Preliminary standardised CPUE analysis of the New Zealand toothfish fishery in Subarea 88.1 from 1997/98 to 2001/02

This report provides the first analysis of standardised catch per unit of effort (CPUE) from the exploratory fishery for Antarctic toothfish Dissostichus mawsoni, which has operated in Subarea 88.1 for five seasons, from 1997 to 2002. Two analyses are presented. The first (all-ground) analysis reviewed catch from 1998 to 2002 (excluding the 1997 season as insufficient data were available), and included a number of areas that had been fished for only one season. The second (main-ground) analysis reviewed CPUE from the two main vessels involved in the fishery, and reviewed their catch from the main area of the fishery which had been consistently fished over most seasons.
For the all-ground analysis, variables area, season, length of line, soaktime, latitude and month in season entered the model, in order. This model explained 32% of the data variability, but was influenced by exploratory fishing activity. For the main-ground analysis, variables area, length of line, season, month, latitude, soaktime and type of set (research or exploratory) entered the model, in order. This model explained 34% of the data variability, because it excludes fishing grounds that were fished for only one season. Annual indices from both models show an increasing trend over the duration of the fishery, except for the 2001 season. Fishing in 2001 was poor, as bad weather and thick ice conditions precluded access to the main fishing grounds. The index for 2002 is the highest in the series, which suggests that the New Zealand toothfish fishery is not under stress from the current level of fishing activity. However, both models have relatively low predictive power, and are a relatively poor fit to the data, and these trends should be interpreted with caution. This is due to the exploratory nature of the fishery, and the unbalanced nature of the distribution of effort among seasons. As only four years of data are available for analysis, these trends are considered to be preliminary indications only.