Bycatch – the accidental capture (and often mortality) of any species – or even a subset of a species (like juveniles) – in fishing does not make for a good fishing trip. It takes up valuable space in your net, it can damage your gear, and it can cause population declines of species accidentally caught. New ways to reduce bycatch are being tried out (some more successfully than others) more and more regularly.
When it comes to gillnets, bycatch of turtles is a big problem. It doesn’t take much for a wayward turtle to find itself tangled up and unable to get out by itself. For fishers, cutting the net to release them is often the only solution. Enter Dr John Wang from the University of Hawaii. He came up with an interesting proposal….what if turtles were better able to see the net, but the targeted fish couldn’t?
In this newly published piece of research, John demonstrates that by simply attaching UV LED lights to the gillnet floatlines (a line at the top of the net has floats on it which keeps it upright in the water), Green sea turtle (Chelonia mydas) bycatch declined by some 40%, but both the target catch size and the value of the catch didn’t decrease.
It all comes down to vision. The turtles are really quite good at detecting UV light…the fish not so much (in this study there was a variety of target species – mainly flounders – members of the family Pleuronectidae). Clever stuff. But John isn’t planning on stopping there. He notes that different turtle and different fish species may react to different colours of UV light. Watch this space for news on how that goes.
The paper is open access – talk a look at it here http://rsbl.royalsocietypublishing.org/content/9/5/20130383
Image: Green sea turtles entangled in a n abandoned small-scale net. Credit Projeto Tamar Brazil/Marine Photobank