Abstract
The U.S. Navy periodically uses a Temporary Maritime Activities Area (TMAA) in the central Gulf of Alaska (GoA), east of Kodiak Island. Current scientific data on affected biological and environmental resources are necessary to conduct analyses required for Navy training, exercise, and technology-acquisition activities. In 2009, the Navy funded a vessel-based line-transect survey that provided density estimates for fin (Balaenoptera physalus) and humpback (Megaptera novaeangliae) whales in the TMAA. However, additional data on marine mammal species were necessary to obtain the regionalized population-density data that Navy and other participating Federal agencies like the Bureau of Ocean Energy Management need to meet their environmental stewardship obligations. In the summer of 2013, the Navy funded a second survey to fill in the gaps of knowledge on distribution, movements, and densities of marine mammals within this training area.
During this survey, the visual team surveyed 4,504 kilometers (km) of ‘full-effort,’ which included 349 km of ‘transit-effort.’ There was an additional 375 km of ‘fog-effort’ (transect and transit). Based on total effort, there were 802 sightings (1,998 individuals) of 13 confirmed marine mammal species, with an additional 162 sightings (228 individuals) of unidentified cetaceans and pinnipeds (including those recorded on transit and during off-effort mode).
The acoustic team conducted round-the-clock monitoring with a towed-hydrophone array for 6,304 km of line-transect effort totaling 426 hours of ‘standard’ monitoring, with an additional 374 km of ~30 hours of ‘non-standard’ and ‘chase’ effort. There were 379 acoustic detections and 267 localizations of six confirmed cetacean species. Additionally, 186 sonobuoys were deployed (success rate of 93.5 percent) with seven confirmed cetacean species detected. Two satellite transmitter tags were attached to monitor movements of cetaceans. One was deployed on a blue whale (B. musculus), which transmitted for 9 days, and the other was deployed on a Baird’s beaked whale (Berardius bairdii), which transmitted for 15 days. Based on photo-identification matches, the tagged blue whale had been previously identified off Baja California, Mexico, in 2005. Photographs of five cetacean species were collected for photo identification purposes: fin, humpback, blue, killer (Orcinus orca) and Baird’s beaked whales.
Density and abundance estimates (uncorrected for proportion of animals missed on the transect line) were estimated from line-transect data for six cetacean and one pinniped species. The abundance of large whales not identified to species was computed and allocated to blue, fin, and humpback whales proportionally within each stratum. Pooled density (D) and abundance (N) estimates for the survey area were: blue whales (N = 78; D = 0.0005; CV = 1.22), fin whales (N = 3,581; D = 0.0217; CV = 0.28), humpback whales (N = 3,054; D = 0.0185; CV = 0.71), killer whales (N = 950; D = 0.0058; CV = 0.73), sperm whales (Physeter macrocephalus; N = 296; D = 0.0018; CV(N) = 0.57), Dall’s porpoise (Phocoenoides dalli; N = 11,924; D = 0.0722; CV = 0.28), and northern fur seals (Callorhinus ursinus; N = 1,770; D = 0.0107; CV = 0.23). A second density and abundance estimate was obtained for sperm whales using acoustic localizations from the towed-hydrophone array (N = 215; D = 0.0013; CV = 0.18). The estimates of abundance and density for five species were obtained for the first time for this region. New information on movements and habitat use were documented using data collected from the first satellite tag deployments on either blue or Baird’s beaked whales within this region. Photographic data contributed to knowledge on seasonal presence of individuals. Overall, this survey provides one of the most comprehensive datasets on marine mammal occurrence, abundance, and distribution within the central GoA, an area rarely surveyed.