CCAMLR

A diet analysis of the Patagonian toothfish Dissostichus eleginoides, trawled in the South Georgia Islands area 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 on the shelves of Shag Rocks and South Georgia, accounting for about 70% of prey. Krill appeared as secondary food, although its importance was overestimated by the frequency of occurrence method. Cephalopods and mysids were infrequent in the stomachs, and only at Shag Rocks and South Georgia, respectively. Lepidonotothen kempi, Champsocephalus gunnari and Chaenocephalus aceratus constituted the main fish prey and their variability between Shag Rocks and South Georgia 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.

Feeding behaviour, ecological role in the marine food web and population trend of the Antarctic Shag Phalacrocorax bransfieldensis and the South Georgia Shag P. georgianus in Antarctica are analysed. The diving depths and duration registered in these shags are the deepest and longest among all flying birds in Antarctica and match deep dives performed by small Antarctic penguins. Shag individuals of both sexes partition foraging depths and food resources, which might diminish intra-specific competition. Like other sub-Antarctic shags, P. bransfieldensis and P. georgianus are bottom feeders that prey predominantly on demersal fish. In the Southern Scotia Arc and west Antarctic Peninsula, nototheniids, mainly Notothenia coriiceps, constitute their main prey. Shag partners alternate the time at sea and, as the energy requirements at the nest increase, they increment the number but reduce the duration of the feeding trips. A steady declining trend in the number of breeding pairs of both species has been observed in the last decade at several Antarctic localities; this phenomenon at the South Shetland Islands might be at least partially explained by the effect of the commercial fishery on shags’ fish preys. In inshore-shallow waters shags occupy the trophic niche of main predators of demersal fish and play an important ecological role as regulators of populations of its main fish prey species that have a marked site fidelity. The potential use of shags as biomonitors in Antarctica is discussed.

Foraging zones used by incubating royal albatrosses (Diomedea epomophora) from the Otago Peninsula and their coincidence with fisheries activities were studied with global positioning system (GPS) loggers. Birds favoured areas around the shelf break of the eastern New Zealand continental mass, with hot spots of activity that coincided with fishing zones actively exploited by commercial trawl fisheries during the study period. Birds appeared to change their behaviours with proximity to fishing events, showing reduced speed and more direct flight when at moderate distances from fishing operations (12.5 – 25 km) than at greater distances. This relationship was significant for speed only (P

At the 2004 meeting of the Working Group on Ecosystem Monitoring and Management (WG-EMM) in Siena, Italy, the UK reported on the by-catch of fur seals (Arctocephalus gazella) in the krill fishery around South Georgia, and on mitigation methods that were being developed and deployed to avoid fur seal deaths in the fishery. WG-EMM requested that the UK provide further details of the methods employed for consideration by the ad hoc Working Group on Incidental Mortality Arising from Fishing (WG-IMAF). Three CCAMLR international scientific observers recorded mitigation measures for fur seal entanglements on krill vessels fishing around South Georgia in the 2004 fishing season. The measures implemented were based on four approaches: physical barrier, barrier plus escape hatch, manufactured seal-exclusion devices and gear configuration. Those vessels initially without mitigation measures were able to introduce them without further cost and minimal disruption to fishing activity during the season. These approaches, aimed at reducing seal entanglements, are similar to the two systems implemented by Japanese vessels during the 2003 krill fishing season around South Georgia (Japan Deep Sea Trawlers Association, 2004).

This paper provides a brief descriptive analysis of some of the available data on the length of longlines used in exploratory fisheries and some of the data describing longline sink rate trials. In Sub-area 88.1 the maximum length of longline used by auto longline system vessels is approximately 15 000 m. The maximum length of longline used by Spanish longline system vessels is approximately 37 500 m. The mean length of research and exploratory sets is very similar for autoline system vessels. However, for Spanish longline system vessels research sets are generally just over half the length of exploratory sets. Based on this review and our knowledge of longline sink rates options for revising Conservation Measure 24-02 (2004) are proposed.

This report describes the activities and preliminary results of the research carried out during January 2005 onboard the FPRV ‘Dorada’ by British Antarctic Survey (BAS) Scientists on behalf of UK authorities.
Survey Objectives
The primary objectives of the proposed survey were to:
• Refine methods for estimating icefish biomass using acoustics.
• Examine temporal changes in the vertical distribution of icefish.
• Assess precision of AUDOS estimates of crab density.
Secondary survey objectives were to:
• ‘Ground-truth ‘ AUDOS estimates of crab density using comparisons with bottom trawls.
• Provide more information on the distribution of the benthos on the South Georgia shelf.
• Monitor commercial fishing activity in the area

On the basis of the bottom trawl surveys carried out by Russia and Great Britain during 2000, 2002, 2004 in the South Georgia area, it is demonstrated that the method by Aitchison and bootstrap method result in different estimates of mean fish density in the length series. Verification of the hypothesis of non-zero observations lognormal distribution for a large number of length groups casts doubt on the correctness of the first method application and therefore also of the method by de la Mare commonly used by CCAMLR in icefish age composition of abundance indices determination. To solve this problem it may be proposed to apply the modern version of the method by MacDonald and Pitcher. The comparison of this method and the method by de la Mare for length series, estimated with Aitchison’s method, were carried out. The results appeared very similar. The method by MacDonald and Pitcher has been tested on the length series obtained with the bootstrap method on the basis of the above mentioned surveys data. To estimate the standard error of the mixture distribution parameters, the “jackknifing-after-boostrap” method was proposed.

During the feeding period icefish aggregations are confined to a frontal zone between opposite flows (coastal circumfluent current and ACC) or formed inside quasistationary circulations, where the largest aggregations of food organisms are concentrated at the beginning of the spring period. Icefish concentrations were detected at the periphery of a cyclonic meander or in the centre of the anticyclonic circulation formed by the Weddell waters. Confinement of the fish to the boundary of water masses between the shelf waters and ACC was also traced. Favourable conditions for formation of dense aggregations resulted from the availability of clear-cut frontal zone caused by interaction of warm deep waters and the coastal waters. Such a confinement of fish aggregations to dynamically active zones arises rather from concentration of food organisms in these areas than as a result of favourable conditions for the fish.
The presence of cold intermediate layer shall be considered to be a negative hydrological factor for formation of icefish aggregations as it impedes descending food objects to the horizons inhabited by icefish and migration of fish to the upper 100m layer. Very high water temperature (above 1.8-2.0°C) for this area in the places of food organism aggregation is another obstacle for performing vertical migrations by foraging fish. All physiological processes of icefish begin to recede at such a temperature, and at a higher temperature the fish evidently falls into a condition close to anabiosis. In such locations the fish are distributed deeper than this temperature layer, most often near the ground.
As a rule, transition of icefish to pre-spawning condition is conditioned by visceral fat content (over 2 points). The spawning begins when near-bottom temperature on the spawning ground increases to 1.6°C. Therefore, the beginning of the spawning period is determined in the first place by oceanological factors.