AMLR 2006 Weekly Report No. 5

12 February 2006

 

1. Our current position is north bound in the South Atlantic in transit to Punta Arenas, Chile from the South Shetland Islands. The joint NSF/U.S AMLR supported near-shore acoustical survey off Cape Shirreff, Livingston Island was completed afternoon of February 8. Personnel J. Warren, S. Sessions, M. Cox, A. Jenkins and W. Trivelpiece and equipment were recovered to the ship along with 9 zodiac loads of materials to be retrograded. In the afternoon February 9, the ship fetched Copacabana field camp. Personnel S. Rogers and four zodiac loads of retrograde material and propane tanks were recovered to the ship from Copacabana. February 10, all science operations concluded for Leg I of the AMLR field season.

 

2. Inshore Survey. The goal of the nearshore survey of the area just north of Cape Shirreff, Livingston Island is to map the distribution and abundance of the krill population and to better understand the physical and biological factors that control this ecosystem. Penguin and fur seal colonies are found on Livingston Island and these nearshore waters serve as the main foraging area for these animals. The broad scale AMLR acoustic and net surveys conducted over the past decades do not survey the nearshore regions due to the inability of vessels to navigate these waters. Therefore starting in 2000 and continuing in 2002, 2004, and 2005, a nearshore survey of the krill population in the waters of Livingston Island. The 2006 nearshore survey consisted of several platforms: the RV Ernest, a 19' zodiac equipped with a meteorological sensor and a dual-frequency echsounder; the RV Roald, a 19' zodiac equipped with a multibeam sonar system; several buoys instrumented with either a dual-frequency echosounder or an acoustic Doppler current profiler; and the RV Yuzhmorgeologiya.

 

Five instrumented buoys were deployed along the 90 m isobath on 11 January 2006. These buoys (three with Acoustic Doppler Current Profilers (ADCP) and two with echosounders) were programmed to record 3 minutes of data every 15 minutes. While the buoys include battery power, it is supplemented by wind generators located on the masts. Unfortunately the calm conditions that made the large-area survey quite pleasant resulted in small wind velocities so that many of the buoys developed problems related to low-battery voltages. Additionally, it appears that an iceberg (or large piece of an iceberg) removed three of the buoys and their moorings as when we returned to check on the buoys on 3 February there was no sign of them anywhere in the area. Analysis of data transmissions supports the iceberg hypothesis as one of the buoys started drifting (and transmitting data) for a few days as it moved throughout the waters north of Livingston Island.

 

The 2006 nearshore survey occurred from 2-8 February 2006. Personnel and equipment were offloaded on the 3 February due to poor weather on 2 February. The Ernest undertook a calibration of the acoustic system using a 38.1 mm Tungsten Carbide sphere, while the Roald began a bathymetry survey of the nearshore waters. Operations were continued from 4-8 February with the Ernest surveying the canyon east of Cape Shirreff and the Roald surveying bathymetry on the western edge of the same canyon. Predator observations were made from both boats during this period. Boat-based operations concluded on the afternoon of 8 February due to concerns about a low pressure system and the resultant weather. During the nearshore survey, the Ernest collected data over 160 n.mi. of transects. On average 5-6 hours each day were spent on the water conducting the survey by both boats. Weather conditions were unusually good with the only detrimental conditions being heavy fog and occasional 3 m seas. During this same time period, the RV Yuzhmorgeologiya conducted several transects covering the region from the 500 m isobath from the western canyon to the eastern canyon. Hydrographic and net tow stations were occupied several times in the western canyon, mid-canyon rise, and eastern canyon. Twenty-five CTD stations and IKMT net tows were conducted.

 

All equipment and data acquisition systems performed without error or breakdown, except for a few small electrical issues in the RV Roald. Initial results from the Ernest survey are similar to previous years, although an initial analysis of the Ernest echosounder data suggests that krill biomass will be higher this year in the nearshore waters. There were large aggregations of scatterers at the edges of the canyons often in waters between 100 and 150 m in depth. Extremely large patches of krill were also surveyed to try and get a measure of the extent in size and shape of these aggregations. The presence of these patches was often related to the observation of penguins, birds, and humpback whales during the survey.

 

3. Oceanography and meteorology. Northwesterly winds averaging below 20 knots from Sunday till Thursday saw the successful completion of the 28 CTD stations for the Nearshore Survey, bringing the total of successful casts to 145. The CTD/carousel instrumentation system and auxiliary sensors performed well. From Thursday the Northwesterlies averaged above 20 knots, with period above 30. Friday and Saturday saw winds peaking at 40 knots, while crossing the Drake. The Antarctic Convergence was crossed in the vicinity of 57 51.733'S, 61 46.378'W.

 

4. Birds and marine mammal observations. Standardized seabird observations, concurrent with an opportunistic marine mammal effort, was conducted during the transit from the AMLR study area to Punta Arenas. Effort began early on the morning of 11 February in the central Drake Passage about 150 NM north of King George Island and ended the following day east of Tierra del Fuego. Eighteen hours of survey effort covered a total of about 223 nautical miles of trackline, primarily in the north-central Drake Passage to a point about 38 NM east of Cabo San Pilar, Isla Grande de Tierra del Fuego. Gale force winds and rain hampered effort for the latter half of 11 February; however, the following day was unaffected by weather. Nevertheless, a high seastate both days (average of around Beaufort 6), had a severe negative affect on marine mammal detections. There were only four sightings of marine mammals: 3 of Peale's Dolphin and a mixed group of Long-finned Pilot Whales and Hourglass Dolphins, all on 12 February. High numbers of Soft-plumaged Petrels were encountered associated with a passing cold front on 11 February. Noteworthy sightings, likely associated with the same cold front, was a Shy (White-capped) Albatross, a first occurrence on an AMLR cruise, and only the second ever Atlantic Petrel. Both were also noteworthy southerly records.

 

A. Jenkins sends.