AMLR 2006 Weekly Report No. 9

13 March 2006

1. The R/V Yuhzmorgeologiya is currently anchored in Ezcurra Inlet, Admiralty Bay, King George Island. For the past two days, the ship has been involved in the closure of two AMLR field camps: Cape Shirreff, Livingston Island; and Copacabana Field station, King George Island. All AMLR field camp personnel are safely aboard the ship and all equipment, materials and rubbish recovered to the vessel via zodiac. Presently the ship’s echosounder is being calibrated in Ezcurra Inlet. Overnight the ship will proceed to the northern Weddell Sea along the southeastern shelf areas of the Antarctic Peninsula’s Joinville Island to continue conducting bottom trawl research survey operations for demersal finfish, benthic invertebrate megafauna, and acoustic krill and seabed habitat characterization.

2. We have successfully completed trawl 57 stations to date using a random depth stratified sampling design, including the easternmost and southernmost stations of the survey, as well as a station positioned at the entrance of the Antarctic sound. In addition, 2 opportunistic hauls were taken north of Livingston Island subsequent to closing Cape Shirreff field camp. As of 12 March, a total of 1751 Kg of finfish (7164 individuals) of 48 species have been captured and processed. Our greatest combined yields of finfish have occurred at stations north of Joinville Island within the 200-300 m depth strata. Finfish species with the greatest biomass, numbers, and ubiquitous presence continues to be Gobionotothen gibberifrons, followed by Chionodraco rastrospinosus and Trematomus eulepidotus.

3. We have encountered a total of 35 notothenioid finfish species. With very few exceptions all finfish species captured have belonged to the families Nototheniidae and Channichthyidae. The only bathydraconids were Gymnodraco acuticeps and Parachaenichthys charcoti. No artedidraconids were caught during trawling operations this week. Buoyancy data, tissues for genetic analyses, and specimens have been collected from a 255 specimens. Our sampling along the Antarctic Peninsula has allowed us to collect specimens of Gobionotothen gibberifrons from the southern edge of the species’ geographic distribution.

4. The species Trematomus eulepidotus will likely commence spawning in 3-4 weeks time, while T. newnesi are likely to start spawning 2 weeks thereafter. Gonads of the icefish Chaenodraco wilsoni were all in resting stage. Most fish we caught were 26-34 cm long, representing 1 or 2 age classes only. Another abundant icefish, Cryodrao antarcticus, was mostly represented in our samples by juvenile fish less than 45 cm long. The few adult fish we caught pointed at a start of the spawning season in 4 weeks time. Otoliths were collected from both species. They will be further processed by an Italian colleague. Chionodraco rastrospinosus was in the middle of the spawning season, with an oocyte diameter of running ripe fish of 4.7-4.9 mm.

5. Stomach content analyses confirmed the picture of Antarctic fish that icefish feed primarily on krill and fish. Feeding intensity was high in C. wilsoni. Prespawning and spawning C. rastrospinosus hardly fed. Only juvenile and post-spawning individuals preyed heavily, primarily on krill. In C. antarcticus, the proportion of empty stomachs was high, though stomachs contents were often regurgitated. Nototheniids are much more diverse in terms of their diet. G. gibberifrons and Lepidonotothen nudifrons were primarily benthic invertebrate browsers, with polychaetes representing one of the most abundant prey items. Trematomus eulepidotus, Lepidonotothen squamifrons and T. newnesi preyed primarily on krill, salps, and jellyfish.

6. The benthic invertebrate composition of the stations conducted this week have been analysed for abundance and biomass of megafauna bycatch. Total bycatch biomass encountered northeast of Joinville Island varied greatly—from less than 1 kg to just under 300 kg. Composition also varied. Bycatch biomass of the eastern most stations sampled were dominated by echinoderms, particularly Bathyplotes holothurians, but also anemones and squids contributed significantly. Although at comparable depths, the other stations in this region were dominated more typically by diverse sponge and tunicate assemblages. Additional notable stations included two taken north of Joinville – one of which for its exceptional diversity of echinoderm species, the other for an extremely high abundance of lamellarian gastropods.

7. Krill densities observed from acoustics have averaged 45 g/m² over 55 survey stations with a high of 338 and a low of 0.09 g/m². Bottom typing is still being analyzed and will not be finished until after the end of the cruise.

8. Seabird observations from 3 March to 10 March: Thirteen seabird species were observed in the 300-meter observation zone astern. The average number of birds sighted per observation during non-fishing and non-discarding periods was 2.6. Trawl deployment, tow and retrieval periods were similar (2.8, 3.1 and 3.3, respectively). Non-fishing periods with discards were slightly lower this week (5.1). A maximum of 31 birds occurred in the observation zone. Wilson’s storm petrels, cape petrels and black-browed albatrosses were the most prevalent species.

9. On Monday the air pressure dropped from 986 to 962 millibars; this was associated with strong north westerly winds reaching maximum speeds of around 37 knots. With the subsequent rise in air pressure the wind speeds moderated to average around 15 knots for the remainder of the week, with some calm periods. The wind direction fluctuated between North-North West and North-North East. The beginning of the week also saw overcast and rainy conditions, with air temperatures staying below 0°C, with the rise in air pressure weather conditions improved and air temperatures averaged around 1-1.5°C, reaching a maximum of 3.2°C.

10. A total of 9 CTDs were successfully completed during the previous week in the area north and north west of Joinville Island, with 4 stations being in the depth stratum between 100-200 m; 1 station in the depth stratum between 200-300m and 4 stations in depth stratum between 300-400 m. According to the Water Zone Classification table all the stations were influenced by Water Zone 5 (Weddell Sea) water type.

C. Jones sends.