CCAMLR

Reported herein are observations of Weddell seals (Leptonychotes weddellii) feeding on Antarctic toothfish (Dissostichus mawsoni) in McMurdo Sound, Antarctica, during 2001-2003 austral summers. In addition to past reports of isolated toothfish captures, the frequency of these observations and the quantity of toothfish captured lead us to suggest that this species is a significant prey item for Weddell seals, and that the recent development of a toothfish fishery in the Ross Sea may have broader impacts than expected. This is especially important in the McMurdo Sound region as toothfish are probably common (as evidenced by more than 30 years of sustained research projects on that toothfish population).

Frank, K.T. et al. (2007: Trends Ecol. Evol. 22, 236–242) provide interesting analysis, after compiling information from 19 subregions, on how the exploited shelf ecosystems of the North Atlantic are structured, either by predation (top down) or resource availability (bottom up), depending on their biodiversity and climate (cold vs warm). By the ecological ‘rules’ laid out, the Ross Sea should be structured by predation. Analysis has shown, however, that some portions of the Ross Sea follow the rules but others do not. This is apparent, though, only because the Ross Sea, unlike the remaining Southern Ocean and other portions of the World Ocean, remains at least for now, intact. If its whales, flightless seabirds, seals and large predatory fish had been severely reduced, as in the North Atlantic, bottom-up structuring likely would prevail.

Size and sex of Antarctic krill taken from chinstrap and gentoo penguin diet were compared to those from scientific net surveys in the South Shetland Islands from 1998-2006 in order to evaluate penguin diet as a sampling mechanism and to look at trends in krill populations. Both penguin diet and net samples revealed a 4-5 year cycle in krill recruitment with one or two strong cohorts sustaining the population during each cycle. Penguin diet samples contained adult krill of similar lengths to those caught in nets; however, penguins rarely took juvenile krill. Penguin diet samples contained proportionately more females when the krill population was dominated by large adults at the end of the cycles; net samples showed greater proportions of males in these years. These patterns are comparable to those reported elsewhere in the region and are likely driven by the availability of different sizes and sexes of krill in relation to the colony.

Our tenth season of seabird research at Cape Shirreff allowed us to assess trends in penguin population size, as well as inter-annual variation in reproductive success, diet and foraging behavior. The gentoo breeding population has decreased marginally from the previous season and is the lowest population size in the 10 years of census data. The number of diet samples containing fish was the highest ever and comparable to the first six years of the study. Unlike 2005-06, 18% of the gentoo penguin diet samples contained juvenile krill. Fledgling success and fledgling weights were slightly below the nine year means for these parameters at our study site.
The chinstrap penguin breeding population has been declining for the past seven years and is at its lowest size in the 10 years of study. Chinstrap penguins ate mainly Antarctic krill, with a strong component of juvenile krill in their diet samples. Juvenile krill were also plentiful in the chinstrap penguin’s diets in the 1997-98 and 2002-03 seasons. The mean foraging trip duration during chick- rearing was approximately one hour longer than in 2005-06. The data collected, using the PTTs and TDRs, on foraging location and diving behavior should assist us in interpreting the foraging trip data. Fledgling success and chick fledging mass in 2006-07 were higher than both last season and the past 10 year mean.

During the 9th research cruise of the R/V Kaiyo-maru, macrozooplankton samples were collected from three layers between the surface and 200 m with RMT 8m2 along the three longitudinal lines in the Ross Sea and neighboring waters. Biomass and abundance (number of individuals) were 0 ~ 32.1 g/1000m3 and 1.8 ~ 2314.3 inds/1000m3 along 175°E line, 1.6 ~ 23.7 g/1000m3 and 226.4 ~ 3224.0 inds/1000m3 along 180°, and 0.1 ~ 8.5 g/1000m3 and 46.8 ~ 619.7 inds/1000m3 along 170°W. Biomass and abundance were extremely low at stations on the continental shelf along 175°E and 170°W except the southern most station located at 78°S, 175°E. Total of 13 taxa occurred at all stations and mean of 7.4 taxa were occurred in each sample. There was no marked difference in numbers of taxa occurred at each station and layer except at 0 ~ 50 m of 72°S, 175°E, where euphausiids only occurred. Copepods and chaetognaths dominated in the north of 72°S, while pteropods and euphausiids occurred besides them in the south of 72°S along 175°E. Pteropods comprised high percentage of total abundance at the southernmost stations along 175°E and 170°W. Stations and layers were categorized into four major groups by cluster analysis based on taxonomic composition. The group 1 comprised of stations with bottom depth of deeper than 1000 m (in the north of 72°S along 175°E) and group 2 to 4 on the continental shelf. The latter three groups are characterized by copepods + chaethognaths + euphausiids, pteropods + euphausiids and pteropods. These were overlapped geologically with different group(s) at different layer(s).

Multifrequency echosounder data were collected during the 2006 BROKE-West summer survey of Division 58.4.2 for the purposes of estimating the unexploited biomass (B0) of Antarctic krill (Euphausia superba) and its associated coefficient of variance (CV). This paper updates the version submitted to WG-EMM in 2006 (WG-EMM-06/16) because a reanalysis of the data has resulted in amendments to the acoustic estimates of krill mean biomass density, biomass and variance. The mean acoustic biomass density of krill, integrated to 250 m depth across the entire survey stratum (1.31 million km2), was 9.48 g m-2. B0 was estimated to be 12.46 million tonnes with a CV of 15.15%. Krill were widely distributed at relatively low densities throughout the survey area; only 13% of the 2-km-alongtrack echo-integration intervals were devoid of krill, 50% of intervals registered densities of 1 g m-2 of krill or less, and 80% of intervals registered densities of 10 g m-2 or less. Mean densities were highest in the waters to the south of the Southern Boundary of the Antarctic Circumpolar Current, particularly in waters to the west which were within the influence of the Weddell Gyre. Half of the cumulative density across the survey was found within 120 km of the 1000 m isobath (the shelf-break/ slope), and 40% within 50 km. This was mostly due to very high densities (up to 1400 g m-2) around the shelf break on 3 of the 11 transects surveyed. The majority of acoustic krill detections were in the top 100 m of the water column, centred around 50 m depth. The krill distributions inferred from both the acoustic data and from net catches were considered in the context of the physical oceanography, from which a case is presented for the subdivision of Division 58.4.2 into smaller, more biologically homogeneous areas. A qualitative critical appraisal of the methods is included by way of contribution to ongoing discussions about acoustic survey and analysis methods for krill.

A field key to early life stages of Antarctic fish caught along with the Antarctic krill is produced. The key includes 8 families and 28 species mainly from the Atlantic sector of the Southern Ocean and uses distinguished characters which permit rapid field identification. In some cases, however, it is impossible to discriminate among species of the same family by remarkable characters. A species key is not shown for such resemble species and a brief summary of the main morphological features of species and genera is provided.

Antarctic krill biomass trends in the South Shetland Island region of Area 48 are presented. Updated time series using the Stochastic Distorted Wave Born Approximation, and a dynamic ?Sv krill delineation model are used to derive krill biomass. This paper provides updated (through summer 2007), acoustic biomass estimates previously presented at the 2006 WG-EMM meeting in Namibia (WG-EMM-06/32). In 2007, biomass in the South Shetland Islands region exceeded 19 million tons. This increase from

The total abundance of krill in the Scotia Sea was estimated from an international echosounder and net survey (CCAMLR 2000) to be 44.3 million metric tons (Mt; CV=11.4%), prompting the Antarctic Treaty's Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) to revise the precautionary catch level for krill in the area from 1.5 to 4 Mt (SC-CAMLR, 2000). By incorporating recent improvements in the remote identification and target strength (TS) of krill, a range of krill biomass was estimated, 108.0 Mt (CV=10.4%) to 192.4 Mt (CV=11.7%), depending solely on the expected distribution of krill orientations. The new methods were then reviewed by CCAMLR, and revised protocols based on the Stochastic Distorted Wave Born Approximation model (SDWBA) were adopted. Here, the protocols are applied to again re-analyze the CCAMLR 2000 data. Using the 120 kHz echosounder data, the resulting estimates of krill biomass in the Scotia Sea are 197.78 Mt (CV=11.06%) and 37.29 Mt (CV=21.20%), depending on whether two- or three-frequencies are used for krill identification, respectively. At 38 kHz, estimates of krill biomass range from 65.64 Mt (CV= 11.50%) to 10.39 Mt (CV= 15.25%); and at 200 kHz from 343.09 Mt (CV= 12.91%) to 38.73 Mt (CV= 14.86%). CCAMLR uses the estimates derived from the 120 kHz data. Results of the three-frequency method are likely less biased owing to better rejection of non-krill species; also the patchiness of krill is better elucidated, resulting in higher CVs. Thus, the revised estimates of krill biomass in the Scotia Sea during the CCAMLR 2000 survey are 37.29 Mt (CV=21.20%), or 15.8% lower than the original estimate, but with a larger CV.

In Antarctic krill, Euphausia superba, sampled by a Japanese scientific observer onboard a krill fishing vessel in the winter of 2003 and 2006 in the South Georgia region, the Antarctic Ocean, approximately 2-5% of sub-samples of 100 krill bore small black spots. The black spots were most often found on the cephalothorax of the body. Three bacteria were isolated from these black spots, and classified into either Psychrobacter or Pseudoalteromonas by the sequences of 16S rRNA genes. Histological observations revealed that the black spots were melanized nodules. A single melanized nodule often contained more than one type of morphologically distinct bacterial cell. More than three bacterial species or strains were also confirmed by in situ hybridization for 16S rRNA. The melanized nodules were almost always accompanied by a tumor-like mass of unknown large heteromorphic cells, which seemed to be derived from a gonadal tissue. These results suggest that the krill were affected by bacterial infections, whereas the presence of multiple bacterial species suggests that the infections were likely to be secondary. The development of the tumor-like cell mass in the gonad may be the primary condition, although this requires further detailed study.