MEPS 277:275-283 (2004)  -  doi:10.3354/meps277275

Trophic relationships between sperm whales and jumbo squid using stable isotopes of C and N

R. I. Ruiz-Cooley1,*, D. Gendron1, S. Aguíñiga1, S. Mesnick2,3, J. D. Carriquiry4

1Centro Interdisciplinario de Ciencias Marinas, Instituto Politécnico Nacional, Apartado Postal 592, CP 23000 La Paz, Baja California Sur, Mexico
2Southwest Fisheries Science Center, NOAA-Fisheries, 8604 La Jolla Shores Drive, La Jolla, California 92037, USA
3Marine Biodiversity and Conservation, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093, USA
4Instittuto de Investigaciones Oceanologicas, Universidad Autonoma de Baja California, Apartado Postal 453, CP 22800 Ensenada, Baja California, Mexico

ABSTRACT: The trophic position and the predator-prey relationship between the sperm whale Physeter macrocephalus and the jumbo squid Dosidicus gigas were examined by measuring stable isotope ratios of carbon and nitrogen. Skin samples of sperm whales and muscle samples of small and large jumbo squid were collected between 1996 and 1999 in the Gulf of California. Gender determination through molecular analysis and field identification of size were used to identify adult male, female and immature male sperm whales. The stable isotope ratios of C and N of females and immature males were significantly different from those of adult male sperm whales; however, between females and immature males they did not differ significantly. The δ13C and δ15N values of females and immature males were higher than large jumbo squid by 1.1‰ and 2.7‰ respectively, suggesting a predator-prey relationship between them. A low isotopic interannual variation among the years 1997 to 1999 was observed in the isotopic signature of females and males. Adult males exhibited a lower isotopic signature than females and immature males, and did not show a trophic relationship with D. gigas. We hypothesized that the stable isotopic signature of mature males reflected their diet from an earlier high-latitude feeding ground. This study shows that stable isotope analysis of sloughed skin samples from free-ranging sperm whales can be an alternative method to stomach content and fecal analyses for evaluating trophic relationships.

KEY WORDS: Trophic relationships · Trophic position · Stable isotopes · Sperm whales · Jumbo squid · Cetaceans

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