Wallagoot Lake case study - updated November 2011
Mapping, monitoring and control work
In September 2007 the Caulerpa infestation in Wallagoot Lake was mapped and the alga was found to exist only in a couple of discrete patches within Scotts Bay and in depths of up to 4 m. The Caulerpa infestation was considered suitable for salt treatment and a fishing closure was implemented in 2007 to prevent further spread of the marine alga. NSW DPI implemented control efforts in October 2007, June 2009, and after consulting with relevant stakeholders, control work utilising salt in Wallagoot Lake was first undertaken in October 2007.
Twenty four tonnes of salt was applied to the Caulerpa populations in Scotts Bay using a specialised salt application punt. However, surveys conducted by staff from the Bournda Environmental Education Centre (Bournda EEC) during the period January-March 2008 found that the treatment had not completely eradicated the Caulerpa and that surviving Caulerpa was spreading rapidly.
Salt was applied to Caulerpa populations in Scotts Bay on five other occasions between 2007-2009 and regular monitoring by NSW DPI staff and Bournda EEC staff was conducted. Salt was applied to Caulerpa infestations using various methods including the specialised salt application punt, a small boat, and in one instance bags of salt were applied by divers and by technical staff from the boat. The success of each treatment attempt was monitored by NSW DPI staff and members of Bournda EEC and it was concluded that salt application was most successful using the specialised salt application punt.
In early 2009, monitoring surveys by NSW DPI staff revealed a 430 m2 patch of Caulerpa north east of the closure area in Scotts Bay. Additional small patches of Caulerpa were found on the eastern side of Scotts Bay by Bournda EEC. The closure area was then extended to include all of Scotts Bay and all known Caulerpa patches were treated with salt in June 2009 using the large specialised salt application punt.
Bournda EEC staff conducted follow up surveys in June and July 2009 and observed that most of the Caulerpa in the salt treated area had been bleached although some appeared to still be viable. A few new patches were also found in the shallows of Scotts Bay ranging in size from 1 m2 to 10 m2. Hincksia, which is a native brown alga and abundant in Wallagoot Lake, had started to grow and cover areas of the lake making identification of Caulerpa patches more difficult.
Further surveys undertaken by Bournda EEC staff between November 2009 and April 2010 have identified only very limited areas of Caulerpa in shallow sections of Scotts Bay. Due to high rainfall in the local area, visibility has been poor since March 2010. A recent survey of Scotts Bay in April 2010 failed to reveal any Caulerpa, but the Bournda EEC staff also reported very poor visibility (“pea soup”), and there was what appeared to be a dark anaerobic layer at the bottom making surveying the deeper sections difficult.
Details of Netting Closure
A commercial and recreational fishing closure prohibiting the taking of fish by all nets (landing nets exempt) was implemented for part of Scotts Bay in Wallagoot Lake in December 2007 to reduce the risk of further spread of Caulerpa. The closure was extended to include all of Scotts Bay in July 2009 and is effective until July 2014.
Community involvement
Community involvement has played an enormous role in managing the outbreak of Caulerpa in Wallagoot Lake. Bournda EEC staff have played a pivotal role in monitoring (including provision of GPS data), conducting advisory work including coordinating community meetings, distribution of brochures, school education activities, sign installation, conducting and assisting with control work and providing logistics such as staff, storage and equipment.
NSW DPI has worked closely with Bournda EEC, Bega Valley Shire Council (Bega Valley SC), Southern Rivers Catchment Management Authority (SRCMA), NSW Office of Environment & Heritage (National Parks & Wildlife Service office at Merimbula) through the Wallagoot Caulerpa Response Group.
In addition to this, NSW DPI has also liaised with the Advisory Council on Recreational Fishing and the Estuary General Management Advisory Committee to ensure a whole of government approach that is well supported and assisted by the local community.
Significant financial assistance has been provided by SRCMA and Bega Valley SC towards the cost of salt and to provide funds for a project officer to assist with routine monitoring and control work at Bournda EEC. Significant in-kind contributions by DECCW have included staff and machinery for salt movement during control works.
Community information sessions were held by Aquatic Biosecurity staff at Bournda (October 2007) and Merimbula (November 2007).
Bournda EEC staff ran a community information session in conjunction with University of New South Wales prawn research program in December 2008.
In 2009, the Wallagoot Caulerpa Response Group was nominated for a Landcare award in the Coastcare division.
What happens next?
A meeting of the Wallagoot Caulerpa Response Group was held in October 2011 to confirm the details of upcoming DPI monitoring event.
This monitoring of the closure area within Scotts Bay will be conducted during the summer of 2012 to estimate the success or otherwise of the salt treatment and control efforts to date.