AMLR 2008 Weekly Report No. 3
Well after last week’s sunny and calm period, we were
reminded about how remote it is to sample
Acoustic biomass estimates for the West shelf showed the
area to be rich with krill. Our estimates indicate that more than 605K tons of krill
were present on the West shelf during January. Density of krill exceeded 1.5 g
m-2. These numbers compare favorably to the numbers from 2007 and
2006. Large patches of krill were visible in the acoustic data many extending
thousands of meters in length. We expect that the biomass in
Due to rough weather conditions and lost or damaged nets
the Elephant Island Area survey was limited to 34 quantitatively useful net samples. Krill were present in all but one of these
with overall mean and median abundance values of 286 and 22 per 1000 m3,
respectively. These values are both ca.
3× larger than those of the West Area.
The largest catch of 8000 individuals (3600 per 1000 m3) was
Because of the overwhelming dominance of the largest
catch it is excluded from considerations of overall krill demography in the Elephant
Island Area. Lengths ranged from 15 to
57 mm but most (85%) were <45 mm and centered around strong modes of 27 mm
and 42 mm. These modes correspond to one- and two-year-old individuals and reflect
strong recruitment success of the 2005/06 and 2006/07 year classes. This marks the third successive year of good
recruitment in the
Juveniles comprised 52% of the catch while immature stages made up 16% and mature stages 33%. The immature stages were largely two-year old males while small two-year old females were mostly mature and reproductive. Overall 25% of the mature females were in advanced reproductive stages (with spermatophore packets, developing ovaries and gravid). However, since the temporal progression from recently mated to gravid individuals appeared to coincide with the survey period it is likely that the major seasonal spawning event here is in late January and early February.
Larval krill occurred in 24 of the 34 (71%) samples with
overall mean and median abundance values of 23 and 5 per 1000 m3. Virtually all of these were early calyptopis stages resulting from spawning two to three
weeks earlier (i.e., early to mid-January).
Greatest concentrations were located over deep basins northeast of
The zooplankton assemblage in the Elephant Island Area
was relatively simple, strongly dominated by just a few taxa
and conforming to the quintessential
Four steep peak and troughs of the barometer across the week resulted in grey skies and Northwesterlies, almost continuously above 20 knots with Monday to Wednesday producing sustained periods of 30 to 40 knots, gusting to 45 knots. The accompanying 3 to 6 m sea swell height resulted in two stations on the eastern line of the West Area, having to be abandoned, but to date, all other stations have been successfully occupied in the Elephant Island Area.
This brings the successful CTD dip total to 67. The CTD data has been processed and verified with the water bottle samples and the Autosal salinometer and field water-typing analysis done. Routine maintenance, and the usual running repairs on the CTD system (mainly underwater connectors), were limited to the transits between stations, resulting in no time being lost due to CTD technical problems. Various arrangements of the two PAR sensors on the CTD frame were installed for calibration purposes.
The remaining portion of the West Area was completed, with 5 m chlorophyll-a being 0.49-0.52 mg m-3. Highest biomass was found at station A1509, with 1.6 mg chlorophyll- a m-3 at 5m; in profile, this station had ~1.5 mg chlorophyll m-3 from the surface to the pycnocline at ~35 m, steadily declining to ~0.1 mg chlorophyll- a m-3 at 200 m. Fifty percent of the Elephant Island Area now completed (32 stations), with 5 m chlorophyll-a concentrations of 0.69-0.60 mg m-3. Highest biomass was located at Station A1107 (2.4 mg chlorophyll- a m-3), and stations A0806 and A0508 also exhibited high biomass (~1.8 mg chlorophyll- a m-3). In the western Elephant Island Area, the blue water zone was found at ~61ºS and west of ~57´W. Along the eastern side of this front (Stations A0402, A0503, and A0504) chlorophyll-a concentrations were ~1 mg m-3, while along the western side of this front (Stations A0702, A0703 A0704), chlorophyll-a concentrations averaged 0.127 mg m-3 and had a deep chlorophyll-a maximum at 75-100 m. Nineteen stations have been sampled for nitrate, phosphate and silicate, with 12 of these at 10, 30, 50, 75, 100, and 200 m depths.
The Integrated Optics Package (IOP) and the Profiling Reflectance Radiometer system (PRR) have been deployed at 7 mid day CTD stations. Water samples have been collected at 8 mid day CTD stations. To date 16 PvsE experiments have been run and analyzed, ap, ad, and as samples from 40 depths have been analyzed, 40 sample have been run on the Coulter Counter, and particulate CHN samples have been collected for 40 depths. HPLC pigments samples from 57 stations have been collected at surface and subsurface chlorophyll maximum. The surface PRR 810 continues to record surface irradiance at 19 spectral channels. Updated composite satellite images of chl-a and sea surface temperature, and recently added a sea ice composite that will allow us to examine the plan for the second leg of the survey.
Birds and Marine Mammal Observations
Data on the distribution, abundance and behavior of
seabirds and mammals were collected during underway ship operations in the
C. Reiss sends.