Diving behaviour of the sperm whale in relation to feeding
1997
Lockyer, C. (Natural Environment Research Council, Cambridge (UK). Sea Mammal Research Unit)
Sperm whales are amongst the deepest and longest diving mammal species. Investigations on dive depth using both indirect evidence of bottom cable entanglements and dietary species from stomach contents, and also direct evidence from both active sonar tracking and passive acoustic listening to sperm whales clicks using directional hydrophones, indicate that dives are possible to depths more than 1,000 m and may even be in excess of 2,000 m. Duration of dive may last up to an hour. In most parts of the world's oceans, the sperm whale feeds on squid, but off Iceland, fish predominate in the diet. Many bottom and deepwater squid species are only known from sperm whale stomachs. The mechanism of food gathering is uncertain. There is a claim that sperm whales are able to stun prey with a beam akin to ultrasound, and another that prey are attracted passively to the whiteness of the mandibular teeth. One matter that is certain is that the teeth are not used for prehension because undigested prey items retrieved from the stomach do not show bite marks. The largest whole item reported was a giant squid nearly 10.5 m in length. In addition, animals with congenitally deformed or broken (but healed) mandibles are still able to feed effectively. Clearly the sperm whale must use some form of powerful suction mechanism in the buccal region to entrap and swallow the prey. At great depths prey will not be seen unless bioluminescent organs are displayed, and prey may only be detected acoustically, and physically from movements creating water pressure fronts and tactile experience. Investigations both anatomically and biochemically indicate that the specialisation of the head region into spermaceti organ and junk may serve a dual function of buoyancy control in diving and acoustically in echolocation. It is clear that there are still many questions unanswered about sperm whale diving and feeding mechanisms.
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