At its 2011 meeting, the Scientific Committee agreed that a time series of relative abundance from a well-designed survey could be a useful input into the Ross Sea stock assessment model. The first survey was completed in February 2012, and the second survey in February 2013. In this paper we provide results of the third survey in the time series. The objectives of this third survey were: (1) To carry out a longline survey to monitor subadult toothfish in the southern Ross Sea (strata A–C) using standardised gear in a standardised manner; and (2) To sample additional experimental stations in an adjacent area to identify areas of high subadult abundance which could be included as strata in future annual surveys.
The 2014 survey was successful in completing all the planned stations. Standardised catch rates for the core strata showed a slight decline across the three surveys but this decline was not significantly different. Age frequency data from the surveys have shown the progression of a cohort from age 7 in 2012 to age 9 in 2014. These results suggest that the surveys are indexing local abundance and will provide a reliable means of monitoring recruitment and estimating recruitment variability. In contrast, standardised commercial catch rates in the core area have been highly variable throughout the history of fishing in the survey area and the age data do not show modal class progression suggesting they are not useful for monitoring recruitment. Stations in the experimental stratum near Ross Island had high catch rates and much larger fish than in the other strata, and warrant future monitoring due to their unique nature. We recommend the survey be continued to provide information on year class strength and an index of local abundance to be incorporated in the stock assessment.