Antarctic Marine Living Resources program

The U.S. Antarctic Marine Living Resources (AMLR) program: 1996-1997 field season activities

JANE E. MARTIN, ROGER P. HEWITT, and RENNIE S. HOLT, Antarctic Ecosystem Research Group, Southwest Fisheries Science Center, La Jolla, California 92038

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:

Krill predators respond to changes in the availability of their food.
The distribution of krill is affected by both physical and biological aspects of their environment.

In the previous eight seasons, the AMLR field program included a research cruise near Elephant, Clarence, and King George Islands, which are among the South Shetland Islands at the tip of the Antarctic Peninsula. Land-based studies were conducted at a field camp on Seal Island, off the northwest coast of Elephant Island. Because Seal Island was found to be unsafe due to landslide hazards, however, research at the camp was curtailed. Beginning this season, the AMLR study area was expanded to include a larger area around the South Shetland Islands, and a new field camp was established at Cape Shirreff, Livingston Island (figure 1). As in the past, research was also conducted at Palmer Station, a U.S. station on Anvers Island farther south on the Peninsula.

The specific objectives of the 1996-1997 field season were the following:

to map the physical structure of the upper 750 meters, including the thermohaline composition, oceanic fronts, water mass boundaries, surface currents, eddies, and turbulent mixing;
to map the distribution of phytoplankton biomass and production;
to map the distribution of zooplankton (krill and other species), including the horizontal and vertical variations in krill density and demographic characteristics;
to conduct bottom trawls at selected sites around the South Shetland Islands as a feasibility study for future surveys of finfish stock abundances;
to establish a new field camp, map the numbers and distributions of seabird populations, re cord the fledging weights of chinstrap penguins (Pygoscelis antarctica), and band 1,000 chinstrap penguin chicks at Cape Shirreff;
to record the fledging weights of chinstrap penguins, the presence of known-aged and previously handled seabirds and pinnipeds, and the abundance of antarctic fur seals ( Arctocephalus gazella ) on Seal Island; and
to describe the reproductive success, feeding ecology, and growth rates of Adélie penguins ( Pygo-scelis adeliae ) throughout the reproductive season at Palmer Station.

The cruise was conducted aboard the chartered research vessel (R/V) Yuzhmorgeologiya . Because of a delay in the arrival of AMLR cargo, the ship departed Punta Arenas, Chile, for Leg I on 19 January 1997, 4 days later than originally planned. Despite the delay, all original objectives were achieved and the leg was completed on 14 February. Following Leg I, the ship was delayed 23 days in Punta Arenas due to a failure of the main engine. After repairs were completed, Leg II was conducted 13-26 March with an abbreviated research plan.

During Leg I, a large-area survey of 106 conductivity-temperature-depth (CTD)/carousel and net sampling stations, separated by acoustic transects, was conducted in the expanded AMLR study area (Survey A, figure 2). Acoustic data were collected at three frequencies using 38-, 120-, and 200-kilohertz transducers. Data for physical oceanography, primary productivity, and krill distribution and condition studies were collected during the survey. Operations at each station included the following:

recording of vertical profiles of temperature, salinity, oxygen, photosynthetically available radiation, light-beam attenuation, and fluorescence;
collection of discrete water samples at standard depths for analysis of chlorophyll- a content, primary production rates, inorganic nutrients, dissolved oxygen, photoadaptational state of phytoplankton, phytoplankton cell size and species composition, and phytoplankton biomass; and
deployment of a 1.8-meter (6-foot) Isaacs-Kidd Midwater Trawl (IKMT) to obtain samples of zooplankton and micronekton.

During Leg II, 16 CTD/IKMT stations, separated by acoustic transects, were conducted around Elephant Island (Survey D, figure 3). Operations at each station included the following:

recording of vertical profiles of temperature, salinity, dissolved oxygen, and pH;
collection of surface water samples (by bucket) for measurement of pH, oxygen, and alkalinity; and
deployment of an IKMT to obtain samples of zooplankton and micronekton.

Also during Leg II, seven bottom trawls were conducted at stations northwest of Robert and Nelson Islands, and west of Elephant Island.

A field team occupied the new camp at Cape Shirreff from 25 January to 8 March 1997. Approximately 100 Zodiac loads of building materials were transferred to the camp for the construction of four structures. The team also initiated abundance and growth studies on seabirds and assisted Chilean colleagues with antarctic fur seal research. Seal Island was occupied by a field team from 11 February to 16 March, which was longer than originally planned due to the ship delay. The team dismantled various camp structures for removal from the island, and conducted limited studies on penguins and antarctic fur seals. Fieldwork at Palmer Station was initiated on 28 September 1996 and completed on 15 April 1997; studies on aspects of the ecology of Adélie penguins were conducted.