Don’t worry about ‘yum, yum, yellow’, sharks are colour-blind
SYDNEY: The US Navy did tests on colours other than yellow for the life jackets pilots wear in case they have to eject and splash down in the ocean.
They found that sharks were less likely to be attracted to red or black than what one wag called “yum, yum, yellow.”
However, those 1970s tests were a waste of time, researchers in Australia have said, because sharks – along with whales, dolphins and seals – are colour-blind. Two or more
‘It may be that the colour isn’t useful to them’
different types of cone opsins – light-sensitive pigments in the photoreceptors in the cells in the retina – are needed for colour vision. Sharks, unlike most other fish, have only one.
Humans have three cone opsins in our eyes, enabling us to pick up blue, green and red light.
Nathan Hart, a neuroecologist at the University of Western Australia, said it was likely that the ancestors of sharks could see in colour but evolution had lost them this facility.
“It may be that colour isn’t useful to them or that they’ve lost the pigments for another reason,” Hart said.
“Throughout evolution there are numerous examples where vertebrate animals have lost one or more of the cone pigments and have a reduced capacity for colour vision.”
He said mammals have done this, reducing their colour vision from four channels (tetrachromacy) to two channels (dichromacy).
And then there is the appropriately named blind cave fish, which lives in the dark all the time. They ditched eyes tens of thousands of years ago because they no longer needed them.
Hart’s research, published in The Royal Society’s Biology Letters, builds on that done by Susan Theiss, a colleague at the University of Queensland. Their work could lead to better designed fishing equipment that would reduce the number of sharks hooked inadvertently.
“Longliner (fishing vessels) often use lures such as fluorescent glow sticks to attract fish to the baits and hooks,” Hart said. “As sharks and fish have quite different visual systems, it may be possible to use different lures that are more visible to target fish species and less visible to sharks.”
So if colour does not come into it, what ought people in the water do to make themselves less attractive to sharks? Perhaps a wetsuit with zebra stripes or a leopard-print pattern that would give camouflage and make you look fuzzy to a shark.
According to Hart: “There are two ways to tackle this one: stand out and look like something unpleasant, or hide against the background, either by matching the background better or breaking up your outline.”
For life jackets, though, those most easily seen from above would be best. There is not a lot of utility in being hidden from those out looking for you. – Sapa-dpa