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August 2016    Download the Entire Issue (PDF) Available to the Public Vol. 42, No. 8   RSS Feed for Undercurrent Issues
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Sharks Have Personalities Too

from the August, 2016 issue of Undercurrent   Subscribe Now

A new paper published in the Journal of Fish Biology offers the first evidence that sharks really do have distinct personalities. In fact, some sharks really may be nicer than others, or whatever the shark equivalent of nice is.

Specifically, the study focused on boldness, defined as "the propensity to take risks," a characteristic that's been used to study personality in marine species from 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 the sharks' 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 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 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, one that varied from one individual shark to another -- in other words, a shark personality trait.

So, some sharks are shy, and some are outgoing; some are adventurous, and some prefer to stick close to what they know. A better understanding of sharks' personalities may help scientists learn more about what drives their choice of things like prey and habitat, and their ultimate survival.

From an article by Cari Room, Science of Us

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