AMLR 2003 Weekly Report No. 10

16 March 2003

1. The R/V Yuhzmorgeologiya is currently in the South Shetland Islands north of Elephant Island conducting a trawl survey of demersal finfish. Additional research activities include characterization of benthic invertebrate fauna, acoustic sampling of krill abundance, seafloor video transects, and seabed habitat characterization of shelf areas within the 500 m isobath of the South Shetland Islands, Antarctica. Although the survey was originally to be conducted in the South Orkney Islands, the access to the northern, western, and southern shelf areas of the islands was blocked by heavy concentrations of icebergs. After failing to find safe passage to the shelf, the South Orkney Islands survey was abandoned and the ship proceeded to the South Shetland Islands.

2. We have completed 17 stations to date in the eastern, southern, and western sectors of Elephant Island using a random depth stratified survey design. As of 16 March, a total of 1168.516 Kg of finfish (4156 individuals) of 32 species have been captured and processed. Our greatest combined yields have occurred at stations on the western shelf of Elephant Island within the 100-200 m depth strata. Hauls in the southern and eastern sectors of Elephant Island have produced smaller yields of finfish per standardized area swept with a greater species diversity.

3. The species composition encountered so far was similar to those observed during previous surveys. Champsocephalus gunnari and Chaenocephalus aceratus were either equally or more abundant. Of interest from an ichthyological point of view were the catch of some high-Antarctic species, such as Neopagetopsis ionah, Gymnodraco acuticeps or Artedidraco skottsbergi. Investigations on the reproductive state of the abundant species indicated that the Chionodraco rastrospinosus, Lepidonotothen squamifrons, and mackerel icefish were in the middle of their spawning season while others, such as Chaenocephalus aceratus and Cryodraco antarcticus were approaching spawning. We were able to collect a large amount of information on reproduction which we are able to compare with data sampled during previous surveys. Feeding studies indicated that species, such as mackerel icefish preyed heavily on krill. More than 95% of the krill taken was small krill of age classes 1 and 2. Scotia Sea icefish and Cryodraco antarcticus preyed on krill and mysids when they were small and fish when they grew larger. Feeding intensity of these two species was low. Ocellated icefish fed on krill and fish, however, with a low intensity due to the height of the spawning season. Lepidonotothen squamifrons took primarily jellyfish and some isopods, amphipods and krill. Polychaetes formed an important prey item in Gobionotothen gibberifrons while others, such as isopods and amphipods, were less frequently found.

4. Four combined video/camera transects have been completed this week. The survey design calls for a number of 1 nm transects to be affected across selected depth strata. The data will serve as a method to describe spatial habitat variability within strata and document habitat utilization by fish fauna. The image data will also ground truth the acoustic seabed classification system and provide in situ observation of epibenthic invertebrate fauna. As the camera system is a new experimental design, camera settings and deployment logistics continue to be refined. Our current design incorporates a small (1 m³) frame that houses the digital still camera, sonar altimeter, and flash assembly that is towed from the ship's traction winch. The self-contained video system (video, light, and twin scaling lasers) is flown from a distance of five meters behind the still camera frame. We plan to deploy the video system in the mouth of the trawl later this week.

5. The invertebrate bycatch from the bottom trawl collected from the east and south sides of Elephant Island maintains the pattern observed during the 2001 AMLR bottom trawl survey, with high diversity and biomass, often dominated by sponges, on the east end and lower diversity and biomass to the south side. Reoccupying similar stations as the 2001 survey will offer a good opportunity for interannual comparisons in spatial distributions and ecological relationships. A little benthic invertebrate trawl (“Little BIT”) was attached to the wing sweep of the bottom trawl to collect a more quantitative sample of benthic megafauna for comparison to the bottom trawl bycatch. After an initial deployment of every second trawl, a protocol for processing the abundant and taxonomically complex benthos was established so that every trawl could be deployed with a Little BIT on the side. The samples of the benthos using the Little BIT indicate a very different sampling capability from the fish trawl. In some cases, only a single specimen of a given invertebrate taxon is represented in the bottom trawl, yet in the Little BIT, it was represented by several hundred specimens and has come close to being the dominant taxon in the sample. In other cases, sponges were easily collected, but urchins and brittle stars were largely absent from the fish trawl. Though it is possible that these smaller organisms are washed through the larger mesh fish trawl, it is more likely that they are low enough to the bottom that they are not picked up at all as the net rolls over them. Thus, the Little BIT appears to be a useful tool by which to assess the impact of the bottom trawl on the benthic invertebrate community. The usefulness of this sampling tool will continue to be explored for the duration of the Leg.

6. Blood and tissues samples were collected from representative specimens from all notothenoiod species to assess the levels of blood antifreeze proteins and number of antifreeze genes in their genome. The presence of the high latitude Antarctic Trematomus and chaenicthyiid species in the warmer waters of the Antarctic Peninsula (Relative to the McMurdo Sound) will allow us to determine the effect of the relatively warm temperatures on the blood levels of the antifreeze proteins and compare the number of antifreeze genes to those of the extremely cold McMurdo Sound populations. In order to survive, the high latitude species must have a full complement of antifreeze proteins (freezing point < -2ºC) while the abundant low latitude notothenioid species have lesser amounts of antifreeze protein (blood freezing points of -1.5ºC) that correlate with their warmer environment. (0 to +1ºC). The relatively low level of antifreeze protein precludes their survival in the year round freezing high latitude waters. In part the distribution of the various Antarctic notothenoiod species may be explained by their level of freezing avoidance that is correlated with their level of blood antifreeze. The effect of warm temperature on the antifreeze level of the high latitude Antarctic notothenioid fishes represents a natural temperature acclimatization experiment that will be compared to laboratory acclimation experiments. The relatively rare high Antarctic species collected thus far are, Trematomus hansoni and bernacchii and Gymnodraco acuticeps. Surprisingly, Dissostichus mawsoni juveniles are relatively abundant relative to the Trematomus species. Similar collections have been made from the abundant Peninsula species and will analyzed at the University of Illinois.

7. Three aspects of notothenioid biology have been investigated: the phylogenetic relationships of notothenioids using DNA sequences from both mitochondrial and nuclear genes, the evolution of buoyancy among notothenioid species, and ecomorphological studies that are attempting to relate morphological differences between closely related species with documented ecological variation (i.e., diet). After four days of sampling the species available for molecular phylogenetic study has increased by three, including a previously unsampled family. Buoyancy data collected over the past week has led to a discovery of the heaviest notothenioid recorded to date, Harpagifer antarcticus. Mouth gape width and the degree of upper jaw protrusion have been collected as ecomorphological data on a total of 21 notothenioid species.

C. Jones sends