Introduction & Objectives

Data collected in this project contributed to information needed for understanding of species overlap within U.S. Navy’s operational area within Behm Canal, Alaska. Prior to surveys being conducted, site specific information on species was limited. In addition, previous NMFS surveys in this region were focused during the summer and were not representative of species occurrence in other seasons.

Technical Approach

Visual line-transect surveys and passive acoustic monitoring for cetaceans and other marine mammals were conducted to determine species occurrence and to estimate density within Navy’s testing range. National Marine Fisheries Service, Alaska Fisheries Science Center and University of Washington, Cooperative Institute for Climate, Ocean & Ecosystem developed and implemented a quantitative survey design for vessel-based visual and acoustic assessment of cetaceans in Behm Canal and Clarence Strait. Survey design was based on previous cetacean surveys in the area and were designed for maximum effectiveness and efficiency and included strata based on known distributions of key species and environmental features. Photographs of key species were collected as practicable for purpose of stock identification (humpback and killer whales) and for abundance estimation. Incidental sightings of pinnipeds and sea otters will also be collected. Sonobouys were also deployed during the vessel-based survey, and long-term passive acoustic hydrophones were utilized to monitor for year-round detection of rare and/or cryptic cetacean species.

Progress & Results

Final estimates of group size, density, and abundance of five species of cetaceans in Behm Canal and adjacent areas for three seasons (summer of 2019, spring of 2023, and fall of 2024) have been established.

Summer survey was completed 19 July-13 August 2019

Spring survey was completed 8-14 April 2023

Fall survey was completed 24-29 September 2024

Preliminary analysis was completed for the spring and fall surveys, as well as a previously conducted summer 2019 survey. A total of 1400.82 km was surveyed in the three years with a total of 1345 sightings. On-effort sightings were used to compute region-specific estimates of abundance for Dall's porpoise, harbor porpoise, fin whale, humpback whale, and killer whale for each season. The majority of the estimates are based on small samples, therefore many of the density and abundance estimates are of relatively poor precision.

The occurrence of marine mammals documented during the surveys in Behm Canal and adjacent areas is largely consistent with historical distribution of cetaceans in this region.

Additional information is included in the final report.