Abstract
Sperm whale, Physeter macrocephalus , distribution was compared to acoustic backscatter observations in the Gulf of California. Forty-three sperm whale groups, totalling 813 individuals, were encountered during 28 observation days. Sperm whales occurred over deep waters (mean depth = 659 m, range: 300–1800 m). A significant correlation was found between the whales' maximum depth of dive and depth of the acoustic scattering layer (N = 36, r 2 = 0.944, P = 0.000). We observed sperm whales dive to the scattering layer and then surface with prey in their jaws: jumbo squid, Dosidicus gigas (10 events) and unidentified fish (one event). The average depth of sperm whale foraging dives to the scattering layer was 342 m, the average diving time was 23 minutes, and the average surface interval between foraging dives was 6 minutes. Sperm whales spent 75% of their time diving and 25% on the surface. Swimming speed at the surface was slower when whales reached scattering layers during a dive (2.4 km/h) compared to dives when no scattering layer was reached (8.9 km/h). Our results establish a direct link between sperm whale distribution and presence of its prey in the Gulf of California.
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