Sharks stealing Hawaiʻi fishermen's catch at record rates, studies show

Sharks are intercepting catch directly off hooks at the highest rates recorded in roughly 20 years of state data collection in Hawaiʻi, with depredation incidents now occurring on at least one in four licensed fishing trips in Hawaiian waters, an aquatic biologist with the state said. The surge has pushed many small-boat fishers who pursue prized bottomfish such as ehu, onaga and opakapaka to the edge of abandoning their livelihoods, according to a fishing industry advocate.

Researchers at the University of Hawaiʻi Mānoa and commercial repellent developers are testing countermeasures — with mixed results so far — while the Western Pacific Regional Fishery Management Council plans further review of the problem at meetings later this month.

Shark depredation — the loss of catch to sharks that strike hooked fish before they can be brought aboard — is occurring on at least one in four licensed fishing trips in Hawaiian waters, according to Bryan Ishida, an aquatic biologist with the state. The rates are currently at their highest on record in roughly 20 years of state data collection, Ishida said, and the trend is threatening the viability of Hawaiʻi’s small-boat fishing sector.

Phil Fernandez, president of the Hawaiʻi Fishermen’s Alliance for Conservation and Tradition, said the economic harm is immediate: fish markets reject any catch that bears bite marks.

“They’re basically losing money because they can’t bring in the fish,” Fernandez said. “The fish markets won’t buy a fish that has a bite on it.”

Many fishers who pursue prized bottomfish such as ehu, onaga and the red opakapaka — a staple of New Year’s tables across Hawaiʻi — are on the verge of giving up the trade, Fernandez said. Some refer to shark depredation as “paying the tax man,” and in their estimation the tax is growing.

An Uncertain Cause

Fernandez, who has been troll-fishing off the Kona Coast since the late 1980s, said depredation was not an issue when he began fishing there. It emerged over the past 20 years, he said, and sharpened into a serious concern for small-boat fishers in recent years.

What is driving the increase remains unclear. Some researchers and fishers suspect that warming ocean waters linked to climate change may be shifting the distribution of the prey species that sharks hunt, bringing the animals into closer contact with fishing grounds.

“There’s a lot of speculation,” Fernandez said.

Many fishers believe that local reef, Galapagos and tiger sharks, along with pelagic oceanic whitetip sharks that frequent Hawaiian waters, have learned to associate small fishing boats with easy meals. Boats working the Penguin Banks fishing grounds off Molokaʻi now move constantly to avoid sharks spotted nearby. Some fishers cut their engines the moment they land a fish, worried that propeller sounds signal opportunity to nearby sharks.

Repellent Tests, Mixed Results

Three categories of shark repellents are under active discussion in Hawaiʻi: magnetic, electric-charge and chemical.

Sharks have a unique sensitivity to magnetic fields that most targeted fish species do not share. Products using magnets and metal alloys to generate magnetic fields in the water can be effective against sharks, said Eric Stroud, a managing partner with SharkDefense, a Florida-based research and development company. He compared the effect to flashing a bright light in a shark’s eyes. Early trials off the Kona Coast have run into practical problems, however.

“They’re too long and they’re the wrong shape,” Fernandez said of the electromagnetic devices his group has tested. “The hooks tend to wrap around these devices, and now the hooks are all tangled up. So it’s a work in progress.”

Devices that create an electric charge in the water near the hook and bait typically cost between $150 and $300 apiece, Stroud said.

SharkDefense also produces a chemical repellent modeled on the scent of decaying sharks. The material — some synthetic compounds, some derived from sharks caught legally off the Florida coast, where such fishing is permitted — is formed into a butter-like substance that is either mixed into fishing chum or placed in a small cage near the hook to dissolve in the water. Stroud said the cost is approximately $1 per hook. All shark fishing is prohibited in Hawaiʻi.

Stroud said combining multiple repellent types may yield the best results because sharks can temporarily suppress a sense when overstimulated. If an animal disables its electromagnetic sensitivity, a chemical deterrent could serve as a fallback.

Stroud said he is particularly interested in testing repellents in Guam, where he said depredation incidents are especially high, and wants to study local fishing practices to adapt his company’s products for conditions there.

Research and Management Response

Scientists at the University of Hawaiʻi Mānoa’s Hawaiʻi Institute of Marine Biology are training local fishers to use forensic DNA kits on bitten and torn fish to identify which shark species are responsible for specific losses. Researchers are also tracking shark movements over time to determine how frequently sharks visit key fishing grounds.

“We are building the first truly comprehensive effort,” said Carl Meyer, a research professor at the institute, “to understand and mitigate shark depredation in these fisheries.”

Shark depredation was among the most pressing concerns raised by fishers across the Pacific during listening sessions held by the Western Pacific Regional Fishery Management Council last year. The council held a follow-up workshop in February and plans to report findings at its Scientific and Statistical Committee meeting March 17. A quarterly meeting is scheduled for March 24-26 at the Ala Moana Hotel in Honolulu.

Mark Fitchett, a pelagic fisheries scientist, said fishers hold a range of views on the sharks and the growing problem. Many are frustrated and believe the animals benefit from excessive environmental protections. Others, he said, recognize depredation as a cost of having a relatively healthy marine ecosystem — and some see the sharks themselves as part of Hawaiian culture.

“A lot of them also recognize that it’s part of their island culture that these animals are sort of … the gardeners of the water,” Fitchett said. “So there’s that respect for the animal.”

Fitchett said the council plans to release a more detailed report on the situation several weeks after the March meeting. The central question before fishers and managers alike, he said, is how much depredation the fishing community can absorb and still remain viable.