Weekly Report No. 4
5 February 2006
are currently sampling as part of the NSF sponsored AMLR supported nearshore study off Cape
SSI. We have completed the broad scale acoustic survey for krill biomass. As
part of the nearshore survey the “Yuzmor”
has been sampling krill along 3 transects during the night, and are
acoustically sampling krill along10 transects over and area of approximately
400 nmi2. At this time we have completed one pass through the entire
grid, and will begin the second pass tomorrow morning. This sampling will
continue until 9 February when the Yuzmor will anchor
off cape Shireff and recover the nearshore team, moorings, and personnel before departing to
for post cruise acoustic calibration.
Oceanography and meteorology. The reliable
performance of the CTD, carousel, auxiliary sensors and onboard salinometer verification system, across the 129 casts of
the main survey area, and the beginning of the Cape
inshore survey area, resulted in no lost survey time, due to equipment maintenance
or repair. The week’s processed CTD data across the Bransfield
Strait showed a predominance of Water Zone 4 type waters, except at the western
end of the strait, where a mixed area of low surface salinity/warm surface
temperature Water Zone 4, 3 and 2 types were sampled.
and Tuesday saw Northwesterlies averaging <10
knots, but a barometric pressure trough of 1003 to 987 to 1005 millibars across Wednesday and Thursday, accompanied by a
wind shift to the northeast, produced wind speeds averaging 32 knots, peaking
at 42 knots on Thursday afternoon and a drop in air temperature to < 1°C.
Krill and Zooplankton – Joinville Island and South Survey Areas. Like the West and Elephant
Island Areas, modest numbers of postlarval krill (Euphausia superba) were
broadly distributed across Bransfield
Strait, where they were present in
5 of 6 Joinville
Island and all 20 South Area net
samples. Concentrations encountered in
the Joinville Island Area (95 and 15 per m3
mean and median values) exceeded those in the Elephant Island Area (24 and
11 per m3) with the largest Survey
A catch (510 per 1000 m3) located here over the Joinville
Island shelf. Smaller concentrations in
the South Area (26 and 8 per 1000 m3 mean and median) were similar
to those of the Elephant Island Area.
usual, the krill age-maturity composition in Bransfield Strait
was much more diverse than in the other areas and represented the inclusion of
smaller and younger individuals. Lengths
in the Joinville Island Area ranged from 23-55 mm,
with modes at 32, 42 and 47 mm roughly corresponding to 1-, 2- and 3-year old
krill. Half of the krill were < 42 mm
in length. Accordingly, juveniles and
immature stages comprised 19% and 29% of the total while the other 52% were mature
stages. Males and females were equally
represented, with 90% of mature females in advanced reproductive stages (i.e.,
with developing ovaries, gravid or spent).
Gravid stages constituted 20% of total individuals here, including
virtually all 2-year old (36+ mm) females collected.
the South Area lengths ranged from 26-59 mm with 34, 42 and 50 mm modes and a
48 mm median. Here juveniles represented
only 5% and immature stages 15% of the total compared to 80% mature forms. This was due primarily to relatively large
numbers of large mature krill associated with input of water from Drake
Passage into northwestern Bransfield Strait.
early stage calyptopis 1 stage krill larvae were
found indicating a late December-early January spawn. The median concentrations in Joinville Island Area (14 per 1000 m3) were
similar to those in the Elephant Island Area (19 per 1000 m3) while
lower concentrations in the South (16 and 0 per 1000 m3 mean and
median) were similar to those in the West Area.
As in the Elephant Island Area, larval krill concentrations appeared
associated with complex fronts and gyres in the eastern portion of the large
contrast to previous years, Salpa thompsoni was virtually absent from Bransfield Strait
confirming its current association with water north of the Southern Antarctic
Circumpolar Current Front (SACCF). The
other salp species Ihlea racovitzai, a marker for Weddell
Sea water, was also rare reflecting the relatively limited
presence of Weddell gyre (Zone 5) water this field season.
comprised the most abundant zooplankton taxon in Bransfield Strait,
but with median concentrations (360 and 770 per 1000 m3) nearly an
order of magnitude lower than in the West and Elephant Island Areas. The coastal species Metridia gerlachei was most abundant followed by
small “other” unidentified species. Mean
abundance of postlarvae of the euphausiid
ranked third after copepods and larval krill in the Joinville
Island Area while in the South Area it ranked second after copepods, followed
by that of chaetognaths and high latitude euphausiid Euphausia crystallorophias.
Of note was the presence of pelagic juvenile Antarctic silverfish, Pleuragramma antarcticum,
in 50% of the Joinville
Island and South Area samples. The distribution of these fish across
Strait suggests input from Gerlache Strait
located to the southwest.
Acoustics and biomass of krill. We have completed
preliminary estimation of the biomass of krill in the Bransfield Strait,
in subareas of Joinville
and in the South area using the EK-60. Only two transects were completed in the
Joinville area during daytime. Thus the biomass
estimate 234 K tons, has high variability (CV=35%) associated with it. Mean
krill density varied widely between the two transects (2.2 and 22 g m2)
contributing to the high variability as well. In the southern area biomass was
low just 134 K tons, and mean density of krill was 5 g/m2. These
numbers continue to be very low and suggest that biomass in the surveyed area was
less than a million tons of biomass present in the South Shetlands.
We will estimate krill biomass using the SDWBA approximation in the final
Phytoplankton. Continued high biomass was encountered
in the Joinville
Island and South Areas. In the Joinville Island Area, 5 meter chlorophyll averaged 0.98 ±
0.66 mg m-3 (5 stations), with integrated values of 64 ± 25 and 38 ±
11 mg chl-a m-2 for integration to 100 m and
1% PAR, respectively. In the South Area, 2.35 ± 1.39 mg chl-a
m-3 averaged at the surface (19 stations), and 100 m and 1% PAR
integrated values of 101 ± 51 and 53 ± 12 mg m-2, respectfully.
Highest chl-a concentrations
were found in the central and northern portions of the entire Bransfield Strait
where 2.63 ± 1.25 mg m-3 was the average at the surface (17 stations)
and 103 ± 53 mg m-2 averaged as integrated to 100 m. The lowest
phytoplankton biomass recorded was measured along the peninsular shelf area
where 0.7 ± 0.26 mg m-3 was averaged for 5 m water (7 stations), and
70 ± 26 mg m-2 was the average for 100 m integrated values.
projects have measured in-situ
radiometric, backscattering and fast repetition rate fluorometry
data from 18 stations, with samples taken for 27 CHN and HPLC pigment, and 10
photosynthesis verses irradiance curves. 6 stations with 18 samples have been
taken for particulate and dissolved iron, iron speciation and organic ligands. Also, 33 radium samples have been analyzed, plus
74 thorium-234 for vertical transport analysis. Approximately 175 samples have been
collected for near-future nutrient analysis of different depths from various
stations within the entire survey grid.
Predator Diet Studies. Lipids have been extracted
from 48 Antarctic fur seal milk samples. A total of 41 scat samples from weeks
1-6 have been processed to date. Thus far, five scats have contained otoliths with week 6 starting to show a higher
concentration of otoliths. The otolith
of G. nicholsi
is dominant in week 6 scats. The nearshore net tows
are finding G. nicholsi
at almost every station which is concurrent with the findings on the fur seal
scats. Krill total length, calculated from the carapace length and width
continues to range between 36-60 mm with the majority of total lengths
averaging between 50-57 mm. The fish that are caught during the nearshore survey nightly net tows will be saved and used in
the bomb calorimeter for total energy concentrations (at the SWFSC). In
addition to the 150 frozen krill already measured, an additional 100 krill will
be measured this week to continue the regression equations and discriminate
Seabirds and Mammals. Data on the distribution,
abundance and behavior of seabirds and mammals was collected during underway
ship operations in the Joinville and South strata. Four
transects were collected in the Joinville area,
totaling 90 nautical miles of survey effort.
Southern Fulmars were abundant during transit between stations, and one
Antarctic Petrel was observed. Twelve
transects were collected in the South area, totaling 250 nautical miles of
survey effort (70% of South area).
Southern Fulmars were very abundant along transects, and were frequently
observed resting on the water in large rafts numbering from 20 to 50+
birds. They were usually encountered
along the northern and southern shelf break regions in Bransfield Strait,
especially near surface slicks. Feeding
aggregations by Cape Petrels
were common along transects in the vicinity of King
George Island. On the westernmost transect in the South area
(Station 15-15 to 17-13), numerous groups (size ranging from 20 to 30+) of
Black-browed and Gray-headed Albatrosses were observed rafting and surface
seizing for prey. These observations
were the greatest densities of albatrosses observed during AMLR 2006. An exceptional sighting of a Snow Petrel was
observed, and enjoyed by all on 1 February.
Humpback Whales were the numerically dominant marine mammals encountered
during the South survey period. Furthermore,
on at least five transects, more than 20+ sightings were recorded of groups
averaging 3 animals. Breaching by Humpbacks
was common, and on several occasions 2 or more individuals were observed
breaching simultaneously. On transit to
station 09-11 south of Admiralty Bay,
5 Killer Whales were encountered.
C. Reiss sends.