AMLR 2006 Weekly Report No. 8
1. The R/V Yuhzmorgeologiya is currently about 50 nautical miles northeast of the Antarctic Peninsula’s Joinville Island conducting a bottom trawl research survey of demersal finfish, benthic invertebrate megafauna, and acoustic krill and seabed habitat characterization of the northern Antarctic Peninsula region.
2. We have successfully completed 43 stations to
date using a random depth stratified sampling design. As of 5 March, a total of 1495 Kg of finfish
(6287 individuals) of 46 species have been captured and processed. Our greatest combined yields of finfish have
occurred at stations north of
3. Finfish species with the greatest biomass, numbers, and ubiquitous presence continues to be Gobionotothen gibberifrons, followed by Chionodraco rastrospinosus. Overall finfish species composition continues to demonstrate a low abundance or absence of peri-Antarctic fish species, and greater presence and abundance of high Antarctic species. Other species observed with relatively high biomass include species within the genus Trematomus, Such as T. newnesi and T. eulepidotus. Species with the widest distribution include the aforementioned, as well as Chaenodraco wilsoni, Lepidonotothen larseni, and L. nudifrons.
4. A total of 34 notothenioid finfish species have been encountered thus far. Buoyancy data, tissues for genetic analyses, and specimens have been collected for all of these species. Record size specimens have been collected for three notothenioid species, Neopagetopsis ionah, Trematomus tokarevi, and Pogonophryne scotti.
5. Reproductive characteristics, and the food and feeding of the most abundant fish species are being investigated. Among the icefish (Channichthyidae) gonads of C. wilsoni are in resting stage 2. The presence of a few individuals in maturity stage 5 (spent) or in transition from 5 to 2 has confirmed that the species had spawned in November–December. Chionodraco rastrospinosus are in the middle of the spawning season. Individuals in stage 3 (maturing), 4 (running ripe) and stage 5 are being observed. Most individuals of a third abundant species in depths below 200 m, Cryodraco antarcticus, are juveniles. The developmental stage of the gonads of the small number of adult fish caught suggested that they were going to spawn in 4 weeks time. Gonads of Pagetopsis macropterus were in resting stage, and the species appears to spawn in the austral winter.
6. Reproductive patterns among the nototheniids, the second family of endemic Antarctic fish, Gobionotothen gibberifrons and the small Lepidonotothen larseni demonstrate gonads in primarily in resting stage, confirming that the species reproduces in the austral winter (July–September). Trematomus eulepidotus, T. newnesi and Lepidonothen nudifrons commence spawning in 4–6 weeks time. Notothenia coriiceps is likely to start spawning in late April/early May. The few individuals of T. pennellii have gonads in stage 5, suggesting that they had spawned recently. The only bathydraconid species investigated has been Gymnodraco acuticeps, which spawn in late winter-early spring (September–October). Gonads were all in resting stage 2.
7. Studies on the food and feeding of the most abundant species confirm observations from other areas in the Atlantic Sector of the Southern Ocean: icefish prey mostly on krill (C. wilsoni), krill and fish (C. rastrospinosus and P. macropterus, juvenile C. antarcticus) and fish (adult C. antarcticus). Trematomus eulepidotus, T. newnesi and L. larseni are primarily krill feeders, N. coriiceps feeds on a broad spectrum of prey from krill, salps, fish to benthos organisms and algae. G. gibberifrons is primarily a benthos feeder but also takes when available. L. nudifrons feeds entirely on benthic organisms. Juvenile G. acuticeps feed on krill and fish while adult G. acuticeps are almost entirely dependent on fish.
8. The benthic invertebrate bycatch composition
of all 18 hauls completed during the course of this week have been analysed in
terms of abundance and biomass of 47 taxonomic groupings. Total bycatch biomass
experienced has been far less than that seen along the
9. Acoustic abundances of Antarctic krill (Euphausia superba) have been taken for 42 trawling stations. Initial abundances range from 0.09 to 193.4 g/m2 with a mean of 41.1g/m2. Acoustic survey lengths have an average of 4.2 nautical miles. Bottom typing analysis for the transects continue to be processed and catalogued.
10. Seabird abundance data is being collected during trawling operations. Estimates of the number of seabirds (by species) within a 300-meter hemisphere astern of the vessel have been made approximately every 30 minutes during non-fishing periods and every 5 minutes during trawling in order to assess a change in seabird abundance during fishing and non-fishing periods.
11. During seabird observations performed from 21-Feb to 3-Mar, sixteen species were observed including black-browed, grey-headed and wandering albatrosses, giant, cape and snow petrels and Antarctic fulmars. A maximum of 105 birds occurred in the observation zone. The average number of birds sighted during non- fishing and non-discarding periods was 7.7. Retrieval and towing periods had a slightly lower average (6.9, 7.1). Deployment periods and non-fishing periods with discard were also similar (~9.8). Black-browed albatross (BBAL) and cape petrels were the most ubiquitous although cape petrels were more common during fishing periods. More BBAL were seen during non-fishing periods and times when fish were being discarding.
12. All Antarctic fur seal scat samples (30 in
total) have been processed for hard parts of dietary components. All samples contained krill, seven samples
contained one or more otoliths, and two samples contained squid beaks. Otoliths from three species have been identified:
13. The first four days of the week saw winds mainly from the south east, with wind speeds averaging between 20-25 knots and reaching over 40 knots on Monday and Tuesday. The strong winds were associated with an air pressure drop from 995 to 970 millibars. The air temperature also dropped from 3.8°C at the beginning of the week to a minimum of -2.8°C on Wednesday. This cold spell brought cloudy weather conditions, with snow and rain for the major part of the week. Towards the end of the week the wind direction changed to north-westerly, with an average wind speed of around 15 knots and periods of calm conditions, this was associated with an air pressure increase to around 986 millibars. Sunny conditions were experienced on Saturday and Sunday, with air temperature rising to an average of 2°C.
14. A total of 13 CTDs were successfully
completed in the area just north of Joinville Island, with 5 stations being in
the depth stratum between 100-200 m; 3 stations in depth stratum between 300-400m
; 4 stations in depth stratum between 400-500 m, and one station over 750 m. According to the Water Zone Classification
table all the stations, except for the deep cast, had a distinct Water Zone 5 (
C. Jones sends.