AMLR 2004 Weekly Report No. 5

 

8 February 2004

 

1. Our current position is in the vicinity of Cape Shirreff conducting a joint ship and small boat survey of the foraging areas used by fur seals and penguins breeding at the Cape. Earlier in the week, operations were successfully completed at Seal Island, approximately 300 km to the northeast of our current position. Although the ship returned to Cape Shirreff on 5 Feb, adverse weather precluded the start of survey operations until 7 Feb. One of the instrumented buoys deployed off Cape Shirreff was apparently hit by an iceberg+ADs- the buoy was recovered, repaired using spare parts, re-deployed and is now operational.

 

2. Seal Island expedition. One of the objectives of the U.S. AMLR program's Antarctic fur seal studies at Cape Shirreff has been to characterize the age distribution of the adult female population. The age of individual seals is calculated by counting the annuli found in a small post-canine tooth. Validation of the technique used has been confined to a very small number of Cape Shirreff females that were tagged as pups in the early 1990's at Seal Island. These few females were immigrants from the approximately 100 fur seal pups that were tagged every year by the U.S. AMLR program at Seal Island from 1986-1994. Three days were to be devoted to an expedition to Seal Island in hopes of finding more known-aged tagged females to increase our sample size and the age distribution of teeth used for validation of our aging technique. From 2-4 Feb a team of four people (M. Goebel, D. Krause, J. Lipsky, and A. Cossio) were put ashore once a day at Seal Island to collect teeth from adult females tagged as pups at Seal Island. Prior to arrival it was not known how many tagged animals still existed in the population. However, in approximately nine hours of shore time, the team was able to process 15 females using gas anesthesia and midazolam, a sedative. In all, six cohorts were represented in the sample. Ten of the 15 females were from the 1991 and 1992 cohorts and the remaining five were from four other cohorts. Captures were random with regard to tags present and the age distribution of the sample likely reflects differential cohort success within the Seal Island population. Additional tagged animals were present but not sampled and, given the brief duration of the visit, it is likely that the taggedpopulation of known-aged animals is substantial at Seal Island.

 

3. Cape Shirreff survey. The original survey design for the shipboard work had to be extensively modified because of a large number of icebergs grounded in waters less than approximately 300 m depth. Shipboard sampling (acoustic transects, CTD casts, and IKMT tows) is now focused along the onshore/offshore axis of each of two submarine canyons immediately to the east and west of the Cape. The R/V Ernest, a 5 m Zodiac instrumented with multi-frequency echosounders, underwater cameras, CTD, flow-through thermosalinograph, meteorological sensors, radar and GPS, will conduct a series of transects crossing the inshore canyons heads. Operations thus far have focused on the eastern canyon.

 

4. Instrumented buoys. The spar buoy, containing a 200/50 kHz echosounder and a 300 kHz ADCP, that was deployed on 14 January on the western flank of the submarine canyon east of Cape Shirreff, was recovered and replaced with an ES60 70 kHz splitbeam echosounder/300 kHz ADCP version. An initial examination of the ES60 and ADCP data from the recovered buoy showed an abundance of acoustic target activity as well as current and tide information. Weather and ice conditions permitted the second planned mooring site (62+ALA- 27.38S 60+ALA- 42.0W) to be approachable by Zodiac, and an instrument buoy with a 38/200 kHz echosounder and 300 kHz ADCP was successfully moored in 85 m of water. A second receiving/logging station was set up at the Cape Sheriff base and the two newly deployed buoys established communications and logged data until 7 February, when they were recovered, repaired and redeployed. The 70 kHz buoy's radio antenna had snapped off and was replaced with a spare. This could be attributed to the rough sea conditions (6 m swells) experienced over the previous two days. The 38/200 kHz buoy had sustained ice collision damage and had to have its mast, solar panels, radar reflector and strobe light replaced. Radio communication was lost with this buoy on Saturday afternoon. Most likely cause was that a 300 x 300 m iceberg that had moved in line with the buoy and shore station and was blocking the radio signal path. The buoy is currently being detected by the ship's radar, so is assumed to be still gathering ADCP data.

 

5. Krill, salps and other zooplankton. Operations at Seal Island afforded the opportunity to examine bio-geographic patterns observed during the first of two survey of the region (Survey A). The zooplankton assemblage sampled was dominated by copepods, notably a coastal species, Metridia gerlachei, that constituted 23+ACU- of the total mean zooplankton abundance. Other common oceanic species, Calanoides acutus and Calanus propinquus, contributed 18+ACU-, thereby boosting copepod abundance to nearly half (46+ACU-) of total. The salp, Salpa thompsoni, followed in abundance contributing 17+ACU-. Other dominant taxa included postlarvae of the euphausiid, Thysanoessa macrura (15+ACU-) and krill (4+ACU-). Krill abundance, length and maturity stage composition reflected strong recruitment success from the 2000-2001 and 2001-2002 year classes and a weak 2002-2003 year class. Total mean zooplankton abundance and abundance of individual dominant taxa were about average with relation to the long term (1992-2004) Elephant Island data base. Their values most resembled those during the 1997-1998 period. A notable exception is the high latitude salp, Ihlea racovitzai, which typically is rare but had elevated values equal to those observed in 1998 when it was also a dominant taxon. An interesting feature this year was the onshore presence of a species rich and abundant zooplankton assemblage. These typically are characteristics of offshore assemblages associated with Drake Passage water. During Survey A this rich assemblage was associated with Bransfield Strait water. This situation was previously observed only during 1998. The concentrations and locations of Ihlea racovitzai within this onshore group (as during 1998) suggest enhanced advection via deep polar slope water.

 

6. Oceanography and meteorology. During Survey A there was a less clearly defined distinction of the classical Water Zone 1 (ACW) waters on the offshore stations in the West area than in previous years. Many stations in this area displayed a mixing of Water Zone 1 and 2 waters. This mixing was also evident in many of the shallower inshore stations, to the north of the islands, where the distinction between Zone 2, 3 and 4 waters were not as distinct as in previous years. Zone 2 waters were predominant around the eastern part of the Elephant Island Area, with an eddy of Zone 3/4 water around Station 04-03. In the Joinville Island and South Areas, mainly Zone 4 waters were found with the inshore stations of the South Area having surface waters (0 to 50 m) with lower salinity and higher temperatures. Winds were predominantly from the west, with brief periods of southwesterly and northeasterly. Wind speeds averaged 15 knots with peaks of 35 knots on Tuesday and Friday. Most of the week was overcast, with rough seas (6 m swells) on Friday.

 

7. Phytoplankton. No new optical or biogeochemical data was collected this week due to activities at Seal Island. This break allowed for the beginning of the processing of the optical data and its integration with the biogeochemical data. CTD data was used to correct for temperatures effects in the measurement of vertical profiles of absorption and attenuation coefficients measured with a Wetlabs AC9. Voltages from the 3 beam transmissometers (660 nm on CTD and 488 nm and 660 nm on IOP Package) have been calibrated with deep water values to provide beam attenuation coefficients. Calibrated vertical profiles of beam attenuation and total absorption are now available for comparison to population structures observed in the water column. Absorption spectra (particulate, detrital and soluble) measured on in-situ water samples taken from the CTD rosettes and analyzed on a Varian Cary 100 dual beam spectrophotometer provide further insight into the dominant composition of the plankton communities in the water column. Together with the before mentioned Chl-a data we can begin to discriminate abundances of autotrophic or heterotrophic plankton in the euphotic zone.

 

8. Predator diet studies. Antarctic fur seal diet (scats) samples have shifted from mainly krill to krill and fish with one sample that included a squid beak. 49 scats have been processed to date covering weeks 1-5. Additionally, krill carapaces have been increasing with an average krill total length of 49 mm ranging between 40 mm-57 mm. Sample processing will continue until the end of Leg I.

 

9. Bird and marine mammal observations. 22 species of seabirds have been recorded during the past week. Four species of Albatross have been observed, and Grey-headed albatrosses were observed feeding on the transect line along the submarine canyon east of Cape Shirreff. Cape Petrels and Chinstrap penguins were the most abundant avifauna in the Cape Shirreff survey. Blue Petrels and Antarctic Prions were abundant in the outer section of the inshore survey, and were primarily observed flying west. An opportunistic photograph was taken at North Anex, Seal Island, of a Macaroni Penguin colony. After reviewing the picture we were able to count the birds, and approximately 57 adults, and 37 chicks were found. A total of 77 Pale-faced Sheathbills were also observed. Other birds observed nesting in dense numbers on the Seal Island and surrounding islets included: Chinstrap Penguin, Cape Petrel, Southern Giant Petrel, and Kelp Gull. The following marine mammals have been observed during this portion of our surveys (in order of abundance): Cetaceans: Humpback, Fin, and Minke Whales+ADs- Pinnipeds: Antarctic Fur Seal, Leopard Seal. Fur seals have been observed in small groups (2-5) in the waters north of Cape Shirreff. On the transect line along the submarine canyon east of Cape Shirreff, 14 Humpback whales, and 3 Minke Whales were observed. Fin whales were common on the transit from Seal Island to Cape Shirreff. Leopard Seals were common in the waters near Seal Island. On many occasions a Leopard Seal was observed pursuing and capturing Chinstrap penguins, and the usual assault seemed to be the removal of the head and upper chest portion. After the kill, Southern Giant Petrels, Cape Petrels, and Wilson Storm Petrels were immediately on the scene, and small multi-species feeding aggregations were observed. Digital video of the Giant Petrel feeding behavior was recorded, and closer examination of the observed intra-specific behaviors is pending.

 

 

Submitted by Roger Hewitt