The population of the globally endangered scalloped hammerhead shark is rapidly declining, and getting killed on baited drumlines is only the beginning of the animal's woes.

Key points: Scalloped hammerheads recently listed as "conservation dependent", which meant it automatically became 'no catch' within Great Barrier Reef Marine Park

Scalloped hammerheads recently listed as "conservation dependent", which meant it automatically became 'no catch' within Great Barrier Reef Marine Park Federal Environment Minister tabled a Senate amendment to allow fishing in marine park

Federal Environment Minister tabled a Senate amendment to allow fishing in marine park Greens and researchers say the sharks need stronger protection to avoid extinction

It is also highly sought-after in Asia for shark fin soup, and its numbers have declined up to 80 per cent in north Queensland since the 1960s, largely to due commercial fishing.

WARNING: some people may find images in this story distressing.

In Australia, the shark is caught in recreational and commercial line fisheries, in gillnets, trawler nets and as by-catch in the Queensland shark control program.

In march, shark experts and activists had high hopes for the species' future when the scalloped hammerhead met the federal eligibility criteria for endangered status in Australia, as it was already considered endangered internationally.

The shark was ultimately listed by the Federal Government as "conservation dependent", which means it does not receive special protection from commercial fishing, but "active management" is required to ensure its conservation.

That listing meant it automatically became a no-take species in the Great Barrier Reef Marine Park, which has its own regulations for "conservation dependent" listings.

But protection within the reef marine park was short-lived, with then-environment minister Josh Frydenberg tabling an amendment in the Senate to allow targeted fishing to continue in the world heritage-listed area.

A challenge now looms in the next week, with Greens senator Peter Whish-Wilson to table a motion to disallow the regulation coming into effect.

Where sharks have been harvested and landed in accordance with the regulations, removed fins can be sold legally. ( Supplied: Australian Marine Conservation Society )

'Heading towards extinction': researcher

Hammerhead fins are sought after for their high fin ray count, and hammerheads are one of the shark types found most regularly in the world's largest market in Hong Kong.

Griffith University shark researcher Johan Gustafson said he was surprised by the amendment allowing targeted fishing of the shark to continue in the Great Barrier Reef.

"It should not be fished, especially commercially … we literally don't know enough about them in Australian waters," he said.

"We need to do more research and actually measure population numbers.

"They generally don't respond very well to fishing pressures, and for the Great Barrier Reef they are quite an icon for divers and tourists to see, and a good indicator of reef health."

According to the WWF, shark fin is highly sought after in parts of Asia. ( WWF )

Mr Gustafson said population trends, both in Australia and globally, predicted a continuous decline in the shark's population.

"If commercial fishing pressures are maintained or they increase, which is what they are now, we are likely to see them wiped out or heading towards extinction in the near future," he said.

The commercial fishing issue is complicated because the same sharks migrate around northern Australia and into Indonesian waters, where fishing regulations are different.

The growth of unreported fishing in Indonesia has been driven principally by the shark fin trade.

James Cook University's Colin Simpfendorfer, who was on the government committee that recommended the "conservation dependent" listing, acknowledged commercial fishing was the major threat facing the shark.

Driven by demand from China's growing middle class, the international shark fin trade is causing hammerhead shark populations to decline. ( ABC )

"The key to recovering shark species generally, and in this situation scalloped hammerheads, is to make sure the settings in fisheries are appropriate to allow to populations to either recover or be sustainable depending on the level they are at," he said.

Professor Simpfendorfer conducted an analysis from Cairns and Townsville from the mid-1960s to the mid-2000s and revealed a "concerning decline" in the shark's numbers.

"Those data show quite significant decline in scalloped hammerhead shark population, in the range of 63-83 per cent — which is obviously a concerning decline," he said.

Scalloped hammerhead sharks are not a target species for the shark control program. ( Supplied: HSI/AMCS/N McLachlan )

A Federal Department of Environment spokesperson said the amendment to allow targeted fishing was made "in accordance with Queensland fisheries legislation and maintains consistency across environmental legislation nationally".

The Great Barrier Reef Marine Park Authority (GBRMPA) supports the amendment to "ensure complementary managing of listed threatened species".

"Although the committee found scalloped hammerhead could be eligible for an endangered listing, its clear recommendation was to list this species in the conservation dependent category," a GBRMPA spokeswoman said.

"Strong management actions agreed with the Northern Territory and Queensland governments for the species's protection and recovery would be implemented immediately under law, including within the area of the Great Barrier Reef Marine Park — this includes limiting the total annual national catch of scalloped hammerhead.

Killed on drumlines despite no known fatal attacks

Nicole Beynon from Humane Society International said more than 14,000 hammerhead sharks had been killed due to Queensland's shark control program since the 1960s.

There has been significant reduction in the number of hammerheads caught since the hooks used in the program were changed in the 1990s, but last year 28 scalloped hammerheads were caught on drumlines, despite not being targeted by the program.

Two have recently been killed as by-catch off Magnetic Island within the Great Barrier Reef Marine Park, where the program has a permit to operate.

Two scalloped hammerhead sharks were caught on drumlines off the coast of Magnetic Island recently. ( Supplied: HSI/AMCS/N McLachlan )

Scalloped hammerheads have comparatively small mouths and teeth, so there have only been three recorded incidents of hammerhead sharks bitting people snorkelling.

It is understood there have been no fatal attacks.

Ms Beyon said Humane Society International was calling for a stop to the shark control program in the Great Barrier Reef.

"In a place like the Great Barrier Reef world heritage area, if we can't protect endangered species there, where can we protect them?" she said.

"Protecting sharks on the reef is essential for ecosystem resilience."

A Queensland Department of Fisheries spokesperson said improvements in the types of nets, hooks, and bait had improved their ability to target key species and reduce non-target catch.

Fisheries Minister Mark Furner said "guaranteeing human safety" remained the number one priority of the shark control program.

Researchers say the hammerheads are very curious and social creatures that pose little harm to swimmers. ( Supplied: HSI/AMCS/N McLachlan )

New commercial fishing regulations

Revised restrictions and reporting requirements on hammerhead shark fishing came into effect in Queensland in January.

They include a total allowable commercial catch of 150 tonnes, and stipulate that hammerhead sharks be kept in a "whole form" once 75 per cent of the quota is reached.

Mr Furner said the changes would prevent catches increasing to unsustainable levels, enable better data to be collected, reduce discards and enable fishers to keep fishing.

"The hammerhead shark catch in Queensland is around 1-3 per cent of the global harvest," he said.

"While Queensland's fisheries have contributed very little to the declining abundance of hammerhead globally, the Queensland Government is doing all it can at a local level to ensure the sustainable harvest of the species in Queensland waters."

Mr Furner said Mr Gustafson's comment the was shark heading towards extinction was "not the view" of the Commonwealth threatened species scientific committee.

He said catch limits were based on the Federal Government's own scientific assessment and backed up by his department's stock assessment, completed in 2015.

"The decision acknowledged that the Queensland Government complied with the threatened species scientific committee's request, which was to limit the catch and improve monitoring and reporting," he said.