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Ocean Watch

Susan Scott

Friday, August 27, 2004


Fish do not swim
around helping others


Last weekend, reader Heeny Yuen and his wife snorkeled in Hanauma Bay near a flat spot covered with small rocks. There they spotted something new to them: a papio (juvenile jack or ulua) circling and swimming back and forth in front of a moray eel tucked among the rocks.

Suddenly, the eel made a dash for the papio, and the two predators swam together, fast, for about 10 yards. Then the eel ducked back under the little rocks.

The two fish did this again and again, Heeny writes.

Since it was obvious the moray was not attacking, the Yuens wondered if the papio might be helping the eel find a suitable home. He writes, "Can you enlighten us on what was happening?"

I can. And it has nothing to do with one fish selflessly offering a helping hand to another. This concept, called altruism, just doesn't happen in the ocean. In fact, it rarely happens on land, either. Members of one species almost never rally round members of another.

No, when it comes to help, animals stick to their own kind. And even then, assisting a nonrelative is uncommon. In the world of nature, it's every unrelated creature for itself.

Except for fiddler crabs. In a recent study, Australian researchers discovered that these crabs, famous for having one enormous front claw, come to the aid of their neighbors.

Male fiddler crabs guard their territory fiercely, fighting off invading males that try to get a piece of the turf. Often the homeowner wins his own battle, but if it looks like he's going down, a neighbor joins in the fight to drive off the intruder.

At first, researchers thought this might be a rare case of altruism. But no. In studying the colonies, the biologists saw that if a crab let an invader whip his neighbor, the bystander would soon be next.

The conclusion is that fiddler crabs help unrelated community members not out of compassion, but to save their own fiddles.

Dolphins also look like they are helping others in their pod out of the goodness of their hearts. Female dolphins without young often help unrelated mothers care for their offspring.

Chimpanzees, too, are known to sometimes save the lives of unrelated chimps.

But much as we love endearing stories about dolphins and chimps, this behavior isn't true altruism. Rather, it's called reciprocal altruism, a term meaning either the beneficiary, or another member of the social group, will return the favor at a later time.

Some seabirds, such as penguins, practice reciprocal altruism by grooming the heads and necks of unrelated birds in their colony.

Fish don't exhibit any kind of altruism, but some behave in the manner described by the Yuens. Young golden trevally (ulua pa'opa'o), for instance, sometimes swim in the blind spots of large predatory fish, like sharks, to catch their leftovers.

Jacks, goatfish and others also sometimes tuck in close to moray eels, which flush small fish and crustaceans from their hiding places as they forage over the ocean floor. Occasionally these hitchhikers even rub against a parked eel to encourage it to get moving.

And that's what I think the Yuens saw: a hungry papio pestering a moray to get out there and rustle up some grub.

In the process, the eel might indeed have found a better home. With such pesky papio in the neighborhood, it needed one.



See the Columnists section for some past articles.

Marine science writer Susan Scott can be reached at http://www.susanscott.net.

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