Status of the coastal stocks of Dissostichus spp. in East Antarctica (Divisions 58.4.1 and 58.4.2)
Exploratory fisheries for Dissostichus spp. have been operating off the coast of East Antarctica (30°E–150°E; FAO/CCAMLR Divisions 58.4.1 and 58.4.2) since 2003. An experiment run from 2005 to 2008 required the tagging of toothfish as a prerequisite for participation in the fishery, with only some Small-scale Research Units (SSRUs, consisting of 10° longitude divisions of the larger areas) being open to fishing. This paper reviews the results of this experiment and explores several methods for arriving at estimates of sustainable yields. Biological data suggest that there are two stocks in the area, one in Division 58.4.1 and one in Division 58.4.2, with the division between them being at about 90°E. The western stock may be centred around Prydz Bay, and appears to be of very low productivity. Estimates of average biomass were made by comparison of standardised catch rates with the Ross Sea, where an analytical assessment has been possible for several years, and through analysis of local depletion events. Results indicated SSRU vulnerable population sizes of about 100–1 000 tonnes per SSRU in the west (Division 58.4.2) and 1 000–1 700 tonnes per SSRU in the east (Division 58.4.1). Although 3 434 tags were released over the period 2003–2007, very few tags have been recaptured (only five where time at liberty was a year or more). These recaptures were inconsistent with expectations given known landed catches. Potential yields were calculated for each SSRU assuming a similar productivity and exploitation state to the Ross Sea, where sustainable yield is 5% of virgin vulnerable biomass. The estimated yield from all assessed SSRUs (260 tonnes) is much lower than the current total allowable catch (1 380 tonnes).