These spearos are volunteers in a tilapia culling program that’s been running for more than a decade through the Queensland Parks and Wildlife Service and Cairns Underwater Association. Its focus is on limiting the ecological impact of Queensland’s most problematic aquatic pest species.

The black mangrove cichlid, or spotted tilapia, isn’t native to Australia. Its first confirmed sighting was in Lake Barrine was in 2007.  Well-equipped to invade and dominate aquatic habitats – with its simple food needs, its ability to thrive in poor water conditions and its resistance to disease – this species aggressively out-competes natives for food and space, leading to declines in biodiversity.

Here to stay 

Like so many other invasive species, now that tilapia is established in Australia it’s proving impossible to eradicate. But in an enclosed water body like Lake Barrine, numbers can be controlled to some degree with intensive long-term fishing.

Electrofishing, line fishing, gill netting, fish traps and artificial egg-laying strata have all been trialled over the years. None were successful in significantly or effectively reducing the population. Then along came the idea of spear-fishing…

John Doherty from the Queensland Parks and Wildlife Service says managing any kind of pest species is time intensive.

“Parks staff were initially used but you need experienced spearers to get good numbers,” he says.  “That’s why we are so pleased about the ongoing involvement of the Cairns Underwater Association. They have the gear and the experience, and they bring in thousands of fish each session. Without them the program would be dead in the water.”

Ant Judge coordinates the spear fishers from the Cairns Underwater Association and says being in the water is a big part of his lifestyle.

“I love it. I spend a heap of time diving in Barrine and Eacham,’’ he says.  “Waterways are integral to living in the region and it’s important to me that they’re being looked after.

“We can immediately see the impacts of culling. When the big breeders are flushed out from their nesting areas, I’ve seen native species move in straight away to eat the eggs.”

The Underwater Association is keen to expand the number of spear fishers participating, and is thrilled that a women’s group, Girls Who Spearfish, has come on board.

“With the addition of this group of talented spear fishers, we can increase cull numbers significantly,” Ant says.

The club runs identification training before culling events, so there is no bycatch. Competent spear fishers wanting to get involved are encouraged to contact the club.

True locals

Not far away, Lake Eacham was home to three types of native fish until their numbers declined with the introduction of other species. While native to Australia, these new species weren’t native to the lake and they outcompeted the original habitants. By 1987 there was only one ‘true local’ remaining, and the Lake Eacham Rainbowfish has disappeared from the lake.