Can Odontocetes Debilitate Prey with Sound?

1. The hypothesis is presented that some odontocetes may debilitate prey by use of brief intense sounds. 2. In several cases, considering the feeding structures of a given odontocete species, it is not apparent how they capture the prey species on which they feed. Especially in these cases, prey should be able to outdistance the odontocete in question or outmaneuver it. 3. Some field observations are strongly suggestive of prey debilitation by odontocetes. Fish have been seen to lose orientation capability in the presence of ensonifying dolphins, and wild fish schools being fed upon by dolphins were found to be so lethargic they could be removed from the water by hand. 4. In the evolutionary development of modern odontocetes, feeding mechanisms have shifted from a modified terrestrial tooth row capable of entrapping prey (the cage jaw), to very elongate jaws (pincers jaws) capable of snapping prey from the water, in early Miocene dolphins, to the loss of such beaks and teeth in many modern forms which made their appearance in middle and late Miocene. The major means of ingestion has become suction, activated by a piston tongue. These trends seem associated with a narrowing of the emitted sound field, probably as an evolutionary response toward the development of increased range by their echolocation pulses. It is hypothesized that as the beam narrowed and intensified it began to disorient prey. These trends are tied to the telescoping and assymetry of the dolphin skull. 5. The sperm whale may catch its swift squid prey leaving no evident tooth marks, and such prey may be alive in sperm whale stomachs. The disparity between the speeds of the sperm whale and squid and the costs of sperm whale acceleration are discussed. Sperm whales eat a very wide-sized range of prey, and small items will not repay the costs of the whale's locomotion. The forehead sound-beaming anatomy is postulated to allow prey debilitation. 6. Bottlenose dolphins are known to emit sounds intense enough to kill fish, and probably also squid. 7. Some evidence implicates snapping shrimp in sonic prey stunning. 8. The major problem for the hypothesis is the lack of recordings of such very intense odontocete sounds at sea.

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