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AI_Assessment

Aleutian Islands 2024 Report Card

Ivonne Ortiz1and Stephani Zador2
1Cooperative Institute for Climate, Ocean and Ecosystem Studies, University of Washington
2Resource Ecology and Fisheries Management Division, Alaska Fisheries Science Center, National Marine Fisheries Service, NOAA
Contact: ivonne.ortiz@noaa.gov
Last updated: November 2024

Current Conditions 2024

The Aleutian Islands ecosystem in 2024 showed signs of a gradient of poor productivity in the west to high productivity in the east, largely based on counts of Steller sea lion pups and non-pups and seabird reproductive success. Despite the overall relaxation of the multi-year warm conditions across the ecosystem and a low abundance year in the biennial Kamchatka pink salmon cycle, groundfish condition remained poor across the ecosystem, which would not typically be expected in a year with relatively cooler conditions and fewer pink salmon. Rockfish continue to comprise the main biomass of pelagic foragers in the area, which means that overall pelagic forager biomass will respond more slowly to changes in the environment than when Atka mackerel and walleye pollock were dominant. Winter sea surface temperature was still among the ten warmest on record (Figure 16). Strong winds and storminess during the 2023-2024 winter through spring contributed to cooler conditions during late spring and summer and were accompanied by a deeper mixed layer in the water column, similar to the previous year. This may have impacted the vertical distribution and availability of prey throughout the water column.

Groundfish condition deteriorated across most species throughout the ecosystem, despite the cooler temperatures. In particular, the condition of Pacific cod, northern rockfish, and POP have been below the long-term mean since 2012 across all regions (Figure 33). The decline in fish condition may also be indicative of several interacting factors including poor prey quality, low availability of prey, competition, and increased metabolic rate (Holsman and Aydin, 2015).

The impacts of the biennial Eastern Kamchatka pink salmon were documented in the AI ESR 2023 (Ortiz and Zador, 2023). Their abundance in 2024 was very similar to that in 2022, around 60,000 mt, which is close to the current total biomass estimate for the Aleutian Islands Pacific cod stock (Spies et al., 2024). Notably, this “low” pink salmon abundance is similar to what was considered high abundance in the 1970s and 1980s (Figure 31). Counts of western DPS (distinct population segment) Steller sea lion non-pup and pups in 2023 continued to show an increasing trend since 2007 (p. 76).

Western Aleutians

Sustained high sea surface temperatures during winter resulted in a moderate marine heatwave in the western Aleutians (Figure 17). Sea surface temperatures cooled in later spring but increased again in summer and has remained above the long-term (1985-2014) average (Figure 17). Marine heatwave conditions returned in late summer and have prevailed through early November. At times during late summer, over 75% of the western Aleutians were in heatwave status and reached the highest surface temperatures across the island chain. Bottom temperatures cooled slightly to below the 1991-2012 mean for the region (Figure 21). Eddy kinetic energy was above the long term average early in the year but is now below average, suggesting that there were higher fluxes of nutrients, heat, and salt through the passes in the western Aleutians early in the year, but then those declined (Figure 24). Warm sea surface temperatures over the western Aleutians have been the dominant trend for the last decade, which may be due to weaker wind-driven mixing, warmer air temperature, or advection of warm water from the North Pacific Ocean.

Based on biomass estimates from the 2024 bottom trawl survey compared to 2022 estimates, apex predator abundance decreased 16% overall, driven by a decrease in Pacific cod and arrowtooth flounder. In contrast, the overall biomass estimate of pelagic foragers increased 6%, driven by northern rockfish and walleye pollock (Figure 61). Small walleye pollock were not only the sole groundfish group whose condition increased in the western Aleutians, their condition was the highest that has been recorded (Figure 34). The below average fish condition of all groundfish, other than small pollock, suggests that they continue to experience either poor prey quality and/or low availability of prey. In fact, the steady decline over the last decade of the biomass of eelpouts and shrimp lends support to this idea (Figures 36, 37). In the case of Pacific ocean perch and northern rockfish, which are both primarily planktivorous, their declining condition may also be due to instraspecific competition for prey, given their sustained high biomass.

The stormier conditions potentially had an impact on seabirds at Buldir. Reproductive success was lower in 2024 than in 2023, with most species across the prey and feeding strategy spectrum having below average reproductive success (8 out twelve, Figures 41, 42) and later than average hatch timing (8 out of eleven, Figure 39). This includes planktivorous auklets as well as fish-eating puffins and kittiwakes. This suggests that there was not enough available prey to support successful reproduction for the majority of seabird species in 2024. Tufted puffin chick diets by weight at Buldir were mainly composed of squids 64% and 22% pollock, while horned puffin chick diets there were primarily composed of Atka mackerel (42%) (Figure 43). The dominance of species in puffin chick diets concurs with stable or increasing biomass of these species based on bottom trawl survey data.

Numbers of Steller sea lions Steller sea lion non-pups and pups declined significantly from 2008 to 2023 (-5.69% y-1 and -3.98% y-1, respectively; Figure 49). Their decline might be linked to the lower prey quality and availability, as observed in Pacific cod diets (Ortiz and Zador, 2023), decreased fish condition, and decreases in fish prey biomass.

Central Aleutians

Similar to the western Aleutians, the central Aleutians experienced a moderate but shorter marine heatwave in winter, with close to average temperatures during spring, and there was no heatwave in summer. While there were warm anomalies over 25% of the central Aleutians in summer, these were not sufficient to register in the spatial mean (Figure 17). Bottom temperatures were cooler than previous years, staying close to the 1991-2012 mean (Figure 21). Eddy kinetic energy in this region is usually lower in magnitude compared to those in the western and eastern Aleutians. Eddy events in this area are characterized either by multiyear or continuous eddies of low intensity. In 2024, eddy kinetic energy was generally below the 1993–2023 average, indicating potentially below-average flux of nutrients and heat across the passes (Figure 24).

Overall pelagic forager biopmass decreased 13% in the area, driven by Atka mackerel and northern rockfish. Apex predator biomass increased 7% (Figure 61). As in the western Aleutians, the condition of all groundfish remained below average; small pollock were not sampled in this area. Eelpouts, shrimp and poachers, which are prey to some of the apex predators, appear to have decreased in the region (Figure 61).

Steller sea lion non-pup counts were statistically stable from 2008-2023. However, there are four rookery complex areas which show a gradient of recovery from west to east. The RCAs located furthest west within the Central Aleutians declined significantly (RCA 2 and 3 with decreases of 2.56% and 3.2% per year, respectively). The RCAs on the eastern portion (RCAs 4 and 5) remained stable. In this region, pups declined significantly from 2008 to 2023 (almost 2% per year), with significant declines in RCAs 2-4 and stability in RCA 5.

We report on school enrollment as an indication of trends in coastal, rural community populations. There is currently only one active public school in the Central region. The state had no report for Adak School. School enrollment bottomed out at the state level in Alaska during 2020–2021 and decreased even further during the 2023–2024 school year (p. 8). Barring renewed activity by the now-closed fish processing plant in Adak and the lost potential to be a hub for clean energy (fuel) along the great circle route, the future stability of the Adak community and school is uncertain. It is unclear whether the school is permanently closed or not.

Eastern Aleutians

As in the central Aleutians, sea surface temperatures were not as high during winter as they were in the western Aleutians (Figure 17). The marine heatwave periods were also shorter, with no marine heatwave over the summer. While there were also warm anomalies over 25% of the region in summer, these were not sufficient to register in the spatial mean (Figure 17). Temperatures were sometimes above the 1985–2014 baseline but mostly close to the mean in the region. Bottom temperatures were cooler than previous years, staying close to the 1991-2012 mean (Figure 21). As in 2023, the predominant wind pattern in 2024 suppressed flows through Unimak Pass. Eddy kinetic energy, which is typically driven by a strong pulse eddy in this area, was significantly lower this year, similar to the generally low value that has largely been observed since 2012 (Figure 24). The exception was the high EKE from mid-2021 to early-2022 associated with a passing eddy. This indicates potentially decreased flows of nutrients, heat, and salt through the passes.

Similar to the rest of the Aleutians, groundfish condition continued to be below average, with the exception of small pollock which had the highest condition recorded in the Aleutians and southern rock sole which had condition above the long term mean. This is a shift from mostly below-average condition throughout the chain since 2010 (Figures 33, 34). There were no significant changes in the overall biomass of pelagic foragers, although there was a notable increase in Atka mackerel, while the rest of the species in the complex decreased. Apex predator biomass decreased 24% in the eastern Aleutians, driven by a 55% decrease in arrowtooth flounder (Figure 61). Poachers and shrimp, common prey of apex predators, also seem to have declined in this area (Figures 36, 37).

This summer continues a successful trend for seabirds breeding at Aiktak Island, where reproductive success has been average or above average since 2019 (there were no surveys in 2020) for most seabird species. This indicates uniformly high prey availability for both nearshore and offshore foragers, including surface feeders and divers and across a broad spectrum of zooplankton to forage fish prey (Figure 41). Late hatch dates might have been impacted by the strong winds and storms (Figure 39). Tufted puffins chicks were fed primarily capelin again this year (50% by weight) followed by pollock (34%), indicating that high-quality forage fish were available to foraging seabirds (Figure 43). Together with the above-average condition of small pollock, this suggests a potentially good recruitment year for pollock.

Steller sea lions non-pup and pup counts in the eastern Aleutians increased significantly from 2008 to 2023 (2.14 and 1.48% decrease per year, respectively, Figure 49). In most regions, and population wide, stability in non-pup counts were preceded by stabilizing of pup counts.

Lab results published this year from a 2023 die-off (an opportunistic report of a die-off of over 150 shearwaters at Akutan Island in September 2023) showed samples tested negative for Highly Pathogenic Avian Influenza (HPAI) and below detectable levels for harmful algal bloom toxins (saxitoxin and its related congeners, STX). Paralytic shellfish toxins decreased significantly this year compared to 2023, but are still above the FDA regulatory limit, posing a continued seasonal concern for human health and food webs in the region. In 2024, maximum concentrations of 556 µg per 100 g were recorded in blue mussels (Figure 54). This is 7x (vs 47x in 2023, and 3.4x in 2022) above the regulatory limit (80 µg per 100 g, FDA). Concentrations above 1000 µg per 100 g are considered potentially fatal for humans. The level of toxins observed this year is still substantially lower than the toxins observed at 75x the limit in Unalaska during 2021.

Lastly, school enrollment in this region declined in 2020–21 and has not fully recovered, although both the elementary schools at Akutan and Unalaska had higher enrollment in 2023-24 (p. 9). Enrollment at Akutan has been steadily increasing and is currently at the same level as in late 1990. Unalaska had a similar enrollment to that in 2022, which is still below the average for the school. High school enrollment continues to slowly decrease, potentially signaling young adults or families with high school-aged children moving out of the area.