AMLR 2009 Weekly Report No. 6
15 February 2009
1. The R/V Yuhzmorgeologiya is currently about 30 nautical miles southwest of the South Orkney Islands easternmost island (Laurie Is.). Primary activities include a bottom trawl survey of demersal finfish biomass, composition, distribution, diet and demographics within the 500 m isobath of the shelf. Other activities include characterization of benthic invertebrate megafaunal bycatch, acoustic and net sampling of krill, physical oceanographic measurements, and underwater video of benthic megafaunal communities and seabed habitat characteristics. Analysis of invertebrate megafaunal biomass and patterns will potentially provide evidence of Vulnerable Marine Ecosystem (VME) risk areas. Additional research activities and sampling efforts for various projects using material collected during the course of the expedition are described below.
2. The first week was spent investigating the northern and eastern shelf regions of Coronation Island and Laurie Island down to 550 m. We have successfully completed 23 stations to date using a random depth stratified sampling design. A total of 2487 Kg of finfish (7004 individuals) of 37 species have been captured and processed to date. Our greatest combined yields of finfish have occurred at stations north of Coronation Island within the 50-150 m depth strata. Hauls in the eastern offshore areas of the South Orkney Islands have produced smaller yields of finfish per standardized area swept. An additional haul was conducted at 770-855 m depth to collect rare notothenioids.
3. The northern shelf area is dominated by low-Antarctic fish species. High-Antarctic species formed only a very minor part of the catches. The most abundant thus far are the yellow notothenia (Gobionotothen gibberifrons) and the Scotia Sea icefish (Chaenocephalus aceratus). The largest catch of a single species (800 kg) was taken when a pre-spawning aggregation of C. aceratus northeast of Laurie Island was encountered. Most other catches have remained below 300 kg. A relatively abundant species below 250-300 m is Lepidonotothen squamifrons, an ubiquitous species which occurs from the southern Patagonian shelf and Burdwood Bank and all around the low- and high-Antarctic zone. Interestingly, the species lacks antifreeze glycoproteins prominent in all other Antarctic notothenioid species. The number of high-Antarctic species increases in waters deeper than 250-300 m. However, their proportion in the catches thus far is still very small. Lepidonotothen squamifrons are in the middle of their spawning season. C. aceratus, P. georgianus, T. hansoni, N. coriiceps, and N. rossii have gonads in pre-spawning state, which suggests that they spawn in 2 months time. Gonads of G. gibberifrons and L. larseni are still in resting stage, indicating winter spawning.
4. A haul taken at 750 - 855 m depth yielded remarkably few notothenioids, the predominant element of the Antarctic bottom fish fauna. The small catch (<10 kg) was mostly formed by the Antarctic grenadier Macrourus whitsoni and the widely distributed Antimora rostrata. Myctophids and the snailfish Paraliparis sp. were also abundant. Of interest was the catch of two individuals of the mostly pelagic icefish Neopagetopsis ionah which occurs only in single individuals in bottom trawl catches. Catches during previous cruises had only yielded individuals >40 cm.
5. The benthic invertebrate bycatch composition thus far has been analyzed in terms of abundance and biomass of 60 taxonomic groupings. The number of taxonomic groupings has been greatly increased since the 2006 AMLR survey in order to incorporate those taxa recently put forward by CCAMLR as indicators of Vulnerable Marine Ecosystems (VMEs). The minimum biomass of these taxa that would lead to designation of VME risk areas to commercial fishing, including long- line and pot fisheries, has not yet been determined for bottom trawl gear, and is currently a topic of considerable international interest. The data being compiled during the course of this cruise, both in the South Orkney Islands and near the Antarctic Peninsula, will be used toward potentially determining VMEs risk areas.
6. Total biomass sorted by the benthic invertebrate team on board thus far totals 3.58 metric tons of benthos. Invertebrate communities of note include those at two Stations north of the eastern end of Coronation Island where almost 5 kg of the beautiful sea pen Umbellula sp., the largest of which had a head disc diameter of 12 cm and its stem was more than 3.5 m long. Umbellula is a VME-indicator taxon. A number of stations located on the outer eastern shelf of the South Orkney Islands have revealed vast communities of Pterobranchia, a little known phyla even amongst scientists and not commonly observed. Of particular note is one Station where 91.9 Kg of pterobranchs was encountered. On the far eastern shelf, 1072 individuals of the sea cucumber, Scotoplanes globosa (known as sea pigs) were brought aboard at a single station, weighing 65.7 Kg. In addition, south of the sea pig community, we collected a very rare predatory tunicate.
7. Selected specimens from 33 species of finfish captured in the first 20 trawls have been sampled for tissue biopsies and whole voucher specimens were fixed in formalin. These specimens will be deposited in the fish collection at the Yale University Peabody Museum of Natural History. We have encountered several rare species that include the dragonfish Prionodraco evansii, the bigeye notothen Trematomus tokarevi, and the icefish Neopagetopsis ionah. The collections include eight specimens of Muraenolepis that are not morphologically consistent with any of the known species in this genus, and may represent a new and undescribed species.
8. To better understand population structure, genetic diversity and phylogeography of selected notothenoid finfish species along the Scotia Ridge, additional muscle tissues for DNA analyses are being collected for further analysis at the Johann-Heinrich von Thünen Institute, Germany. To date, 359 individuals of Channichthyidae and
Nototheniidae were sampled for this purpose. The main species were Chaenocephalus aceratus, Pseudochaenichthys georgianus, Gobionotothen gibberifrons and Lepidonotothen larseni. In addition, 28 specimens of the myctophids Electrona antarcticum and Gymnoscopelus nicholsi were sampled.
9. A total of 736 otoliths from 15 species of finfish (C. gunnari, C. aceratus, G. gibberifrons, L. squamifrons, P. georgianus, T. eulepidotus, C. rastrospinosus, G. nicholsi, L. larseni, N. coriiceps, E. antarctica, N. rossii, L. nudifrons, D. mawsoni, T. hansoni) have been subsampled thus far. These otoliths are to be used in age estimation and stock assessment studies based at the Center for Quantitative Fisheries Ecology (CQFE), Old Dominion University (ODU), Norfolk, Virginia. In addition, otoliths and gonads for C. aceratus are being collected for examining age and growth, reproductive biology, and population structure of this species. Otoliths of P. antarcticum, D. eleginoides, D. maswoni, and N. coriiceps are also being targeted towards the fulfillment of connectivity and population structure projects based at the CQFE. This week, 121 (of the 736 total otoliths collected) were C. aceratus; 23 N. coriiceps. A total of 40 gonads (mixed sexes and stages) were collected from C. aceratus, and the gonads of four other species (C. rastrospinosus, P georgianus, N. coriiceps, N. rossii) are also being targeted for histological studies based at the CQFE and the CNR in Ancona, Italy.
10. A total of 4 camera deployments were completed at selected stations toward collection of direct evidence of VMEs and habitat characterization. Continual experimentation with different camera settings as well as improvements to the operating software has resulted in a steady increase in the quality and consistency of the footage collected. Intermittent faults to the sea cable resulted in some down-time, but have been rectified since and precautionary measures were put in place. Adjustments to the weight and towing setup resulted in much improved performance.
11. Acoustic data are continuously recorded on 4 frequencies (38, 70, 120, and 200 kHz). Krill NASC values (Nautical Area Scattering Coefficient) were measured for Euphausia superba to later be turned into acoustic biomass estimates once length-frequency is determined from the IKMT krill catches. Very little scattering was seen on the northwest to north shelf of the South Orkney Islands. Highest concentrations of krill were found just to the east and south of Laurie Island. NASC values range from 0 to 143.
12. Antarctic fur seal scat is being processed onboard for dietary components. A random sample of 25 krill carapaces are isolated from each sample and measured for length and width. Additionally, all otoliths are removed from each scat. To date, 52 scats have been processed. Of the 52 scats, all but one contained krill, five contained one or more otoliths, and two contained squid beaks. Also, lipids are being extracted from milk samples collected from lactating fur seals. Currently, 71 milk samples have had lipids extracted. Remaining work includes processing 18 more scat samples, identifying the otoliths obtained from scat samples, and extracting lipids from 39 more milk samples.
13. A total of 12 CTD’s were successfully completed with one station cancelled due to rough seas. Standard maintenance was carried out on the system, mostly on the underwater connectors, and measures were taken to prevent freezing of the oxygen sensor during transit.
14. A gradual barometer drop from a 1000 to 990 millibar resulted in overcast skies with periods of rain, fog and snow, accompanied by calm seas for most of the week. Air temperatures dropped steadily ranging between 4 and -1ºC, averaging around 1ºC during the latter part of the week. A sharper drop from 990 to 970 millibar between Thursday and Friday resulted in strong Northwesterly winds in excess of 30 knots accompanied by swells of 2-3 m on Saturday.
C. Jones sends.