CCAMLR

A large body of data and techniques are available for re-assessing the biological parameters and recruitment of Patagonian toothfish, Dissostichus eleginoides, in the Heard Island region. A new survey of the Heard Island Plateau was undertaken in May - June 2001, providing the sixth survey over 11 years on this stock with other surveys including part of this stock. This paper describes the results of that survey, the time series of abundances and assessments of growth, recruitment, mortality and selectivity of this species. The results indicate that D. eleginoides is faster growing that originally thought with growth rates similar to South Georgia. The new estimates of growth parameters enabled a more accurate reassessment of the recruitment time series, which was likely to have been over-estimated in the past. An estimate of natural mortality indicates that mortality of young fish, ages 3-8, may be much greater than older fish. This may need to be taken account of in the assessment process. An approach is proposed to estimate age selectivity to the trawl fishery in the region. In conclusion, the overall analysis shows a promising way forward in understanding the dynamics of D. eleginoides in the Heard Island region. Clearly, a longer time series of data will be useful to better estimate recruits and natural mortality. A question to be addressed is the extent to which these stocks are connected to the wider Kerguelen Plateau as evidenced by some of the movement patterns and interannual variation in distribution.

A bottom trawl survey was conducted in the northern half of the South African EEZ around the Prince Edward Islands in April 2001. Due to the paucity of bathymetric data, it was not possible to design a statistically rigid survey, consequently this first survey is regarded as a pilot study to ascertain the feasibility of conducting future trawl surveys, and to collect relevant data to aid in the design of such surveys should they be deemed practical.
The maximum operating depth for the survey vessel was 1 500metres. Over 90% of the survey area is deeper than 1 500m and, therefore, cannot be surveyed by bottom trawl. The small area above the 1 500m isobath is scattered over 28 hills and seamounts (of various sizes and heights). This combination of factors makes the design and execution of bottom trawl surveys extremely difficult.
A total of 55 trawls were completed and these show a relationship between Patagonian toothfish density and latitude and/or depth. Although this pilot survey was not designed to yield a biomass estimate, a first, crude for Patagonian toothfish estimate is presented. 51 Patagonian toothfish were tagged and released.

Commercial fishing is having an increasingly negative impact on marine biodiversity with over 70% of the world’s fish stocks being fully exploited and in many cases overexploited. On top of this, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) has granted commercial fishing permits in the most remote marine environment on earth, the high latitude Southern Ocean. The primary target of these new commercial fishing ventures is the large pelagic piscivorous predator, the Antarctic toothfish, Dissostichus mawsoni. Unfortunately little information is available on the demography, genetics or life history of this large fish. Without such information we have little idea as to the effects of commercial fishing on the population structure and survival of this species. In this study we focus on patterns of genetic diversity within and between geographically disparate populations of the Antarctic toothfish using randomly amplified polymorphic DNA (RAPD) markers. Results of our study showed high levels of genetic similarity within and between populations. Despite high levels of genetic similarity, genetic analyses detected significant population structure including fixed differences among populations, a significant fixation index (Fst) and between population differentiation via a Mantel test. From a conservation perspective, low levels of genetic diversity may be indicative of relatively small populations that would not be able to withstand heavy commercial fishing pressures. Given that there is evidence for significant genetic structure, it will be important to manage these fisheries in a manner that will help prevent the loss of unique genetic variation from regional overfishing.

New Zealand has undertaken a tag recapture study of skates (Family Rajidae) in Subarea 88.1. The objective of the programme is to determine the probability of released skates surviving. Skates have been tagged in the 1999/00 and 2000/01 seasons. Results from 1999/00 were presented in WG-FSA-00/55. This paper provides a brief update on the 2000/01 results and the tagging protocol in use.