Tuesday, January 29, 2008

Nature shock - Mystery of the killer dolphins

See below for an interesting report (picked up by Andrew Sullivan) about some non-cuddly traits of the friendly and intelligent bottlenose dolphin. It reminded me of some idle musings about dolphins that occurred to me several decades ago.

=> Then as now, we constantly hear about how charming and likable dolphins are, and most of the time that seems to be true. Let me be clear: I'm genuinely fond of dolphins. What follows is a purely analytical puzzle.

In the things I read about dolphins, one piece of evidence offered to demonstrate their good-natured benevolence was the claim that dolphins sometimes save drowning sailors by pushing them in toward shore. That sounds nice of them, and I have no reason to doubt that there are such cases..

But then I couldn't help wondering ... what if this is just a misleading impression created by sampling bias? That is, what if a dolphin sees a drowning sailor as a kind of bathtub toy, and enjoys pushing him (or her) around in the water in a spirit of good-natured play? And let's imagine--to continue the hypothesis--that such sailors would get pushed around randomly in different directions. That would mean that about a quarter of the sailors get pushed toward shore, while the other three-quarters get pushed either out to sea or parallel to the coastline. Well, the only sailors we hear from afterward are the ones who got pushed toward shore, right? The other 75% are eliminated from the sample, so to speak. So maybe this impression that the dolphins are doing it to help the sailors is just an unwarranted inference produced by systematically biased data? (After all, what have humans ever done for dolphins that would make them so eager to help us out?)

All this is just speculation, of course ... but I wouldn't want try getting an experiment designed to test this hypothesis approved by an IRB.

=> At all events, getting back to observable reality (and real science) ... the story below comes with a striking video.

--Jeff Weintraub
=========================
Daily Telegraph
January 25, 2008
Killer dolphins baffle marine experts
By Nigel Blundell

It's hard to visualise but the intelligent and ever-friendly dolphin can also be a determined killer.

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    New evidence has been compiled by marine scientists that prove the normally placid dolphin is capable of brutal attacks both on innocent fellow marine mammals and, more disturbingly, on its own kind.

    When tell-tale teeth-marks were identified, the dolphin - the mammal classified as one of the world's most intelligent, sensitive and sociable creatures - became the official suspect.

    Confirmation of the murders came by way of two shocking films shot by holidaymakers.

    The first was initially believed to show a dolphin fishing for salmon - until closer examination revealed a relentless attack on a porpoise, its body spinning round with such force that its back was broken and its soft tissue shattered.

    Marine experts now believe that these displays of attacks on non-rival, non-predatory, peace-loving porpoises and, more shockingly, of dolphin infanticide, may have always taken place.

    It is only now, with dolphins' more human-friendly behaviour taking them closer to tourist boats and beaches, that the violence is being witnessed first hand. Until the shocking realisation, dolphin-watchers in America had believed they were watching the mammals at play with their young.

    Four years ago, members of Scots charity the Cetacean Research and Rescue Unit discovered a lifeless porpoise near the harbour at Whitehills, near Banff.

    The team described the mammals' injuries as "perhaps the worst example of inter-specific aggression any of us had ever seen. This young female had literally had the life beaten out of her."

    Inspection showed multiple lacerations and puncture wounds all over the body which could not have been caused by any other attacker than a bottle-nosed dolphin.

    Two of these fatal attacks by dolphins feature in the documentary The Dolphin Murders, being shown in the channel Five series Nature Shock on Tuesday, January 29.

    Watching the films, Aberdeen marina biologist Dr Ben Wilson explains yet another shocking phenomenon - that the dolphins use their incredible ultra sound abilties to home in on the vital organs of their victims that will cause most damage.

    "The blows are carefully targeted," says Dr Wilson, who is a member of the Scottish Association for Marine Science. "And the attacks are sustained, sometimes up to 30 minutes.

    "The film was a key piece of evidence. It crystalised our suspicions. We realised the dolphins' victim was trying to escape from being attacked with such force that any one single blow could kill it.

    "It was, Oh my God!, the animals I've been studying for the last 10 years are killing these porpoises."

    Theories abound on the reason behind the mammal murders. These have included territorial clashes and feuds over food resources. But food is not in short supply and the victims are not just chased away but pursued to the death.

    Another belief is that dolphin attacks on their young may be down to mating instincts, because when her calf dies the female dolphin is ready for mating again. But the experts are still not positive that it is only males who do the attacking.

    And, incredibly, they can only guess that the attacks by bottle-nosed dolphins on Scotland's harbour porpoises is some kind of bizarre 'target practice.'

    For the one common link between the attacks here and America is that the victims are of a similar size and weight.

    Perhaps the dolphins' instincts has them practising the same skills required to separate a porpoise from its school, pursue it and kill it as are needed for attacks on its own kind.

    Nearly half of the harbour porpoises' bodies examined have died as a result of the dolphin attacks.

    Perhaps some answers will be found as Dr Wilson - who has written several research papers on dolphins - and his team continue their Bottlenose Dolphin Project throughout the Scottish waters this winter. The field work is expected to end in the summer.

    But as the experts of the Cetacean Research and Rescue Unit are forced to declare: "These killings represent yet another example of the hard brutality and evolutionary pressures of the marine world."

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