Bamboo sharks which have been trained in a range of visual discrimination tasks, such as distinguishing between squares, triangles and lines, remembered the learned information for a period of up to 50 weeks, after which testing was terminated despite the absence of reinforcement. This indicate that sharks are capable of long-term memory within the framework of selected cognitive skills.
Researching the intelligence of the grey bamboo shark a team of researchers at Rheinische Friedrich-Wilhelms-University in Bonn, Germany showed that sharks could be trained to recognise and remember shapes for an extended period of time.
First juvenile sharks were subjected to three different cognition experiments, one at a time, and then tested to see how long the sharks could remember their training.
During one experiment sharks were placed in a special holding tank and an image of a basic shape was projected onto one of its walls. Some of the sharks were shown a triangle and would received a small piece of food for pressing their nose on the triangle. Other sharks were taught to always recognise a square for which they were similarly rewarded.
Some sharks were faster learners than others and individuals varied in their ability to learn and retain memories. Up to 50 weeks later however, almost all the sharks still remembered which shape to select, significantly more than the 7-seconds that is, often incorrectly, associated with fish.
At that juncture the researchers ended the study, to begin investigating which part of the shark brain is responsible for such feats of memory. Unlike with mammals, it is currently completely unknown how and where in the brain sharks process, store, and retrieve memories.
These are ideally suited to a predator living in a complex, variable and unpredictable environment allowing them to adapt behaviour, ultimately improving their feeding efficiency. Grey bamboo sharks which were used in the experiment are, however, benthic feeders, swimming along the ocean floor, scooping up sand with its mouth and hoping to catch small fish, worms, shrimps, mollusks and crabs.
This implies that visual hunters such the Great white shark and Tiger sharks might be capable of even greater mental feats.