Ecosystem Assessment: The Status of the Gulf of Alaska 2024

Bridget Ferriss, Resource Ecology and Fisheries Management Division, Alaska Fisheries Science Center, NOAA Fisheries
Contact:bridget.ferriss@noaa.gov
Last updated: November 2024

This Assessment reflects the recognition that the western and eastern GOA ecosystems (divided at °W) have substantial differences (Waite and Mueter, 2013; Mueter et al., 2016). 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 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 highlight differences in the ecosystem state for the western and eastern GOA ecoregions in the Report Cards and Assessment.

Summary 

The Gulf of Alaska’s (GOA) marine ecosystem experienced a relatively productive year in 2024, generally higher and more spatially consistent than 2023. The winter El Niño conditions were more moderate than expected, although surface and deeper waters did experience some associated warming. Some highlights of the year include indicators of above average primary and secondary (zooplankton) production, suggesting a good prey base for forage fish, juvenile and plankton-eating adult groundfish, and seabirds. Capelin populations continue to rebound across the GOA, and herring populations continue to persist at relatively high levels in southeast AK. Humpback whale crude birth rates in the eastern GOA recovered to pre-2014 values for the first time since their post marine heatwave decline. Conversely, GOA commercial salmon landings were some of the lowest since 1985, driven by unexpected low returns of pink salmon in Prince William Sound. While the GOA continues to warm over the long term, 2025 is predicted to be cooler than the 1991 – 2020 average due to developing La Niña conditions.

El Niño Winter 2023/2024

The GOA experienced El Niño conditions during the winter and spring of 2023/2024, after three years dominated by La Niña, and is predicted to transition back to La Niña status in the fall of 2024. The El Niño was one of the top five strongest events since 1950, though weaker in strength than the ecologically impactful 1997/1998 and 2015/2016 events. However, the impact of El Niño in the GOA was moderated by its relatively short duration, a reduced potential for increased counterclockwise circulation and northward transport of warm surface waters due to a weak Aleutian Low, and variable/eastward winds in the winter and spring (Lemagie and Bell, p.30). The GOA also did not experience extended warm or marine heatwave conditions, as it did in 2016 when the strong El Niño coincided with additional sources of heat from the North Pacific (i.e. the “Blob”).

While the GOA experienced warmer ocean temperatures in the winter and spring, a strong ecological response to warming pressure was not evident in the system. For example, the frequency and extent of harmful algal blooms remained somewhat average (they tend to increase with warm waters) (Farrugia et al., p.175). The intertidal communities retained their local, spatial variation, a pattern that becomes homogenous in the presence of overriding external environmental drivers such as marine heatwaves (Coletti et al., p.183). Seabird productivity was average to above average across the GOA (they can respond negatively to warmer conditions and related impacts on prey resources) (Drummond et al., and Whelan et al., p.152). The potential impact of a warmer first half of 2024 on groundfish recruitment, which could be expected to include strong year classes of rockfish and sablefish (favored by warm spring/summers) or weak year classes of walleye pollock, Pacific cod, and northern rock sole (favored by cool winter/springs), will become apparent when they begin to be observed in surveys, in a few years’ time.

Gulf of Alaska Shelf 2024

Ocean surface temperatures were warmer than average across the GOA shelf in the winter and spring, ranging from 4 °C/5 °C (March) to 12 °C/14 °C(Aug) in western and eastern GOA respectively (Lemagie, p.43). The eastern GOA surface temperatures exceeded the marine heatwave threshold for most of Dec.-May, covering up to ~75% of the eastern GOA shelf area, remaining warm through the summer. The warm late spring/early summer surface temperatures in the eastern GOA may have been favorable for feeding and survival conditions of larval sablefish and rockfish. During the western GOA winter, warm surface temperatures cooled more quickly and returned to average by March (Lemagie and Callahan, p.43). The warm late winter and early spring surface temperatures did not appear to exceed egg and larval temperature thresholds of early spring spawners (e.g., walleye pollock, Pacific cod, northern rock sole) and may have favored their growth.

The warming of deeper shelf waters in the western GOA appeared to be limited, due to decreased coastal downwelling that would transport heat to depth and the resulting potential for increased incursion ofcooler, more saline, lower dissolved oxygen slope waters onto the shelf in the western and northern GOA (Pages and Hauri, p.64). Spatially limited surveys observed some moderate heat at depth in the spring (central GOA, Danielson, p.43) and summer (southeast AK inside waters, Fergusson, p.43), but not in January in Shelikof Strait (Jones et al., p.43).

Increased winter and spring counter-clockwise circulation and surface transport were reflected in numerous metrics, as expected with El Niño events. It is likely the circulation could have been even stronger if the Aleutian Low was stronger and anomalous winter/spring eastward winds were not present to moderate the westward flow. Eddies were stronger than usual along the shelf edge in the regions off Kodiak and Haida Gwaii (Cheng, p.56). The modeled northward surface transport in southeast AK, from the Papa Trajectory Index, increased from weaker (2023) to the long-term average (2024) (Stockhausen, p.61). The GAK1 mooring (near Seward) measured lower salinity in the surface waters, reflecting increased transport of freshwater from southeast AK (Danielson, p.72). The larval survival of slope spawning arrowtooth flounder, Pacific halibut, and rex sole may have increased due to transport to preferred coastal habitat.

The spring oceanographic conditions supported high energy transfer through the base of the food web. The phytoplankton community was dominated by the larger celled diatoms (Hennon p.70), similar to 2021 and 2022, and higher than 2023. Diatom production is supported by upwelling in the central GOA gyre, bringing nitrate-rich waters to the surface and onto the shelf through increased advection (Conte et al., 2024). The Northern Gulf of Alaska Oscillation index measures upwelling at the center of the Gulf gyre, which was positive (weaker upwelling) in January and February, but then negative (stronger upwelling) in the spring, supporting this theory (Pages, p.64). Strong diatom production supports larger, more energy rich zooplankton species (euphausiids and copepods), verified by an increase in observed spring euphausiid biomass in Seward Line surveys (Hopcroft, p.83). The resulting above-average spring zooplankton biomass provided good prey resources for zooplankton-eating adult groundfish (e.g., walleye pollock, Pacific Ocean perch, dusky and northern rockfish), and larval/juvenile groundfish. Planktivorous seabird reproductive success, an indicator of zooplankton availability and nutritional quality, was above average across the GOA, and increased from 2023 (Drummond et al., and Whelan et al., p.152).

The GOA forage fish populations varied across the GOA but were generally average to above average in 2024 (similar to 2023). Capelin continues to rebound from a population decline during the 2014 – 2016 marine heatwave (McGowan et al., p.101, Arimitsu et al., p.96), which is beneficial for seabirds, marine mammals, and piscivorous groundfish. Also, herring continue to have relatively elevated populations supported by the strong 2016 and 2020 year classes (Hebert and Dressel, p.105, Morella et al., p.188). Forage species that are relatively lower in abundance include eulachon, sand lance, and juvenile salmon (Arimitsu et al., p.96, Pochardt et al., p.109). The reproductive success of fish-eating seabirds was variable but generally above average across the GOA reflecting adequate prey availability for groundfish with forage fish in their diets (e.g., P. cod, sablefish, and arrowtooth flounder; Drummond et al., and Whelan et al., p.152).

The GOA 2024 commercial salmon fishery landings were within the five lowest years since 1985, largely driven by low pink salmon returns. The returns of pink salmon were unexpectedly low, primarily in Prince William Sound, while southeast AK was the exception, meeting its 2024 forecast (Whitehouse, p.113, Vulstek et al., p.124, Strasburger et al. p.116). Potential reasons driving the low returns include (a) reduced early marine survival in 2023, due to low zooplankton biomass, including evidence of smaller average length and lower body condition of juvenile pink salmon in 2023 in SEAK (Yasumiishi, 2023; Fergusson and Strasburger, 2023); and (b) poor survival of juveniles/adults in their offshore habitat due to poor ocean conditions and/or increased competition with the strong odd year class of pink salmon in this oceanic region (environmental and prey conditions are unknown) (Ferriss, p.26).

Multi-year Trends/ Community Dynamics

Oceanographic trends reveal long-term unidirectional changes in the GOA (with interannual variation), while ecological communities reflect less predictable, multi-year shifts in dynamics. The GOA shelf’s long-term sea surface temperature continues to increase from 1900 through 2024, across the winter and summer months (Thoman, p.43). Temperatures at depth in the central GOA (200m – 250m) have increased since at least 1975 (GAK1 mooring, Danielson, p.72). Over the same 50 year time period, stratification has increased (reducing vertical mixing in the water column), and salinity has decreased at the surface (fresher water) while increasing at depth (more saline waters) (GAK1, Danielson, p.72). The decreased surface salinity suggests increased transport of the Alaska Coastal Current during fall, winter and spring months, coupled with potentially higher freshwater runoff (Danielson, p.72).

The GOA’s marine communities continue to reflect a mixture of short- and long-term dynamics. While some species’ populations respond within the same year to environmental changes (e.g., zooplankton), others have a more lagged response that manifests after a few years of consistent conditions. In the past 10 years, the GOA has experienced marine heatwave-dominated years (2014 – 2016 and 2019), followed by three consecutive La Niña years (2020 – 2023) that brought a cooling pressure, an El Niño event in 2024 with moderate warming, and a predicted return to La Niña in 2025. Explorations of shifts in ecosystem states around 2014 within Gulf of Alaska marine ecosystems have mixed results (Suryan et al., 2021; Litzow et al., 2020) but perhaps due to differences in spatial scales and species studied. Ferriss et al. (Submitted) analyzed indicators primarily used in the Gulf of Alaska Ecosystem Status Report, and concluded that a community shift occurred around 2014 in most components of the eastern and western GOA (oceanography, lower-trophic, mid-trophic, seabirds), largely persisting through 2022. At a species-level, some populations that were greatly reduced due to the 2014 – 2016 marine heatwave are still responding to that event. Pacific cod and sand lance populations remain depressed. The capelin populations were observed to continue rebounding in 2024 for a second year, and the crude birth rate of humpback whales increased to pre-2014 levels in southeast Alaska for the first time. While population dynamics of humpback whales may have contributed to their lagged recovery, the elevated herring and euphausiid populations (and reduced pink salmon predation on zooplankton) provided a good prey base for them in 2024. Other populations that experienced strong year class survival and resulting population increases from the 2014 – 2016 marine heatwave are transitioning away from that event, including the shift of large young cohorts of sablefish off the shelf as they age (Goethel and Cheng, 2024), and reduced Tanner crab biomass as the large 2016 cohort declines (Worton, p.128).

There have been longer-term (beyond 10 years) changes in relative biomass of the top groundfish species, as estimated by NOAA’s bottom trawl survey (last surveyed in 2023; Callahan p.139). Pacific ocean perch biomass has been increasing, and the once-dominant arrowtooth flounder has been decreasing, since approximately 2003. Pacific ocean perch replaced arrowtooth flounder as the top groundfish biomass in 2017. Arrowtooth biomass has been slowly increasing in more recent years, along with its predation pressure on key groundfish (i.e., walleye pollock and P. cod; Adams, p.133), but remains in second place. The relatively high biomass of zooplankton predators in the GOA is supported by high biomass of P. ocean perch (highest groundfish biomass), walleye pollock (3rd highest groundfish biomass) and pink salmon in odd years (including high returns in 2021 and 2023). The impacts of this shift in prominent trophic dynamics in the GOA are uncertain.

Looking Ahead to 2025

La Niña conditions are predicted to develop in the fall of 2024 and persist through the winter of 2025. In the GOA, La Niña events are associated with cooling sea surface temperature. Despite the predicted cooling pressure, the Sitka air temperature index predicts integrated water column temperatures at GAK1 (off Seward) to be warmer than average in 2025 (Hennon and Danielson, p.40). This counter-intuitive prediction potentially reflects the delayed onset of La Niña conditions and/or the long-term warming of GAK1 temperatures, with temperatures more consistently above the long-term average (but perhaps less so in 2025). A productive spring zooplankton community and approximately average (baseline 1985 – 2014) temperatures in the fall of 2024 are conducive to potentially favorable groundfish larval growth in 2024 and survival into 2025. The predicted cooling, or slight warming, predicted in the winter and spring of 2025 are generally favorable for adult groundfish in 2025.