Aquatic pest eradications

An infestation of the exotic black striped mussel Mytilopsis sallei (aka Congeria sallei) was discovered in Darwin marinas in late March 1999. Recognising the potential adverse impact on the Australian economy and biodiversity if the bivalve was to become established in Australian waters, the Northern Territory Government (NTG) implemented an immediate containment and eradication program that resulted in the World's first eradication of an established marine pest population.

The eradication program cost the Northern Territory Government in excess of $2.2 million. The small, delicate bivalve with a propensity toward fouling is a native of tropical and subtropical western Atlantic waters, extending from the Gulf of Mexico to Colombia.

Mytilopsis sallei has been classified as a serious pest as a result of its potential to cause economic and environmental damage. It is believed to have invaded Fiji (prior to 1900), India (ca 1967) where it has cost the Indian Navy many millions of dollars, and has since been found in Japan, Taiwan (1970s) and Hong Kong (early 1980s).

The ability of Mytilopsis sallei to settle on almost any surface to the exclusion of all other life is of great concern to our fishing, aquaculture, tourism, defence and port industries, and our marine environment.

For commercial operators, the cost of controlling Mytilopsis sallei has the potential to put some of them out of business. The presence of Mytilopsis sallei on boat hulls can increase drag, reduce speed and damage the hull surface. The mussels are known to clog the cooling water intakes of a boat's engine, causing serious overheating and damage to motors. Despite achieving a maximum size of 2.5 cm in length, an individual mussel is mature at four weeks (~1cm) and is capable of producing 50,000 offspring.

At four weeks of age these offspring represent a possible 100 kg of fouling material which may settle on hulls, chains, ropes, nets, mooring buoys, piles and floating pontoons, pipe inlets and outlets, and on any other surface in contact with water. Stormwater drains and seawater intakes for industrial plants and mariculture facilities are also vulnerable to fouling by this mussel. In its preferred inshore, low estuarine habitats, introduced populations of black striped mussel are capable of forming mats 10 to 15 cm thick.

The black-striped mussel Mytilopsis sallei is a marine relative of the freshwater zebra mussel Dreissena polymorpha that was accidentally introduced to the Great Lakes system of America in the 1980s. Since its introduction, the zebra mussel has cost the American economy US$600 million in control and remediation measures.

Mytilopsis sallei possesses many similar traits to its freshwater relative Dreissena polymorpha.
In April 2001, a program was undertaken in Alice Springs to eradicate a number of isolated populations of the mosquito fish, Gambusia species, from backyard ponds. This was undertaken after an initial population discovered in Ilparpa Swamp was eradicated,with the assistance of Alice Springs Regional Waterwatch Coordinator Robbie Henderson.

The publicity about the Ilparpa Gambusia sp. eradication exercise encouraged local residents to come forward declaring populations of the noxious species in their own backyard ponds.

It is thought that the original fish may have been introduced to the water body by some well meaning member of the public who did not realise they were in possession of an illegal fish. The individual would no doubt have been ignorant of the potential harm the exotic species could impact on the pristine natural waterways of the Northern Territory.

During mid 2005, attention was focused on the abundance of a non-native fish species within a storm water drain adjacent to Charles Darwin University (CDU), the drain feeds directly into the Rapid Creek system.
The fish was identified as the tuxedo platy (Xiphophorus maculatus), a hardy, alien-freshwater species, often introduced into natural waterways once being discarded from home aquariums.

As a consequence of the high rainfall that occurs in Darwin during the Wet Season months, overflow from the University’s Chinese garden pond had carried the platies through a drainage grate, depositing them in the drain, which is maintained with a constant supply of freshwater from the regular backwashing that occurs.

Eradication of the platies was undertaken over two stages. The initial stage involved chemical treatments of the overflow grate and storm water drain with a chlorine solution. The second stage encompassed the controlled drainage of the pond and relocation of the majority of native crustacea and fish species to the university's aquaculture facilities.

All remaining platies were then eradicated through further chemical treatments.

During the ongoing monitoring program by Aquatic Biosecurity, one month after the platies had been eradicated and the pond refilled, a few individuals were discovered within the pond, via a suspected reintroduction. It is unlikely that they will re-enter the creek system, as advanced technology had since been fitted to the drainage grate, preventing future overflow issues.

The jewel cichlid (Hemechromis bimaculatas) is a native of Africa and a prohibited import to Australia. The exotic fish is a prolific breeder and highly competitive and effective at displacing native species. Destruction of the population was essential to ensure maintenance of native biological diversity and discourage translocation by inquisitive individuals

The cichlid population was resident in the drainage channel of the Darwin Turf Club, known locally as 'Racecourse Creek'. It is thought that the original fish may have been introduced to the water body by some well meaning member of the public who did not realise they were in possession of an illegal fish.
The individual would no doubt have been ignorant of the potential harm the exotic species could impact on the pristine natural waterways of the Northern Territory.

In April 2001, a program was undertaken in Alice Springs to eradicate a number of isolated populations of the mosquito fish, Gambusia species, from backyard ponds.

This was undertaken after an initial population discovered in Ilparpa Swamp was eradicated,with the assistance of Alice Springs Regional Waterwatch Coordinator Robbie Henderson.The publicity about the Ilparpa Gambusia sp. eradication exercise encouraged local residents to come forward declaring populations of the noxious species in their own backyard ponds.

Aquatic Biosecurity staff visited Alice Springs to coordinate the eradication exercise. Gambusia sp. were eradicated from two backyard ponds and the Todd Street Mall Church pond using a combination of biodegradable poison (rotenone) and pumping the ponds dry.