Shark depredation reports rise as app developer, experts push for more research

A citizen science research project is trying to quantify the impact sharks are having on fishing experiences and Australia's seafood stocks.

Depredation — when a shark preys on a fisher's catch — is being increasingly reported in many regions.

Data collection expert Stefan Sawynok said experiences while running fishing tournaments led him to investigate the issue of shark interactions.

"Every fisherman's got his idea of the local hot-button issue, but the one consistent topic around the country was shark depredation," he said.

"If you lose half the fish you catch in a day to sharks, that's you effectively having to catch twice your bag limit to be able to take fish home."

In his quest to collect data, Mr Sawynok has developed an app called Shark'd that he says will have "two basic functions".

"One is for people to report their interactions — if they go out and lose fish to sharks they'll be able to report that and add photos so we know what's happened," he said.

"Secondly, they'll be able to check up the stats in their area find out how many reports have been made."

Concerning trends at sea

Fishing teacher and 33-year charter industry veteran Ryan Moody has lived near the Hinchinbrook Channel in North Queensland since 2006.

He says human-shark interactions are "out of control" in the region, where a friend of his was recently recently attacked while diving.

"There's a lot of people getting harassed, buzzed by sharks," he said.

"The problem is getting gradually worse."

Mr Moody said that the impact of sharks could cripple the valuable charter and recreational fishing scene in Queensland's north.

"People don't want to spend hundreds of dollars on fuel, bait and tackle only to come home with two fish out of the 40 they hooked," he said.

App research welcomed

Brisbane-based fisheries researcher Jon Mitchell conducted the first Australian research on shark depredation as part of his PhD at the University of Western Australia in 2018.

He says there needs to be more research done the issue.

"Anecdotally, there's been a lot of [shark] reports coming in," he said.

"The main areas seem to be the north-west of Western Australia and also northern Queensland."

The UWA research deployed cameras to mimic a fishing set-up and showed that sharks learned to respond to the presence of boats over multiple days.

Sharks were attracted by the sound of engines and disturbances in the water and came to associate boats with an accessible food source.

Dr Mitchell found lemon sharks, black-tipped sharks, spot-tipped sharks and grey reef sharks were the main species responsible for depredation in the research zone.

In North Queensland, Mr Moody said whaler sharks – particularly large bull sharks – were damaging to inshore fisheries.

"In my last year of charters, just over two years ago, I lost 30 barramundi over a metre long to bull sharks in the Hinchinbrook Channel," he said.

Key information

Much of Dr Mitchell's research in north-west WA was based on boat ramp surveys where some 900 fishers were interviewed.

"It was great to get support from fishers — that was key to getting valuable data on the ground," he said.

While commercial operators have log-books for filing information on sharks, Dr Mitchell said a similar option for amateurs could prove beneficial.

"Citizen science is a really key thing," he said.

Mr Moody said he hoped that more information available to fisheries authorities and anglers would help guide policy in the future.

"We really need an app like this to get a better idea of how many fish are being lost to sharks," he said.

Conservation complications

Dr Mitchell said the impact on fishing stocks from depredation was yet to be fully understood.

"You've got extra fish being lost on top of those caught, an extra level of mortality," he said.

"It's also potentially affecting sharks because it's leading to changes in their behaviour — they're getting hooked themselves or killed in retaliation."

Research also found that commercially, the loss of gear as well as extra time spent at sea with labour and fuel costs was significant for some fishers.

Mr Sawynok said that the often emotional debate around shark behaviour and numbers could be better addressed with solid facts in hand.

"Collecting data is a way to take the heat out of that conversation," he said.

"I take fishers at their word that they are having more interactions.

"We really don't know where, when, how often, or even how many fish are being taken.

Mr Moody said he expected the app data to confirm the impact of large numbers of certain species in his local waterways.

While he supported preservation of endangered tiger and hammerhead sharks, he said protections for whaler family species, such as the bull shark, needed to be reassessed.

"The bull sharks are so hardy," he said.

"They live in fresh water, they're a very hardy, aggressive shark and their population is expanding."

Solutions canvassed

Fishing operators across the recreational, charter and commercial sectors have started to adapt to the phenomenon with a variety of strategies.

"Breaking up the predictability of fishing and trying to fish over a broader range of sites is a really important thing," Dr Mitchell said.

Mr Moody said damage was occurring to fish stocks and recreational anglers needed to play their part preserving fish stocks.

"If they go to a spot and lose the first two or three fish to sharks, they need to move, get the hell out of there and move somewhere else," he said.

Many commercial fishing operators already avoid certain areas due to background knowledge, which is the type of information Mr Sawynok hopes will flow from the app.

"I think the big takeaway for the recreational and commercial sector is a first step towards some level of self-management," he said.

In the long term, Dr Mitchell said improvements to electrical shark-deterrents could prove useful for reducing depredation.