CCAMLR

Catch rate and catch composition of male snow crabs were compared for four sampling methods. These methods were: (1) large-meshed commercial traps, (2) small-meshed traps, (3) bottom trawl deployed during the day. and (4) bottom trawl deployed at night. Catches were characterized in terms of crab body sizes, shell conditions, and claw allometry. We concluded that: 1) mean and modal size of crabs captured in large-meshed traps was larger than those captured in small-meshed traps which, in turn, were larger than those caught in the trawl; the size of crabs caught in the trawl at night was larger than those caught during the day; 2) large-clawed crabs predominated in the catches from traps whereas small-clawed animals predominated in the trawl catches; 3) soft-shell crabs were more common in trawl than in trap catches whereas old-shell crabs were more common in trap than in trawl catches; 4) mean size of the crabs caught increased with depth for all sampling methods, but especially so for traps; and 5) catch per unit effort for both large- and small-clawed crabs increased with depth for all sampling methods.

Change-in-ratio and index-removal estimators are presented in a general form suitable for fisheries studies. We also show how to combine the two approaches in a single estimator. It is necessary to sample the population before and after the fishery, and to determine the total harvest and its composition, in order to use these methods. We use the methods to estimate the population of legal-size snow crabs (Chionoecetes opillio) in St. Mary's Bay, Newfoundland, before and after the fishery, and to estimate the catchability coefficient and exploitation rate. It is also possible to estimate the abundance of pre-recruits but this requires the assumption of equal catch ability of all animals, a condition that may not be met. These methods have been largely neglected by fishery scientists; however, they seem to be ideally suited for studies of many populations of large crustaceans.

The reproductive performance of commercially important crustaceans may be considerably affected by symbiotic nemertean egg predators and parasitic castrators. Because these parasites commonly affect only females or feminize males, they may be protected by management practices that protect females. To manage a parasitized stock, we suggest that strategies should vary depending on the recruitment dynamics of both host and parasite. For a certain spatial scale, recruitment to a population may be "open" or "closed" depending on the behavior of planktonic larvae, the duration of these planktonic stages, and the flush rate of the environment of the adult host. Both hosts and parasites may have open or closed larval recruitment. We developed mathematical models to investigate the impact of protection of females on a hypothetical fishery for different combinations of host and parasite recruitment dynamics. The models suggest that the common practice of releasing females is not advantageous when a fishery is affected by a parasite. Retaining females in the catch is preferable in most cases. Treating or culling infected females may be advisable when host recruitment is closed.

A method is developed for calculating asymptotic confidence intervals for trawl surveys using the swept area method, using likelihood ratios from Aitchison's delta distribution. Simulation tests of the method show that unbiassed estimates of the density and biomass can be obtained and that the estimated confidence intervals have close to the nominal coverage probability. Performance deteriorates in cases where few of the hauls contain fish, and the coefficient of variation is high. The lower confidence bound appears to be more reliable than the upper.

On the basis of analyses and review of published data on the biology and distribution of Electrona carlsbergi, as well as on the hydrological patterns of the Southern Ocean - especially concerning the structure and spatial variation of the Antarctic Circumpolar Current (ACC) - this paper describes possible ways and means (mechanisms) by which this species carries out meridional migration in various frontal zones. The yearly transport of E. carlsbergi into the waters of the Southern Polar Frontal Zone (SPFZ) occurs regularly although its intensity changes in time. The densest concentrations are observed here in the spring-summer period (November to February) when zooplankton. the main dietary component for E. carlsbergi, is undergoing rapid development. In various areas of the SPFZ and in all sectors of Antarctica E. carlsbergi is represented by immature specimens 7 to 8 cm in length and 2 years of age, indicating dominance by a single cohort. Moreover, a very similar size composition in the SPFZ is evident from both a seasonal and interannual point of view. The proportion of immature specimens in the Subantarctic zone, classified as a breeding area, decreases to 20-40%, while the number of mature specimens 8.5-11 cm in length and 3-5 years old increases. Based on the dynamic processes of the Southern Ocean and taking account of the locations of spawning areas and distribution of E. carlsbergi in the early stages of its life cycle, a theory has been put forward concerning the presence in the notal region and various sectors of Antarctica of several reproductive zones coinciding with areas of large scale disruptions to the zonality of transport by the ACC under the influence of topogenic factors. This paper examines the fate of large swarms (in terms of biomass) of E. carlsbergi transported beyond the notal region and the possibility of a part of the population returning to the reproductive zone. There is a strong likelihood that E. carlsbergi migrates from the SPFZ into the Subantarctic zone by means of eddy formations which occur periodically in the ACC system. These eddies play an important role in the meridional exchange of waters between frontal zones. The paper also discusses questions of the within-species structure of E. carlsbergi and an ecological assessment of the impact of fishing on the ecosystem of the open waters of Antarctica.

Analysis and synthesis of results of Russian and foreign research into the trophic relationships of myctophids demonstrate that this group of mesopelagic fish plays a significant role in the community of marine organisms of the Southern Ocean. The trophic status of myctophids has been determined - they are zooplankton-eaters who consume a considerable amount of meso and macroplankton which determines their high abundance and biomass. Thus, according to a preliminary estimate the yearly consumption of zooplankton by Electrona carlsbergi, the most numerous species of myctophid, ranges from 196 to 364 million tonnes. According to its position in the trophic system of the Southern Ocean, myctophids occupy the third trophic level and are consumers of the second order. Myctophids play a major role as producers, in turn guaranteeing the production of organisms at higher trophic levels (certain species of squid, notothenoids, sea birds and mammals). The large deepwater squid Mesonychoteuthis hamiltoni each year consumes approximately 48 to 57 million tonnes of myctophids. A summary table of the trophic relationships of myctophids is presented, based on general patterns of energy transformation from one trophic level to the next.