CCAMLR

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.

Data collected from the FN American Champion during Phases 1 and 2 of the experimental crab fishery were analyzed with generalized additive models and depletion estimators. Results from the generalized additive models show that the density of fishable P. spinosissima is highest off the northern coast of South Georgia and at depths between about 100 and 300 fathoms. The Phase 1 results suggest that it would not be appropriate to extrapolate local estimates of abundance to the whole of Subarea 48.3 solely on the basis of depth-specific seabed area; extrapolations must consider location. Linear models fit to CPUE and cumulative catch data from the Phase 2 depletion experiments did not have significant, negative slopes. The insignificant regressions were probably a result of inter-haul variability in CPUE and crab movement and suggested that depletion estimators will not be appropriate tools for estimating local abundances of P. spinosissima. Approximately 6000 crabs were tagged and released during Phase 2. Four of the tagged crabs were recovered, and these crabs were at liberty for about 1 to 5 weeks. The recaptured crabs moved at rates between 0.08 and 0.25 n. mi./day. Mark-recapture estimates of standing stock and density were made for the area around Phase 2's third depletion square. The assumptions of the mark-recapture model were probably violated, but attempts were made to account for biased sampling of recaptured crabs and the movement of crabs away from their release sites. Density estimates from the mark-recapture data were on the order of 50,000-100,000 crabs/n. mi2, and there was a lot of uncertainty associated with these estimates. In general, the experimental harvest regime was successfU1. The regime provided important information about crab distribution and facilitated evaluation of local depletion estimators for use in stock assessment, but the WG-FSA may wish to re-evaluate the design of Phase 2.

Estimates of the number of seabirds taken incidentally in longline fisheries on Patagonian toothfish (Dissostichus eleginoides) are still based on limited information. We report here on observations on the by-catch of seabirds during a cruise of the Chilean longliner 'Puerto Ballena' in Statistical Subarea 48.3. A total of 118 dead black-browed albatrosses, 3 dead grey-headed albatrosses, 46 dead white-chinned petrels were reported by the observer and crew members. In addition 21 black-browed albatrosses, 4 giant petrels, 1 white-chinned petrel and 1 unidentified penguin became hooked alive and were released alive. Our preliminary analysis confirmed results from last year that black-browed albatrosses are particularly at risk when longlines are set during the day and/or the streamer line is malfunctioning. If setting of lines had been restricted to nighttime as required in order to comply with Conservation Measure 29/XIV(CCAMLR, 1995) the number of black-browed albatrosses and white-chinned petrels taken incidentally would have been substantially lower. The by-catch of both black-browed albatrosses and white-chinned petrels appeared to decline towards the end of April/begriming of May. The estimated total catch for all observed sets was 312 black-browed albatrosses and 213 white-chinned petrels. This estimate should be regarded as tentative as there rue still problems associated with extrapolating observed numbers of dead seabirds from a subsample of hooks to the total number of hooks in a set which warrant further investigation. However, even if we consider the number of dead birds recorded by the observer and by crew members as a minimum estimate, these figures appear by far too high to be sustainable by both black-browed albatrosses and white-chinned petrel populations in the area.

Results of the analysis of three consecutive cruises to subarea 48.3 are analyzed. A significant variance component associated with the formation of clusters of stations was found as well as a general trend for increasing densities since 1994. The significant variance component obtained for clusters formed with stations at 8.0 nautical miles implies that considering all stations as independent (as in the estimation of the variance of the mean density) might result in a gross underestimation of the variance. The spatial pattern of density across years might be applied to construct a model of density variability to minimize the variance of estimates of regional parameters.

A diet analysis of the patagonian toothfish Diissostichus eleginoides in the Subarea 48.3 in March/April 1996 was carried out by frequency of occurrence (F%) and coefficient "Q" (%) methods. The samples consisted chiefly of immature specimens, with predominant length ranges of 30-70 cm (TL). Fish was by far the main food at SR and SG (63 % as sole prey). Krill appeared as secondary food, although its importance was overestimated by the frequency of occurrence method. Cephalopods and mysids occurred scarcely in the stomachs and only at SR and SG respectively. Lepidonotothen kempi, Champsocephalus gunnari and Chaenocephalus aceratus constituted the main fish prey and their variability between SR and SG depended on their local abundance. The large proportion of fish exhibiting stomachs full or close to fullness (together 62 %), suggests that feeding intensity of the species was high.

The diet composition of the icefish Champsocephalus gumari caught in the Subarea 48.3 in March/April 1996 was analyzed using Frequency of occurrence (F%) and coefficient "Q" (%) methods. Krill was by far the main food around South Georgia and Shag Rocks (F= 85%, Q= 99%). Other prey items, known as an important alternative food in years of krill scarcity, were ingested only occasionally (Themisto gaudichaudii, F= 1 8%, Q= 1 % at SG; mysids, F= 11 %, Q= 1.1 % at SR) or in negligible amounts (Thysanoessa sp.). Many empty stomachs (56%) were found in the sampling area, in levels even higher than those reported for the 1991 and 1994 years of krill shortage. The analysis of the ovarian maturation stages showed that a high proportion of the mature fish sampled (79 %) were 1996 spawners, a fact which may be related with a large availability of food (= krill). It is suggested that krill was present in the region in levels equivalent to the historical years of high abundance.