Dolphins attacking a shark?
A drone operator has captured (see below) rare footage of four false killer whales hunting and catching a young shark off the coast of Sydney, Australia.
One of the least studied members of the dolphin family, false killer whales are like their better known cousin the killer whale in that they hunt both other mammals and fish for food. And even though they range widely throughout tropical waters, false killer whales live mostly in the open ocean, rarely spotted near the shore, and have been observed mostly from specimens that have been beached.
The startling drone footage shows a team of four false killer whales chasing a much smaller shark until the latter appears to tire, then the lead false killer whale grabs it in his jaws. “National Geographic guys would wait months to get such a thing,” says drone photographer Bruno Kataoka. “We just happened to be there at the right moment at the right time.”
False killer whales average 4.3 to 5.96 metres in length, weigh upwards of 1,360 kg and mostly travel in groups of 20 to 100.
They have been known to develop long-term associations not only with others of their species but also with related dolphins. A 17-year study conducted off the coast of New Zealand of 61 false killer whales found that they were all linked in a single social network and that, surprisingly, they developed partnerships with bottlenose dolphins that lasted more than five years and spanned up to 650 km in distance.
The teaming up seems to be for mutual protection, according to Jochen R. Zaeschmar, researcher from Massey University, New Zealand. “The anti-predatory function of mixed species associations is mostly achieved through a greater chance of detecting a predator through more eyes watching out,” says Zaeschmar. “However, it is hard to say if this is mutualistic or parasitic, that is whether the two species actually co-operate or whether one just opportunistically exploits the detection ability of the other. Lastly, as both species are highly social, sociality may also play a role.”
It has long been known that dolphins use echolocation to find their way around in the ocean depths, sending out click-like sound waves that bounce back when they come upon an object -in the water, a dolphin’s hearing has a frequency range of 120 kHz, far outpacing human hearing (20 kHz) and even that of dogs (45 kHz) and cats (65 kHz).
But only recently have scientists fully grasped the inner workings of the dolphin’s sonic processing. Researchers from Emory University took brain images of the preserved brains of two dolphins who died after beaching more than a decade ago and found not only amazing complexity but also unlikely similarities between the dolphins’ neural auditory systems and those of that other specialist in echolocation, the bat.
“This is surprising because dolphins and bats are far apart on the evolutionary tree,” says neuroscientist Gregory Berns, lead author of the study.
“They diverged tens of millions of years ago but their brains may have evolved similar mechanisms for using sound not just to hear, but to also create mental images.”