Abstract
Despite numerous studies across the large geographic range of the sperm whale (Physeter macrocephalus), little is known about the diet and mitochondrial DNA haplotypes of this strongly female philopatric species in waters off Southeast Asia. A female sperm whale found dead in Singapore waters provided the opportunity to study her diet and mitochondrial DNA haplotype. Here we report on the identification of stomach contents and mitochondrial DNA haplotype of this individual, and we include coastal hydrodynamic modelling to determine the possible geographic origin of the whale. At least 28 species of prey were eaten by this adult female whale, most of which were cephalopods. The mesopelagic squids Taonius pavo, Histioteuthis pacifica, Chiroteuthis imperator,and Ancistrocheirus lesueurii made up over 65% of the whale’s stomach contents. Plastic debris was also found in the whale’s stomach. Based on the diet, genetics, and coastal hydrodynamic modelling that suggest an easterly drift of the whale carcass over several days, the dead sperm whale in Singapore probably originated from a pod in the Southern Indian Ocean. This study provides an increase in the understanding the diet and natural history of the sperm whale in Southeast Asia. The combined analyses of stomach contents, DNA, and hydrodynamic modeling could provide a context to future studies on the sperm whale strandings, and have broader applicability for other marine mammals in the region.
Highlights
The sperm whale Physeter macrocephalus Linnaeus, 1758 has a large geographic range encompassing all oceans in temperate and tropical waters (Rice, 1989)
Taonius pavo was the species with the highest percentage total (31.4%), and at an average estimated mass of 1.11 kg per individual, was probably the most important prey item, followed by Histioteuthis pacifica (19.1%; estimated weight not available), Chiroteuthis imperator (8.34%; 323 g), and Ancistrocheirus lesueurii (7.07%; 325 g)
Current circumstantial evidence from the diet, origin of ingested plastic debris, mitochondrial DNA haplotype, and hydrodynamic modeling suggests that the sperm whale could have originated from a population in the Indian Ocean, close to Cocos (Keeling) Islands or Indonesia
Summary
The sperm whale Physeter macrocephalus Linnaeus, 1758 has a large geographic range encompassing all oceans in temperate and tropical waters (Rice, 1989). They are typically found in regions with deep, off-shore waters, and their diet, which consists mainly of cephalopods—with regional differences in species composition—has been studied in the Atlantic, central, eastern and northern Pacific, and Southern Oceans Pelagic and benthic fishes (actinopterygii and chondrichthyes), crustaceans, and tunicates are eaten in smaller quantities, indicating different modes of foraging (Kawakami, 1980; Best, 1999; Evans & Hindell, 2004; Santos et al, 2002). Sperm whale population structure and genetic studies of the maternally-inherited mitochondrial DNA have shown differentiation between populations, suggesting female philopatry (Richard et al, 1996; Lyrholm et al, 1999; Engelhaupt et al, 2009; Mesnick et al, 2011; Alexander et al, 2016)
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