CCAMLR

The examination of the sexual ratio of D. eleginoides between the first week of March and the third week of July 1996, in the subarea 48.3 shows that the sex ratio departs from the expected 1:l ratio being the females more abundant in the longline samples, except during May, when the males at size of first maturity join the female population. After the first week of June, the sex ratio turns back to a higher number of females. Because the longline remains most of the time close to the bottom habitats, this finding suggests that: or the females remain in higher proportion in the habitat sampled by the longline because the males move to other habitats or, the females are more vulnerable to the longline fishing techniques, or both sexes rise in the water column for spawn. No one of these hypotheses could be tested using the fishery data.

This note describes a successful method for tagging Dissostichus eleginoides and presents an analysis of a tag-recapture experiment carried during the Macquarie Island fishery for this species during the 1995-96 season. Simple population and tag accumulation models are used to account for the tags being released at various times throughout the season, and the effects of the removals by fishing. By assuming that recaptures have a Poisson distribution, maximum likelihood estimates are obtained for the pre-fishing abundance of the population in the season of 996 000 fish. However, this is adjusted to 901 000 fish if a small number of recovered but unreported tags are taken into account.

Estimates of absolute numbers of recruits to the stock of patagonian toothfish around the Heard Island region are calculated from density at length data derived from stratified trawl surveys. The estimates are referred to the four year-old age class. The parameters for a lognormal recruitment distribution suitable for use in a population model are calculated.

An experimental longline fishing cruise targetting D. eleginoides has been realised in the deep-sea zone (300 - 1700 m) off the Kerguelen islands (Division 58-5-1) from February to April 1996. The by-catch has been identified with 10 species of fish reaching a important part (36,1%) of the total catch in number. The grenadier Macrourus carinatus and two species of skates Bathyraja eatonii and Bathyraja irrasa are the dominant species in the by-catch. The morid Antimora rostrata is also a common by-catch. The other species are rare but the predatory effect of the two big sharks Somniosus microcephalus and Lamna nasus on longline caught D. eleginoides must be considered as not negligeable. Geographical and bathymetrical differences in the by-catch species distribution is noted. The mean abundances follow the differences. Size distribution in the main by-catch species show that some, like the grenadiers and the skates, have a commercial potentiality if a deep-sea fishery occurs in the future.

A number of weighted smoothing splines were fit to data on carapace length and size-specific, median chela height of Paralomis formosa. The second derivative of the spline which made the best tradeoff between goodness of fit and smoothness was used as an estimate morphometric size at maturity. Bootstrapping techniques provided a bias-corrected estimate of morphometric size at maturity (sBc) equal to 80- carapace width, and Pr(72mm ≤ sBC ≤ 90mm) ≈ 0.95. The spline modeling technique appears to overcome some of the philosophical and statistical problems associated with estimating size at maturity by fitting linear models to log-transformed morphometric data (see Somerton 1980a and 1980b), but improvements could be made to make the spline technique more robust to outliers in Y-space (crabs with regenerating claws). Given the uncertainty in sBC and the lack of information about body size growth rates, a wide range of alternative size limits are likely to be feasible options for managing the P. formosa fishery, but, despite the availability of new data and the arbitrary nature of the current size limit on this species, there does not seem to be a sufficiently strong biological reason to revise the size limit regulation set forth in CM 91/XIV, Paragraph 10.