Posted on 14. Nov, 2014 by Lauren Veale in Long Swamp Restoration Trial, News
While others may have been losing their money on horse races over the long weekend in November, I had the pleasure of meeting with some passionate members from the Australia New Guinea Fishes Association (ANGFA) and showing them around Long Swamp.
One of the main purposes of the fieldtrip was to trial some control and eradication techniques for the introduced eastern gambusia (Gambusia holbrooki). Since first detected during monitoring in 2012, the abundance of gambusia has increased considerably in Long Swamp, but at present the species is largely confined to one area of wetland. If this species continues to increase in abundance and expand its distribution into re-created aquatic habitat made available through restoration, it has the potential to seriously interfere with the ecology of resident populations of key native fish species in Long Swamp.
(John Lenagan, Lauren Veale (NGT), Gerard Carmody and Finn Wrigley prepare to board the canoes. Photo: Greg Martin (ANGFA).)
As seen all over the world, this introduced species can alter freshwater ecosystem function, impact genetic integrity and increase the transmission of parasites and disease, resulting in high ecological, economic and social damage. There are a numbers of distinct life history traits that make this species a highly efficient invader:
- maturity is reached at one to two months of age
- fertilisaton is internal with young being born as free swimming fish
- females can have several broods in a breeding season and store viable sperm in their oviducts for several months (this means that a single individual may successfully colonise new aquatic habitat); and
- the species predates on the eggs, larvae, juveniles and even adults of native fish.
Previous experiments conducted elsewhere in Australia, involving baited box traps have shown some success in targeting gambusia in freshwater systems. In our trials, box traps were set overnight at the gambusia ‘hot spot’ of Long Swamp in a variety of ways. Overall, the trials were a success and provided anecdotal evidence that captures of Gambusia may be increased by:
- setting traps in fringing vegetated habitats as opposed to the open water
- setting traps on the surface of the water (where temperatures are naturally higher) instead of the bottom (traditional way).
- adding a light/heat source (such as the ‘lunker lights’ we used)
- using berley pellets rather than cat food as bait.
The modified box traps used to target Gambusia. Photos: Greg Martin (ANGFA).
It was also remarkable that only a very small numbers of native species (e.g. Yarra pygmy perch, southern pygmy perch, dwarf galaxias) were caught using these refined techniques. Therefore, setting the baited box traps on the surface of the water and adding a light source allows you to effectively target Gambusia due to their inherent attraction to light and/or heat.
Inspecting the catch from the baited box traps. ‘Lunker lights’ were found to successfully attract Gambusia. Photo: Greg Martin (ANGFA).
The troops from ANGFA enjoyed their time at Long Swamp and are looking forward to being involved with further restoration works planned for early next year. Greg Martin summed up the experience for all, by saying “we loved the whole experience; the adventure of getting to the site through those surreal pine plantations, trekking down through the dense tea tree, wading through that “floating” path of reeds and then finally, the tranquility of being out on that water in the canoe.”
NGT is grateful for the help of ANGFA in conducting these trials and looks forward to working with them again in the future.
Dense patches of Triglochin are important refuge habitat for native fish species in Long Swamp. Photo: Greg Martin (ANGFA).
A nice spot for a picnic lunch. Photo: John Lenagan (ANGFA).