CCAMLR

Two primary issues are at question for hydroacoustic assessments of krill, The first is the methods applied to establish biomass in a survey area and the second is the improvement in accuracy of target-strength measurements. In the case of statistical methods, there are no clear guidelines for deciding what method is most appropriate, this is made even more difficult by the fact that most survey methods assume the population is fixed in space, relative to the sampling interval. There remain several unsatisfied needs for improvements in sampling design and tests for systematic trends in survey data collected from non-stationary populations, which have not been well addressed by present techniques. However, this does not invalidate the use of available methods to conduct surveys and analyze results. In the case of target-strength accuracy, even if the present values were very accurate, the issue of interest would seem to be not the absolute amount of biomass present in an area, but rather how it is distributed. The issue of patchy years vs more even distribution would seem to have more impact on ecosystem management than absolute accuracy of biomass estimates.

The hydroacoustic survey found a low krill abundance in most areas covered by last years survey. The total biomass in the vicinity of Elephant Island was estimated from 120 kHz data to be 260 k tons and that in the Bransfield Strait South of King George Island was 39 k tons for a total of 299 k tons in the combined areas. The estimated 200 kHz survey data were higher, giving 715 k tons near Elephant Island and 83 k tons in the Bransfield Strait. The survey results apply to 7,453 nm2 near Elephant Island and 2,894 nm2 in the Bransfield Strait. The full survey found (120 kHz data) 385k tons (in 7,787 nm2) in the Bransfield Strait and the area North of King George Island and 309k tons (in 8,836 nm2) in the expanded area around Elephant Island.

A general framework is presented to develop, test and integrate component models of the distribution and dynamics of Antarctic krill population at various spatial and temporal scales. We suggest that models of increasing complexity be developed iteratively for variability and patchiness of krill abundance. Incremental models should then be compared to statistical descriptions of the observed distribution patterns at various scales of observation to ascertain the plausibility of the model and identify critical processes to be added. An analysis of spatial distribution of krill in the Bransfield Strait area reveals that purely physical models of turbulent redistribution are not sufficient to explain krill distribution at small scales. We therefore propose to develop a modified diffusion-reaction model incorporating spatially variable growth rates of krill, krill loss rates due to predators, density-dependent attraction of krill to account for the small scale aggregations.

In the vicinity of the northern tip of Antarctic Peninsula, the Bransfield Straits and South Shetland Islands, cold polar waters from the Weddell Sea meet warmer circumpolar water from the Pacific Ocean. A series of fronts form which collectively are referred to as the Weddell-Scotia Confluence. Within the Confluence region the Weddell Gyre water is separated from the Pacific or Scotia Sea water by a zone of varied width (10 to 100 Km) of water which can best be considered as continental margin water, advected into the region along the extreme western edge of the Weddell Gyre. It is relatively cold and low in salinity through-out the water column and prone to deep reach convective events, even as far north as the Bransfield Straits. Along the northern boundary of the Weddell-Scotia Confluence (the Scotia Front), where the Pacific water is encountered, there are indications of vigorous mixing processes of Bransfield Straits water (derived from the Weddell, with further local modification): an intrusive layer of Pacific derived relatively warm-salty water near 300 meters depth and deeper intrusions (500-1500 meters; e.g. SEIDLECKI stations 217, 226, 231, 235, 236 and 250) of Pacific water, as the Scotia Front protrudes to the south, perhaps associated with meso-scale structures.
The Weddell-Scotia Confluence in the Bransfield Straits is associated with abundant Krill populations. It is speculated that mixing of Weddell and Pacific waters near the tip of Antarctic Peninsula is an important environmental feature related to this abundance.

The report describes the land based ecosystem monitoring studies conducted in three separate areas of the Antarctic Peninsula marine mammal s and birds. In addition, a joint U.S./Chilean cruise to track fu r seals and penguins at sea is described.

As part of the NMFS/AMLR program to provide information for the effective management of Antarctica’s marine living resources, three permanent monitoring sites were established on the western side of the Antarctic Peninsula. Listed from north to south, these were Seal Island (Elephant Island), Admiralty Bay (King George Island) and Palmer Station (Anvers Island). During 1987 - 1988, preliminary data on the breeding success, fledging weights, growth rates and diets of Chinstrap and Adelie Penguins were obtained. Although it is too early to draw conclusions on any aspects of the data, this report provides a current summary of the results of AMLR directed seabird research at the three monitoring sites.