AMLR 2006 Weekly Report No. 7

27 February 2006

1. The R/V Yuhzmorgeologiya is currently about 30 nautical miles north of the Antarctic Peninsula’s Joinville Island, conducting a bottom trawl survey of demersal finfish biomass, composition, distribution, and demographics. Other activities include additional finfish research, characterization of benthic invertebrate megafauna, acoustic sampling of pelagic krill abundance, and seabed habitat characterization of shelf areas along the Trinity Peninsula and Joinville/ D’Urville Island regions of the Antarctic Peninsula.

2. We have successfully completed 24 stations to date using a random depth stratified sampling design. One station was invalidated due to gear loss. As of 26 February, a total of 754 Kg of finfish (3387 individuals) of 37 species have been captured and processed. Our greatest combined yields of finfish have occurred at stations north of Joinville Island within the 100-200 m depth strata. Hauls in the southern coastal areas of the Trinity Peninsula survey region have produced smaller yields of finfish per standardized area swept, though relatively higher diversity.

3. Finfish species with the greatest biomass and numbers thus far has been Gobionotothen gibberifrons and Trematomus newnesi. The overall finfish species composition encountered thus far demonstrates a considerable contrast relative to previous AMLR surveys conducted along the South Shetland Islands across the Bransfield Strait. Of interest is the low abundance or absence of dominant peri-Antarctic fish species, and greater presence and abundance of high Antarctic species. Dominant species observed at the South Shetland Islands, such as Champsocephalus gunnari and Chaenocephalus aceratus, appear to be replaced within similar depth strata by species such as Chaenodraco wilsoni, C. rastrospinosus, and T. newnesi, and Cryodraco antarcticus. Of interest from an ichthyological point of view is the presence of the rare species Aethotaxis mitopteryx, Dacodraco hunteri, Pagetopsis macropterus, and Neopagetopsis ionah. We also sampled a very rare pre-spawning aggregation of T. newnesi (985 specimens in a single trawl) north of Joinville Island.

4. The benthic invertebrate bycatch composition of all 24 successful hauls have been analysed in terms of abundance and biomass of 47 taxonomic groupings. Total bycatch biomass has been extremely high ~50% requiring subsampling each weighing over 1 metric ton. This was so particularly along the shelf of the Trinity Peninsula where the bycatch was often dominated by enormous hexactinellid (or glass) sponges measuring approximately half a metre in height and girth. These sponges, also known as volcano sponges, were large enough for a person to climb into - although none dared to do so out of a healthy respect for its notoriously nasty glass spicules. Some specimens required 4-5 people to lift. Despite the notably large bycatches encountered at these southern Bransfield Strait stations, the largest bycatch biomasses recorded so far were at Station 33 north of D’Urville at Island 231 m and Station 40 north of Joinville Island at 142 m each of which contained around 2 metric tons of bycatch.

5. A total of 120 specimens sampled from 28 notothenioid finfish species have been sampled for buoyancy, gape width, jaw protrusion, and genetic analyses. Three fairly rare notothenioid species are included in this sample. One of these species, Aethotaxis mitopteryx, has never been collected in an AMLR fish survey. Also, A. mitopteryx has been suspected as a neutrally buoyant species, but has never been measured. We were able to measure buoyancy in two specimens and both were neutrally buoyant. This is a significant result that will have broad interest among biologists studying notothenioid fishes.

6. Tissue samples have been taken from 130 fish specimens representing 28 notothenioid species. Tissues sampled included muscle, heart ventricle, spleen, and testis. The fish were preserved in formalin as voucher specimens for the Yale University’s Peabody Museum tissue collection. The tissue samples will be used to refine our knowledge of the evolution of the notothenioid suborder and to study the process by which the icefishes (16 species in the family) have lost the capacity to produce red blood cells and hemoglobin.

7. Acoustical data are continually being taken for krill abundance and also bottom typing. Initial acoustical krill abundance ranged from 0.097 to 80.3 g/m². A few dense patches of krill were observed during trawl transects contributing to large abundances. Average acoustic transects for trawls were 4 nautical miles. Bottom typing data are still being analyzed. Bottom depths are being used to create an in situ bathymetric chart used in finding locations suitable for trawling.

8. Antarctic fur seal scat is being processed onboard for hard parts of dietary components, and lipids are being isolated from milk samples. To date, 27 scats have been processed. Of the 27 scats processed: all contained krill; seven contained one or more otoliths; two contained squid beaks. Remaining work includes processing 3 additional scat samples; identifying, sorting, and fully labeling all otoliths; and processing all milk samples (22 in total).

9. A total of 18 CTDs from a possible 24 stations were successfully completed, with the western station showing mainly Water Zone 4 (Bransfield Strait) waters and the stations north of the Antarctic Sound/ Joinville Island area having Water Zone 5 (Weddell Sea) influence.

10. Predominantly overcast skies with periods of rain and fog saw air temperatures ranging between 0 and 4.5°C (average around 2°C) during the week, with only short periods of sunshine. Gradual barometer increase from 985 to 1017 millibars produced a South Westerly wind with speeds averaging between 15 and 20 knots, with a maximum wind speed of 36 knots recorded on Friday. The barometer dropped towards the end of the week to around 987 millibars and winds calmed down to around 3 knots, thick fog was experienced for this period.

C. Jones sends.