O-fish-al take over

There are fish a-plenty out at East Chapman, but unfortunately, of the wrong kind.

NACC staff along with the Batavia Coast Maritime Institute (BCMI) team, visited waterways located at the beautiful East Chapman Junction, to survey populations of local aquatic species in the river.

Among the findings were about 1000 animals including fish, turtles and yabbies, but sadly only a fraction of them were native, explains BCMI’s Conservation and Biodiversity Project Manager Colin Johnson.

“As part of the Noxious Invasive Species Control project, we survey fish populations in the river to see if there is expansion in the range of tilapia (a pest fish) and what kind of native fish or other pest species are found there too,” Dr Johnson said.

“Aquatic pests generally are a major problem for the natural biodiversity in this river.”

“For example, at a recent trip out to this site, we caught about 1000 animals, which is normal, but scarily, only about 20 of them were native fish.”

Tilapia (Oreochromis mossambicus), located in the estuary of this river, are an extremely invasive introduced fish species, capable of displacing native species through their aggression and by habitat alteration through their dietary habits.

Other species commonly found in this section of the river include the native species, the Swan River Goby, Pseudogobius olorum and the Empire Gudgeon, Hypseleotris compressa as well as the Mosquitofish, Gambusia holbrooki, which was introduced to unsuccessfully reduce the number of mosquitoes.

In order to monitor how many invasive aquatic animals are in the river, and consequently how many native fish are surviving, traps are laid in the river for a 24-hour period.

The species are then separated, sized, sexed and weighed for data collection, and once caught, pest fish are humanely killed, as per the Department of Fisheries regulations whilst native species are released.

Dr Johnson said one of the most alarming findings from his recent survey, was the lack of native fish found in the river, which he said could lead to bigger problems if not managed.

“Before you create a pest management plan, you need to determine where the pest species are and where they aren’t, which is really what our aim is at the moment,” he said.

“The lack of native species and creatures is [the] most alarming finding from our results.”

“On one hand, having a large number of introduced species is an issue, but it’s the lack of native species that is the bigger issue.”

“Ultimately these sorts of results could lead to range declines and local extinctions. Fortunately, we don’t have this issue in our region yet, but it is happening elsewhere in the country.”

For more on this project or for guidelines about the noxious species, visit BCMI’s website.

This project is a partner project between Northern Agricultural Catchments Council and Batavia Coast Maritime Institute, through funding from the Australian Federal Government.

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