Summary of holdings of Patagonian toothfish (Dissostichus eleginoides) otoliths and size-at-age estimates from Heard and McDonald Islands (Division 58.5.2)

Scientific observers aboard vessels in the Australian fisheries in 58.5.2 have collected Dissostichus eleginoides otoliths since the fishery commenced in the 1996/97 season. This program has yielded data which has assisted with understanding age structure and growth rates of toothfish in this Division. This paper summarises the otolith collection housed at the Australian Antarctic Division, including individuals collected during research and commercial fishing, tag recaptures, and those individuals which have been processed by the Central Ageing Facility to provide size-at-age estimates. Over 21000 otoliths have been collected from toothfish in 58.5.2, and more than 2500 otolith pairs have been collected from recaptured tagged fish. More than 3200 otoliths have been processed to provide size-at-age estimates from fish captured between 1997 and 2003. A growth model based on these size-at age data is currently used in the assessment to predict growth and assign length-at-age to catch-at age, however an alternative method to assign catch at age is age-length keys. Relatively few otoliths have been collected or aged from the annual trawl survey or the longline fishery, making constructing historical season by season age-length keys for these fisheries impossible. It is likely that sufficient otoliths have been collected from the main trawl ground to construct age-length keys, however the feasibility and benefit of proceeding to age-length keys in terms of precision of stock assessment requires simulation analysis.