2009/746 Could harvest from abalone stocks be increased through better management of the size limit/quota interaction?

By Hugh Jones, David Tarbath and Caleb Gardner

Abalone fishery assessments are very basic relative to other fisheries of comparable value and provide only general guidance for management. Consequently, management of the stock tends to evolve through adaptive management in response to year-to-year trends in catch and catch-rate trends, and anecdotal information. The majority of the catch is taken in Tasmania where the management controls include legal minimum length (LML), zone quotas and block catch caps. Setting of the LML addresses a management plan requirement that average animals should be able to spawn at least twice before reaching LML.

Tasmanian Seafoods has observed that landed catch can have predominantly old/fouled shells, darker meats, lower meat yield and poorer survival in freight, caused by excessively low harvest rates in some areas. They proposed the use of shell traits to classify shells as either "new shell", "medium", or "old shell". The project also addressed the need for information on density dependent growth in abalone - put simply, can production be increased by "thinning out" the stock. This is a fundamental question that is of interest for abalone stocks around Tasmania and also interstate.

The aims of this project were to:

1. Quantify density-dependent effects on wild abalone growth and meat quality
2. Develop a statistical tool for classification of shell age
3. Use length-based models to test the adequacy of shell age performance measures
4. Use length-based models to determine the sustainability and cost-effectiveness of an LML that optimises the proportion of ‘old’ shell within 5mm of the LML.