Standardised CPUE analysis of the Antarctic toothfish (Dissostichus mawsoni) fishery in the Ross Sea for the years 1997/98 to 2005/06

The Ross Sea toothfish fishery has operated during the Antarctic summer (December–May) since 1997 in CCAMLR Subareas 88.1 and 88.2. Previously, standardised analysis of toothfish CPUE (catch per hook) have been carried out for the Ross Sea (Subarea 88.1 and SSRUs 88.2A–B) for the 1998 to 2005 fishing years. This report revises and updates the previous analysis with the addition of data from the 2006 season for the Ross Sea using the revised location data for (a) all vessels and (b) core vessels that have been in the fishery for at least 4 years. We estimate indices using both lognormal generalised linear models and a Tweedie mixed model.
The variables included in the analysis appeared reasonable and were consistent between the models presented here and CPUE analyses for previous years. The yearly indices were relatively stable between 1998 and 2003, with a decline in 2004, and an increase in 2005 and 2006. Possible explanations for the decline in 2004 were gear conflict and competition between vessels to set lines, in addition to extreme ice conditions that limited where lines could be set. None of these factors were believed to be important in 2005 or 2006.
The CPUE indices for the Ross Sea have increased more than 50% since the beginning for the fishery in 1998. Favourable ice conditions, fisher learning and experience, including improved knowledge of optimum fishing practise, and improvements in gear are the most likely explanations for the increase in CPUE indices, rather than toothfish abundance. Hence the CPUE indices developed here are of limited use as indices of toothfish abundance at the current time.