Aleutian Islands Executive Summary - 2018

Executive Summary of Recent Trends in the Aleutian Islands (pdf)

This section contains links to all new and updated information contained in this report. The links are organized within three sections: Physical and Environmental Trends, Ecosystem Trends, and Fishing and Fisheries Trends.

Physical and Environmental Trends

North Pacific

•The North Pacific atmospheric-ocean climate system during fall 2017 to summer 2018 was similar to that during 2016-2017 (p. 40).

•The prominent sea surface temperature anomalies during 2017-18 tended to be positive, with persistent warmth in the subtropical eastern North Pacific Ocean (p. 40).

•A weak La Niña developed during winter 2017-2018 along with a weaker than normal Aleutian Low, similar to the previous year (p. 45).

•The Pacific Decadal Oscillation (PDO) was slightly positive during the past year, with a decline to near zero in the summer of 2018 reflecting the wide-scale warm pattern across the North Pacific Ocean (p. 45).

•The North Pacific Index (NPI) was strongly positive from fall 2017 into 2018 due to the relatively high sea level pressure in the region of the Aleutian Low, which was displaced to the northwest, over Siberia, and causing persistent warm winds from the southwest over the Bering Sea last winter (p. 41).

•The North Pacific Gyre Oscillation (NPGO) declined from a small to a large negative value from 2017 to early 2018, implying that flows in the Alaska portion of the Subarctic Gyre weakened and low nitrate levels along Line P extending from Vancouver Island to Station PAPA (p. 45).

•The climate models used for seasonal weather predictions are indicating about a 70% chance of a weak-moderate El Niño for the winter of 2018-19, and warmer than normal SSTs in both the western and eastern mid-latitude North Pacific in early 2019 (p. 45).

Aleutian Islands

•The Aleutians Islands region experienced suppressed storminess through fall and winter 2017/2018 with predominant winds from the southwest (p. 40).

•The Alaska Stream appears to have been relatively diffuse on the south side of the eastern Aleutian Islands (p. 40).

•Eddy energy in the Aleutian Islands region has been low from the fall 2012 through 2018, indicating the likelihood of smaller than average fluxes of volume, heat, salt, and nutrient fluxes through Amukta Pass (p. 49).

•A new satellite-derived SST indicator presents seasonal anomalies over time in the Aleutian Islands ecoregions. There was a general consistency in temperature anomalies within each year for the central and eastern Aleutian Island areas, whereas the western Aleutian Island region was more likely to diverge from the other areas in the direction of temperature anomaly within a season. The indicator shows that summer and winter temperatures were anomalously warm from 2014-2017, then cooled during summer 2018 (p. 50).

•Sea surface temperature values were moderately warm from fall 2017 through spring 2018 but then cooled to normal during summer 2018 (p. 41).

•The temperature anomaly profiles from the biennial AI bottom trawl survey suggests that there was a return to slightly cooler conditions in 2018 relative to 2016, but that 2018 is still amongst the warmer years over the survey time series, with warm anomalies penetrating deeper and distributed more extensively across the Aleutian archipelago than in 2014 (p. 52).

•The Aleutian islands bottom trawl survey of structural epifauna showed variable distributions. Sponges are caught in most tows in the AI west of the southern Bering Sea. Abundance of coral in all areas has declined since about 1991-1993 surveys and is at generally low levels in all areas, but the frequency of occurrence has remained steady. Soft corals occur in relatively few tows, except in the eastern Aleutian Islands. Sea anemones are common, but sea pen abundance is low (p. 56).

•In the Bering Sea region north of the Western and Central Aleutian Islands that is sampled by the Continuous Plankton Recorder, spring diatom abundances have remained above average 2013-2017 (p. 60).

•However, copepod community size anomalies have remained negative from 2014-2017 indicating a community biased towards smaller species than is typical in this ecosystem (p. 60).

•Jellyfish mean catch per unit effort in the biennial AI bottom trawl survey is typically higher in the western and eastern AI than in the central AI. Catches and frequency of occurrence steadily increased across the AI from 2012 to 2016, but decreased in 2018 (p. 63).

•Length-weight residuals (a measure of groundfish condition) in 2014 and 2016 were negative for all species except arrowtooth flounder in 2014 and southern rock sole in 2016. In 2018, condition continued to be strongly negative for Pacific cod, northern rockfish, Pacific Ocean perch and arrowtooth flounder (p. 65)

•The depth distributions of rougheye rockfish, Pacific ocean perch, shortraker rockfish, and northern rockfish have been shallower in the most recent bottom trawl surveys of the Aleutian Islands. The mean spatial distribution of northern rockfish is trending westward. There are no significant trends in mean-weighted temperature distributions for any rockfish species (p. 67).

•Benthic communities and other non-target species sampled incidentally in the biennial bottom trawl survey. There has been a notable decline in eelpout biomass in the western AI in the last 4 surveys. Echinoderms and poachers have been increasing in the eastern AI ecoregion in the last 3 surveys (p. 71).

•The overall biomass in the summer bottom trawl survey in 2018 was very similar to that in 2016. The largest difference was a decrease in arrowtooth flounder, which occured in the central Aleutian Islands ecoregion (p. 8).

•Pacific cod showed a large decrease in the western Aleutian Islands ecoregion, but the overall pattern was balanced by increases in the eastern and central Aleutian Islands ecoregion (p. 8).

•The long term trend reflects a continuing shift in the pelagic foraging biomass from that dominated by Atka mackerel and pollock to that dominated by rockfish (p. 8)

•In general, seabirds in the Aleutians did not experience widespread failures like they did in the Gulf of Alaska during the marine heat wave of the past few years. However many piscivorous seabirds did poorly in 2018 at Buldir (western AI) and had mixed success at Aiktak (eastern AI), while planktivorous seabirds have remained generally successful. This pattern suggests that zooplankton availability was sufficient to support chick-rearing at both colonies, but that forage fish prey were insufficient to support chick-rearing at Buldir (p. 73).

•The western AI Steller sea lion adult population decreased rapidly at approximately 7% per year and sub-area population trends improved to the east through the western Gulf of Alaska, where the annual trend increased approximately 4% per year. Regional trends in pup production are similar to trends in non-pup counts, with continued relatively steep declines in the western AI, a less steep decline in the central AI, and improvement in the eastern AI (p. 2).

•A new indicator demonstrates that the stability (inverse biomass coefficient of variation) of groundfish biomass in the Aleutian Islands bottom trawl survey has been relatively constant from 2010-2018. There has been a gradual decrease over this time, but with a non-significant linear trend that is influenced by variability in Atka mackerel biomass (p. 76).

•A new indicator tracks fluctuations in the size of groundfish sampled over time by the Aleutian Islands bottom trawl survey. The mean length of the groundfish community in 2018 is the highest value over the time series, but in general has remained stable over time (p. 77).

•A new indicator tracks the mean life span of the groundfish sampled by the Aleutian Islands bottom trawl survey over time. This indicator serves as a proxy for the mean turnover rate of species and communities” and is intended to reflect ecosystem stability and resistance to perturbations. The mean lifespan in 2018 is above the long term mean, but has been largely stable over the time period with some interannual variation due to high biomass estimates of pollock or Atka mackerel (p. 79).

Fishing and Fisheries Trends

•Since 1993 discards and discard rates of groundfish in federally-managed Alaskan groundfish fisheries have generally declined across the trawl pollock, non-pollock trawl, and fixed gear sectors in the Aleutian Islands. To date in 2018, discard levels across all sectors appear to be consistent with levels during the previous 5-year period (p. 81).

•In 2017, non-target catch of Scyphozoan jellyfish in trawl fisheries in the Aleutian Islands increased substantially from that in 2016. The catch of structural epifauna (sponges, corals, and bryzoans) is variable and was the third highest in 2017. The catch of assorted invertebrates (mainly seastars) has been level from 2015-2017 (p. 84).

•The incidental catch of seabirds in Aleutian Islands groundfish fisheries in 2017 was the highest estimate in the 2007-2017 time series. This was primarily due to a large increase in the numbers of shearwaters caught (p. 86).

•With the Arctic FMP closure included, almost 65% of the U.S. EEZ of Alaska is closed to bottom trawling (p. 90).

•At present, no Bering Sea/Aleutian Islands groundfish stock or stock complex were subjected to overfishing, known to be overfished, or known to be approaching an overfished condition (p. 96).

•The percent of area disturbed due to commercial fishing interactions (pelagic and non-pelagic trawl, longline, and pot) has decreased slightly or remained steady in the Aleutian Islands (p. 92).

•Landings (pounds) are used in a new indicator to characterize commercial seafood production. Land- ings in the Aleutian Islands are primarily composed of pelagic foragers and apex predators. Atka mackerel dominate the pelagic forager catch. Landings of apex predators decreased in 2011 due to a decrease in Pacific cod catches (p. 101).

•Subsistence salmon harvest in the eastern Aleutian Islands has varied over time, but has been declining in the central Aleutian Islands, with none reported to have been caught in the most recent year, 2016. Subsistence halibut catches have also been generally declining since 2004, but this trend may be related to subsistence survey methodology (p. 103).

•Economic values of 5 functional groups (apex predators, benthic foragers, motile epifauna, pelagic foragers, and salmonids) are presented in a new indicator. Ex-vessel values have been increasing for pelagic foragers since 2010 primarily due to Atka mackerel and rockfish and decreasing for Pacific cod. First-wholesale value shows similar trends. Contrary to the Gulf of Alaska and Eastern Bering Sea, the first-wholesale total catch unit value in the Aleutian Islands has an increasing trend since 2009, with the value in 2017 being close to the all-time high of 2011-2012 (p. 106).

•Unemployment rates in Aleutian Islands fishing communities from 1990 to 2017 were lower than state and national rates, reflecting stability in the commercial fishing and seafood processing industries (p. 110).

•As of 2017 the total population including all Aleutian Island communities was 5,755 people. The eastern AI has had the most steady population increase between 1880 and 2015, whereas the central and western AI experienced fluctuations. The western AI has had no residents wince 2011 (p. 114).

•While Unalaska schools in the eastern Aleutian Islands have maintained relatively stable enrollment since 1996, Nikolski, Akutan, and False Pass have diminished dramatically and are no longer viable. Both Adak and Atka schools in the central Aleutian Islands have experienced declining enrollment (p. 117).