Hawaii’s deep-set longline fishers could be required to change their fishing gear in an attempt to reduce the mortality of hooked endangered oceanic whitetip sharks.

The Western Pacific Fishery Management Council, or Wespac, is scheduled this week to decide on potential rule changes that would prohibit the use of wire leaders in Hawaii’s largest fishery and replace them with monofilament nylon leaders.

The rule changes could also include a requirement to remove trailing gear from hooked oceanic whitetip sharks.

For months Wespac advisory committees have discussed replacing the material for leaders, which are attached to hooks on one end and main fishing lines on the other, and requiring the removal of trailing gear after recent studies showed that doing so can reduce the mortality of oceanic whitetip sharks that are caught and released.

Since 1998 nearly all fishing vessels in Hawaii’s deep-set longline fishery have used wire leaders to catch target fish like bigeye tuna. Oceanic whitetip sharks sometimes get hooked on fishing lines, and even if they are let go, they often take some of that line with them.

Sharks have an increased chance of dying days or even weeks after being hooked and released, a recent study shows.

The 140 or so Honolulu- based vessels in the association hook somewhere between 1,200 and 1,700 oceanic whitetip sharks per year, Hawaii Longline Association Executive Director Eric Kingma said.

On average, oceanic whitetip sharks that get hooked and released take with them around 18 feet of fishing line, or trailing gear. And the longer the trailing gear they carry around, the more likely a shark is to die within a few days of being hooked.

That gear can cause physiological damage to sharks or be swallowed and lead to infection.

Steel wire leaders make the removal of gear from a hooked shark more difficult than monofilament nylon leaders. Switching the leader material from wire to monofilament and requiring the removal of trailing gear could reduce the post-release mortality of oceanic whitetip shark catch and mortality by 36%.

The changes are also expected to reduce the mortality of other protected species, such as the endangered leatherback turtle, that can also get hooked on fishing lines.

The removal of wire leaders is actually already underway for many vessels in Hawaii. HLA in November announced it would voluntarily begin switching to monofilament nylon leaders for the vessels in its fleet.

Kingma said just about all the boats will switch from wire leaders in the coming weeks.

He told a Wespac advisory committee Wednesday that HLA is “stressing the crew safety aspect” as they switch out their leaders. Wire leaders currently being used help prevent “flyback” — when a line with hooked catch is being hauled back to a boat and snaps, recoiling back toward fishers — which can injure the crew on board.

Kingma is exploring the use of different products, including sliding weights that can be placed on fishing lines, to prevent flyback. Training material for crew members is also coming to the HLA website.

“It’s going to take both active flyback prevention as well as, maybe, some passive gear measures that would prevent flybacks,” he said.

Senior attorney for Earthjustice Brettny Hardy told a Wespac advisory committee Wednesday that monofilament lines and gear removal requirements are a good start to protecting oceanic whitetip sharks from overfishing, which is their biggest threat.

But she said additional measures — namely, removing the shallowest hooks on a fishing line — should also be considered.

“There still remain serious questions about whether that will be enough to end overfishing,” Hardy said. “Right now the council is not considering an alternative that would look at shallow hooks, because of the costs. We just want to emphasize that we’re dealing with a listed species, and the council’s first job is to protect listed species.”

Keith Bigelow, a fisheries research scientist with the National Oceanic and Atmospheric Administration, explained in an advisory committee meeting in May that 40% of oceanic whitetip sharks are caught on the six shallowest hooks in Hawaii’s deep-set longline fisheries. Removing them and switching leader material could reduce the post-release mortality of oceanic whitetip sharks by more than 60%.

He also said the economic impact of switching to monofilament leaders would actually increase annual deep-set fishery revenue by about $2.7 million, but removing shallow hooks would reduce revenue by $11.5 million.

The average annual revenue of the fishery was $96.1 million between 2015 and 2019.

If Wespac agrees to the switch to monofilament leaders and updated gear removal requirements, it would amend the rules in the Pacific Pelagic Fishery Ecosystem Plan.

A draft of the amendments has been created with measures that would include other fisheries covered by Wespac, such as those around American Samoa, Guam and the Commonwealth of the Northern Mariana Islands, although in March the council indicated that it preferred to limit the amendment to just Hawaii’s deep-set longline fishery.

The rule changes could encourage similar rules to be established in international fisheries, which have a much larger impact on oceanic whitetip shark populations, Kingma said.