Sharks biting fishers' catch off lines highlights concern about increased interaction

Some sharks have learned to associate boats with food. (Supplied: Daniel Zovko)

A professional fisherman is sharing captivating vision of sharks taking his catch, to raise awareness of increased interactions between sharks and fishers, and the impact that could have on wild fish stocks.

Richard Gilmore's underwater camera captured the apex predators biting a fish he had hooked in half, before returning seconds later to snatch what was left.

The owner of Pristine Reef Fish, who works the Great Barrier Reef between Cairns and Lizard Island using handlines, said he was "racing" sharks "pretty much every day".

"There's a lot of areas that we just can't go and fish anymore, purely because of the shark numbers," Mr Gilmore said.

"On any given day, if the sharks are switched on, you just won't beat them.

"It's not possible, so we change tactics, change species.

"We don't sit there and keep feeding sharks, we move on."

Shark depredation is the term used for when sharks take fish off hooks before they can be retrieved to the boat.

"The shark interaction's phenomenal these days," Mr Gilmore said

"Which makes it very difficult when you look at stock assessments, shark depredation in a lot of those stock assessments is not interpreted."

Close encounter

Further south in Moreton Bay, marine biologist Ben Diggles filmed an "obnoxious" encounter with circling sharks, more than half the size of his 4.8 metre-long tinny, on the hunt.

"There is a tuna, that I just hooked before, that is being chased by these sharks," he said as he captured the interaction.

"There you go, they've got him! It's why we're not swimming in Moreton Bay at the moment.

"They look like adult bronze whalers in a large pack and there's a few extra marks on the boat now where they bounced off."

Shark protection

In Queensland critically endangered eastern grey nurse sharks, white sharks, hammerhead, sand, tiger, and spear tooth sharks are fully protected, as well as all sharks over 1.5m long.

There is a recreational bag limit of one shark or ray per person, or two sharks or rays per boat.

Dr Diggles, who has kept personal fishing logs since the 1980s, said shark interactions had considerably increased.

"Based on what we used to have, say, in the '80s in the '90s, it's more like eight to 10 times more interactions that's in my logbook," he said.

"I certainly wouldn't have been, you know, sticking their hands or feet in the water the other day.

"It's quite dangerous when sharks switch and turn into that feeding frenzy mode."

The aquatic animal health expert said he believed fisheries management had worked, and it may be time to allow targeted catches of larger, more prolific shark species.

"Grey nurses and white sharks are vulnerable to fishing because they have quite low reproductive rates," Dr Diggles said.

"But there's quite a lot of other species that are far more productive and some of them can be problematic in large numbers.

"I think there would be no trouble targeting and dispatching those smaller ones humanely to eat."

Recreational fishers like Alan Ladru have had close encounters too.

"We were fishing the shipping channel 13 kilometres offshore from Bribie [Island]," Mr Ladru said.

"After catching a big kingfish and trying to hold it in, one shark [arrived] … then two, three, and they were just jumping out of the water [in] a frenzy. They would have been 2-2.5m sharks.

"We said to each other 'we're going to need a bigger boat'."

Queensland Seafood Association executive officer David Bobbermen said the research to date had shown that commercial fishermen had a much lower depredation rate compared to recreational fishermen.

Mr Bobbermen said if sharks were taking fish, and fishers were still taking their bag limits or quotas, there would be major implications for managing fish stocks.

"It will have a massive impact on the way Fisheries Queensland will have to assess catch rates for all fishing sectors," Mr Bobbermen said.

"And how they then use that in determining the harvest strategies and the stock assessments for different fish species."

For the first time, the Queensland Department of Agriculture and Fisheries is researching shark depredation.

Marine Biologist Jonathan Mitchell, who earned his PhD studying shark depredation in Western Australia, is two years into a three-year project collecting data from the east coast Spanish mackerel fishery.

The aim is to assess the percentage of catch lost to sharks in both the recreational and commercial sectors.

"We've done 40 observer trips on commercial fishing vessels where we recorded a depredation rate of approximately 7 per cent of all the fish that are being hooked being taken by sharks," he said.

"And then we've had a group of recreational fishers collecting data for us through a citizen scientist program.

"They've sent us data from 57 of their recreational trips and they experienced a depredation rate that was a fair bit higher, around 35 per cent."

Asked whether it was a case of increasing shark numbers, or sharks getting smarter about associating boats with food, Dr Mitchell answered "both".

"Definitely in areas where there's a lot of fishing effort, and particularly an overlap of commercial and recreational fishing effort, the sharks are getting this constant opportunity to feed on hooked fish or discarded fish," he said.

"That's really driven a change in their behaviour.

"But in terms of shark abundance, at this stage we don't really have very good long-term data sets to look at the abundance of most of these species and that's something that we're really trying to address."

Dr Mitchell said researchers were using both DNA swabs from catches that had been bitten by sharks, and underwater cameras, to identify shark species involved in depredation.

"Those two methods have allowed us to identify at least 12 shark species now around Australia that are responsible for this," he said.

"It does tend to vary depending on the location and the time of year and the depth of fishing as well."

The scientist said that, in Queensland, researchers were finding the four main species involved in depredation were bull sharks, pigeye sharks, spinner sharks, and sandbar sharks — all species in the Whaler family.

Conservationists concerned

In a statement, Humane Society International marine biologist Lawrence Chlebeck said he did not believe that sharks should be commercially fished in Queensland.

"They are one of the most imperilled groups of fishes globally and are cornerstone apex and meso-predators that are absolutely critical to maintaining the health and resilience of marine ecosystems," Mr Chlebeck said.

"While depredation has definitely increased in recent years, it could be attributed to a decline in their prey species.

"Changing our fishing behaviour and reducing the take of sharks' prey species is a better solution to the issue of depredation than an open season on the species that maintain the health of our oceans."

Minimise the risk

Dr Mitchell said ways to reduce interaction with sharks included:

• Using handlines or electric reels and higher breaking strain lines to get fish to the boat as quickly as  possible.
• Using lures or jigs, instead of bait, to reduce odour cues.
• Avoiding using berley or live bait.
• Moving location frequently when fishing, especially as soon as sharks arrive.
• Rotating fishing areas so you aren't visiting the same spot too regularly.
• Try to avoid areas where there are already other boats present, as research has shown higher  concentrations of vessels can lead to higher depredation.
• Have fishing gear set up and ready to go so you can start fishing as soon as you reach your spot, to  maximise the time you have available before sharks arrive.
• Use release weights to return fish quickly to depth if you are going to release them, to reduce the injury to the fish from barotrauma and reduce the chances of sharks predating on them.
• Clean your catch on land, rather than at sea.
• Consider diversifying your target species, for example, target dolphinfish at offshore Fish Aggregating  Devices, instead of Spanish mackerel.
• If you're a recreational fisher new to an area, talk to local fishers and tackle shop owners to get information about areas to fish where there are less likely to be sharks.