Mike Castellini in Antarctica

Official NSF Report
Antarctic Pack Ice Seals (APIS) Site Report No. 2

January 3-9, 2000

1. General (Bengtson): During the past week, we have been moving easterly along the fast ice margin of Marie Byrd Land, between Cape Colbeck (158 W) and Cape Burks (137 W). Sampling of seals, their prey, and environmental conditions is proceeding well; mostly favorable weather has aided our good progress to date. The open water north of this fast ice represents a polynya approximately 50 km wide and 500 km long, situated over the continental shelf. The ice edge and fast ice on the southern edge of this polynya are situated over the continental shelf, one of the few place in our study area with ice-covered shelf habitats, due to this year's sea ice distribution. Therefore, our transit along this coastal feature provided an excellent opportunity to conduct APIS sampling in a distinctive type of ice edge/shelf slope habitat that will not be encountered anywhere else during our cruise.
   
   
2. Seal abundance and distribution (Bengtson, Boveng, Laake): For the past week, we have conducted line transect surveys, primarily in the land-fast ice, along the coast of Marie Byrd Land. This zone is inhabited mostly by Weddell seals, but we also observed crabeater seals, some at surprising distances from the open water. Although Weddell seals were found in low densities throughout the fast ice, several aggregations of up to 40 seals were observed, including a probable breeding colony located in Siniff Bay, named for our colleague Prof. Donald Siniff. To date, we have flown 17 helicopter surveys which covered over 4500 km during 27 flight hours. During the flights we counted approximately 3000 seals and 3700 emperor penguins. Initial analyses demonstrate large gradients in the density of seals and penguins. We have deployed, and are receiving data from satellite transmitters on a total of 5 crabeater seal pups and 3 Ross seals. Several partially molted adult crabeater seals have been observed, which means that we may be able to begin deploying satellite transmitters on them in the next few weeks.
   
   
3. Seal condition and nutrition (Castellini): The focus this last week has been the collection of samples from seals along the coastal polynya east of the Ross Ice Shelf. This effort required a different set of logistics to reach the seals, most of which were back from the ice edge on fast ice. While we worked with a our first leopard seal and several crabeater seals, most of the effort has focused on Weddell seals and has utilized using both sleds and helicopter support. We continue to collect samples through both our efforts and through collaboration with the genetics teams (Siniff, Stewart). Our blood analysis this week shows that more seals have been feeding compared to the numbers that we found in the pack ice. While several seals have shown signs of medical anomalies in the blood (see Yochem report), we have not found any animals that show indications of nutritional stress or malnourishment. For example, we have been able to weigh several animals and have found very close agreement between the predicted and actual weights of the animals. In addition, blubber thickness measurements in the Weddell seals have exceeded 50 mm. Finally, we have been able to collect specimens of fish and krill from the Quetin and Torres projects for analysis of lipid types to match with blubber samples taken from the seals.
   
   
4. Seal health (Yochem, Stewart): We have continued to examine and collect biomedical samples from seals during the past week, including animals found on the fast ice along the coastal polynya east of the Ross Ice Shelf. Our efforts through 9 January 2000 have yielded blood samples from 35 seals including 16 crabeater seals (8 adult males, 4 adult females, 1 adult of unknown sex, 1 juvenile male, 2 juvenile females), 13 Weddell seals (5 adult males, 4 adult females), 5 Ross seals (1 adult female, 4 juvenile males), and 1 leopard seal (adult male). Of these, we have conducted complete physical exams on 20 and have cultured microbiological swabs from 29. We continue to bank serum, plasma, and tissue samples for further analyses when we return to our home institutions. Although our analyses are very preliminary, four seals (2 Weddells and 2 crabeaters) have shown some changes in their blood suggestive of inflammation or infection. A general scan of fecal enteric bacteria in seals cultured to date has revealed a variety of organisms commonly found in fish-eating mammals.
   
   
5. Immunogenetics (Stewart (in field), Lehman): Our tactical goals under the APIS project are to: a) document the molecular genetic variability at loci that direct the synthesis of key elements of the immune system response to invasion by bacterial and viral pathogens, and b) assess the relationship between this genetic variability and biotic and abiotic explanatory variables (e.g., individual physical health, prey ecology, oceanographic variability, physical environmental parameters). Based on results from those analyses our strategic objectives are to determine the potential for rapid responses of pack ice seal populations to new and re-emergent pathogens in the Antarctic. Project status through 9 January 2000: Skin samples have been collected from 90 seals in the pack ice of the Ross sea and along the fast ice east of the Ross Ice Shelf from Sulzberger Bay to just beyond Cape Burks. This sampling includes 7 Ross seals, 54 Weddell seals, 28 crabeater seals, and 1 leopard seal. A smaller number of blood samples was collected from each species. White blood cells were isolated from those for comparative extraction of DNA. Laboratory analyses to be conducted later in the U.S. will include DNA extraction, amplification, and sequencing.
   
   
6. Seal genetics (Siniff and Stirling): Our APIS project centers on the exploration of two hypotheses: 1) the relationship between life history patterns and genetic variation among regions of the Antarctic pack ice, for the four species of Antarctic pack ice seals, and 2) a molecular investigation examining the evolutionary history and origin of the pack ice seals. In addition , our project is responsible for soliciting and organizing genetic samples collected by other national APIS programs, and serving as the depository for storage and analysis of these samples. Our sample collections since the last report have been supplemented with 8 additional crabeater samples and 30 additional Weddell seal samples. The proximity of the ship to the Ross Sea Polynya and the adjacent fast ice near the Ross Ice shelf has given us an opportunity to sample groups of Weddell seals. These have come from three primary locations and may represent members of resident colonies. The majority of these individuals have been sub-adults and non breeders. To date, the paucity of leopard seals seen from both aerial and ship-based surveys suggests that this species will be the most difficult group from which to collect an adequate sample.
   
   
7. Fish, squid, and zooplankton (Torres and Daly): Over the last week we have completed an additional 11 trawls for a total of 18 and, with a few additional developments, things have stayed pretty much at status quo. We have dipped the HTI an additional 21 times since the last sitrep for periods varying between 30 minutes and 4 h usually either preceding or accompanying net tows. The dominant fish in the water column is juvenile/postlarval Pleuragramma, which we are capturing at very low densities. Biomass in the upper 100 m is composed mainly of euphausiids. The HTI corroborates the results from the nets, showing virtually all acoustic targets in the upper 80 m. We completed a net/acoustic series designed to examine the transition in fauna across the shelf-slope continuum, and particularly, the Antarctic slope front. Acoustic measurements indicated that layering of targets was more common on the shelf; net tows suggested that layers were composed mainly of E. superba, E. crystallorophias, and juvenile Pleuragramma. Pleuragramma first appeared well seaward of the shelf-slope. We completed one bottom trawl at a depth of 500 m during this sitrep interval, and found an enormous biomass of fishes and invertebrates. We captured a total of 200 fishes representing over 20 species. Clearly, the most predictable hunting sites for seals and penguins on the shelf will be associated with the bottom.
   
   
8. Krill and zooplankton (Quetin (in field) and Ross): The past week we have been towing a 1-m Mocness System and diving at the edge of the fast ice once a day. We have had many catches where copepods dominate and only a few with Euphausia crystallorophias present in any abundance. Euphausia superba were caught when towing in the western shelf region at 40 - 60 m deeper than we observed in pack ice. There is a strong trend toward lower zooplankton and krill biomass on the shelf compared to the pelagic zone, and perhaps a slight trend toward lower krill and zooplankton biomass in the eastern region of the shelf compared to the western region in our sampling area. Dive observations are restricted to the upper 20 m of the water column. Schools of E. crystallorophias have been observed at 5-7 m depth at the very edge of the fast ice, but E. superba have not been observed under the fast ice on any of our dives on the shelf.
   
   
9. Sea ice and hydrography (Ackley (in field) and Jacobs): Continuous observations of sea ice, and several core samples were taken, including four in the landfast ice. The fast ice had significant color at the top and interior of the ice. Snow covers of 0.5 to 1.0m were frequently observed. Surface flooding was also observed at most sites, so surface or near-surface ice biology communities appear to dominate here rather than the bottom ice algal communities observed (for example) in McMurdo Sound. The aerial surveys for seals also had digital downlooking video, that looks feasible to map fast ice extent and to differentiate between fast ice formed in situ (level ice) and that formed by deformation in the early freezing season. Ice coring opportunities in conjunction with diving operations are providing links between the ice properties and physical and biological processes observed at the ice underside. The hydrography section at the western end of the coastal line was successfully completed. Physical changes across the shelf-slope boundary were subtle but a significant biological difference was seen using fluorometry and transmissometry on the CTD cast. These changes showed evidence of an ice edge bloom at the pack ice side, relatively low biology at the shelf-slope (perhaps due to deeper mixing), and a coastal shelf increase in these in situ parameters. CTD's and XBT's were used on the coastal section.

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