CCAMLR

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.

Little is known about the bycatch of skates, rays and macrourids in the target longline fishery for toothfish in the Ross Sea. Following concerns about the accuracy of reporting of bycatch raised by the 2001 CCAMLR bycatch subgroup, the processes for recording bycatch in this fishery were reviewed and the accuracy of data recording was investigated. Current systems were considered to be appropriate, and current bycatch protocols were found to perform adequately against CCAMLR guidelines. Insufficient data have previously been available to evaluate the usefulness of a standardized CPUE analysis of macrourid bycatch in this fishery. The review of data suggest that the toothfish fishery has not yet had a detectable effect on the CPUE, and hence probably the abundance of rattails. Standardised CPUE analysis may be a useful method for the on-going monitoring of this bycatch species, and continued monitoring of CPUE is suggested.

Results from the 2002 season of the New Zealand toothfish fishery in Subarea 88.1 & 88.2 are reviewed and compared to previous seasons. Catch and effort data and biological information for Antarctic toothfish (Dissostichus mawsoni) and Patagonian toothfish (D. eleginoides) are presented. The catch for the 2002 season was almost double that for 2001, and CPUE was the highest for any year. The principal bycatch species continues to be the rattail Macrourus whitsoni, with skates, particularly Amblyraja georgiana, the only other significant bycatch.

A summary of current research underway in New Zealand on seabirds vulnerable to fisheries interactions is provided in two referenced tables, one describing population research and the other describing foraging range data available.

Antarctic toothfish (Dissostichus mawsoni) from the Ross Sea (CCAMLR sub-area 88.1) have been aged assuming that one translucent zone is formed annually in the otoliths of this species. However, no evidence to validate this assumption has previously been presented. In the current work, sagittal otoliths were examined from D. mawsoni that had been injected with oxytetracycline some years before recapture. The number of zones between the fluorescent oxytetracycline line and the otolith margin indicates that one translucent zone is formed annually in otoliths of post-mature D. mawsoni. Otoliths from four distinct juvenile length-frequency modes were also examined, and the translucent zones counted. Zone counts were consistent within modes, and increased by one in each consecutive mode. This indicates that the modes represented year classes and that one translucent zone is formed annually in otoliths of juvenile D. mawsoni. Mean fish lengths at ages 0.5, 1.5, 2.5, and 3.5 years were estimated to be 14, 28, 37, and 46 cm TL, respectively. These estimates agree with growth curves calculated previously from a sample of data that was large but lacked any fish younger than 3.5 years. Counting translucent zones in the otoliths of D. mawsoni appears to be a valid method for determining the age of this species.

Samples of macrourid rattail bycatch from the toothfish fishery in sub-areas 88.1 & 88.2 in 2002 were identified by observers and returned to New Zealand for subsequent confirmation of their identity by NIWA researchers. Two species were found, Macrourus whitsoni and M. holotrachys. A previously aged sample from 1999 was confirmed as being M. whitsoni based on otolith comparisons and the geographic source of the aged sample. This confirms the preliminary age estimates from the ageing study. Regression equations relating total length to snout-vent length, total length to weight, and snout-vent length to weight were generated. For all regressions there were significant differences between the sexes and between the data origins (NIWA and observer). Observer data were derived from fresh specimens and NIWA data were derived from frozen-and-thawed specimens. The age and length at maturity for M. whitsoni males is 12 years and 46 cm TL, for females it was 14 years and 50 cm TL.