true

ISRA FACTSHEETS

NORTH AMERICAN PACIFIC

ISRA FACTSHEETS

NORTH AMERICAN PACIFIC

East Agattu Island ISRA

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East Agattu Island ISRA

East Agattu Island

Summary

East Agattu Island is located in Alaskan waters of the United States of America. It is situated east of Agattu Island and next to the Buldir Pass, in the western part of the Aleutian Archipelago. The area is characterised by sandy and rocky substrates, coral and sponge communities, and strong eddy activity that promotes primary productivity. Within this area there are: reproductive areas (Butterfly Skate Bathyraja mariposa).

East Agattu Island

East Agattu Island

DESCRIPTION OF HABITAT

East Agattu Island is located in Alaskan waters of the United States of America. It is situated east of Agattu Island (the second largest of the Near Islands) and southeast of Shemya Island. It sits next to the Buldir Pass, in the western part of the Aleutian Archipelago (Zimmermann & Prescott 2020). This is the largest (~130 km) pass in the region and separates the Aleutian Trench (Pacific Ocean) and the Bering Sea (Hunt & Stabeno 2005; Khudyakova et al. 2025). The area is characterised by sandy and rocky substrates with sponge and coral communities (Rooper et al. 2014; NOAA-AFSC 2026).

This area is influenced by the Alaska Stream, an intense boundary current flowing westward along the shelf break and the Aleutian Trench (Budyansky et al. 2022). This current enters into the Bering Sea through the deepest straits of the Aleutian Archipelago, including Near Strait (Khudyakova et al. 2025). It has strong eddy activity that transports relatively warm, salty, and nutrient-rich waters promoting primary production and defining the water flow through all the straits in the Aleutian Islands (Rogachev & Shlyk 2018; Mordy et al. 2023). Bottom water temperature ranges ~3.5–4.5°C (NOAA-AFSC 2026)

This Important Shark and Ray Area is benthic, subsurface, and is delineated from 100–190 m based on the depth range of Qualifying Species in the area.

CRITERION C

SUB-CRITERION C1 – REPRODUCTIVE AREAS

East Agattu Island is an important reproductive area for one ray species.

Between 1982–2025, the Alaska Fisheries Science Center (AFSC) – National Oceanic and Atmospheric Administration (NOAA) conducted trawl surveys during the late boreal spring and summer in the Bering Sea, the Aleutian Islands, and the Gulf of Alaska (NOAA-AFSC 2026). Temporal coverage of the surveys varies per region with most conducted annually (e.g., continental shelf surveys in the Bering Sea), or biennially (e.g., Gulf of Alaska) since 1999 (Hoff 2016; Siple et al. 2024; Markowitz et al. 2025; Dowlin et al. 2026). The continental slope survey in the Bering Sea stopped in 2016 (Markowitz et al. 2025). Surveys are conducted at fixed stations or following a stratified random survey design and covering depths from 0–1,000 m divided in multiple depth strata across 300–500 stations per region. In general, otter trawls of ~25 m headrope and ~34 m footrope were used and tows lasted between 15–30 minutes at a speed of ~3 knots. Catch-per-unit-effort (CPUE) was estimated as the number of individuals/number of egg cases per square kilometre (no/km2) and the area swept (km2) as the linear distance towed, multiplied by the mean net width (Hoff 2016; Siple et al. 2024; Markowitz et al. 2025; Dowlin et al. 2026).

Between 2009–2022, the presence of Butterfly Skate egg cases was recorded in 34 tows during trawl surveys across the whole region surveyed, four (11.8%) of which were recorded inside this area in July 2012 and 2016 at depths of 100–187 m (NOAA-AFSC 2026). The highest mean CPUE (mean = 137.6 egg cases/km2; 40.8–338.3) of Butterfly Skate egg cases was recorded in this area compared to the whole region surveyed (mean CPUE outside the area = 98.3 egg cases/km2; 36.0–784.4).

East Agattu Island

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