Turns Out Sharks Have Personalities, Too

Photo: Dave Fleetham/Design Pics

Does anyone else think that the sharks are the real heroes of Finding Nemo? Unsung ones, to be sure, but clearly the fish that’re most deserving of the title. Consider our titular protagonist, his father, Merlin, and happy-go-lucky sidekick, Dory — all of them are mostly just swept along on their adventures by circumstance and currents. Bruce, Anchor, and Chum, on the other hand, are doing things. And by things, I mean real, substantive work on behalf the shark community.

I am a nice shark, not a mindless eating machine,” they remind each other. “If I am to change this image, I must first change myself. Fish are friends, not food.” (Sure, Bruce later loses it at the scent of blood and goes into a ravenous, murderous feeding frenzy. Let he who has ironclad willpower cast the first stone.)

Even if these friendly, fish-loving sharks are just a figment of some animators’ imaginations, though, some sharks really may be nicer than others, or whatever the shark equivalent of nice is: A new paper published in the Journal of Fish Biology offers the first evidence that sharks really do have distinct personalities.

Specifically, the study focused on boldness, defined as “the propensity to take risks,” a characteristic that’s previously been used to study personality in marine species from tadpoles to zebrafish to crabs. Using Port Jackson sharks (a nocturnal species found off the coast of southern Australia), the researchers ran two tests, one designed to test their boldness and the other to see how they reacted to stress. For the first, they placed each shark in a small enclosure within a tank, timing how long it took for the animal to poke a head or a fin out of the box, and how long it took them to swim completely into the open. For the second, they held each shark out of the water for a minute; once they put it back, they recorded how many times per minute it beat its tail through the water, a marker of anxiety.

For both tests, the results spanned a wide spectrum: Some sharks emerged from their box in just two seconds, while others took a full 20 minutes; tail-beat frequency was similarly all over the place, though the sharks that had emerged most quickly in the first test were also more active in the stress test, suggesting that they were making more of an effort to escape the stressful situation. Based on these differences, the researchers concluded that boldness wasn’t a behavioral pattern that held firm across all members of the species, but rather a that varied from one individual shark to another — in other words, a shark personality trait.

Down the road, the study authors write, a better understanding of sharks’ personalities may help scientists learn more about what drives their choice of things like prey and habitat. Some sharks are shy, and some are outgoing; some are adventurous, and some prefer to stick close to what they know, information that could prove useful in making sense of larger species-wide behavior patterns. But unfortunately for misadventure-prone clown fish everywhere, all of them, save for a handful of animated Disney exceptions, still see fish as food, not friends.

Turns Out Sharks Have Personalities, Too