PBS - The Voyage of the Odyssey - Track the Voyage - MALDIVES
The unusually loud clicks and whistles detected on the acoustic array were heard from Odyssey's bow. Bob cut the engine and Peter deployed our wideband hydrophone system that can record ultrasound frequencies in an effort to capture the unique sounds of the Risso's - recordings of this species in the wild are rare. The dolphins hastily changed course and headed directly toward Odyssey at high speed, which we found surprising as boats do not normally hold a strong attraction for Risso's dolphins, which usually maintain a comfortable distance. However, these Risso's seemed to be so pre-occupied, they barely noticed our close proximity. The group consisted of roughly 20 animals, 8-10 of which were intent on the pursuit of a single dolphin, presumably a female that attempted to remain ahead of her pursuers.
They continued rolling and leaping around the lead animal as it swam back and forth beneath Odyssey's bowsprit in what appeared to be an effort to escape. Several animals spy-hopped (lifted their heads vertically above the surface), affording us a rare close up of their scratched rounded melons, large eyes and open mouths, others swam on their backs, their milky-white bellies and flippers exposed and facing the sky. We were certain that the purpose of this behavior was mating. This was perhaps our best opportunity of the voyage so far to observe rarely seen dolphin behavior at exceptionally close range.
For over forty-five minutes the Risso's surrounded Odyssey, swimming furiously only feet from the hull, the calm sea conditions giving the crew a perfect view and the opportunity to capture the entire sequence on film.. The scientists and crew has often commented on the severe scratching and scarring that is characteristic of this species while speculating about the cause.
A Risso's dolphin rolls on its side to take a look at the Odyssey.
Photo: Chris Johnson
Risso's dolphins primarily feed on squid. Most other odontocetes (toothed whales) that specialize in squid usually have teeth in the lower jaw. This is evident in sperm whales, and several beaked whale (Ziphiids) species, which are usually characterized by the absence of all but one or two pairs of mandibular teeth. It has long been recognized that male odontocetes of certain species use these lower teeth to rip and tear at each other's bodies in fights for access to receptive females.
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