Blue Ocean Institute

Jul 17th
2013

Do sea turtles see the [LED] light?

Guest Blog by Jesse Senko                                                                       When I first visited Lopez Mateos, a small fishing community on the Pacific coast of Baja California Sur, Mexico, I remember walking a 40 km stretch of beach littered with dead sea turtles. At times the stench of rotting turtle carcasses was so intense I had to wear a bandana around my nose to avoid throwing up. It didn’t always work.

How could so many sea turtles wash ashore dead on such a small stretch of beach? Along the coast of Lopez Mateos, North Pacific loggerhead turtles aggregate in high numbers in search of their main food source, pelagic red crabs. Unfortunately, halibut and other fish species that fishers are trying to catch also eat pelagic red crabs, putting loggerheads in danger of being caught as bycatch in local, small-scale bottom-set gillnet fisheries. This fishing gear entangles virtually everything that makes contact with the net, including endangered sea turtles that become trapped on the seafloor and eventually drown. In fact, the offshore area adjacent to Lopez Mateos produces among the highest recorded sea turtle bycatch rates on the planet. In addition to sea turtles, gillnets catch many other non-target species, including marine mammals, crabs, squid, sharks, rays, and even target catch species that are too small to keep.

Last year I wrote a blog article that talked about a possible solution to reduce loggerhead bycatch at Lopez Mateos while keeping fishers fishing. Specifically, my collaborators and I tested the effects of illuminating gillnets by placing AA battery powered LED lights every 10 meters along the net. The idea behind illuminating gillnets is simple –sea turtles and other bycatch species can use the LEDs as a visual cue to see the net and hopefully avoid it, whereas target species that fishers are trying to catch may not be able to pick up the same wavelength. This ideally creates a “win-win” scenario in which fishers continue to fish in their desired locations, but in a more sustainable way.

Left photo: Author Jesse Senko (right) with Mexican fisheries colleague holding up LED lights pulled off the illuminated gillnets. © Jesse Senko
Right photo: Setting illuminated gillnet (note green LED light clipped to float line) for nighttime deployment at sunset 20 miles offshore the Pacific ocean. © Jesse Senko

In order to test whether or not the illuminated nets worked, I had to live on a fishing boat 20 miles offshore the Pacific Ocean for 2 weeks – in the heart of the loggerhead hotspot. Sometimes in the middle of the night I would hear the “swoosh” sound of sea turtles surfacing to breathe out of my small cabin window. While on the boat, we fished “control” nets without LEDs attached and illuminated nets (with LEDs) and then compared differences in target catch, loggerhead bycatch, and overall bycatch.

Author Jesse Senko holding up a live loggerhead turtle just prior to release. This turtle was captured in an experimental gillnet. © Jesse Senko

So, did the LEDs work? While our results are preliminary and more trials are needed, we found that illuminated nets decreased loggerhead bycatch rates by 50% at night. But even more surprising, the illuminated nets caught more halibut (the main target species) while reducing non-turtle bycatch (fish, crabs, and squid) during both day and night periods. This resulted in a massive reduction in overall bycatch biomass– all animals that are normally tossed overboard dead. Fishers were particularly excited about the prospect of not having to remove all that bycatch, turtles included – a time consuming process that also uses more fuel because the nets become heavier and more difficult to haul!

Although more testing is needed, our initial results suggest that illuminated gillnets may be promising for reducing bycatch of sea turtles and other species in gillnet fisheries. We hope that one day this research culminates in more sustainable gillnet fisheries, both at Lopez Mateos and in other parts of the world.

 

Jesse Senko is a PhD student in biology at Arizona State University and a sustainable seafood consultant for the Blue Ocean Institute. You can follow him on Twitter @ jesseSenko (https://twitter.com/jesseSenko).

 

 

 


 

Comments:  2

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2 Comments

  • Aug 7th 2013 at 3:22am
    ataplaut wrote:

    wow great experience,

    would u mind sharing the specification of LED.
    Where i could buy and how much the prize

    i want to try it in my place

    thanks

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