Marine biologists are increasingly aware of the importance of the aquatic soundscape to animal navigation, communication, and hunting. We’ve known for some time that marine mammals are capable of processing complex acoustic stimuli, and recent investigations have proven that several species of bony fish can also distinguish between subtle differences in sound and respond differently to varying musical cues.
Yet little is understood about how much cartilaginous fish like sharks and rays – known to use vision, smell, and electroreception to find prey – rely on their auditory organs.
So, a research duo from Macquarie University, Australia, decided to test whether a local species of nocturnal shark has the ability to learn that a musical stimulus signifies the presence of food.
It turns out that a majority of Port Jackson sharks can grasp that jazz means food, yet it all goes out the window when you introduce classical as well. But don’t underestimate their intelligence or report them to the music snobs just yet.
"The task is harder than it sounds, because the sharks had to learn that different locations were associated with a particular genre of music, which was then paired with a food reward,” stated Culum Brown, one of the authors of the paper now published in Animal Cognition.
For their study, the researchers took eight juvenile Port Jackson sharks, hatched and raised in captivity, and trained them to associate musical stimulus – a jazz song – with a reward that was located on either the left or right side of the end of a rectangular tank. The musical cue was played 20 to 40 seconds after the sharks were introduced into the experiment tank, and they had 180 seconds to eat the treat.
A separate set of trials were performed to verify that the sharks recognized the cue instead of simply learning to swim to one side of the tank.
After these experiments, a series of trials evaluated whether the petite predators could learn to distinguish between the jazz song – meaning the food reward was located on the side they previously associated it with – and a classical song – played when the morsel was presented on the opposite side of the reward zone.
The series of tests revealed that five of eight sharks successfully learned that the jazz song meant food was available in a specific location. But when the classical played?
“It was obvious that the sharks knew that they had to do something when the classical music was played, but they couldn't figure out that they had to go to a different location," said Brown. “Perhaps with more training they would have figured it out."
"Sharks are generally underestimated when it comes to learning abilities,” added first author Catarina Vila-Pouca.
"However, they have really big brains and are obviously much smarter than we give them credit for”.
Though the study was limited by its size, the findings are in line with other experiments that indicate sound is an important sense in both bottom-dwelling and open-water shark species, particularly nocturnal ones such as Port Jacksons.