Weedy prawns

WALLAGOOT Lake is one of the crown jewels of the Far South Coast of NSW, set in Bournda National Park. The lake is an intermittently opening coastal lagoon but since the onset of drought the lake has been closed to the ocean for the past 13 years. The lake must be open to the ocean for the juveniles of coastal spawning prawn species to naturally gain entry (known as “recruitment”) to Wallagoot. With the lake closed for so long, no natural recruitment has taken place for a long time, which made the lake an obvious candidate for stocking of eastern king prawns.

The trial prawn-restocking program commenced in February 2007 with the release of 3 million eastern king prawn larvae into Wallagoot Lake and a further 1 million larvae into nearby Back Lake at Merimbula. To date 9 million prawn larvae have been released into Wallagoot Lake under the pilot program and anglers have reported superb catches of big king prawns with some prawns weighing over 50 grams, a 10,000 fold increase in weight from the release size of 5 mg! The prawn restocking has been funded by the NSW Recreational Fishing Trust and is a collaborative project between the University of New South Wales, NSW DPI and the Australian Research Council. NSW DPI is now undertaking a statewide environmental assessment of marine stocking for a number of species to enable ongoing stockings in other estuaries, including Wallagoot Lake.

But in order to keep this beautiful lake in good condition, prawn anglers need to do their bit to stop the spread of a noxious marine pest.

In July 2007 the noxious marine algae Caulerpa taxifolia (Caulerpa) was discovered in Wallagoot Lake in a small patch in Scotts Bay. Caulerpa is spread by fragments, it can survive out of the water for up to three days and is a potential threat to our native seagrasses and biodiversity. To help prevent its spread, Scotts Bay has been closed to all forms of netting and NSW DPI has put in place a comprehensive control and monitoring program with the assistance of other agencies and the community. Over 100 tonnes of salt have been applied to the weed to date in an attempt to kill it.

Bournda Environmental Education Centre (Department of Education and Training) staff have played a critical role in monitoring the weed, assisting with control work as well as educating visitors to the lake on how to prevent further spread of the weed. The control work has been greatly assisted by other agencies such as NPWS as well as local fisheries officers and with financial support from Bega Valley Shire Council and the Southern Rivers Catchment Management Authority. Divers have had to brave the chilly winter waters of the lake with temperatures dipping below 10 degrees at times. Strong backs are required to deliver the salt to the purpose built punt and hopper with NSW DPI staff and volunteers handling up to 500 25kg bags of salt a day. So far the weed has been kept in check and NSW DPI will continue to monitor the lake to assess the results of the control work.

All waterway users, anglers and prawn fishers are requested to keep out of the Caulerpa closure in Scotts Bay to help prevent the spread of the weed and keep this fantastic prawn fishery and iconic lake healthy. The netting closure area is marked with buoys and signs. Don’t forget to check with your local fisheries officers if you are uncertain about the rules and regulations that apply to prawning and fishing.

You can help NSW DPI control Caulerpa and other pest species by reporting any sightings outside Scotts Bay or in any other local waterway to or by ringing the 24 hour recorded pest hotline on 02 4916 3877. If you find any Caulerpa on your fishing gear or anchor place it in a bag and dispose of on land in a bin. If you’d like to assist with monitoring the eastern king prawn enhancement program, call Adrian Ferguson at the University of NSW on 02 9385 8635 to arrange a sampling kit and data sheet.


Evil Caulerpa taxifolia in Wallagoot Lake. Picture: NSW DPI


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