Distribution of the Steller sea lion Eumetopias jubatus during winter in the northern Sea of Japan, along the west coast of Hokkaido, based on aerial and land sighting surveys

Authors

  • Hiroshi HOSHINO,

    1. Division of Marine Environment and Resources, Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611,
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    • a

      Present address: Division of Innovative Research, Creative Research Initiative ‘Sousei’, Hokkaido University, Sapporo, Hokkaido 001-0021, Japan.

  • Takeomi ISONO,

    1. Econixe, Shimonopporo Technopark, Sapporo, Hokkaido 004-0015,
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  • Takuma TAKAYAMA,

    1. Division of Marine Environment and Resources, Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611,
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  • Tsuyoshi ISHINAZAKA,

    1. Laboratory of Theriogenology, College of Bioresource Sciences, Nihon University, Fujisawa, Kanagawa 252-8510, and
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    • b

      Present address: Rausu Ranger Office, Shiretoko National Park, Ministry of the Environment, Rausu, Hokkaido 086-1822, Japan.

  • Akihiko WADA,

    1. Hokkaido Wakkanai Fisheries Experimental Station, Wakkanai, Hokkaido 097-0001, Japan
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  • Yasunori SAKURAI

    Corresponding author
    1. Division of Marine Environment and Resources, Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611,
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*Tel: 81-138-40-8861. Fax: 81-138-40-8861. Email: sakurai@fish.hokudai.ac.jp

Abstract

ABSTRACT:  Aerial and land-based sighting surveys were conducted to clarify the distribution of Steller sea lions during winter in the northern Sea of Japan, along the west coast of Hokkaido, from 2001 to 2003. Aerial surveys revealed that sea lions gathered around the Rishiri-Rebun Islands in March 2002 and 2003, and between Iwanai and Cape Obana in February 2003. Higher numbers of sea lions were also confirmed at Cape Ofuyu and Cape Kamui on the central-west coast compared to that at the haul-out sites in the 1980s on the upper-west coast in March 2002 and 2003. Additionally, fisherman observed sea lions along the coast of the Tsugaru Strait from February to May 2003, where the presence of sea lions was not reported in the 1980s. These facts suggest that sea lions have recently expanded their distribution southward. Land-based surveys at the recent haul-out sites indicated that sea lions in the central-west coast were composed mainly of adult and subadult males (average: Cape Ofuyu 75.2%, Cape Kamui 69.5%), which stayed from November 2002 to May 2003. In this area, sea lions arrived earlier and stayed longer than in the 1980s.

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