Last year, we found out that sharks have social personalities. Now comes evidence that they can identify shapes and optical illusions — and remember what they've learned for a full year, and maybe even longer.

In a new study published in Animal Cognition (read the full scientific paper here), Institute of Zoology researchers from Germany's Rheinische Friedrich-Wilhelms-University in Bonn studied the memory retention of juvenile gray bamboo sharks. Training sessions schooled the sharks in how to distinguish between shapes, as well as visual illusions like Kanizsa figures, in which triangles and other shapes are suggested by the arrangement of Pac-Man shaped configurations around their borders. They were good students, almost across the board.

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Amazingly, though the lessons weren't revisited repeatedly, the sharks recalled what they'd been taught 50 weeks later, and the experiment ended there, so it's actually unknown how long they would have retained the information. The study did note, however, that sharks have selective memory for purely practical purposes:

In fish, as in other vertebrates, memory windows vary in duration depending on species and task; while it may seem beneficial to retain some information for a long time or even indefinitely, other information may be forgotten more easily to retain flexibility and save energy. The results of this study indicate that sharks are capable of long-term memory within the framework of selected cognitive skills. These could aid sharks in activities such as food retrieval, predator avoidance, mate choice or habitat selection and therefore be worth being remembered for extended periods of time. As in other cognitive tasks, intraspecific differences reflected the behavioral breadth of the species.

The BBC report on the study noted that the German researchers are moving on to study shark brains more closely, specifically trying to determine which part of the brain controls these surprisingly robust memories. (The BBC also couldn't help name-dropping Great White Sharks, because what's scarier/more awesome than a giant, hungry shark with a giant, awesomely complex brain?)

Unlike with mammals, it is currently completely unknown how and where in the brain sharks process, store, and retrieve memories.

The grey bamboo shark is a benthic feeder, swimming along the ocean floor, scooping up sand with its mouth and hoping to catch small fish, worms, shrimps, mollusks and crabs. This shark species was a much better visual learner than expected, but species that are visual hunters rely much more heavily on their sight than benthic feeders.

That means visual hunters such the Great White Shark might be capable of even greater mental feats.

Grey bamboo shark photo by Citron.


Contact the author at cheryl.eddy@io9.com.