Colour-blind sharks

3 02 2011

A few weeks ago I was interviewed on Channel 10 (Adelaide) about some new research coming out of the University of Western Australia regarding shark colour vision.

I’ve received permission from Channel 1o to reproduce the news snippet here. The first bloke interviewed is Associate Professor Nathan Hart, the study‘s lead author. I’m the bald one appearing in the middle at at the end.

It certainly was an interesting story, although two claims were made that probably needed better contextualisation.

First, the authors claim that because of this taxon’s colour blindness, they probably notice pigment transitions more when using visual cues to identify potential prey. What this means is that bright colours set against duller backgrounds might provide that contrast enough to attract sharks. The upshot from the interview is that brightly coloured and patterned togs (bathers) might make sharks think you are potentially a tasty treat.

One should understand though how sharks hunt and find prey. The first sense they use is sound, namely because it travels so far (a colleague once told me a shark could hear flailing fish 100s of kilometres away – not sure about that). As they approach the potential prey source, the second sense invoked is smell (probably 10s of kilometres). As they get nearer and spot the prey, then visual senses are invoked. The kill itself is probably more guided by their electro-sense via the ampullae of Lorenzini. So it’s basically a spatial scale hierarchy of senses, probably with certain overlap at the fringes of the senses’ ranges.

photo by Jason Tanner

Indeed, when we dive in southern Australia, it is mandatory that we wear electric field-disrupting ‘shark shields’ (basically, a little battery with a long, trailing conducting line – see photo of me to the right) that purportedly interfere with a shark’s orientation during the attack phase. I don’t really know if it works, but it’s a little feeling of presumed security when underwater.

So, back to bright togs – I personally think a shark would have to be pretty interested in you already if it came down to the ‘kill’ (or even, the ‘bite’) before it would even invoke the visual cue of your fashion’s colour pattern (don’t know about the ‘ruffles’ – see video above). In other words, I don’t think dull bathers will save you. Considering the extremely low likelihood of shark attack, the change in probability would be negligible at best.

The second claim is that such knowledge could assist in designing fishing lures that were less attractive to sharks, thus reducing unwanted bycatch. Well again, my same trepidation holds. I think if baits are used, the shark would use smell and finally electroreception to target a baited hook. If just a lure, well, how do you make one that is attractive to say, tuna, and not sharks? Bit of stretch, although I’d be happy to be proven wrong.

CJA Bradshaw
Hart, N., Theiss, S., Harahush, B., & Collin, S. (2011). Microspectrophotometric evidence for cone monochromacy in sharks Naturwissenschaften DOI: 10.1007/s00114-010-0758-8



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