AMLR 2005 Weekly Report No. 7
1. Our current position is
approximately 55 nautical miles southwest of
Provisions, propane, fuel and personnel (J. Hinke) were transferred ashore by zodiac. Survey-D began 22 February, but abruptly our progress was brought to a stand still for 24 hours due to a strong gale with easterly winds sweeping into the South Shetland archipelago. The survey was resumed once the weather moderated. Survey operations in the West Area were completed this past week. Despite our coarse beginning recent agreeable weather and sea conditions put us back on schedule.
2. Krill, salps
and other zooplankton. West Area Summary.
Results from net sampling in the West Area during Survey-D were quite
similar to those last month. A generally
depauperate zooplankton assemblage numerically
dominated by Salpa thompsoni,
copepods (notably Metridia gerlachei)
and post larval Thysanoessa macrura. Mean salp
abundance (817 per 1000 m3) was half of that in January but the
median was somewhat greater (635 vs. 424 per 1000 m3) reflecting a
more even distribution across the area.
This was associated with mixing of oceanic (Zone 1) and coastal
waters. Greatest concentrations were northeast
Mean and median abundance of
copepods (805 and 337 per 10003) and post-larval T. macrura
(179 and 566 per 1000 m3) were about 3 times greater than in
January. Largest concentrations of both
occurred over the
Krill were again sparse with mean and median abundance values (7.8 and 1.4 per 1000 m3) equal to those in January. The majority of individuals were large mature stages representing the 2000/2001 and 2001/2002 year classes. Males and females were more equally represented (1.6.1 ratio) than before with mature males comprising 51-25 of the catch. The majority of females were in early reproductive stages (3a-b) and only 36-25 of mature forms were advanced (3c-e) suggesting a delayed spawning season. This is supported by low concentrations, and early stages, of krill larvae.
3. Krill biomass and dispersion. We have completed acoustic estimates of the krill biomass in the West area of the AMLR survey grid. Preliminary data processing has resulted in an abundance of 13.14 g/m2, almost half of the biomass of leg one, 24.68 g/m2. The preliminary results for the mean biomass for the West area are about 20-25 greater than 2004 leg 2 results. There was significant noise on two of the transect lines but the cause was later identified and fixed.
4. Phytoplankton. For the West Area lying east of Line 11, surface chlorophyll concentrations averaged 0.93-0.68 mg m-3, with integrated concentrations being 72 (to 100 m) and 40 (to 1-25 incident light) mg chl-a m-2. These values are higher than found during January, primarily due to increased phytoplankton concentration for pelagic waters. Offshore surface concentrations (12 stations) were 0.43-0.36 mg chl-a m-3 as compared with average values of 0.01 mg chl-a m-3 last month.
Integrated values were
approximately 37 and 24 mg chl-a m-2 for
values integrated to 100 meters and 1-25 incident PAR (meter depth), respectfully.
Surface concentrations for the shelf and shelf-break (~2000 meter bottom depth,
9 stations) were also found slightly higher than January values, being 1.59-0.32
mg chl-a m-3 values integrated over 100 m
depth averaged 119 mg chl-a m-2, and
integrated over depth to 1-25 incident PAR(~43 m) averaged 62 mg chl-a m-2. Stations D14-08 and D15-09 (located
in the central shelf-break region of the
5. Oceanography and
meteorology. February 22, after the first station on the big survey grid
was completed, the wind direction changed from
During the week some problems occurred with the CTD system and data acquisition computer. The Datasonics Altimeter stopped logging data and was removed from the CTD system and replaced with a spare unit. The Seatech Transmissometer was found to be giving suspect data and was removed for repairs. The data acquisition computer “froze” during certain CTD casts and had to be rebooted on occasion, with loss of some SCS data during these periods. Problem with dirty contacts on graphics card was also experienced.
6. Predator diet studies.
Scat samples 2361-80 (Weeks 7 and 8) have been processed and the data entered.
Scat samples 2381-90 (Week 9) as well as 12 raw and duplicate milk samples were
transferred to the ship from
7. Bird and marine mammal
observations. The crossing of the Drake Passage (20-21 February) and the
AMLR West area surveys, northwest of the South Shetland Islands (22-26
February), featured possibly unprecedented numbers of petrels of the genus Pterodroma. To
date, we have encountered five Kerguelen Petrels, P.
eight Mottled Petrels, P. inexpectata, and more than 580 Soft-plumaged Petrels, P. mollis.
Many of the latter have shown signs of wing molt, while others have not,
suggesting the presence of two age classes. The overwhelming majority of these
petrels have been located in the deeper water sections of the survey transects,
with the largest concentrations noted near the Shackleton
Fracture Zone. Most appear to be traveling to the west. The nearest known
breeding colonies of P. mollis are on Tristan de Cunha
and Gough islands in the
Submitted by A. Jenkins.