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Patterns of stable carbon and nitrogen isotopes in the baleen of common minke whale Balaenoptera acutorostrata from the western North Pacific

Authors

  • Yoko MITANI,

    Corresponding author
    1. Division of Applied Biosciences, Graduate School of Agriculture, Kyoto University, Sakyo, Kyoto 606-8502 and
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    • a

      Present address: Texas A & M University at Galveston, 5007 Avenue U, Galveston, TX 77551, USA.

  • Takeharu BANDO,

    1. The Institute of Cetacean Research, 4-18, Chuo, Tokyo 104-0055, Japan
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  • Noriyuki TAKAI,

    1. Division of Applied Biosciences, Graduate School of Agriculture, Kyoto University, Sakyo, Kyoto 606-8502 and
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    • b

      Present address: Shimoda Marine Biological Station, College of Bioresource Sciences, Nihon University, Shimoda, Shizuoka 415-0014, Japan.

  • Wataru SAKAMOTO

    1. Division of Applied Biosciences, Graduate School of Agriculture, Kyoto University, Sakyo, Kyoto 606-8502 and
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    • c

      Present address: Kinki University, 3153, Shirahama-cho, Nishimuro-gun, Wakayama 649-2211, Japan.


*Tel: 1-409-740-4713. Fax: 409-740-5002. Email: mitaniy@tamug.edu

Abstract

ABSTRACT:  Stable carbon and nitrogen isotope ratios were determined in the baleen plates of 17 common minke whales Balaenoptera acutorostrata from the north-western Pacific Ocean off Japan, as well as prey species (krill Euphausia pacifica, Japanese anchovy Engraulis japonicus and Pacific saury Cololabis saira) collected in the stomach contents, to investigate the trophic relationship between the minke whales and their prey. A few δ15N-depleted peaks occurred along the length of baleen plates for 10 males irrespective of stomach content (anchovies and sauries). Similar δ15N-depleted peaks were also found for one female and two immature individuals. It was likely that these δ15N-depleted peaks formed in early summer. The stable nitrogen isotope ratio (δ15N) values in Pacific saury (9.3 ± 1.4‰) did not differ significantly from that in Japanese anchovy (8.8 ± 0.9‰). In contrast, δ15N in krill (7.2 ± 0.5‰ in July and 8.0 ± 0.2‰ in September) were significantly lower than in the Pacific saury. Thus, these peaks may reflect the dietary change from krill to fishes in the feeding migration of the whales. Growth rate of the baleen plate was estimated to be 129 mm/y, and it appeared that a dietary record of about 1.4 years remained in the baleen plate. For two immature whales, the maximum value of δ15N occurred at the tip of baleen. This δ15N enrichment may possibly be useful for discriminating weanlings and older whales.

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