true

ISRA FACTSHEETS

NORTH AMERICAN PACIFIC

ISRA FACTSHEETS

NORTH AMERICAN PACIFIC

Amchitka & Tanaga Passes ISRA

15/68

Amchitka & Tanaga Passes ISRA

Amchitka & Tanaga Passes

Summary

Amchitka & Tanaga Passes is located in Alaskan waters of the United States of America. It includes Amchitka Pass, Tanaga Pass, and multiple islands of the Andreanof Islands group, 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 (Butterfly Skate Bathyraja mariposa); and reproductive areas (Mud Skate Bathyraja taranetzi).

Amchitka & Tanaga Passes

Amchitka & Tanaga Passes

DESCRIPTION OF HABITAT

Amchitka & Tanaga Passes is located in Alaskan waters of the United States of America. It extends from Amchitka Pass in the west to Tanaga Pass in the east and across multiple islands of the Andreanof Islands group, in the central part of the Aleutian Archipelago. Amchitka Pass is one of the largest passes in the region and, along with Tanaga Pass, 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 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 100–323 m based on the depth range of Qualifying Species in the area.

CRITERION B

RANGE RESTRICTED

This area holds the regular presence of Butterfly 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 Butterfly Skates was recorded in 117 tows during trawl surveys across the whole region. During this period, Butterfly Skates were recorded in 30 (8.3%) tows within this area in all biennial surveys (NOAA-AFSC 2026). The highest CPUE (mean = 111.5 individuals/km2; 36.9–535.4 individuals/km2) for Butterfly Skate in the whole region was reported from this area in relation to the whole region surveyed (mean CPUE outside the area = 66.6 individuals/km2; 33.8–484.4 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). Individuals were caught mostly at depths between 100–323 m and bottom temperatures of 2.9–5.6°C (NOAA-AFSC 2026). This species only occurs in the Aleutian Islands Large Marine Ecosystem (LME).

CRITERION C

SUB-CRITERION C1 – REPRODUCTIVE AREAS

Amchitka & Tanaga Passes is an important reproductive area for one 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 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. 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 2004–2024, the presence of Mud Skate egg cases was recorded in 90 tows during trawl surveys across the whole region surveyed, 12 (13.3%) of which were recorded inside this area in July 2012, 2014, and 2022 mostly at depths of 100–323 m (NOAA-AFSC 2026). The highest mean CPUE (mean = 110.2 egg cases/km2; 38.4–513.6) of Mud Skate egg cases was recorded in this area compared to the whole region surveyed (mean CPUE outside the area = 73.5 egg cases/km2; 23.0–1,032.1).

Amchitka & Tanaga Passes

SUBMIT A REQUEST

ISRA SPATIAL LAYER REQUEST

To make a request to download the ISRA Layer in either a GIS compatible Shapefile (.shp) or Google Earth compatible Keyhole Markup Language Zipped file (.kmz) please complete the following form. We will review your request and send the download details to you. We will endeavor to send you the requested files as soon as we can. However, please note that this is not an automated process, and before requests are responded to, they undergo internal review and authorization. As such, requests normally take 5–10 working days to process.

Should you have questions about the data or process, please do not hesitate to contact us.

    * indicates required

    Industry or sector (*)

    Under the terms and conditions of our User License Agreement , full and appropriate acknowledgement is required in any materials and publications derived from the data (and copies should be sent to the IUCN SSC Shark Specialist Group through the contact form). For any publications making substantial use of the data, the ISRA welcomes the opportunity for co-authorship, collaboration, and to comment prior to publication.


    Furthermore, we need to know whether you are a commercial or non-commercial user. Non-commercial includes scientific research, education or conservation. Commercial is defined as follows: any use by, on behalf of, or to inform or assist the activities of a commercial entity (that operates ‘for profit’) or use by a non-profit for the purposes of revenue generation

    Type of use(*):

    Please specify which layer (ex. all layers, layers within a specific Region, layers within a Jurisdiction or a single ISRA): Purpose (*):

    Please provide a description of how you intend to use the ISRA GIS Dataset. The more details you provide, the faster we can respond to your request. We may require further clarification prior to providing access. (min. 100 characters – max 1,000 characters)



    File format request (*)

    By providing your personal data, you consent to its processing as described below. The IUCN SSC Shark Specialist Group will use the information you provide on this form to send the documents you requested. You can change your mind at any time by writing to the ISRA Data Coordinator www.sharkrayareas.org/contact. All personal details provided will be treated with respect. For any information you can visit our Privacy Policy.
    Please read the User License Agreement and ISRA Layer Metadata Description

    This form uses Google reCaptcha to reduce spam. Privacy - Terms