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The U.S. Antarctic Marine Living Resources (AMLR) program has developed and conducted a research plan tailored to the goals of the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR), part of the Antarctic Treaty System. The Convention manages antarctic fisheries to conserve targeted species, while also taking into account the impact fishing activities might have on other living organisms in the antarctic ecosystem. CCAMLR's unique management regime has come to be known as the "ecosystem approach." In keeping with CCAMLR's mandate, the impact of the krill (Euphausia superba) fishery upon dependent predators must be understood.
The AMLR program monitors finfish and krill fisheries, projects sustainable yields where possible, and formulates management advice and options. In addition, the program conducts field research with the long-term objective of describing the functional relationships between krill, their predators, and their environment. The field program is based on two working hypotheses:
Similar to the past seven field seasons, the 1995-1996 field program included a 2-month research cruise near Elephant, Clarence, and King George Islands, which are among the South Shetland Islands at the tip of the Antarctic Peninsula ( figure 1). The cruise was conducted aboard the chartered research vessel (R/V) Yuzhmorgeologiya. Land-based studies were conducted at a seasonal field camp on Seal Island, off the northwest coast of Elephant Island, and at Palmer Station, a U.S. scientific station on Anvers Island farther south on the Peninsula (figure 1).
The specific objectives of the field season were the following:
The R/V Yuzhmorgeologiya departed Punta Arenas, Chile, on 18 January 1996 to begin Leg I of the AMLR cruise; the leg was completed on 16 February. Following a mid-cruise port call, Leg II was conducted 19 February to 17 March. A large-area survey of 91 conductivity-temperature-depth (CTD)/ rosette and net sampling stations, separated by acoustic transects, was completed once during each leg near Elephant, Clarence, and King George Islands (Survey A on Leg I, Stations A1-A91; Survey D on Leg II, Stations D1-D91; figure 2). Data for physical oceanography, primary productivity, and krill distribution and condition studies were collected during the large-area surveys. Operations at each station included the following:
During Leg I, acoustic data and four IKMT samples were collected along two transects (Transects AB1 and AB2) when entering and leaving Admiralty Bay, King George Island, to describe krill abundance and distribution; these data complemented foraging studies on Adélie penguins in the area. An antarctic fur seal (Arctocephalus gazella) census was conducted throughout the South Shetland Islands during Leg I; fur seal pups were counted, newly established or previously unknown fur seal colonies were identified, and sightings of previously tagged fur seals were recorded. During Leg II, 21 CTD/rosette stations (Stations X1-X21) were completed along three cross-shelf transects to describe water mass structure: north of King George Island, north of Elephant Island, and south of Elephant Island ( figure 3). Twenty-three directed net tows were also conducted in these areas using a Multiple Opening Closing Net Environmental Sampling System (MOCNESS) to correlate acoustic data with species and target sizes.
A field team occupied the camp on Seal Island from 21 January to 5 February 1996 and again 12-23 February 1996. The team conducted research on the abundance and growth of antarctic fur seals, chinstrap penguins (Pygoscelis antarctica), and macaroni penguins (Eudyptes chrysolophus) breeding on the island. Fieldwork at Palmer Station was initiated on 10 October 1995 and completed on 27 March 1996; studies on aspects of the ecology of Adélie penguins were conducted.