Stock assessment of the Heard Island and McDonald Islands (HIMI) toothfish fishery currently uses an integrated population model. This model relies on estimates of parameters that predict the productivity of the population e.g. growth rates, mortality rates, recruitment rates and spawning stock biomass. Advice on sustainable catch limits for toothfish use decision rules developed by CCAMLR, which seek to ensure that there is sufficient escapement of spawning biomass to ensure the productivity of the stock is not reduced by fishing. Hence stock assessments are very sensitive to estimates of size at maturity, as this determines the proportion of the population that is mature and contributing to the spawning stock. Currently, the size and age at which toothfish mature at HIMI is unknown. The estimate used in the model is derived from spawning fish sampled in the French EEZ around Kerguelen Island. There are clear linkages between the French and Australian stocks, however the differing fishing history and environment in the French EEZ means using the French data for HIMI toothfish may create bias in the assessment. With demersal long lining commencing in 2003 and fishing of deeper slope waters in recent years, spawning toothfish have been captured by demersal longlines for the first time in 2009 and again in July 2010, and hence an opportunity now exists to collect data on spawning activity in the Australian EEZ for the first time.
The urgency of this project is high, due to the need for understanding of the spawning dynamics to assist in forthcoming discussions with France, scheduled for mid 2011, as to how complementary harvest strategies can be developed for toothfish across the region. Establishing the existence and extent of a spawning stock in the Australian EEZ will be important in ensuring Australia gets fair and equitable access to this resource.