Jan 19

Sharks, including species such as the blacktip shark (Carcharhinus limbatus), the bull shark (Carcharhinus leucas) and the bizarre-looking spotted wobbegong (Orectolobus maculates), may be colour blind according to new research.

Bull shark photo

The bull shark has the remarkable ability to survive in both saltwater and freshwater.

It was found that some sharks only have one type of cone cell (a colour-sensitive cell found in the retina of the eye that is responsible for colour vision). In contrast, humans have three types of cone cell which detect red, blue and green wavelengths of light. This allows humans to tell the difference between different coloured objects.

Colour vs. contrast

The study, which looked at the retinas of 17 different species of shark caught off the coast of Queensland and Western Australia, found that 10 species did not appear to possess cone cells at all, while the remaining 7 species had just one type of cone cell present.

Photo of a spotted wobbegong lying on sandy seabed

The strange spotted wobbegong is perfectly adapted to life on the seabed.

Rod cells, which are much more sensitive and function at much lower light levels than cone cells, were the most common cell types found in the retinas of the sharks.  

The investigation shows that for sharks, contrast against the background may be more important for detecting objects, rather than their colour.

Although having a single type of cone cell is rare in species that live on land, it is possible that it may be a common strategy in the marine environment, with many aquatic mammals such as whales, dolphins and seals also possessing a single, green-sensitive, cone type.

Making objects ‘less attractive’

Dr Nathan Hart, who led the team of scientists carrying out the study, said that this research could help to prevent shark attacks on humans and assist in the development of fishing gear to reduce the number of sharks that are caught accidentally in long-line fisheries.

It may be possible to make objects such as long-line fishing lures and swimwear ‘less attractive’ to sharks by designing them to have a lower visual contrast, Dr Hart suggests. Looking at behaviour will be the next step, with much more research needed to determine which patterns might work best to deter sharks.

Photo of a diver freeing juvenile blacktip shark caught on longline hook

A blacktip shark being released from a long-line hook by a diver.

Read more about the study, carried out by Dr Hart and colleagues from the University of Western Australia and the University of Queensland, Australia, in the journal Naturwissenschaften.

Find out more about sharks on ARKive.

Helen Roddis, ARKive Scientific Text Author