AMLR 2008 Weekly Report No. 2
After successfully completing the fur seal survey, the
field-camp crew was dropped off at
Acoustic data for the use in generating biomass estimates of krill will be completed for the next update. We await the completion of the final 7th transect of the West Area. All acoustic instruments have worked flawlessly, at condition up to 5 meter seas, and 30 knot winds. We have been able to make 10-12 knots most of the survey with high quality data recorded.
Postlarval krill were widely distributed across the region north of
The krill length-frequency distribution was strongly bimodal with peaks centered on 28 mm juvenile and 50 mm adult lengths. Juveniles comprised 36%, immature stages 14% and mature individuals 50% of the total catch. These results suggest fairly strong recruitment success from last years (2006/07) reproductive effort. This would be the third year in a row with good krill recruitment.
Virtually all of the mature krill were in the early reproductive stages, with female stage 3A and 3B making up 30% of the total krill catch. These results, plus the fact that most of the spermatophore packets attached to 3B females appeared to be fresh, suggest that sampling occurred during a massive synchronous mating event. The infrequent occurrence (42% of samples) and low concentrations (mean 2 per 1000 m3) of early calyptopis stage krill larvae support the idea that this is the first major reproductive event of the season.
The remaining zooplankton assemblage was numerically
dominated by copepods (primarily Calanoides acutus, Metridia gerlachei, Pareuchaeta sp.
and other unidentified species), postlarval Thysanoessa macrura and chaetognaths. Salpa thompsoni was
present in 14 of the 19 samples with mean and median abundance values of 16 and
10 per 1000 m3, respectively.
Largest concentrations of this salp species
were over shelf and slope areas northwest of
A slowly falling barometer, and winds from the west, saw calm
seas, mild overcast weather during the Drake crossing. The convergence’s
northern edge was well defined and crossed at latitude 58°S, on the southbound
transit. Two periods of strong winds,
mainly from the west, peaking to forty knots were experienced on Tuesday and
Sunday. This was associated with a sharp drop in barometric pressure. The
average wind speed for the above mentioned period was around fifteen knots. An
extra transmissometer (blue) and a second 2PI PAR
sensor were installed and interfaced to the CTD system and 24 casts were
successfully completed, during the acoustic calibrations and the stations of
the South Area, including 4 additional stations that very completed during the
initial seal survey. A further four drifters were deployed north of
Only 50% of the West Area samples have been processed at
this time. For the area north of
Scripps Institution of Ocenaography
collaborators have deployed bio-optical instruments daily, and have collected
water samples for analysis from the mid-day CTD cast. To date, the Integrated
Optics Package (IOP) and the Profiling Reflectance Radiometer system (PRR) have
been deployed at 3 mid day CTD stations. Water samples have been collected from
various mid day CTD depths for photosynthesis vs. irradiance (PvsE) experiments, analyses of particulate absorption (ap/ad) and dissolved material absorption (as), HPLC
pigments, particulate CHN, and measurement of particle number and size distribution
(Coulter Counter). HPLC pigments samples
have been collected at surface and subsurface chlorophyll max have been collected
at 20 stations. Additionally the surface
PRR 810 has continuously recoded surface irradiance at 19 spectral channels
since beginning the
Birds and Marine Mammal Observations
Data on the distribution, abundance and behavior of
seabirds and mammals were collected during underway ship operations in the West
stratum. Twenty transects were collected totaling approximately 540 nautical
miles of survey effort. The seabird
community consisted primarily of
C. Reiss sends.