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ISRA FACTSHEETS

NORTH AMERICAN PACIFIC

ISRA FACTSHEETS

NORTH AMERICAN PACIFIC

Seguam Pass ISRA

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Seguam Pass ISRA

Seguam Pass

Summary

Seguam Pass is located in Alaskan waters of the United States of America. It is situated between Amlia and Seguam islands, in the central part of the Aleutian Archipelago. The area is characterised by sandy and rocky substrates with coral and sponge communities, and strong eddy activity that promotes primary productivity. Within this area there are: undefined aggregations (e.g., Mud Skate Bathyraja taranetzi).

Seguam Pass

Seguam Pass

DESCRIPTION OF HABITAT

Seguam Pass is located in Alaskan waters of the United States of America. It is situated between Amlia and Seguam islands, in the central part of the Aleutian Archipelago (Zimmermann & Prescott 2020). This is one of multiple small passes (~30 km long) that separate 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).

The 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 the Bering Sea through the deepest straits of the Aleutian Archipelago, including Near Strait (Khudyakova et al. 2025). It has a strong eddy activity that transport 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 100–460 m based on the depth range of Qualifying Species in the area.

CRITERION C

SUB-CRITERION C5 – UNDEFINED AGGREGATIONS

Seguam Pass is an important area for undefined aggregations of two 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, 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 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 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 1991–2025, 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, 162 (11.5%) of which were recorded inside this area in June–July of all surveyed years and at depths of 100–459 m (NOAA-AFSC 2026). The highest CPUE of Whiteblotched Skates in the region was reported from this area (20.6–4,956.8 individuals/km2; average = 613.9) compared to the whole region surveyed (CPUE outside the area = 15.3–4,697.8 individuals/km2; average = 201.7). Multiple individuals (>5) were recorded in 87 tows (53.7% of the tows with Whiteblotched Skates captured inside this area) with 127 Whiteblotched Skates being the maximum number of individuals recorded in a single tow. Most individuals caught in the area were between 65–105 cm TL (Dowlin et al. 2026) with many near or above the reported size-at-maturity (94–101 cm total length [TL] for females and 89–96 cm TL for males; Last et al. 2016), indicating that aggregations are primarily composed of mature individuals.

Between 1999–2025, aggregations of Mud Skates were regularly recorded in this area. During this period, Mud Skates were recorded in 1,048 tows during trawl surveys across the whole region, 59 (5.6%) of which were recorded inside this area in June–July of all surveyed years and at depths of 106–459 m (NOAA-AFSC 2026). The second highest CPUE of Mud Skates across the whole region surveyed (CPUE outside the area = 18.4–1,812.5 individuals/km2; average = 126.1) was reported from this area (38.4–2,638.9 individuals/km2; average = 218.8) after the area between Amukta and Samalga passes (CPUE = 32.3–3,356.2 individuals/km2; average = 237.4). Multiple individuals (>5) were recorded in 14 tows (23.71% of the tows with the species captured inside this area) with 60 Mud Skates being the maximum number of individuals recorded in a single tow.

Additional information is required to understand the nature and function of these aggregations.

Seguam Pass

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