Oceanic sharks & ray populations have declined >70% in the last 50 yrs. ExeterMarine lecturer Dr Phil Doherty recently published an exciting paper using a novel device, “SharkGuard”, which uses electric pulses to deter sharks from fishing hooks in an effort to reduce bycatch. This may provide hope for the future of sharks and rays – read on as we chat with him about this work.
Dr Phil Doherty, Lecturer in Marine Conservation Science, University of Exeter
Hi Phil, thank you for joining us. To start with, can you give us a bit of background about yourself and your research?
Hi, thanks for inviting me – my research largely focuses on the presence and movement of large vertebrates, particularly sharks. For example, my PhD focused on tracking basking sharks in UK waters. I tend to use different technologies and methods to try and look at where things are, when they’re there, and what they might be doing there. I also try to inform on implementing some sort of management or policy strategy to try and make sure that times when these species of conservation concern are vulnerable, or are in places in high numbers, that they have some level of protection, whether that’s an MPA or another form of mitigation.
This has developed more recently into using fisheries data to look into catch composition and seasonality of fisheries landings to try to look at ways to prevent certain species being caught, certain sizes being caught, and more recently looking at bycatch (unwanted or unintentionally caught species) specifically. We are trying to get a grip on species that are being caught when they shouldn’t be, or aren’t wanted, and what we can do about that. Are there ways that we can prevent things being caught in the first place?
Bluefin tuna (Thunnus thynnus) catch onboard a longline vessel in southern France.
Photo Credit: Fishtek Marine.
Focusing on shark bycatch, which is the subject of your recent paper, what is the issue there?
Sharks and rays are groups of species that span most trophic levels, provide many ecosystem services, and are found in every ocean; so, talking about sharks and rays in general is quite difficult. However, in terms of larger bodied sharks and rays, and especially oceanic and pelagic species, their populations are under massive strain and most of that is from fishing pressure. Some of this is intentional capture, where sharks and rays are caught as the target species, but more often sharks and rays are caught as bycatch, as these species are often found in similar areas, exploiting similar resources as the target species.
This is having a massive impact on populations and these oceanic species that show more broad-ranging movements get caught a lot, due to high overlap with the big fisheries – the big purse seine and longline fisheries. This can cause a problematic scenario, which is often is a two-way thing, the fisheries quite often don’t want the sharks and obviously the sharks don’t want to be caught, but the numbers currently caught is really detrimental.
And so, what research have you been undertaking recently?
We have been working with Fishtek Marine, a conservation engineering company based in Devon. They develop all sorts of devices and mitigation strategies to try and prevent lots of different bycatch, from seabirds to turtles to cetaceans; and now for sharks and rays. They’ve developed a device called SharkGuard, which is a small device that you can fix just above a fishing hook on a longline, and it emits a pulsed electrical field around the baited hook.
Sharks and rays possess an extra sensory capability that bony fish and mammals largely lack. Sharks and rays have organs called ampullae of Lorenzini that are made up of small pores around their nose and mouth that can detect faint electrical impulses. It’s often how sharks and rays find prey, whether they’re buried in the sand or moving at the surface. The aim of SharkGuard is to overstimulate these electrosensory organs to deter the sharks and rays from engaging with the hook. It is quite effective in the sense that it’s a very short-range pulse, localised around the hook. Sharks have what’s known as a hierarchy of senses; switching between senses as they approach their prey ending with electrosensory capabilities very late on, just before biting the bait, only centimetres from their prey. Therefore, we have this short pulse, where we’re hoping that the shark might come close to the hook, but it won’t actually attempt to take the bait and therefore will swim away unharmed.
We trialled SharkGuard in a longline bluefin tuna (Thunnus thynnus) fishery in southern France, where they target bluefin tuna, a very prized resource, but the fishery is has a large bycatch component comprised mostly of blue sharks (Prionace glauca) and pelagic stingrays (Pteroplatytrygon violacea).
Schematic diagram depicting the effect of the SharkGuard electrical pulse.
Photo Credit: Fishtek Marine.
And you’ve had some very exciting results?
Yes, we tried this out with an experimental design where we aimed to have fishing operations exactly as it would be normally for the fishers. We alternated a control hook (normal fishing set-up) with a SharkGuard device attached to it. So, we had normal hook, SharkGuard hook, normal hook going all the way out. Two boats set longlines of 1000 hooks, 500 of each hook type, and they fished all summer like they would normally. We compared the catch rates for blue sharks, pelagic stingrays, and the target species, bluefin tuna to see if there was any difference between the hook types.
We found that the SharkGuard hooks significantly decreased the catch of both blue sharks and pelagic stingrays by huge amounts – a 91% reduction for blue sharks and a 71% reduction for pelagic stingrays.
Whilst we’re not trying to claim that we’ve solved bycatch for sharks and rays, this is a really important step to showing that this kind of device is effective for this sort of scenario. We’re now trying to look at other opportunities to try it in different fisheries to see how well it works, or how we might tweak the design to make sure that it can work for different species and in different environments.
We also want to make sure it is suitable for different target catch, because obviously fisheries aren’t going to uptake this kind of device if they don’t catch the things they do want to catch. So, it’s finding that balance, but we’re really impressed with the first trial results as we know it does work, it can work, and it’s important to try and start reducing this kind of bycatch.
SharkGuard devices attached to longline hooks in setting bins ready for deployment.
Photo Credit: Fishtek Marine.
Have there been any other kind of mitigation efforts like this before for shark bycatch?
Not quite like this. Researchers have tried all sorts of stuff, lights on hooks, sound, different smells to try and deter sharks, fishing at different depths, different times of the day – lots, and lots of different approaches. There was quite a push a while ago of trialling rare-Earth metals and magnets to try and almost create the same kind of effect that we were just talking about with a magnetic field. However, these effects don’t last very long in saltwater, so can be quite laborious as you have to change them quite often and their effectiveness reduces over time. The electrical deterrent side of things has focused more on development for personal use, so for people surfing or out on kayaks with wristband type designs, having mixed results. The development from this side of things is quite novel in terms of putting electronic devices on the hook. The technology and the idea have been around for a while, but this kind of application is new.
Do you think that the devices will be well accepted by fisheries?
Yes, I really hope so – we’ve had some pretty positive feedback so far. I think it’s because we’re not trying to tell people to not fish, we’re trying to just say if you fish, can you maybe put these devices out and maybe give the sharks and rays a chance. The fishers that we worked with in France liked it because it didn’t change how they set up their gear or approached fishing activities. They still had their same way of putting the hooks on the line and bringing the catch back to the boat. It didn’t get in their way, and it wasn’t extra work.
Normally, when they do have bycatch, they just cut the line, so, potentially the shark or ray is cut loose with a hook in its mouth and trailing fishing line with the thought that it swims away and survives, but this may not be the case. The fishers then have to spend time fixing the line and attaching replacement gear. Also, catching a stingray that’s not very happy or a shark is dangerous for the fishers and as such don’t want them on the line. Plus, any hook that doesn’t have a shark on it could have a tuna on it instead, so the benefit could be huge.
Fishtek are in the process of developing induction charging bins, so when the hooks are placed back in the bins after hauling a set, it automatically charges the SharkGuard devices reducing effort for the fishers and removing need to replace batteries. We’re trying to make it as bulletproof as possible. Yes, there’s a large financial outlay in the beginning, but once setup you’re good to go.
Take a look at the video below to see the story so far…
SharkGuard (the story so far…) – YouTube
Read the full paper: PD Doherty, R Enever, LCM Omeyer, L Tivenan, G Course, G Pasco, D Thomas, B Sullivan, B Kibel, P Kibel, BJ Godley (2022). Efficacy of a novel shark bycatch mitigation device in a tuna longline fishery. Current Biology: https://doi.org/10.1016/j.cub.2022.09.003.
