Shark Week

Shark Senses

Sharks of some sort or other have been swimming around in the ocean for 420 million years. This tells us a few things – that sharks have successfully adapted to their marine habitat, and this includes their sensory systems. It was once thought that sharks were voracious feeding machines with little nuance. But we are finding all sorts of subtle, and not so subtle clues that they are far more complex than our initial terrified imaginations would allow. Some sharks like to play, they have pals they like to hang out with, and some take care of their babies.

A few years back I was at an event that hosted free-diver and writer James Nestor. Free diving is a breathing discipline that allows divers to submerge for long stretches of time – typically 5 to 10 minutes, although longer times have been recorded. One of the advantages of free diving is that there are no bubbles from scuba gear or other pressurized breathing apparatus that can spook sea animals.

James spoke with us about playing with great white sharks. He said that sharks a naturally curious, and given that the don’t have hands, when they check something out, they use their teeth. This is probably why surfers and divers may get bitten by sharks, but rarely eaten. The important thing, then, is to know when the shark is approaching, and face them head-on. So his shark adventures relied on shark spotters who would let him know if a shark was approaching.

He said that once you spot a shark, it was important to establish eye contact – which he says “lets the shark know you are also a predator.” Then it’s “game on!” He would grab on to the shark’s fin, and the shark would take him for a ride, then shake him off – and then come back and pick him up again! I’m not sure this would be the sort of “chase and tag” game I’d like to play, but it is somehow comforting to know that sharks can be playful.

Until not too long ago it was thought that sharks also had strong nose for blood, and that they could smell in the water miles away from the source. But fisheries biologist Arthur Myrberg turned that assumption around in the late 1960s, while spear-fishing in the Florida Keys. After having speared a fish or two he noticed sharks honing in on his catch. But they were coming from up-current, the opposite direction of the blood drift. It occurred to him that the sharks were more likely attracted to the sound of the low-frequency thrashing of a fish in distress. He went on to expand on this understanding in a number of seminal research papers.

While their sense of smell may reach 100m, they can hear sounds of interest over several kilometers. Something to remember when you are thrashing around in the ocean…