Gulf of Alaska Assessment - 2021

Ecosystem Assessment (pdf)

Bridget Ferriss, Resource Ecology and Fisheries Management Division, Alaska Fisheries Science Center, National Marine Fisheries Service, NOAA

Last updated: November 2021

This assessment reffects the recognition that the western and eastern GOA ecosystems (divided at 147°W) have substantial differences. The GOA is characterized by topographical complexity, including islands, deep sea mounts, a continental shelf interrupted by large gullies, and varied and massive coastline features such as the 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.

The Gulf of Alaska: Multi-Year Trends

There have been large fluctuations in the GOA groundfish community biomass at a species and functional group level, since the 2014-2016 marine heatwave, with increases in certain species (e.g., sablefish, Pacific Ocean perch, herring) and decreases in others (e.g., capelin, Pacific cod, arrowtooth flounder). Seabirds (e.g., common murres) and marine mammals (e.g., Prince William Sound humpback whales) have also undergone large changes in abundance. The GOA is still in transition from this period, in terms of shifts in species-specific biomass. The Pacific Decadal Oscillation has become negative (p.31) and ocean temperatures had a second consecutive year of temperatures closer to long-term averages (p.39), which are more characteristic of pre-heatwave environmental conditions. However, despite these environmental shifts, we have not observed a complete return to the pre-heatwave biological community. Potential explanations of this continued transitional status are briefly described below. If 2022 continues to experience cooler ocean temperatures, as predicted (p.36), it will be interesting to see if the biological community continues to recover or if alternate biomass trends and food web dynamics persist.

  1. Cumulative effects of and variable recovery times> to the 2014-2016 and 2019 marine heat wave years (Suryan et al., 2021; Arimitsu et al., 2021). Some species continue to have reduced populations since the heat wave periods, and have not responded to cooler waters and periods of improved lower trophic productivity of 2017/2018 and 2020. Examples of these species include capelin, common murres, Prince William Sound humpback whales, groundfish condition (consistently below average for a subset of species), and abundance of some groundfish species (e.g., Pacific cod). Delayed species' effects and responses to the heatwaves may be due to life history (long-lived species will respond and recover more slowly, e.g., common murres), changes in age structure or population demographics (e.g., capelin), asynchronous recovery of the Gulf food web, or reduced system productivity (see #2 below). Changes in epifaunal habitat, such as a seven-year decline in sponges (as sampled by the AFSC bottom trawl survey, p.59 andfishery observer data, p.213), may also hinder the recovery of structure-oriented species (e.g., certain rockfish).
  2. Lower system productivity in the GOA. The GOA may be experiencing continued, reduced productivity at the base of the food web, due to below-average chlorophyll-a in the eastern GOA since 2016 and three of the lowest levels in the western GOA in the past six years (p.63). In addition, the GOA has experienced a persistent shift in euphausiid species community composition and larger lipid-rich copepods have had reduced abundance (with exceptions in certain years) since the 2014-2016 marine heatwave (Arimitsu et al., 2021, p.70, Hopcroft pers. comm.). The body condition (weight at length) of a subset of groundfish species continues to be below average since 2015 (including southern rock sole, Pacific Ocean perch, age 2+ walleye pollock, southern rockfish, northern rockfish, dusky rockfish, and arrowtooth flounder) (p.130), and age-0 walleye pollock from around the Semidi Islands have had negative condition from 2015-2019 (2021 data are not available, p.88). Juvenile sablefish are shifting their distribution to deeper than traditional waters off the shelf, potentially in response to poor foraging conditions (Goethel et al., 2021). In addition, the total biomass of apex groundfish predators (Pacific cod, sablefish, Pacific halibut, arrowtooth founder) is still one standard deviation below the long-term mean (although the sablefish population has been increasing) (p.174). Certain seabirds (e.g., common murres) and humpback whales (Prince William Sound whales) also remain at reduced population sizes (p.206). There are numerous examples of other species that have recovered and/or exceeded pre-heatwave abundances (e.g., SEAK herring and sablefish), adding complexity to this theory.
  3. Pink salmon have high returns in 2021, with potential for competition and predation impacts, within the past year (p.106). Pink salmon feed on zooplankton, squid, and small fish, which can lead to reduced abundance of large copepods (grazing pressure) and increased large diatoms (reduced grazing pressure from copepods) (Batten et al., 2018), reduced reproductive success of black-legged kittiwakes (Zador et al., 2013), changes in diet and reduced size of other salmon species (Tadokoro et al., 1996; Ruggerone et al., 2003), and reduced condition of short-tailed shearwaters (Toge et al., 2011). While trophic cascades in open ocean systems is debated, these trends were supported in 2021 with observations of increased diatom abundance (p.65), regions of reduced large copepods (around Kodiak Island, p.70, but not along the Seward Line, p.76), and reduced black-legged kittiwake reproductive success on Middleton Island and Semidi Islands, but not on the Barren Islands (p.152).

Interestingly, at a broad ecosystem level, the Gulf of Alaska groundfish community is relatively stable and resilient, although it has gone through an approximately seven year period of variability at the species level, with implications for key commercial fisheries and the human communities upon which they depend. In aggregate, the decreasing biomass trends in certain groundfish species have been offset by increasing biomass of others. Key metrics of stability in the groundfish community, including high total biomass (p.184), low average biomass variability over time (p.176), high species richness and diversity (p.186), and stable (eastern GOA) or slightly increasing (western GOA) mean length and lifespan of groundfish (p.178 and p.181), point to overall high stability and resilience in the GOA (represented by species regularly caught by the AFSC bottom trawl survey). These stability indicators show trends in ecosystem structure and function, related to total optimum yield, and longer-term ecosystem context.

Current Environmental State - Gulf of Alaska 2021

Western Gulf of Alaska 2021

The western Gulf of Alaska had a second consecutive non-marine heatwave year, with temperatures at surface and depth generally hovering around long-term averages. An exception was warmer surface waters in the western GOA in the late winter/early spring (p.39). No above-average temperatures were observed at depth in 2021, indicating the residual subsurface warmer temperatures from previous marine heatwave years (as observed in 2020) have cooled (p.39). These average temperatures fit within the expected conditions associated with a negative Pacific Decadal Oscillation and La Niñna winter conditions (p.31). Surface temperatures are predicted to continue cooling into 2022, consistent with a second La Niñna winter (p.36). The 2020/2021 winter experienced northward transport (southerly winds) (p.53). Westerly winds in the spring and summer reduced the northward transport and created upwelling favorable conditions that contributed to the cooling ocean temperatures (p.32). Strong, persistent eddies were located along the shelf edge off Seward and Kodiak in the winter and spring, with higher than average winter eddy kinetic energy indicating greater transport of nutrients across the shelf (p.49). Spring winds in Shelikof Strait were downwelling-favorable northeasterly winds (conducive to enhanced retention of pollock larvae and juveniles) (p.56). The peak spring phytoplankton bloom was approximately average, with lower than average spring phytoplankton biomass (similar to 2016 and 2019) (p.63). A large, 3 week, phytoplankton bloom was observed in central GOA in April (Hopcroft pers. comm.), however the ecological response of this large bloom was not immediately apparent in the upper trophic levels.

Zooplankton had mixed trends across the western GOA. The zooplankton and larval groundfish community metrics around Kodiak Island were characterized by a warmer signature (lower abundance of large copepods, larval walleye pollock, Pacific cod, and northern rock sole) (p.70, p.85). Seabird reproductive success on Chowiet (south of Kodiak) was low to average for planktivorous seabirds (black legged kittiwakes, parakeet auklets) (p.152). Closer to the central GOA, the Seward Line survey observed average to above average spring abundance of large calanoid copepods in association with the large phytoplankton bloom (p.76). This productivity was not re ected in higher trophic levels as planktivorous seabirds had below average reproductive success in this region (East Amatuli fork-tailed storm petrels) (p.152). In the western GOA overall, adult pollock and Pacific Ocean perch (both planktivorous) continued to have lower than average condition (weight at length) reflecting food limitation (p.130).

Forage fish were potentially more available, although the community composition was supplemented by a more diverse suite of species. Of the more typical forage species, capelin (a colder-water associated forage fish) remains depleted since the 2014 marine heatwave, although some larger numbers were observed around the Shumagins and Barnabas Trough (p.99, p.94). Sand lance (warm-water associated) was locally abundant but patchy, and was present in Middleton Island seabird diets in moderate proportions (p.94). Age-1 pollock and cod were observed in relative high abundances. Less common species, such as nearshore greenlings are prominent in Middleton Island seabird diets (p.94). In general, piscivorous seabirds had average to above average reproductive success, indicating adequate forage availability and condition, and perhaps re ecting their ability to find alternative prey (Chowiet glaucous-winged gulls, common murres, tufted puffns) (p.152). Some piscivorous groundfish had improved condition (weight at length) relative to 2020, although most remained negative (p.130). While not considered forage fish, other prey species including Tanner crab and shrimp around Kodiak continue to increase (p.135, p.149). The reasons for increased abundance of shrimp around Kodiak are not known; however, contributing factors could include favorable environmental conditions and decreased predator abundance, including walleye pollock, Pacific cod, and Pacific halibut.

Adult salmon returns improved from the lows of 2020, largely driven by high pink salmon returns (p.106). High abundance of adult pink salmon reflects good marine survival in 2020, which was also a good survival year for larval cod and pollock.

HABs continued to be observed in 2021. The frequency and concentration of paralytic shellfish toxins in shellfish on Kodiak Island decreased in 2021 (from 2020 and 2019), resulting in fewer shellfish samples exceeding the regulatory limit for human consumption (p.189). Middleton Island (central GOA) experience a seabird die-off event, of which the primary suspect was botulinum toxin type C (p.24). While analysis is ongoing, this has not been linked to changes in prey availability, or algal toxins, however this may be an indicator of naturally occurring toxins expanding northward with warming oceans and changing weather patterns.

Eastern Gulf of Alaska 2021

The eastern GOA continued a second consecutive year of approximately average ocean temperatures, entering the fall of 2021 with average surface temperatures on the shelf and inside waters of Icy Strait, and slightly above average at ≈ 200 m depth on the shelf and upper slope (p.39).

Productivity at the lower trophic levels was at average to reduced levels in 2021, with potentially higher production in SEAK inside waters. At the base of the food chain, chlorophyll-a concentrations continued a six-year trend below average. However, the peak phytoplankton bloom timing was slightly early, which can be conducive to improved feeding conditions for larval fish, relative to a late bloom (p.63). Total zooplankton density in Icy Strait (inside waters) increased from 2020 to above average, driven by increases in euphausiids and small calanoid copepods, with a slight decline in large calanoid copepods (but still above average) (p.78). Contrary to the more productive inside waters, zooplankton indicators from the eastern GOA shelf (planktivorous seabird reproductive success on St. Lazaria Island, p.152) show average to below average zooplankton quantity and quality (p.152).

Despite the lower to moderate plankton productivity, forage fish were observed in higher abundance. Herring spawning stock biomass continues to increase after their strong 2016 year class (p.102), supporting upper trophic level species such as piscivorous groundfish, the increasing population of humpback whales in Glacier Bay (p.164), and fisheating seabirds (average reproductive success, p.152). Juvenile salmon in Icy Strait were less available but higher quality prey, with below average abundance but generally above average energy density (p.109, p.113).

Adult salmon returns improved from the lows of 2020, largely driven by high pink salmon returns, p.106), including 10th highest return to Auke Creek (p.116). Other salmon trends remain low, including sockeye which had the 10th lowest escapement of adults to Auke Creek (p.122). Chinook salmon populations still remain low.

HABs continued to be observed in 2021. The frequency and concentration of paralytic shellfish toxins in shellfish decreased in 2021 (from 2020 and 2019), resulting in fewer shellfish samples exceeding the regulatory limit for human consumption (p.189). The lower levels were likely due to cooler ocean conditions.

Prince William Sound 2021

Prince William Sound continues to show lagged effects of 2014-2016, and 2019 marine heatwaves. Ocean temperatures have returned to approximately average (often one year lagged from shelf conditions) (p.195). Herring stocks remain low but have followed the increasing trend observed in SE AK following the large 2016 year class (p.202). The humpback whale population also remains low following the warm periods, either explained by mortality or a change in distribution (p.206). Intertidal algae and invertebrate communities experienced a shift in community composition in 2016 that continues to persist. Primary producers (Fucus) and predators (sea stars) remain in relatively low abundance, whereas secondary consumers (mussels) remain positive or near the long-term mean (p.197).

Review of the Gulf of Alaska 2020 Ecosystem State

While COVID-19 caused disruptions to human communities, fisheries, and numerous research and monitoring programs, most data normally included in the GOA ESR were collected and analyzed in 2020 as expected. Notable exceptions include missing seabird reproductive success data, due to cancelled field camps by the Alaska Maritime National Wildlife Refuge (USFWS), and delayed lab analysis of zooplankton, larvae, and ichthyofauna samples.

The 2020 GOA marine environment was characterized by a partial return to long-term average conditions after the 2014-2016 and 2019 marine heatwave years, with some indicators showing continued residual and lagged responses in the system. The GOA ocean temperatures trended toward to long-term average conditions, ending the 2019 marine heatwave conditions. Sea surface temperatures returned to long-term mean levels for winter and spring (western and eastern GOA), followed by elevated temperatures in the summer and fall in the western GOA. The eastern GOA sea surface temperatures oscillated around the heatwave threshold throughout the summer and remained warm through the fall. Residual heat remains at depth, as seen along the Seward Line, which remains a concern for lagged ecological recovery from these heatwaves. Cooler or average temperatures indicated improved spawning conditions (relative to 2019) for late winter/early spring shelf spawners such as Pacific cod, walleye pollock, and northern rock sole. Results of these improved spawning condition were observed in 2021 survey results showing relatively abundant age-1 pollock and cod. Chlorophyll-a data indicated early peak phytoplankton bloom timing, and approximately average phytoplankton biomass in western and eastern GOA.

The North Pacific atmosphere-ocean climate system of 2020 included anomalously high sea level pressure (during winter 2019/2020), indicated by the strongly positive state of the Arctic Oscillation, resulting in westerly winds. These caused eastward and southward ocean surface transport, and upwelling conditions in the eastern GOA. Indicators of surface transport show upwelling inducing westerly winds in the winter, and south and eastward winter transport. High eddy kinetic energy in the central GOA transported phytoplankton and nutrients away from the coast, and spring wind trajectories were toward the southwest in Shelikof Strait (conducive to increased age-1 pollock abundance).

Forage conditions in the GOA improved relative to 2019, with average to increased zooplankton biomass (increased large copepods) and mixed forage fish trends (although very limited data). These trends suggest an improved prey base for planktivorous and piscivorous fish, seabirds, and marine mammals (with exceptions as described below). Zooplankton indicators suggest zooplankton prey were not limiting. Spring biomass estimates of large copepods and euphausiids were near the long-term average along the Seward Line (May 2020). Zooplankton density in SEAK inside waters (Icy Strait, summer) was near the long-term average, but had increased values of large copepods, decreased small copepods, and decreased euphausiids. A lack of additional zooplankton data makes these trends diffcult to extrapolate across the western and eastern GOA, including offshore waters, due to an \off-year" of NOAA GOA surveys and COVID-related cancellations of planktivorous seabird surveys. Continuous Plankton Recorder data on transects across the central shelf show zooplankton biomass anomalies were higher than average, with more abundant smaller copepods and average diatom abundance, potentially reflecting the warmer surface temperatures. Herring (mature spawning, age 3+) continued to increase in biomass from the 2019 high levels in Sitka Sound and Craig (ocean in uenced populations). Juvenile salmon abundances in SEAK inside waters (Icy Strait) remain below average but continue an increasing trend since a low in 2017. COVID-related cancellations of piscivorous seabird surveys resulted in a lack of additional forage fish data. Forage fisheating seabirds (surface feeding and diving) at Middleton Island found sufficient prey to successfully rear chicks, although chick diets were diverse and included an unusual increased proportion of greenlings. These diets suggested that the more typical forage fish, such as capelin, were not abundant.

groundfish biomass trends in 2020, an \off-year" for the GOA-wide bottom trawl surveys, are based on ADF&G surveys off Kodiak Island over Barnabus Gully and in two inshore bays. Catch rates were below the long-term mean for arrowtooth ounder, athead sole, Pacific cod, Pacific halibut, skates, and walleye pollock. Catch rates were above the long-term mean for Tanner crab. Southwest wind trajectories in Shelikof Strait and an early spring phytoplankton bloom (similar to 2017 and 2018) predicted good age-1 walleye pollock in 2021, which was born out in 2021 surveys.

Paralytic shellfish toxins (saxitoxins) concentrations in phytoplankton and shellfish were lower in 2020, relative to 2019, possibly due to the rainy summer and cooler temperatures in 2020. Saxitoxin concentrations in Kachemak Bay and Kodiak Island were generally below regulatory limits, while some samples exceeded this threshold in southeast Alaska

Salmon commercial harvest was low across most of GOA, and lowest in SEAK since 1976, resulting in numerous request for the State to declare salmon fishery disasters. The low returns in SEAK were primarily driven by low chum and sockeye. Low adult returns are tied to juvenile mortality in 2017 (and years since then for certain life histories) but the mechanism driving that trend (e.g., environment, predation) is still uncertain. Juvenile salmon energy density in Icy Strait (SEAK) was at or above average (decreasing for pink and sockeye and increasing for chum and coho, relative to 2019), indications of potentially improved future adult returns (although not a direct relationship).

Seabirds and marine mammals had mixed trends in 2020, with continued effects of the marine heatwave years. Humpback whales counts in Prince William Sound remained lower in 2020 than pre-2014 heatwave levels. Humpback whale productivity and juvenile survival in Glacier Bay and Icy Strait returned to more typical, pre-2014 heatwave levels, reflecting good feeding conditions (for females) from 2018-2020. This could include the increased herring abundance described above. Overall, the status of seabirds was fair to good in the western GOA in 2020. Colony attendance remains low in some populations compared to historic levels, however, when birds did arrive to breed, reproductive success was fair to good for both surface, fisheating birds and diving, fisheating birds. Seabird bycatch in 2020 declined from 2019 by 50% in the GOA, led by declines in catches of black-footed albatross and gulls (the lowest western GOA seabird bycatch in 10 years). This decline reflects COVID-related reductions in fishing effort and shifts in sablefish fishery gear from hook-and-line to pots.

The marine heatwave years (2014-2016, 2019) continue to have cumulative and lagged effects throughout the system. Residual heat at depth was observed along the Seward Line ( ≈150m) with potential implications for early survival of groundfish that use these habitats for spawning (e.g., Pacific cod). There were mixed trends in forage fish abundance (although limited data), with continued decreased abundance of capelin, a key prey species. Some groundfish (e.g., Pacific cod), seabird (e.g., common murres), and whales (Prince William Sound humpback whales) are still lower abundance than pre-heatwave levels.