Bycatch Threatens Shark Populations Worldwide (Image Credits: Imgs.mongabay.com)
Florida – Researchers unveiled a simple, inexpensive device that creates electric fields to keep sharks away from baited fishing hooks in coastal waters.
Bycatch Threatens Shark Populations Worldwide
Commercial fishing operations targeting tuna and swordfish often ensnared sharks unintentionally. These accidental catches contributed to declines in more than 100 shark species, with over one-third facing extinction risks from overfishing.[1][2]
Longline fisheries deployed thousands of hooks, amplifying the problem. Discarded sharks frequently died due to their slow reproductive rates and vulnerability. Scientists sought practical solutions that preserved target catches while protecting these apex predators.
Florida Atlantic University teams focused on sharks’ acute electrosensory abilities. Their innovation exploited this trait without complicating fishers’ routines.
A Galvanic Reaction Powers the Deterrent
Zinc and graphite blocks, positioned near each hook, reacted in seawater to produce a small electric field roughly the size of a beach ball. This galvanic process mimicked natural bioelectric signals that sharks detect through ampullae of Lorenzini.[1]
The materials cost pennies and required no batteries or power sources. Zinc anodes wore down gradually but proved easy to replace, much like those used on boat hulls for corrosion prevention. Stephen Kajiura, a biology professor at FAU and lead researcher, explained the appeal: “Sharks have an incredible ability to sense even the smallest electric fields, and our tests show that this new approach can be used to keep them away from baited hooks.”[2]
Target species like swordfish and yellowfin tuna ignored the fields entirely. This selectivity promised economic benefits for fishers by boosting hook efficiency.
Field Trials Deliver Strong Results in Florida
Trials off Florida’s coast targeted demersal longlines near the seafloor. Hooks fitted with zinc-graphite blocks caught far fewer sharks than controls.[3]
Catches dropped by 62% to 70% compared to untreated gear. Specifically, 58 sharks struck treated hooks versus 155 on plastic controls and 190 on bare hooks. Atlantic sharpnose and blacktip sharks from the Carcharhinidae family avoided the fields most effectively.
| Treatment | Sharks Caught | Reduction vs. Untreated |
|---|---|---|
| Zinc-Graphite | 58 | 69.4% |
| Plastic Control | 155 | – |
| No Block | 190 | – |
Pelagic tests yielded too few sharks for firm conclusions but confirmed no harm to commercial fish. Kajiura noted, “It’s no good if it impedes the fisherman’s ability to get what they want. And that’s the cool thing about this type of repellent … it only repels sharks and not anything else.”[1]
Limitations Highlight Need for Broader Testing
Results varied by species and habitat. In Massachusetts demersal trials, piked dogfish from the Squalidae family ignored the fields, devouring bait indiscriminately.[1]
- Carcharhinidae sharks responded strongly in Florida waters.
- Squalidae species like dogfish showed no deterrence.
- Pelagic offshore efficacy remains unproven due to low sample sizes.
- Commercial prototypes require refinements for user-friendliness.
A patent-pending status and fisher feedback guided ongoing development. Experts like Eric Gilman called findings “robust” and “extremely promising,” though more trials across fisheries were essential.[1]
Key Takeaways
- Zinc-graphite fields cut Florida shark bycatch 62-70% without affecting target fish.
- Costs stay low with everyday materials familiar to fishers.
- Species-specific effects demand targeted applications.
This breakthrough offered hope for sustainable fisheries amid shark declines. Even modest adoption could safeguard populations and ecosystems. What steps should fisheries take next to implement such tools? Tell us in the comments.
