A simulation approach to the evaluation of recruitment surveys for D. eleginoides for the Heard Island Plateau region (Division 58.5.2)

Assessments of long-term sustainable yield using the Generalised Yield Model (GYM) and the setting of total allowable catches (TAC) for Patagonian Toothfish, Dissostichus eleginoides, for the Heard Island Plateau region (Division 58.5.2) are based on data obtained from annual random stratified trawl surveys (RSTS) and from targeted commercial fishing operations via an observer program. Evaluation of both the current RSTS design for Division 58.5.2 and some options for future modifications of the design is carried out in a simulation environment using the program Fish Heaven with data analysis carried out using Splus. Fish Heaven is a simulation program that uses a spatially-explicit, age-structured fish population dynamics model. Recruitment, movement, mortality, growth, and fishing (both commercial and research) were simulated for the Patagonian Toothfish for the Heard Island Plateau region. Census of fish stocks by age class were compared to population estimates based on simulated RSTS hauls. For a series of 10 years of survey, age 4 recruitment was estimated using 111 RSTS stations, assuming the age of every fish caught in the surveys is known without error and assuming knife-edge fishing selectivity at age 4, using either (a) the age 4-alone RSTS results or (b) age 4 to 8 RSTS results using back-projections from each age to age 4 for each of 6 cohorts.