AMLR 2003 Weekly Report No. 2
1. Our current position is
approximately 30 miles north of
2. Krill, salps
and other zooplankton. 32 plankton samples have been collected from the South
and West Areas. Antarctic krill (Euphausia
superba) were present in 28 (88%) of these with a total estimated catch of
ca. 5000 individuals. Greatest concentrations were encountered in the South
Area reflecting a high degree of patchiness relative to the West Area; median
catches in the South and West were respectively 1 and 7 per 1000 m3.
Lengths ranged from 13-54 mm, but the majority was small juvenile and immature
stages: 52% of individuals were 29-33 mm and 10% 18-22 mm in length. Overall,
juveniles comprised 46% and immature forms 47% of the total catch. Large mature
krill were represented in oceanic water offshore of the
The salp, Salpa thompsoni, was present in 26 of 32 samples (81%). Like krill their distribution was much patchier in the South compared to the West Area with median catches, respectively, of 2 and 34 per 1000 m3. Virtually all salps were in the aggregate stage. Individual animals ranged in length from 4-52 mm. The largest length suggests initiation of production in early October; median and modal lengths (26 and 28 mm respectively) suggest peak production during mid-November.
Copepods and post-larvae of the euphausiid, Thysanoessa macrura, were present in all samples; with median catches of 140 and 113 per 1000 m3, respectively, these numerically dominated the zooplankton. Larval T. macrura were scarce, suggesting that seasonal reproduction of this species along with that of krill and salps, was delayed during winter-spring 2002. Delayed reproduction could be related to thepersistence of extensive sea ice coverage well into spring (i.e., early November) during this period.
3. Krill biomass and dispersion.
Krill were detected acoustically throughout the West Area with highest biomass
densities mapped in the center of the
4. Phytoplankton. Phytoplankton biomass in the South Area were generally low, with 5 meter chlorophyll averaging 0.4 +/- 0.2 mg m-3 and integrated values (to 100 meter) of 22 +/- 8 mg m-2. This compares to a historical average of 1.32 mg chl m-3 for 5 meter depth in the South Area during January derived from 1993-2002 AMLR data. Lowest values occurred in 1993, 1994, and 1998, averaging 0.75 mg chl m-3, while highest values occurred in 1995 and 2001, averaging 2.20 mg chl m-2. The highest biomass thus far measured was at Station A10-12 having a 5-meter chlorophyll of 1 mg m-3. Very low biomass was also measured on the most western section of the West Area, with 5 meter values averaging 0.09 +/- 0.03 mg chl m-3 and integrated chlorophyll (to 100m) of 13 +/- 6 mg m-2. Although these chlorophyll values are preliminary (i.e., awaiting post-cruise calibration of instruments), the low biomass is corroborated by recent SeaWiFS chlorophyll distributions of the area (provided by M. Kahru, SIO), and profiling in-situ transmissometer and fluorometer data.
In cooperation with WOCE, two
drifter buoys were released north of
5. Oceanography and meteorology.
Oceanographic conditions in the
Fine weather conditions and calm seas, accompanied by a gradual rise in atmospheric pressure were experienced throughout the week. There were extensive sunny periods and moderate air temperatures around 2-3°C with two short periods of 6.5°C. Low wind speeds of 5-13 knts prevailed, with a short spell reaching 25 knts. Winds were predominantly from the N to NW.
6. Predator diet studies. 11 fur
seal scats from
Krill carapaces were present in all scat samples to date, and overall were smaller compared to last year's carapaces (most common size class was 35-45 mm). 51 fresh krill have been sexed and measured for total length, carapace length and carapace width in order to verify equations used to infer length from exoskeleton remains in scat samples. Lipids have been extracted from 24 milk samples.
7. Bird and marine mammal
observations. Systematic bird and marine mammal surveys were conducted during
daylight hours in the