Last Thursday, I attended a very good lecture on this topic at the University of Western Australia. Each of 3 lecturers took it in turns to present their unique findings: Prof. Shaun Collin, Assoc. Prof. Nathan Hart and Dr Ryan Kempster, all from the School of Animal Biology.
So what have we learnt?
The presentation started with describing their findings of the shark senses. Being living animals, it is not surprising that they have the 5 senses: sight, hearing, smell, taste, touch. These will be explained below.
They have found that sharks are monochromats, having peaks in receptors for the green-yellow wavelengths (with a secondary low peak at purple). Practically, this means they are somewhat “colour-blind”. Characteristics of colour-blind animals is that they are very good at detecting contrasts. They’ve found the greatest density of receptors in their eyes lie in the posterior-ventral part of the retina and this means that their line of best site is diagonally above, and in front of them. However, their visual acuity is only moderate which means they have to get close to see more clearly.
On sound, sharks do have ears. The opening to the ear is in the dorsal surface (top) of the head, a slight distance behind the eye. It detects vibrations and hydrodynamic sounds (e.g. waves, splashing, eating, bubbles). They have good directional hearing, meaning they can tell where sound is coming from. Of the 10 shark species studied, they’ve found they can hear low frequency sounds, in the range of 10-800 Hz (cf humans 20-20,000 Hz).
Sharks have nostrils and they point downwards. They have folded skin to increase the surface area, making them able to detect as little as 1 drop of blood in a olympic-size swimming pool. This said, the olfactory bulbs in the brain of different elasmobranchs differ in size, so we can’t quite make sweeping generalisations.
Sharks have no external taste buds. Their taste buds are located in the oropharynx, basihyal (tongue) and gill arches. The highest concentration of taste buds are behind their teeth. This explains why they need to bite, or to mouth at things, in order to taste it.
I think I was late in to the lecture, and might have missed this section, or maybe they didn’t cover it. But if you’re reading this, and you were there, please do elaborate in the comments section. Thank you.
So, sharks have all the 5 senses that we have. But they have a couple more! Firstly, like all fishes, they have a “lateral line system“. These are little pits along the length of the body, each pit contains hairy cells and the pits are connected to adjacent pits by a channel. The lateral line system detects water motion and low frequency sounds (20-200 Hz). It is used for detecting obstacles.
The second special sense they have is called the “ampullae of Lorenzini“. These a small pits around the area of their snout and within the pits is a gel-like substance that helps conduct electrical currents from the environment to the electroreceptors within. These are so sensitive that they can detect electrical currents as low as 1 billionth of a volt! They use this to detect prey since all fishes produce small electric fields. Thus, electrical stimuli actually attract sharks to check things out. The abundance of these ampullae vary between species. A Port Jackson shark has only 200 pits, making them less adept at locating electrical stimuli, whereas the hammerhead shark as as many as 3000 pits, making them finely tuned. The great white shark has 800 and the shovelnose ray has 1200.
So now we know about their 7 special senses, how do we use this knowledge to our advantage? How do we create safer beaches for swimming? How do we create personal protective devices for divers?
Stay tuned to find out in my post next week.