Killer Whale Predation on Sperm Whales: Observations and Implications

In October 1997 we observed a herd of approximately 35 killer whales (Orcinus orca) attack a pod of nine sperm whales (Physeter macrocephalus) 130 km off the coast of central California. During the four hours we watched, adult female killer whales, including some with calves, attacked in waves of four to five animals in what was apparently a “wound and withdraw” strategy. Adult male killer whales stood by until the very end when one charged in and quickly killed a seriously wounded sperm whale that had been separated from the group. The sperm whales appeared largely helpless: their main defensive behavior was the formation of a rosette (“marguerite”-heads together, tails out). When the killer whales were successful in pulling an individual out of the rosette, one or two sperm whales exposed themselves to increased attack by leaving the rosette, flanking the isolated individual, and leading it back into the formation. Despite these efforts, one sperm whale was killed and eaten and the rest were seriously, perhaps mortally, wounded. We also present details of two other encounters between sperm whales and killer whales that we observed. Although sperm whales, because of various behavioral and morphological adaptations, were previously thought to be immune to predation, our observations clearly establish their vulnerability to killer whales, We suggest that killer whale predation has potentially been an important, and underrated, selective factor in the evolution of sperm whale ecology, influencing perhaps the development of their complex social behavior and at-sea distribution patterns

Sperm whale population structure in the eastern and central North Pacific inferred by the use of single-nucleotide polymorphisms, microsatellites and mitochondrial DNA

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Mesnick et al_Physeter genotypes_17 Nov 2010_n=287.xls

The sample set consisted of 287 North Pacific sperm whale samples for which six hypervariable microsatellite loci and 36 SNP loci have been genotyped. Samples obtained between 1972 and 2007. Samples were collected from solitary or groups of free-ranging sperm whales by directed biopsy or the collection of sloughed skin during cetacean research surveys and also from dead animals stranded on beaches, floating dead at sea and from incidental fishery takes. Sample locations refer to the waters of the eastern and central North Pacific. See manuscript for additional details on samples