true

ISRA FACTSHEETS

NORTH AMERICAN PACIFIC

ISRA FACTSHEETS

NORTH AMERICAN PACIFIC

Stalemate Bank ISRA

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Stalemate Bank ISRA

Stalemate Bank

Summary

Stalemate Bank is located in Alaskan waters of the United States of America. It sits in the Near Strait, in the western part of the Aleutian Archipelago. The area is characterised by sandy and rocky substrates and strong eddy activity that promotes primary productivity. Within this area there are: range-restricted species (Leopard Skate Bathyraja panthera); reproductive areas (e.g., Leopard Skate); and undefined aggregations (Whiteblotched Skate Bathyraja maculata).

Stalemate Bank

Stalemate Bank

DESCRIPTION OF HABITAT

Stalemate Bank is located in Alaskan waters of the United States of America. It is situated ~145 km west of Attu Island and sits in the Near Strait, in the western part of the Aleutian Archipelago. This is the widest strait 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 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°C (NOAA-AFSC 2026).

This Important Shark and Ray Area is benthic, subsurface, and is delineated from 100–400 m based on the depth range of Qualifying Species in the area.

CRITERION B

RANGE RESTRICTED

This area holds the regular presence of Leopard Skate as a resident range-restricted species. This species has been regularly recorded during trawl surveys conducted in the area for several decades. Between 1982–2025, the Alaska Fisheries Science Center (AFSC) – National Oceanic and Atmospheric Administration (NOAA) conducted trawl surveys during 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 by 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 were conducted at fixed stations or following a stratified random survey design and covering depths from 0–1,000 m divided into 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 2006–2024, the presence of Leopard Skates was recorded in 300 tows during trawl surveys across the whole region. Of these tows, 25 (8.3%) were recorded inside this area in all biennial surveys conducted over this period (NOAA-AFSC 2026). The highest CPUE (average = 338.4 individuals/km2; 37.2–1,078 individuals/km2) for Leopard Skate in the whole region was reported from this area (average CPUE outside the area = 134.4 individuals/km2; 34.4–754.2 individuals/km2). Skates are known to aggregate, with temporal changes in aggregations related to sex and life-stage segregations (Swain & Benoît 2006; Frisk 2010; Hoff 2010). Skate aggregations are usually related to high density areas where large catch quantities occur (Bizzarro et al. 2014). In surveys undertaken in 2022 and 2024, sizes of Leopard Skates have ranged between 20–110 cm total length (TL; Dowlin et al. 2026). While size-at-birth and size-at-maturity for the species are unknown, the lengths recorded suggest that all life-stages occur in the area. Individuals were caught at depths between 100–310 m and bottom temperatures of 3.1–4.6°C (NOAA-AFSC 2026). This species occurs primarily in the Aleutian Islands Large Marine Ecosystem (LME) and marginally in the West Bering Sea LME and Eastern Bering Sea LME.

CRITERION C

SUB-CRITERION C1 – REPRODUCTIVE AREAS

Stalemate Bank is an important reproductive area for two ray species.

Between 1982–2025, AFSC conducted trawl surveys during late spring and summer in the Bering Sea, the Aleutian Islands, and the Gulf of Alaska (NOAA-AFSC 2026). Temporal coverage of the surveys varied per region with most surveys 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 into 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. 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 2008–2024, the presence of Whiteblotched Skate egg cases was recorded in 46 tows during trawl surveys across the whole region, eight (17.4%) of which were recorded inside this area in July and August 2010, 2014, and 2022 at depths of 100–164 m (NOAA-AFSC 2026). The highest CPUE (average = 712.0 egg cases/km2; 158.1–4,329.9) of Whiteblotched Skate egg cases was recorded in this area compared to the whole region surveyed (average CPUE outside the area = 297.7 egg cases/km2; 25.1–1,816.7).

Between 2010–2024, the presence of Leopard Skate egg cases was recorded in 31 tows during trawl surveys across the whole region, five (16.1%) of which were recorded inside this area in August 2010 and 2012 at depths of 100–369 m (NOAA-AFSC 2026). The highest CPUE (average = 2,197.3 egg cases/km2; 85.3–8,809.0) of Leopard Skate egg cases was recorded from this area compared to the whole region surveyed (average CPUE outside the area = 108.2 egg cases/km2; 39.2–304.9). The distribution of this species is restricted to the Aleutian Islands, and this is one of the only two areas where egg cases of Leopard Skate have been regularly recorded, highlighting its importance for this Data Deficient species.

CRITERION C

SUB-CRITERION C5 – UNDEFINED AGGREGATIONS

Stalemate Bank is an important area for undefined aggregations of one ray species.

Skates are known to aggregate, with temporal changes in aggregations related to sex and life-stage segregations (Swain & Benoît 2006; Frisk 2010; Hoff 2010). Skate aggregations are usually related to high density areas where large catch quantities occur (Bizzarro et al. 2014). Between 1982–2025, AFSC conducted trawl surveys during late spring and summer in the Bering Sea, the Aleutian Islands, and the Gulf of Alaska. Temporal coverage of the surveys varied per region with most surveys 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 into 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. 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 1991–2024, aggregations of Whiteblotched Skates were regularly recorded in this area. During this period, Whiteblotched Skates were recorded in 1,402 tows during trawl surveys across the whole region, 131 (9.3%) of which were recorded inside this area in June–August of all surveyed years and at depths of 100–400 m (NOAA-AFSC 2026). The highest CPUE of Whiteblotched Skates in the region was reported from this area (34.7–4,697.8 individuals/km2; average = 601.7) compared to adjacent areas in the region (CPUE outside the area = 15.3–4,956.8 individuals/km2; average = 213.1). Multiple individuals (>5) were recorded in 80 tows (61% of the tows with the species captured inside this area) with 107 being the maximum number of individuals recorded in a single tow. Most of the individuals caught in the area were between 90–100 cm TL (Dowlin et al. 2026) which is near or above the reported size-at-maturity (94–101 cm TL for females and 89–96 cm TL for males; Last et al. 2016), indicating that aggregations are primarily composed of mature individuals. Additional information is required to understand the nature and function of these aggregations.

Stalemate Bank

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