title: Distribution of Dall's Porpoise, Phocoenoides dalli, in the North Pacific and Bering Sea, Based on T/S Oshoro Maru 2012 Summer Cruise Data.
abstract: Dall's porpoise (Phocoenoides dalli) is a small toothed cetacean, widely inhabiting the North Pacific Ocean and adjacent seas, between about 30 and 62°N; however, only limited studies of its ecology have been made in nearshore areas. A cetacean sighting survey lasting 60 days was conducted during the 2012 summer cruise of the T/S Oshoro Maru (Hokkaido University, Japan) in the North Pacific Ocean and Bering Sea. Based on this data, the distribution of Dall's porpoises and the factors controlling it in the pelagic habitat were investigated. A total of 808 individual Dall's porpoises in 166 groups were sighted during a total of 469.6 hr and 4946.6 nm observations. The cruise consisted of three legs and the average porpoise group size was significantly larger in Leg 1. The sightings were concentrated at water depths of less than 1000 m and near eastern Aleutian passes. Sighting clusters were found on the 200 m isobath of the southeastern Bering Sea continental slope. There was a peak in sightings where the sea surface temperature (SST) was relatively cold, between 5 and 7°C. Although similar track routes were taken in Leg 1 and Leg 3, the number of sightings per unit effort was larger in Leg 1. This difference may have arisen from the significant rise in SST as the season progressed. Relatively large group size found in this study might relate with prey abundance along the Aleutian Islands.
authors.affiliation: 1 Department of Life Science, International Christian University, 3-10-2 Osawa, Mitaka, Tokyo 181-8585, Japan.
authors.forename: Sachiko
authors.initials: S
authors.lastname: Suzuki
authors.affiliation: 2 Graduate School of Arts and Science, International Christian University,3-10-2 Osawa, Mitaka, Tokyo 181-8585, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Sekiguchi
authors.affiliation: 3 Field Science Center for Northern Biosphere, Hokkaido University, 20-5, Hakodate Research Center for Fisheries and Ocean, Benten-cho, Hakodate, Hokkaido 040-0051, Japan.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Mitani
authors.affiliation: 4 Faculty of Fisheries Science, Hokkaido University, 3-1-1 Minato-cho,Hakodate, Hokkaido 041-8611, Japan.
authors.forename: Hiroji
authors.initials: H
authors.lastname: Onishi
authors.affiliation: 1 Department of Life Science, International Christian University, 3-10-2 Osawa, Mitaka, Tokyo 181-8585, Japan.
authors.forename: Takehiko
authors.initials: T
authors.lastname: Kamito
mesh_terms: D063147:Animal Distribution / Q000502:physiology*; D000818:Animals; D010140:Pacific Ocean; D019576:Porpoises / Q000502:physiology*
keywords: Bering Sea; Dall's porpoises; North Pacific Ocean; Phocoenoides dalli; distribution; sighting survey