CCAMLR

Data from individual trawls carried out by vessels operating in the krill fishery at South Georgia are examined and a range of descriptive measurements reflecting the operation of the fishery are produced. The measurements indicate that the krill fishery at South Georgia is geographically focussed, operating in a limited area along the shelf edge on the northern coast of the island. Each day a large number of trawls were undertaken by each ,vessel, with trawls being shorter in duration during the middle of the day. Daytime trawls were also generally deeper and produced a larger catch. Individual trawls were examined to establish the time required for each phase of the operation. The times associated with shooting and hauling the net were usually short and showed little variation, whereas the time associated with the actual trawl phase was longer and more variable. The distance between consecutive trawls was generally small, indicating that little effort was spent searching beyond the near neighbourhood. However, this phase of the operation took almost as long as the trawl itself and showed similar levels of variability. The range of measurements indicate that differences existed between years. Particular aspects of the variability are discussed in relation to the biology of krill, others are discussed in relation to the fishery operation.

The Polar Front (PF) forms the southern boundary to the Polar Frontal Zone (PFZ) along the northern edge of the Antarctic Circumpolar Current (ACC). In a number of areas the position of the PF (and thus the PFZ) is known to be influenced by topographic steering, while local bathymetry has also been implicated in the movement and retention of various associated mesoscale features. In this paper we examine the structure and position of the PF as it passes over the rugged bathymetry to the north of the Scotia Sea. Results are presented from an oceanographic transect crossing the PF to the northwest of South Georgia and from a pair of shorter transects south of the PF but north and east of the first. Associated with the PF was a narrow, high-speed flow embedded in broader, slower moving regions. This high-speed flow was found to have a geostrophic component of velocity that was slower than estimates for other regions of the PF. Comparisons with output from recent oceanographic models were found to be consistent with the physical observations. A second examination of the region after a period of 30 days suggested that the surface expression of the PF had shifted southward by approximately 35 km but that the PF was essentially in the same position over the southern edge of the Maurice Ewing Bank. An advanced very high resolution radiometer image taken during the cruise provided additional information about the position of the surface expression of the PF and the extent of mesoscale features that were present to the north of the study area. Immediately to the north of South Georgia, water in the eastward flow of the ACC meets colder, more saline water flowing west along the north coast of the island. The area where these two flows meet was found to be variable over the 30-day timescale of the cruise. This area is known to be of major biological significance, and variability in the local oceanography is possibly of crucial importance to many predator species breeding at the northern end of South Georgia.

For three austral spring and summer field seasons, 1994-97, the Antarctic Site Inventory project has collected data and information about Antarctic Peninsula visitor sites. These data and information are intended to assist in establishing baselines for: future environmental assessments under the soon-to-be-effective Antarctic Environmental Protocol; designing future monitoring programmes to detect changes in fauna, flora, and other major features at these sites; and how best to minimize potential adverse impacts of human visitor activity. CEMP Standard Methods were relied upon in establishing the project's methodology, particularly with respect to counting penguin nests and chicks. At each site, investigators attempt to select and establish prospective control (seldom disturbed) colonies and experimental (frequently disturbed) colonies to census. The intent is to repeat censuses regularly both near and far from landing beaches where visitors access a site, allowing comparisons over time between areas that have much human activity and those without such activity. A power analysis indicates the Inventory's methodology fully conforms with sampling strategies recommended by the CEMP working Group, enabling the Inventory to detect a 10% or 20% change in a parameter with a significance level as. 01 and a statistical power P (= 1-ß) ≥ 0.8.

Data on salp by-catch and green krill were analyzed based on Logbook data of Japanese krill trawlers. Inter-annual and seasonal variability of the timing, duration and strength of salp bloom were indicated. Salp by-catch and occurrence of green krill seemed to show reverse correlation, implying the competition for phytoplankton between krill and salps.

This paper summarizes Japanese krill catch data during austral summer in 1995/96 season. Main fishing grounds were persistently formed in the north of Livingston Island throughout the season. CPUE in December was high but from January through June CPUE was comparable to the value of Livingston area in the previous fishing season. From January through early May, modal size of krill differed between shelf area and slope/outer shelf area. However, from mid-May through late June, no difference in length frequency was observed, and showed only single component with modal size of 47-48mm.

Proportional recruit indices and CPUE in Subarea 48.1 (Antarctic Peninsula region) from 1980 through 1996 were calculated based on the log book data from Japanese commercial krill trawlers. Proportional recruits calculated from fisheries data showed similarity with those from scientific data (Siegel et al., 1997), and showed close relationship to sea ice indices. CPUE (catch/towing volume) in Livingston area showed a decreasing trend during the study period. Alternation of operational strategy in relation to the product quality and decrease of krill density in the areas were considered as the possible reasons. On the other hand, CPUE in Elephant area showed greater inter-annual variation without any trend.

Results from two net surveys in the Elephant Island area during January-March indicated moderate krill abundance and lower recruitment success of the 1995/96 year class relative to that of 1994/95. These occurred after a relatively early 1996 spawning season that theoretically should have promoted good krill recruitment. However winter 1996 was characterized by slightly below average winter 1996 sea-ice conditions. These observations strongly suggest that winter sea-ice extent greatly affects larval survival and recruitment even when krill spawning is relatively early. Salp abundance values during March Survey D were second only to those observed during February-March 1993 and, like 1993, resulted from massive population growth during summer. This bloom, as those in previous "salp years", followed a winter with relatively low sea-ice development. The other zooplankton collected included a diverse taxonomic assemblage. Copepods, salps, and postlarval Thysanoessa macrura were the numerical dominants during both surveys. Day-night catch differences and interspecific relationships among various zooplankton taxa observed during January-February Survey A are described here.

Data from 1995-1997 US Antarctic Marine Living Resources (AMLR) Program surveys in the Elephant Island area are examined to determine the level of sampling effort required to adequately assess the (1) abundance and demographic structure of Antarctic krill and (2) relative abundance and interspecific relations of krill, salps and other macrozooplankton taxa in the Elephant Island area during summer months. Both parametric and nonparametric techniques are used. Between-survey and between-year comparisons are made to examine possible changes in sampling adequacy resulting from ecological changes operating on seasonal and interannual time scales. The results of these analyses indicate that minimal efforts such as 8 station transects are generally unreliable. Results from most analyses indicate that the data from at least 55 stations are required to adequately estimate krill, salp, and other zooplankton abundance, describe krill length-frequency and maturity stage composition, and assess the abundance relations of krill, salps, and other zooplankton taxa in the Elephant Island area.