It was once thought that sharks were just feeding machines led about by their sense of smell – and that they could smell blood in the water over a mile away. Some of this mythology was promulgated by military training films in response to sharks being attracted to sinking vessels and downed aircraft – that were often accompanied by bleeding sailors or airmen.
But sometime in the mid-1960’s biologist Arthur Myrberg was spearfishing in Florida and noticed sharks coming in to investigate his catch were coming up-current from the plume of blood that his catch left downstream. This got him thinking that perhaps hearing was more important to sharks in locating their prey. He found in his research that sharks were particularly attracted to irregular low frequency sounds such as what might be produced by a thrashing fish or a panicked human swimming under stress – sounds of opportunity you might say.
A number of years ago I was speaking with some shark research biologists from the University of South Florida. There had been a noticeable upswing in “human/shark accidents” in their area and the public wanted some answers. One thought we tossed around was that the noise from an increase in personal watercraft use was drowning out the hearing and thus masking the hunting field of the sharks. With a limited hunting range perhaps the sharks were becoming hungrier, and thus less discriminating about their food sources.
Like many speculations about the impacts of noise on marine life this one had to remain a speculation. Getting Florida tourists to stop using personal watercraft in a particular area for a long enough period to collect longitudinal data on human/shark interactions would be difficult. I also suppose that having shark-bitten people being one of the study variables might wrinkle up the noses of some research funders.
But if you do find yourself in the water with hungry sharks, do your best to remain calm – and quiet…