AMLR 2003 Weekly Report No. 12

31 March 2003

1. The R/V Yuhzmorgeologiya is currently east-southeast of King George Island conducting a trawl survey of demersal finfish, net and acoustic based characterization of invertebrate fauna, and habitat classification within the 500 m isobath of the South Shetland Islands, Antarctica.

2. We have completed 67 stations to date. We are conducting the final station of our South Shetlands Island Survey. As of 31 March, we have completed 36 stations in the lower South Shetland Islands. Most targeted stations in the lower South Shetland Islands were successfully completed. One station in the 300-400 m depth strata will be relocated from west of Deception Island to Southeast of King George Island. Following this station, we will proceed to the Antarctic Peninsula to complete stations north of the entrance of the Antarctic sound to conclude the 2003 AMLR field season.

3. As of 31 March, a total of 6168 Kg of finfish (16,263 individuals) of 45 species have been caught and processed. The species with the greatest yield in weight as of 31 March has been Gobionotothen gibberifrons (1633 Kg), followed by Notothenia coriiceps (1365 Kg) and two species of icefish: Champsocephalus gunnari (880 kg) and Chaenocephalus aceratus (493). The largest catch by number has been C. gunnari (3770) followed by Gymnoscopelus nicholsi (3381).

4. Catches in the lower South Shetland Islands shallower than 100 m were dominated by Harpagifer antarcticus, Notothenia coriiceps and the bathydraconid, Parachaenichthys charcoti. Individuals of the first two species were all sexually mature, while P. charcoti were all juveniles. Catches in the 100-200 m depth zone were dominated by Champsocephalus gunnari. Most fish were in the 22-45 cm length range with few larger individuals. No fish of the age class 1+ (14-18 cm) were observed. The dominant fish species from 200 to 400 m depth were Gobionotothen gibberifrons, Chaenocephalus aceratus, Pseudochaneichthys georgianus and Chionodraco rastrospinosus. However, below 250 m the proportion of high-Antarctic species, such as Lepidonotothen squamifrons, increased. The abundance of myctophids, primarily Gymnoscopelus nicholsi mixed with a small proportion of Electrona antarctica, increased in catches below 300 m. Of interest from an ichthyological point of view were catches of individual Pagetopsis macropterus and Neopagetopsis ionah (Channichthyidae), Racovitzia glacialis and Gymnodraco acuticeps (Bathydraconidae), Pogonophryne scotti (Artedidraconidae), and Trematomus scotti and T. tokarevi (Nototheniidae).

5. The reproductive state of the abundant species showed several remarkable changes. In C. gunnari east of Livingston Island, primarily spent fish were caught with very few fish still in maturing stage (stage 3). North and west of Livingston Island, most fish were stage 3 with very few spent fish taken. The proportion of spent C. aceratus and C. antarcticus was higher than in previous surveys, indicating that the spawning season was more progressed. C. rastrospinosus were either spent or very close to spawning. While spawning C. gunnari likely move inshore for reproduction (as they do at South Georgia and Kerguelen) the other three icefish species apparently spawn in many parts of the shelf with no specific areas preferred. L. squamifrons were either in maturing stage or spent. It is likely that they spawn elsewhere (in deeper water?). Maturation of gonads in N. rossii and N. coriiceps were well progressed which suggests that the species spawn in April-May and May-June respectively. Extensive material was collected which will be analyzed over the next couple of months.

6. Diet studies conducted on 4,054 individuals from all species encountered confirmed observations from the previous two weeks and from the 2001 survey. C. gunneri preyed on more than 95% krill. Larger individuals fed occasionally on myctophids while smaller individuals (< 25 cm) took a small proportion of the euphausiids Thysanoessa macrura and Euphausia frigida and the hyperiid, Themisto gaudichaudii. Feeding intensity in C. aceratus and Cryodraco antarcticus was low. However, it is likely that the feeding intensity of these two species has been underestimated. An unknown proportion of stomach contents appears to be regurgitated. An accurate proportion of regurgitated stomachs is difficult to assess because stomach walls seem to be contracted fairly quickly after regurgitation. Only in a few cases does the stomach remain fully extended. Juveniles (< 30 cm) of the two species prey on mysids (Antarctomysis maxima) and krill while larger individuals rely primarily on fish and only to a small extent on krill. The change in diet is also clear from the load of endoparasitic nematode larvae (mostly Contracaecum sp.), because the number of heavily parasitized fish increases dramatically in fish larger than 28-30 cm. Chionodraco rastrospinosus had empty stomachs when still in prespawning condition and immediately after spawning. Later, when gonads are being resorbed, fish took krill and fish to a lesser extent. Gobionotothen gibberifrons fed on a variety of benthic organisms and occasionally salps and jellyfish. N. coriiceps took krill, fish, and to a lesser extent benthic invertebrates.

7. Studies of evolutionary phylogenetic relationships and variation of buoyancy between species benefited by the capture of two rare Antarctic species, Rakovitzia glacialis and Gerlarhea australis. Also, in the past week we had the opportunity to measure the buoyancy of nearly fifty specimens of the relatively rare species, Harpagifer antarcticus.

8. Blood and tissue samples were collected from representatives of all notothenoid and non-notothenoiod (Zoarcids and eel cods) species. Muscle tissue was collected from all Dissostichus mawsoni (50), Trematomus bernacchii and hansoni specimens for future population biology studies since these species are also present in large numbers at McMurdo Sound. The tooth fish is especially of interest because it is now commercially fished in the Ross Sea. Analyses of these samples should allow determination of whether specimens caught in the vicinity of Elephant Island and the South Shetlands represent populations different from those that reside in McMurdo Sound which have been extensively studied.

9. All Antarctic fishes that possess blood antifreeze proteins also have them in their intestinal fluids. They are neither digested nor reabsorbed. Their synthetic origin is unknown but recently we have found a synthesis signal in the esophagus-stomach complex. Thus, intestinal tract tissue samples were collected in a manner that will allow isolation of antifreeze mRNA along their length beginning with the pharyngeal-esophagus to the pyloric sphincter. This will allow determination of the exact location where the digestive tract antifreeze glycoproteins are synthesized.

10. Krill abundance and dispersion is being acoustically mapped at each trawl location and a mean Nautical Area Scattering Coefficient (NASC) value is calculated for each station. NASC values may also be thought of as the number of krill (m²) per 1 nm² of sea surface. Stations on the north shelf of King George Island show increased variability in NASC values with an evident trend of lowered NASC values than those computed for the Elephant Island area. NASC values range between 6.5 and 803.2, with greatest concentrations of krill between the 400 and 500 m isobaths along the shelf slope to the northeast of King George Island. Moderate concentrations are visible along the western most shelf between Snow and Smith Islands, seaward of the 300 m isobath.

11. The Questar Tangent seabed classification system is now functional as a new patch from the company has been sent to the ship and successfully installed. Ground truthing of the acoustic seabed classification catalogue continues with nightly video/still camera transects and sediment grabs. To date, 9 sediment grabs, c. 2200 high resolution (2100 × 1700 pixel) digital still images and > 21 hours of color video have been obtained from the transects. We have also opportunistically collected video and digital camera data from within the caldera at Deception Island and inside Admiralty Bay, King George Island. A surprising number of C. gunnari were observed within Deception Island, in addition to what is believed to be T. scotti.

12. A total of 26 CTD deployments have been made within the 500 m isobath of the S. Shetland Islands to characterize environmental properties of finfish habitat and water mass distribution. Around Elephant Island, 12 deployments were made across all depth strata and each broad shelf area. In the lower S. Shetlands, 14 CTD deployments were made primarily to the north of King George, Robert, Greenwich, Livingston, Snow, and Smith Islands in addition to deployments in the Boyd Strait and west of Deception Island. These data will be incorporated into a model that characterizes spatial features of demersal and benthic marine organisms based on environmental predictors.

13. As we have progressed southwest along the South Shetland Islands, the invertebrate bycatch has continued to shift from the sponge dominated, high diversity, community found off the northwestern tip of King George Island to an echinoderm (sea star) dominated community with a relatively low total species count. A few shallow stations off Livingston Island were dominated by tunicates, and further southwest, deeper stations were dominated by octopus biomass. The diversity of sea star species is extremely high, though often there is only one representative of each of several species in a single trawl. The most prevalent echinoderm species, the sunstar, Labidiaster radiosus, is observed in the video and still footage feeding in the water column by extending its many arms above the seafloor, enabling it to capture planktonic prey such as krill or salps from the near bottom layer. Two trawls stood out as unusual, one with very high numbers of crinoids (feather stars) located between Snow and Deception Islands, and the other dominated by brittle stars at the northeastern end of the steep shelf break off the South Shetland Islands.

14. Although the contents of the Little BIT continue to approximately parallel the composition of the fish trawl bycatch, it differs significantly in many respects. The most significant of these is in the sampling of the ophiuroids (brittle stars). In some trawls, the bycatch contains few, if any, of these important members of the benthic community. However, the Little BIT always brings up ophiuroids, often in large numbers. At station 57, about halfway down the northwestern part of the South Shetlands, the Little BIT yielded 399 ophiuroids totaling nearly 5 kg, almost all of the same species, Ophionotus. This community was also dominated by the isopod Serolis. The superabundance of these 2 species at this locality was also evident in video and photo transects of this area, but not from the fish trawl bycatch. The Little BIT is also sampling infaunal, or near infaunal, taxa that the trawl does not catch. Scaphopods, burrowing bivalves, and tubicolous polychaetes seldom, if ever, turn up in the bycatch, but are occasionally strongly represented in the Little BIT.

15. Various photographic field guides have been developed during AMLR 2003 with the objective of providing essential information for the identification of freshly collected material. None of these guides are complete and all are considered to be works in progress to be augmented and elaborated upon during future field seasons. These guides are briefly summarized.

a. Zooplankton and Nekton of the South Shetland Island Area. This volume provides photographs, line drawings, identification aids, distribution and life history information for taxa collected during the AMLR krill stock assessment surveys. It is intended to provide basic information for new participants in the zooplankton team as well as present images useful for the identification of freshly caught (vs. preserved) animals. The work currently comprises 150 pages and 97 photographs covering 50 taxonomic categories regularly collected during January-March.

b. Finfish of the South Shetland Island Area. To date this work includes photographs of 36 fish species collected during the 2003 fish stock assessment survey. Multiple images (including stills and videos of fish swimming in tanks) were taken for most species to permit elucidation of key identification aides and to assist in identification of fish recorded in situ with underwater videos and cameras.

c. Fish Maturity Stage Atlas. During the current fish stock assessment survey concerns were raised over the consistency of maturity stage identification. As a result, we collaborated in developing a photographic record of male and female gonadal development for as many species as possible. To date, at least one stage has been photographed for each of 16 species; most species are represented by at least 2 of 5 male and 2 of 5 female stages. Recognizing seasonal constraints, this work is intended to be more fully developed during future surveys.

d. Benthic Invertebrates of the South Shetland Island Area. This is the initial phase of a photographic guide for the species identification of benthic invertebrates collected as bycatch during the fish surveys. As with the fish images, these photographs are intended as an identification aid for freshly collected material with images provided by underwater videos and cameras. Currently the 300 page guide includes ca. 230 photographs and identification information for 25 taxonomic categories. Sea stars comprise the largest group treated to date, with photographs and identification aides for 32 species.

f. Photographic Atlas of Fish Otoliths. This final volume will provide photographs of otoliths removed from fish collected during the 2003 fish survey. Together with line drawings obtained from Gon and Haemstra's “Fishes of the Southern Ocean” these are intended to help in predator diet studies at Cape Shirreff.

C. Jones sends