Assessing egg oiling as a long term management tool for overabundant Silver Gull populations interacting with Southern Bluefin Tuna aquaculture operations
University of Adelaide
Agencies responsible for management of the aquaculture industry in collaboration with industry stakeholders are committed to incorporating principles of Ecologically Sustainable Development (ESD) into aquaculture regulatory processes (Fletcher 2004). One of the key objectives of ESD is "to protect biological diversity and maintain essential ecological processes and life-support systems". Addressing the ecological impacts of an overabundant legacy population of Silver Gulls in close proximity to tuna operations in Port Lincoln has been identified as a priority by ASBTIA, in consultation with DEW and PIRSA, to address this ESD objective. The project is a collaboration between resource management agencies and the tuna aquaculture industry in Port Lincoln. It seeks to expand on the research of Harrison (2010) to assess a three-year trial of Silver Gull egg oiling on selected off-shore islands near Port Lincoln and its impact on local reproductive success and population numbers of Silver Gulls. In doing so it aims to assess the efficacy of egg oiling as a possible management technique to control growth of Silver Gull populations and thereby reduce the current detrimental economic, social and environmental impacts associated with recent increases in Silver Gull numbers in the Port Lincoln region. Information provided through the research project will inform any ongoing monitoring and management of over-abundant Silver Gull populations within the frameworks of the region's National Park Management Plans and within PIRSA Aquaculture policy objectives. The efficacy of egg oiling and indices measured in the project will also be assessed to provide guidance on any future egg oiling management intervention.
1. Undertake a review and Cost Benefit Analysis (CBA) of over-abundant seabird population management strategies. This will be a project Stop/Go point to assess whether egg oiling provides the best management option for Silver Gull population control, and will determine whether the project proceeds as planned.
2. Estimate Silver Gull population size and structure through counts of breeding pairs (nest) and juveniles at up to five islands near Southern Bluefin Tuna aquaculture operations. Compare estimates with historical information for population trend analyses.
3. Obtain estimates of breeding success from oiled (treated) versus non-oiled (control) Silver Gull nests for use in population modelling.
4. Quantify short term effects of egg oiling on juvenile abundance, through measurement of the ratio of juvenile to adult Silver Gulls present at Southern Bluefin tuna aquaculture farms over three years and assess this indicator's efficacy in providing evidence of egg oiling management.
5. Assess Silver Gull breeding schedules, movement and habitat use within the study area.
6. Develop population models to assess the sensitivity of Silver Gull populations to reductions in breeding success from egg oiling and inform ongoing management targets for Silver Gull population numbers.