CCAMLR

The results of the current monitoring program of fjord fish at Potter Cove, South Shetland Island are updated, showing a recovery of Notothenia rossii to levels comparable to those observed in and the disappearance of Gobionotothen gibberifrons from the catches since 2007.

Scientific observation was conducted in the commercial trip on the long-liner "Simeiz", operating under the Ukrainian flag, in the south-western Atlantic Ocean outside the exclusive (marine) economic zones of the foreign states (FAO statistical area 41) in the period from December, 11, 2007 till September, 10, 2008. Samples of crabs selected from bycatch during target fisheries for Patagonian toothfish Dissostichus eleginoides were selected on Patagonian slope (subarea 41.3.1) between 42 and 47 ° S on depths 700-2000 m. Catches of Paralomis formosa did not exceed 25 kg per a long-line set. Crabs occurred on depths of 984-1810 m. The length карапакса самцов crabs made 2,1-8,9 sm, the weight of-4-383, average length and weight самцов were equaled 7,1±0,02 sm and 207,0±3,6 accordingly. The carapace length of females varied within 3,0-8,2 cm, the body weight changed within the limits of 12-224 g, the average length and weight of females was 7,1±0,19 cm, and 108,0±1,7 g, accordingly. Sex ratio was 1:1 in the period from April till May, and 2:1 in the period from June till September, males prevailed. Reproduction was observed in crab population: spawning of eggs on pleopods and their incubation. Shells of the most crabs were clean and firm or with a small amount of parasites. The data on the distribution of crabs in area of toothfish fishery on the Patagonian continental slope were given.

For the first time Lepidion schmidti was recorded in the Southern Ocean. Measurements of the examined specimen which the author had time to do were presented.

1. 2009 data have been incorporated in to the catch-at-age based CASAL model for toothfish in Subarea 48.3. 2. Fits to the survey data are good for the early 2000s, particularly 2004 to 2006. Fits to the catch at age data are good, except for 2009 where large numbers of age 7 and age 9 fish are not well estimated. Fits to tag recapture data are also good. 3. Projections made using median lognormal recruitment suggest a long-term yield of 3900 t. Using a recent subset of estimated cohorts suggests a lower yield.  

The results of the histological analysis of the Antarctic toothfish (Dissostichus mawsoni) reproductive system, caught in December - February 2005/2006 in the Ross Sea are presented. The morphological parameters, indices of gonads and condition by Fulton have been described. The histological criteria of the assessment of the ovary maturity stages, cytological parameters of oocytes and type of the toothfish oogenesis have been determined. At the maturing of toothfish, ovaries from the stages III to IV showed a slow increase in oocyte diameter. It was obtained that for Antarctic toothfish during the fishing period the individuals with gonads of the late III stage of maturity were dominated. Their ovaries contained two groups of vitellogenous oocytes. The large oocytes of the nearest spawning season with average diameter 2000 - 2200 ·10-6 m have composed 13.3% of total cell number.

For the first time, the investigations on feeding of Antarctic toothfish (Dissostichus mawsoni) from the bottom longline catches in the Lazarev Sea were carried out. The analysis of food composition for males and females in the eastern Lazarev Sea showed that dominant food objects for individuals of both sexes include icefish (Chionobathyscus dewitti), Antarctic squid (Mesonychoteuthis hamiltoni), and grenadier (Macrourus whitsoni). During the investigation period the total indices of fullness of stomach for females and males were 1.68% and 2.25%, respectively. The closeness of parameters by both food composition and feeding activity evidenced a lack of competition in food relations among fish of different sexes.

On the basis of our own data and literature materials, the schematic posters showing spatial and vertical distribution of two toothfish species during their whole life cycle, changes in food interrelations and size composition on the shelf and continental slope, are presented. The comparative analysis of these parameters revealed essential differences in food spectra both at the first pelagic stage of their life cycle and during the period of their habitation on the shelf and continental slope. At that, under the common regularity of exploration of pelagial and then different depths on the shelf and slope Patagonian toothfish off the South Georgia (48.3) has a more abundant food base and its individuals are much larger on the average than in the area of Kerguelen Archipelago (58.5.1.) (Posters 1 and 2). In turn, Antarctic toothfish individuals in the seas of Indian Sector (58.4) are larger than in the Pacific Ross Sea (88.1) (Posters 3 and 4) that is determined , in large extent, by abundant food base in pelagial, on the shelf and slope of continental seas in the Indian Sector of Antarctica.

As a means of testing the accuracy of observer identifications and to provide additional data on benthic invertebrate by-catch; observers operating aboard the longline fishing vessel Antarctic Chieftain were asked to identify and retain all benthic invertebrate by-catch from a recent voyage to Heard Island and McDonald Islands (HIMI) for onshore verification by taxonomists at the Australian Antarctic Division (AAD). Observers displayed a high level of accuracy (89%) in the identification of longline invertebrate by-catch. Common taxonomic errors included the misclassification of stylasterids, bryozoans and alyconarians; an issue prevalent in similar fisheries. This suggests the need for further training in the classification of cnidarians (stony corals, soft corals and stylasterids) and coral-like organisms (bryozoans), particularly as these groups are of high conservation value and are potentially vulnerable to the cumulative impacts of bottom fishing

Catch-at-age proportions can be estimated directly using a simple random sample (SRS) of fish in the catch, determining the ages in the sample, and calculating proportions in each age class. This “direct” method can be replaced by the age length key (ALK) method if there are in addition to the SRS of ages, which have also been measured for length (the age-length sample), a large SRS where fish are measured only for length and tallied by length bins (the LF sample). The ALK method uses the extra information in the LF sample to calculate proportions by age by multiplying the probability by length bin estimated from the LF sample by the conditional probability of age given length bin estimated from the age-length sample and summing over the bins. Since this conditional probability is employed, the ALK method can be used to obtain unbiased estimates from age-length samples that have been collected using unequal probability schemes with respect to length such as length bin random sampling (LBrs). LBrs can be easily implemented by directing observers to sample length-bins for fish to have their otoliths removed until a fixed number of fish in each length bin have been obtained and further sampling from any “full” bins is discontinued for the remainder of the cruise. LBrs ensures that the tails of the length frequency distribution, and thus that of the age distribution, are over-represented in the age-length sample compared to a SRS scheme. Formulae for the precision of the estimates of proportion by each age class are given for each of the direct, ALK_SRS, and ALK_LBrs sampling/estimation methods. Since the formulae depend on the values of proportion by length bin and conditional probability of age given length as well as sample sizes, typical values were generated to allow the comparison of precision. The ALK_SRS method always has a greater precision across all age classes than the direct method, with the difference diminishing as the sampling fraction of the LF sample that is sub-sampled for age determination increases. The ALK_LBrs method is slightly inferior to the other two sampling/estimation methods for most of the age classes that dominate the catch but is significantly superior for the less well represented age classes. For older, mature-age fish this improvement in precision, being important in estimation of spawning stock biomass, may more than compensate for the slight loss of precision for the younger age classes in terms of the accuracy of integrated assessments that employ catch-at-age proportions.