Ecosystem Assessment (pdf)
Ivonne Ortiz1 and Stephani Zador2
1Cooperative Institute for Climate, Ocean and Ecosystem Studies, University of Washington
Last updated: October 2022
The Aleutian Islands ecoregions
The Aleutian Islands ecosystem assessment and Report Card are presented by three ecoregions. The ecoregions were defined based upon evidence of significant ecosystem distinction from the adjacent ecoregions by a team of ecosystem experts in 2011. The team also concluded that developing an assessment of the ecosystem at this regional level would emphasize the variability inherent in this large area, which stretches 1900 km from the Alaska Peninsula in the east to the Commander Islands in the west. For the purposes of this assessment, however, the western boundary is considered the U.S.–Russia maritime boundary at 170° E.
Figure 5: The three Aleutian Islands assessment ecoregions.
The three Aleutian Islands ecoregions are defined from west to east as follows (Figure 5). The western Aleutian Islands ecoregion spans 170° to 177° E. These are the same boundaries as the North Pacific Fishery Council fishery management area 543. This ecoregion was considered to be distinct from the neighboring region to the east by primarily northward flow of the Alaska Stream through wide and deep passes (Ladd, pers. comm.), with fewer islands relative to the other ecoregions.
The central Aleutian Islands ecoregion spans 177° E to 170° W. This area encompasses the North Pacific Fishery Council fishery management areas 542 and 541. There was consensus among the team that the eastern boundary of this ecoregion occurs at Samalga Pass, which is at 169.5° W, but for easier translation to fishery management area, it was agreed that 170° W was a close approximation. The geometry of the passes between islands differs to the east and west of Samalga Pass (at least until Amchitka Pass). In the central ecoregion the passes are wide, deep and short. The Alaska Stream, a shelf-break current, is the predominant source of water (Figure 6). There is more vertical mixing as well as bidirectional flow in the passes. This delineation also aligns with studies suggesting there is a biological boundary at this point based on differences in chlorophyll, zooplankton, fish, seabirds, and marine mammals (Hunt and Stabeno, 2005).
Figure 6: Ocean water circulation in the Aleutians. Currents are indicated with black lines. Currents are indicated by grey arrows. Selected passes are indicated by straight light grey lines
The eastern Aleutian Islands ecoregion spans 170° W to False Pass at 164° W. The passes in this ecoregion are characteristically narrow, shallow and long, with lateral mixing of water and northward flow. The prominent source is from the Alaska Coastal Current, with a strong freshwater component. This area encompasses the NPFMC fishery management areas 518, 517 (EBS) and the western half of 610 (GOA).
Aleutian Islands Ecosystem Assessment
In the Aleutian Islands as a whole, there are large gaps in knowledge about the local physical processes due largely to geographic constraints. For example, persistent cloudiness preclude obtaining comprehensive satellite-derived data, and strong currents preclude the use of various unmanned underwater vehicles. The long distances involved in surveying the island chain make comparing west-east trends in indicators difficult due to time lags during oceanographic surveys across the region. The archipelago is also influenced by different processes in the eastern than in the western Aleutian Islands. Differences in survey timing and longitudinal gradients may also affect de- tection of biological patterns, as gradients are seldom monotonic in any direction. Integrative biological indicators such as fish or marine mammal abundances may be responding to physical indicators such as temperature, but are less sensitive to timing of when they are surveyed compared with direct measurements of temperature. Also, the extensive nearshore component of the ecosystem is a long, narrow shelf relative to the entire ecosystem, and strong oceanographic inputs mean that some metrics commonly used as ecosystem indicators in other systems may not be as informative in the Aleutian Islands. Therefore, our synthesis of ecosystem indicators by necessity includes speculation.
The Alaska Fisheries Science Center completed the standard bottom trawl and Steller sea lion surveys in 2022. There was no bottom trawl survey in 2020 due to COVID-19. Indicators from the bottom trawl and Steller sea lion surveys were last updated in 2018. 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 Alaska Fisheries Science Center’s Ecosystem Status Reports are informed by the continuation of survey- and lab-based data streams, as well as information contributed through new and existing partnerships.
Current Conditions 2022
The past year was characterized by continuing moderate La Niña conditions and a continued negative PDO phase that followed the marine heat wave years of 2014-16 in the NE Pacific ocean. The weak Aleutian Low is consistent with the decline in the PDO during this time (Figure 7) The expected decrease in sea surface temperature to average levels through winter and early spring 2022 materialized in fall 2021 and early December, but temperatures then increased to a sustained moderate or higher heatwave level through September 2022. This was particularly the case during winter and summer in the western and central Aleutians, with this year recorded as one of the warmest on record and summer marine heatwaves periodically reaching severe levels in the western Aleutians (Figure 15). Mid-depth and bottom temperatures were above average in 2022, as they have been since 2014. Winds during winter 2022 favored northward flow through Unimak Pass, and a strong eddy (the first since 2012) remained in the eastern Aleutians from the second half of 2021 through the first half of 2022, also favoring higher nutrients and fluxes through Unimak Pass. The NPGO index has remained negative since late 2013, while the PDO changed to a negative phase in 2020 and the NPI has been positive (i.e. weak Aleutian Low) five out of the last 6 winters (except winter 2018-2019). Jointly, these indices suggest physical conditions that support increased zooplankton availability (Bond et al., 2011; Goyert et al., 2018).
Seabirds at Buldir (western Aleutians) and Aiktak (eastern Aleutians) Islands had average or early hatch dates and average or above-average reproductive success, indicating favorable foraging conditions across a broad spec- trum of prey from zooplankton to forage fish prey (Figure 40). While groundfish condition was slightly improved compared to previous years, the condition of all species except for southern rock sole remained below average, indicating that their prey resources were limiting. In general, pelagic forager groundfish seem to be doing better on average than apex predator piscivorous fish feeding close to the bottom. For example, the abundances of most apex predator groundfish (large flatfish and Pacific cod) decreased compared to that observed during the last survey in 2018, while the abundance of all the main pelagic-foraging groundfish (rockfish and Atka mackerel) increased.
2022 was a low abundance year for Eastern Kamchatka pink salmon, indicating that there was likely less com- petition for prey and weaker trophic cascades than have been shown in years of high abundance of pink salmon (Springer and van Vliet, 2014; Batten et al., 2018; Springer et al., 2018). The notable steep increases in Eastern Kamchatka pink salmon abundance trends in 2009 for high abundance years and in 2014/2016 for low abundance years, has made a biennial signal potentially driven by the extreme shifts in pink salmon abundance more notice- able across ecosystem components. For example, there is a newly noted biennial signal in primary productivity as measured by satellite chl-a (often a proxy for phytoplankton biomass) that may present further support for ecosystem-wide impacts of pink salmon (Figure 22).
The western DPS (distinct population segment) of Steller sea lions as a whole began to rebound in 2002 from an earlier declining trend. However, regional trends tell a different story in the Aleutian Islands and in the Gulf of Alaska. West of Samalga Pass, sea lion counts have shown little to no signs of recovery, including with the new counts this year. Steller sea lion non pups and pup counts continue to decline in the western Aleutians. In contrast, counts in the central Aleutians as a whole continued a stable trend. However, this was due to an apparent increase in counts in the easternmost central Aleutians that offset the declines observed in the westernmost central Aleutians (Figure 45)
Lastly, paralytic shellfish toxins were 3.4x above the regulatory limit in 2022, which is substantially lower compared to toxins observed at 75x the limit in Unalaska during 2021. Despite the decrease, paralytic shellfish toxins continue to pose a risk to human health and food webs in the region (Figure 51). More details on this year’s trends are in the regional highlights section below.
Overall, there seem to be three major drivers of the multi-year patterns observed across the Aleutian Islands: persistent warm conditions, increasing pink salmon abundance, and increasing Pacific Ocean perch abundance. Jointly, these factors might indicate a transition of the ecosystem to a new state. The likelihood and detection of such a transition may depend on how long the current conditions prevail. Analyzing the food web to see if predator/prey relationships have changed over time would help to determine whether or when such a transition occurs. This would require both more diet sample collections (from fish, birds, and mammals), as well as analysis, to inform the underlying changes in the structure of the ecosystem. The data-poor nature of this ecosystem relative to the eastern Bering Sea or Gulf of Alaska, , including the biennial schedule of the bottom trawl surveys (in low pink abundance years), limits the ability to identify the extent of cascading or cumulative effects of these drivers.
Persistent warm conditions since 2013: Surface to bottom waters have remained above the long term mean since 2013/14, the cause of which is not fully understood (Figure 19). The warm temperatures can be attributed in part to slower at-depth processes, involving several mechanisms, such as weaker wind/mixing, warmer air temperature, and advection of warm water from the North Pacific Ocean, the relative importance of which is hard to assess without a detailed heat budget analysis. Other aspects of the physical environment continue to show variability. For example, a large eddy formed in the eastern Aleutian Islands this year (Figure 21).Phytoplankton have also shown notable patterns but have often remained in lower abundances over the same time period. Both large diatoms and satellite chl-a (increased in 2021 from the previous year. However, satellite chl-a decreased again this year, reverting to a generally lower-than-average abundance that began in 2010-2014. This coincides with the decrease in satellite chl-a observed in the off-shelf region of the eastern Bering Sea (Hennon et al, EBSESR 2022). Cumulatively, these conditions suggest that there has been lower productivity across the system, concomitant with increased bioenergetic needs for fish, faster growth rates for zooplankton and larvae, and shorter incubation periods for eggs due to the warm conditions. These changes in bioenergetics and development rates can poten- tially lead to mismatches between egg hatching/larvae release and prey availability, which can negatively affect recruitment. Fish condition has remained below the mean since 2012 (Figure 30), which also indicates that fish are not meeting their optimal bioenergetics needs. Note that the beginning of the period of lower fish condition and satellite chl-a seem to coincide with the step increase of Eastern Kamchatka pink salmon in 2009 and 2014/16 for odd and even year-classes, respectively.
Eastern Kamchatka pink salmon abundance in odd years continues to increase: The biennial pattern of high pink salmon abundance in odd years and low abundance in even years continues. This year was also the second-highest abundance on record for even year-classes (Figure 28). However, since 2009, high abundances of odd year-classes have doubled and even tripled (315 million adult fish) compared to prior levels of around 100 million fish. Low abundance [even] years reached the 100 million fish mark in 2016 and 2018 (perhaps related to higher temperatures mentioned above) but also had a notable increase in 2014 from previous years (48 million compared 24 million in 2012 and 14 million and 10 million in 2010 and 2008 respectively). In 2020, pink salmon abundance decreased to pre-2014 levels, perhaps due to low availability of prey as the large meso-zooplankton negative anomaly would suggest (Figure 25). Several papers report that the pink salmon biennial pattern seems to be cascading through the system by consuming zooplankton which impacts fish growth (Atka mackerel, citealtMatta2020), and food available for seabirds (Zador et al., 2013; Springer and van Vliet, 2014; Springer et al., 2018). The following indicators tracked in this ESR also show a biennial pattern: satellite chl-a (lower in even years), catch estimates of age-2 Atka mackerel (Lowe et al 2022), age 3+ number of fish in the Pacific Ocean perch stock assessment (Spencer et al. 2022 hatch time of tufted puffins (earlier in odd years), and bycatch of all seabirds combined (increases in years of high pink salmon abundance and decreases during low pink salmon abundance, Figure 55). The timing of some of these biennial patterns coincides with the step changes in Eastern Kamchatka pink salmon abundance, perhaps suggesting that a threshold has been reached where potential ecosystem impacts increase. Interestingly, the biennial pattern seen in age-2 Atka mackerel catch has not been observed in recruitment estimates or surveys. The biennial pattern in puffins indicates they find more favorable conditions in winter/ spring when Eastern Kamchatka pink salmon is low, however the abundance of pink salmon does not correlate with their reproductive success in a given year. Further evaluation is needed to assess the influence of Eastern Kamchatka pink salmon in the system.
Rockfish have replace Atka mackerel and pollock as the main pelagic foragers: The increase of rockfish across the Aleutians has slowly changed the ratio of Atka mackerel/pollock to northern rockfish/Pacific ocean perch, with rockfish now contributing a higher percent of the local biomass across the archipelago. Stock assessment estimates support rockfish remaining dominant, although decreasing. An ecosystem state where sustained high biomass of Pacific Ocean perch and northern rockfish may be outcompeting or displacing pollock and Atka mackerel would signal a return to conditions that existed before Pacific Ocean perch was heavily fished by the foreign fleets. The effect of rockfish dominance on the ecosystem is best captured by the mean lifespan of the groundfish community, a proxy for the mean turnover rate of species (Figure 49). Mean lifespan has increased from 35 years in the 1980s to 60 years in 2018-22. Longer-lived species help to dampen the effects of environmental variability, and in ecological terms, increases the stability of the ecosystem (see Figure 47). The persistent low fish condition suggest that Pacific Ocean perch and northern rockfish could potentially be experiencing density dependence. Also, rockfish prefer habitats with vertical structure (Rooper 2019), particularly deep coral and sponges, and may be exerting spatial pressure on other fish in this habitat. This in turn might lower the availability of Atka mackerel and pollock to other predators such as Pacific cod, whose diet shows small amounts of Atka mackerel consumed in NMFS areas 543 ad 542 in 2016 and 2018, but an increase in area 541. It is unclear whether this change in pelagic foragers (Figure 66) has contributed to the decline of harbor seals (AI ESR 2021) and/or Steller sea lions.
Sustained high temperatures particularly in winter and summer, resulted in a sustained moderate marine heat wave which at times reached strong and severe levels in May and July-Aug 2022 (Figure 12). This led to a prolonged marine heat wave through early September with most of the region affected by the high temperatures. SST briefly subsided to average through October and are currently slightly above the long term mean but below the heat wave threshold. This reprieve from high temperatures during fall was also observed last year. The heatwave has potential impacts during the spawning season of Atka mackerel when they move to shallower areas. It may have raised temperatures close to 11-11.5° C, the upper limit of the observed temperatures during and after Atka mackerel spawning. Atka mackerel nests are typically found between 32–144 m depth (Lauth et al., 2008) potentially making the shallowest nests more vulnerable to the heat wave. The fall temperature reprieve could potentially offset the impact on incubation times. Bottom temperatures averaged 4.4° C, well below the lethal temperature of 15° C. Eddie kinetic energy was slightly below average but close to the long-term mean, suggesting low fluxes of nutrients, heat and salt through the passes (Figure 21). Satellite-derived chl-a concentration, was below average throughout spring, and improved somewhat in fall (Figures 22, 23).
The persistent decline in fish condition in the region may be indicative of a variety of factors: poor prey quality, low availability of prey and/or density dependence. Based on biomass estimates from the 2022 bottom trawl survey compared to 2018 estimates, apex predator abundance increased 3% overall. This increase was driven by Pacific cod (20%), rougheye/ blackspotted rockfish (84%) and large sculpins (2%), while all large flatfish decreased. The below average fish condition of Pacific cod and arrowtooth flounder suggests that they experienced either poor prey quality and/or low availability of prey. In contrast, the overall biomass estimate of pelagic foragers increased 35%. This increase was driven by Pacific ocean perch and Atka mackerel (33% and 58%), while pollock decreased 63%. The fish condition for all three was below average, and while this would suggest low quality and/or availability of prey, in the case of Pacific ocean perch it may also be due to density dependence, given its increasing biomass trend.
In general, fish-eating seabirds (tufted and horned puffins, thick-billed murres, glaucous winged gulls) had suc- cessful reproduction during 2022, continuing the improvement from already-favorable conditions in 2019, which had been preceded by poor reproductive success. Tufted puffin chick diets at Buldir were mainly composed of Irish lord (23%) and squids (35%), while horned puffin chick diets there were primarily composed of Atka mackerel (42%). The dominance of species in puffin chick diets concurs with stable or increasing biomass of these species based on bottom trawl survey data. Long-term average hatch dates for fish-eating seabirds are between mid-June to late July (Dragoo et al., 2019), along with average hatching periods of 30 to 42 days. This year hatch dates of fish eating seabirds were earlier or average, suggesting prey were available in the early spring and potentially for commercial groundfish as well. Zooplankton-eating seabirds (auklets) serve as indicators of zooplankton pro- duction; their reproductive success has been above average since 2019, including this year. These species feed their chicks mainly euphausiids and copepods. Their earlier or average hatch dates this year suggests favorable foraging conditions throughout the preceding months. The increase of rockfish in seabird diets observed in 2021 was not observed this year, as Sebastes spp. was only 1% of the chicks’ diets. It will be interesting to see if the increase in age-0 rockfish in chick diets in 2021 lines up with future estimates of 2021 rockfish age-classes.
Steller sea lion numbers in the western Aleutians (Rookery Complex Area 1) continued to decline and show no signs of recovery. Pup numbers in this region have declined 95% since their peak in 1984 (38 years); non-pups declined 97% over the same time period. Non-pups have declined 99% since 1971, which is the earliest modeled count for this region. The Buldir rookery has entirely disappeared. Just over 5,000 non-pups were counted in 1979. Since 2010, counts have ranged from 0–28 (Fritz et al., 2013). The decline in Steller sea lion counts coincides with the overall low fish condition in the region, which makes for poor prey quality for sea lions. Although Steller sea lions can dive to at least 400m, the increase in biomass of rockfish at depths within 100-200 meters, where a large portion of Atka mackerel, pollock and Pacific cod are found, may decrease their ability to easily find their preferred prey.
Similar to the Western Aleutians, the central Aleutians were under a moderate marine heat wave through most of the year, at times reaching strong or severe levels. Overall, the region experienced a particularly warm winter and summer during 2022. The heat waves, however, were less extensive than those in the western Aleutians (Figure 12). Sea surface temperatures have subsided since mid-September, remaining slightly above average but below the heat wave threshold. In this ecoregion, bottom temperatures have been above the ecosystem-wide mean tem- perature several times, such as during 2010, 2006, and 2004. This year again, the average bottom temperature was slightly higher than in the other regions. Mid-water temperatures (100-300 m) from the longline survey were cooler than in 2016, but warmer than those observed in 2012 and earlier. Eddy kinetic energy north of the islands is usually the lowest in magnitude compared to those in the western and eastern Aleutians. In this area, events are characterized either by multiyear or continuous eddies of low intensity. In 2022 eddy kinetic energy was generally above its long-term average except for a brief period during early winter, indicating potentially above-average flux of nutrients and heat across the passes. Phytoplankton biomass, as represented by chl-a concentration, was generally below average (Figures 22 and 23).
Steller sea lion counts in the rookery complex areas (RCAs) 2-5 had mixed trajectories, with counts improving from west to east. Non-pups and pups were stable in the region . However, counts in the two western RCAs (2 and 3) declined for both pups (-5.10% and -5.38%, respectively) and non-pups (-3.55% and -3.14%). RCA 4 was stable for all age-sex classes. Counts in RCA 5 increased (4.09% y-1; 95% CI 0.86 – 7.98). However, the survey in this area was fairly incomplete as it missed one rookery and several haul out sites. Further data is necessary to confirm whether this is a true increase.
Groundfish survey biomass estimates for apex predators decreased 24% overall in the area compared to 2018 except for large sculpins. The overall survey estimate of the pelagic forager groundfish guild biomass increased driven by Atka mackerel and to some degree by northern rockfish. Within this guild, the biomass of Pacific ocean perch and walleye pollock decreased (25 and 50% respectively). This is the only area where walleye pollock condition improved in 2018 and 2022, as did that of southern rock sole. There are no seabird surveys in this area.
School enrollment bottomed out at the state level in Alaska during 2020-2021 and did not recover in the Central Aleutians during the 2021-2022 school year. Barring renewed activity by the now-closed processing plant, and the potential to be a hub for clean energy (fuel) along the great circle route, the future stability of the community and school is uncertain.
This area encompasses the islands east of Samalga Pass. As in 2021, sea surface temperatures in the eastern Aleutians during 2022 were not as high during winter as in the western and central Aleutians. The marine heat wave periods were also shorter, primarily restricted to summer, and of lower intensity, as most were considered moderate with only a few short events considered strong. That said, overall sea surface temperature during 2022 was mostly higher than in 2021, except for August–September 2021 when temperatures rose sharply. In contrast, late August–September 2022 temperatures were above the mean but below the heat wave threshold level (Figures 12 and 13). Mid-water temperature profiles for 2022 show a warm band of water between 150-250 m with cooler temperatures above and below (Figure 17). The predominant wind pattern blowing from the west to the east during 2022 favored flows through Unimak Pass. Eddy kinetic energy, which is typically driven by a strong pulse eddy in this area, was significantly higher this year, breaking the generally low strength observed since 2012 (Figure 21). Spring phytoplankton biomass, as suggested by chla-a concentration, was above the climatological mean south of the islands in May, but otherwise also below average (Figure 23).
Fish-eating seabirds, such as murres, puffins and gulls, all had above average reproductive success. No auklets (primarily zooplankton-eaters) were surveyed in the region. Storm-petrels, which feed on a mix of invertebrates and zooplankton, had average to above average reproductive success. Fork-tailed storm-petrels earlier hatch dates but average reproductive success. Leach’s storm-petrels had both average hatch dates and average reproductive success (Figures 40, 38). There were few reports of dead seabirds (20-50 birds) in Cold Bay and Unalaska (Figure 42). While these indicators suggest good availability of forage fish to rear chicks and potentially for fish-eating groundfish, there were no data collected on planktivorous seabirds. However storm petrels and murrelets, which feed on fish, invertebrates and zooplankton, had average or above average reproductive success. While it is unclear whether the conditions were as favorable for obligate zooplankton-eating seabirds as for fish-eating seabirds, the overall reproductive success suggests there was enough prey to support combined diets. Tufted puffins chick diets were primarily pollock (51%) followed by Pacific sand lance (21%), indicating that forage fish were available to foraging seabirds. Steller sea lions were surveyed in 2022, but counts are still being analyzed. Previous counts suggest that the sea lion populations have been recovering in this area.
Increases in survey biomass estimates of northern rockfish and pollock offset decreases of Pacific ocean perch and Atka mackerel, for an overall 10% increase in pelagic foragers biomass compared to 2018. In contrast, overall apex predator fish biomass decreased, with the exception of arrowtooth flounder, Pacific cod and large sculpins (Figure 66). While the condition of Pacific cod sampled in the survey was above the long term average, condition remained below average for the other sampled species (Figure 30)
Shellfish samples from several locations including Little Priest Rock in Summer Bay, Unalaska are collected weekly and analyzed for harmful algal blooms. Monitoring indicated that peak toxin levels occurred during June this year. Blue mussels had toxins only 3.4x above the regulatory level (Figure 51), which is the lowest documented in the past three years. Public awareness efforts continue in the area to minimize impacts on human health. Lastly, school enrollment declined in 2020-21 and did not recover in 2021-22. The decrease in the eastern Aleutians enrollment was driven by a large decline at Unalaska Elementary. All other schools (Akutan, False Pass, and Unalaska Jr. and Senior High School) had increased enrollments.