the 2022 Papa Trajectory Index (an indicator of winter surface transport) had the second most southerly endpoint since the 1970’s (Stockhausen, p.50), (2) tanner crab and shrimp CPUE around Kodiak continue to increase (Worton, p.113), and (3) commercial catches of certain GOA salmon stocks, particulary in southeastern Alaska, remain below-average (Whitehouse, p.100). Another year (2023) of similar ocean conditions would be informative as to the relative persistence of these trends.