Adding green LED lights to fishing nets could help marine mammals avoid being caught : NPR

SCOTT SIMON, HOST:

Gillnets are walls of netting that hang in water and trap fish. They are the most widely used fishing device in the world but also often trap sharks, sea turtles and rays who can’t escape and die. It’s known as bycatch. Now new research shows that attaching green LED lights to the nets could help avoid the indiscriminate trapping of fish. Jesse Senko is a research professor and senior sustainability scientist at Arizona State University. Thanks so much for being with us.

JESSE SENKO: Thanks for having me, Scott.

SIMON: Let’s understand the size of this problem. It’s huge, isn’t it?

SENKO: Yeah, this is a global problem. Anywhere where you have a coastal region, you almost certainly have gillnets. And they essentially catch everything that passes them.

SIMON: And this can include, obviously, threatened and endangered species and fish that are not in any way harvested for consumption but are simply living their best fish lives.

SENKO: That’s correct. This is a particular problem when it comes to these threatened and endangered species. They’re often tossed back dead or injured. And by them being killed in these fisheries, you have ecosystem-wide effects. So it really has profound implications for the health of the world’s oceans.

SIMON: Yeah. So what is there about green LED lights that change things?

SENKO: Well, the truth is we don’t really know. So we use green lights for three basic reasons, right? One is sea turtles and most marine megafauna – I mean sharks, seabirds, marine mammals – They can see green really well. Green also transmits well in water, so it can sort of attenuate pretty well. And the third reason is it’s energy efficient relative to other colors.

SIMON: So the whole idea is they illuminate the fishing net in a way a lot of species of fish will be able to observe and avoid.

SENKO: We think so. That at least was the idea behind this. And if you think about some of these animals – so particularly what we call the air-breathing marine megafauna – so these would be the sea turtles, the seabirds, the marine mammals but also several sharks that need to keep moving to breathe – the idea is they’re going to see this net. Of course, they don’t know it’s a fishing net.

SIMON: Yeah.

SENKO: But they know it’s a type of hazard, right? They know it’s something that, if they get entangled in it, they can’t get up to the surface to breathe, or they…

SIMON: Yeah.

SENKO: …Can’t keep swimming.

SIMON: They wouldn’t swim into it any more than they would swim into a wall.

SENKO: Exactly. But the truth is, you know, it may, in fact, be that the light just repels them – that the light might be an annoyance. They might not like the light. We don’t know yet, and that’s what’s really fascinating about this line of research.

SIMON: When you say LED lights, what kind of LED lights? And how long do they last? Don’t the bulbs have to be changed?

SENKO: These are basic LED lights. There’s two little LEDs on the light bulb. They’re powered by two AA batteries, so they do need to be changed. Generally speaking, they’ll last about three to four weeks. And so this does create a very serious recurring operational cost. One thing that we’ve done to circumvent that is we’ve developed a solar-powered light. It basically doubles as a buoy – as a float line buoy on the net. And what’s really cool about this light is it can basically remain lit for about a week with only 30 minutes of sunlight.

SIMON: And this is potentially good for the fishing industry, isn’t it?

SENKO: Absolutely. And we’re always looking for those win-win opportunities. Traditionally, a lot of conservation and management approaches have basically just said, shut them down – shut all gillnet fisheries down. We’ve taken basically the opposite approach. We’ve basically said, how can we make this fishing gear more selective? How can we modify gillnets so that they still can catch the target fish, but they reduce all these other bycatch species from being caught in the nets? This particular study – it actually showed a reduction in the haul back time. We basically recorded the time it took the same fishing crew to retrieve and then sort through the net. And not too surprisingly, it turns out, when the net doesn’t have a lot of bycatch in it, it’s easier to pull in, right? You – less animals, less hydrodynamic drag when you’re pulling in that net. And also, there’s just less animals to sort and remove. And, you know, removing turtles, removing sharks, removing these Humboldt squid – they’re really difficult to remove from the nets.

SIMON: Jesse Senko is a research professor and senior sustainability scientist at Arizona State University. Thanks so much for being with us.

SENKO: Thanks for having me, Scott.

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