Estimating toothfish biomass in Subarea 48.3 using local depletions

We investigated local depletions of toothfish under concentrated fishing effort as a means of estimating toothfish density at South Georgia. Over the four years 2000-2003, we found 25 areas of 12’ by 12’ where there had been forty or more hauls in any particular year. There were 62 individual vessel fishing events in these areas over this period, 40 of which appeared to be depletions. Applying a Leslie method we derived toothfish densities in these areas which were linearly correlated with the initial CPUE experienced by the fishing vessels. Using this correlation, combined with the average CPUE over the four years and multiplying by the total fishable area in Subarea 48.3 we arrived at an estimate of total toothfish biomass of 55,666t. Clearly this method requires development, but it does hold out some possibility of potential as an alternative assessment method for toothfish.