Reassessment of important population parameters for Dissostichus eleginoides on the Heard Island Plateau
(Division 58.5.2) based on time series of surveys and fishery data

A large body of data and techniques are available for re-assessing the biological parameters and recruitment of Patagonian toothfish, Dissostichus eleginoides, in the Heard Island region. A new survey of the Heard Island Plateau was undertaken in May - June 2001, providing the sixth survey over 11 years on this stock with other surveys including part of this stock. This paper describes the results of that survey, the time series of abundances and assessments of growth, recruitment, mortality and selectivity of this species. The results indicate that D. eleginoides is faster growing that originally thought with growth rates similar to South Georgia. The new estimates of growth parameters enabled a more accurate reassessment of the recruitment time series, which was likely to have been over-estimated in the past. An estimate of natural mortality indicates that mortality of young fish, ages 3-8, may be much greater than older fish. This may need to be taken account of in the assessment process. An approach is proposed to estimate age selectivity to the trawl fishery in the region. In conclusion, the overall analysis shows a promising way forward in understanding the dynamics of D. eleginoides in the Heard Island region. Clearly, a longer time series of data will be useful to better estimate recruits and natural mortality. A question to be addressed is the extent to which these stocks are connected to the wider Kerguelen Plateau as evidenced by some of the movement patterns and interannual variation in distribution.