Assessment of yield and status of Macrourus carinatus on BANZARE Bank in the southern Indian Ocean: implications for managing by-catch in CCAMLR fisheries

This paper assesses the status and abundance of M. carinatus on BANZARE Bank (Statistical Division 58.4.3/1). The long-term precautionary yield was estimated using the Generalised Yield Model (GYM) used previously by the CCAMLR Working Group on Fish Stock Assessment. Estimates of population and biological parameters were not available for this species at BANZARE Bank. Length and weight data were taken from a trawl survey conducted at Macquarie Island in 1999. Where parameters were not directly available for M. carinatus, estimates were obtained from the literature for similar species elsewhere in the world. The trawl survey data was used to calculate estimates of biomass and density for the area and showed that M. carinatus did not appear to be aggregated over any part of BANZARE Bank. The long-term annual yield calculated for M. carinatus was 550 tonnes, based on a critical value of y of 0.033 (the proportion of the estimate of pre-exploitation biomass) found using the CCAMLR decision rules. The binding rule for this assessment was the decision rule on the probability of depletion below 0.2 of the median pre-exploitation spawning biomass. This assessment could be used as a basis for setting catch rates of M. carinatus in longline fisheries targeting Dissostichus eleginoides. Applying the critical y to the mean density observed in the survey results gives a catch rate of 5.81 kg/km2 which translates into a precautionary yield of 17.9 tonnes per fine-scale rectangle. Such a yield represents 18 % of the total catch allowed for D. eleginoides in fine scale areas in new and exploratory fisheries. This catch rate may be useful in setting general by-catch rules for M. carinatus to protect the species from localised depletions.