CCAMLR

Patagonian toothfish (Dissostichus eleginoides) is a large notothenioid fish that supports valuable fisheries throughout the Southern Ocean. D. eleginoides are found on the southern shelves and slopes of South America and around the sub-Antarctic islands of the Southern Ocean. Patagonian toothfish are a long-lived species (> 40 years), which initially grow rapidly on the shallow shelf areas, before undertaking an ontogenetic migration into deeper water. Although they are active predators and scavengers, there is no evidence of large-scale geographic migrations and studies using genetics, biochemistry, parasite fauna and tagging indicate a high degree of isolation between populations in the Indian Ocean, South Georgia region and the Patagonian Shelf. Patagonian toothfish spawn in deep-water (circa. 1000 m) during the austral winter, producing pelagic eggs and larvae. Larvae switch to a demersal habitat at around 100 mm (1 yr old), and inhabit relatively shallow water (< 200m) until 6-7 years of age, when they begin a gradual migration into deeper water. As juveniles in shallow water, toothfish are primarily piscivorous, consuming the most abundant, suitably sized, local prey. With increasing size and habitat depth the diet diversifies and includes more scavenging. Toothfish have weakly mineralised skeletons and a high fat content in muscle, which helps neutral buoyancy, but limits swimming capacity. Toothfish generally swim with labriform motion, but are capable of more rapid sub-carangiform swimming when startled. Toothfish were first caught as a by-catch (as juveniles) in shallow trawl fisheries but, following the development of deep-water longlining, a fishery rapidly developed throughout the Southern Ocean. The initial rapid expansion of the fishery, which led to a peak of over 40,000 tonnes in reported landings in 1995, was accompanied by problems of bird by-catch and over-exploitation as a consequence of illegal, unreported and unregulated fishing. These problems have now largely been addressed, but continued vigilance is required to ensure the species is sustainably exploited and the ecosystem effects of the fisheries are minimised.

Antarctic silverfish (Pleuragramma antarcticum) is a key link between plankton and the community of top predators in the shelf waters of the Ross Sea. In spite of their abundance and important role in Antarctic food chains, very little is known of many ecological and biological aspects of this species. A combined trawl and acoustic survey of silverfish was carried out on the western Ross Sea shelf during the New Zealand International Polar Year Census of Antarctic Marine Life research voyage on R.V. Tangaroa in February–March 2008. Multi-frequency acoustic data (12, 38, 70 and 120 kHz) allowed discrimination of silverfish marks from those of krill and other associated species. Mark identification was achieved using targeted midwater trawls. Additional midwater and demersal trawls were carried out at randomly selected locations over the shelf as part of the core biodiversity survey. Silverfish were widely distributed over the Ross Sea shelf. Adult silverfish tended to form layers at 100–400 m depth and were some times present close to the bottom, where they were frequently caught in demersal trawls shallower than 500 m. A weak layer at about 80 m depth was associated with juvenile silverfish of 50–80 mm standard length. Acoustic backscatter strength from both silverfish and krill marks increased with increasing frequency (i.e., was highest at 120kHz), which is characteristic of species without an air-filled swimbladder. Acoustic target strengths (TS) for silverfish at 12, 18, 38, 70, and 120 kHz were estimated from anatomically detailed scattering models based on computed tomography (CT) scans of frozen specimens. The relationship between TS and fish length at 38 kHz was sensitive to estimates of density and sound speed contrast within the fish, especially for small specimens (less than 110 mm SL). Our best estimate of the acoustic biomass of silverfish in the study area was 592 000 t (95% confidence interval 326 000–866 000 t). However, the biomass of juvenile silverfish was highly uncertain due to large differences between TS model results.

Demersal fishes were sampled using a large fish trawl during two surveys carried out in February and March 2004 and 2008 in the Ross Sea, and around seamounts and islands just to the north at 66°S. The distribution and abundance of 65 species collected in these surveys were examined to determine if demersal fish communities varied throughout the area, and what environmental factors might influence this. Species accumulation with sample frequency did not reach an asymptote, but the rate of new species was low suggesting data were adequate for describing the main components of the communities. Three broad assemblages were identified, in the southern Ross Sea (south of 74°S), central–northern Ross Sea (between latitudes 71°–74°S), and the seamounts further north (65°–68°S) where some species more typical of sub-Antarctic latitudes were observed. Multivariate analyses indicated that environmental factors of seafloor rugosity (roughness), temperature, depth, and current speed were the main variables determining patterns in demersal fish communities.

We measured the otolith chemistry of adult Scotia Sea icefish (Chaenocephalus aceratus), a species with a long pelagic larval phase, along the Antarctic Circumpolar Current (ACC) and compared the chemistry with simulated particle transport using a circulation model. Material laid down in otolith nuclei during early life showed strong heterogeneity between the Antarctic Peninsula and South Georgia consistent with a population boundary, and evidence of finer-scale heterogeneity between sampling areas on the Antarctic Peninsula. At South Georgia, the nucleus chemistry was similar between the eastern and northern shelves, indicating a single, self-recruiting population. Consistent with the otolith chemistry, simulations of the large-scale circulation predicted that particles released at 100-300m depth on the Antarctic Peninsula shelf during spring, corresponding to hatching of icefish larvae from benthic nests, are transported in the southern ACC, missing South Georgia but following trajectories along the south Scotia Ridge instead. These results suggest the timing of release and position of early life stages in the water column substantially influence the direction and extent of connectivity. Used in complement, the two techniques promise an innovative approach to generate and test predictions, and resolve early dispersal and connectivity of populations related to the physical circulation of oceanic systems.

Incidental seabird mortality associated with longline commercial fishing is a worldwide conservation concern. To build conservation strategies it is essential to estimate likelihood of seabird bycatch and amount of overlap between bird’s foraging and commercial fishing areas. We tracked 21 adult white-chinned petrels (Procellaria aequinoctialis) breeding on Kerguelen Island, Southern Indian Ocean, during breeding period in 2006 and 2008. At-sea foraging distribution of white-chinned petrels was mainly confined in Antarctic waters. Commercial longline fisheries targeting toothfish were operating in both French Exclusive Economic Zone (EEZ) and other Commission for the Conservation of Antarctic Marine Living Resources areas during the study. We analysed concurrent data on the position of both birds and vessels to estimate overlap. Static analysis using indices (home range and utilization distribution overlap) revealed that at a large scale spatial and temporal overlap occurred and varied among areas and with breeding stage. Dynamic analysis (detection for each bird location of any operating vessel within a time/space window) revealed few overlap at a small scale. Our study revealed a mismatch between large and small scale overlap estimates, suggesting that birds and vessels occupy the same overall zone with infrequent co-occurrence (19% of birds in the vicinity of vessels). This result was confirmed by the relatively low occurrence of fishery-related items (4 to 22%) in chick food samples. However given the large size of seabirds populations, overall large numbers of birds overlap with vessels and Management Authorities should maintain and promote strict mitigation measures implementation to further reduce bycatch.

On the basis of the biological material collected on some by-catch fishes during Antarctic toothfish fishery from 2002 till 2008 in different areas of the Southern Ocean (Collaboration Sea, D'Urville, Ross and .mundsen Seas) it was established that spawning of C. dewitti and species X occurred on the continental slope and raisings at depths about 1000-1500 m, C. antarcticus - on the continental shelf at depth of 300-600 m during summer season (may be autumn for sp. X) of the southern hemisphere, generally. Probably, the significant part of C. dewitti mature females missed spawning, and the spawning portion of some large females was only about 1000-1500 yolk oocytes One of the by catch fish species is supposed to be a monocyclic. The revealed aspects and uncertainty factors available at present concerning knowledge of by-catch fish reproductive biology should be taken into account while managing Antarctic toothfish fishery.

The results of the comparative histological analysis of the Antarctic toothfish (Dissostichus mawsoni) reproductive system, caught by the longliner in the Amundsen Sea in February 2006 and 2007 are presented. The morphological parameters, indices of gonads, condition by Fulton and cytological parameters of oocytes have been described. Antarctic toothfish ovaries reached mainly the late III (57.1%) in 2006 and IV stages of maturity (83.3 %) in 2007 and testes – the IV stage (55%) in 2007. In 2007 the oocytes in the ovaries of 16.7% investigated fish has reached the completed maturation and definitive size 6484·10-6m, therefore, Antarctic toothfish was ready to spawn in the Amundsen Sea in March.

In order to clarify the stock status and biological characteristics of Dissostichus spp. In Division 58.4.4 a & b, we proposed the research plan for toothfish in the Division by Shinsei Maru No. 3 to be conducted throughout the whole four SSRUs (A-D) in the Division in April-June 2011 in the WG-SAM 2010 meeting. However, during the first survey in 2009/10, when the research was surveyed throughout the whole SSRUS, evenly spaced 10 nautical miles apart, only one tagged fish was recaptured. Then, following advice taken in WG-SAM 2010 meeting that research should concentrate effort on a subset of the management area where the probability of recapture is low (WG-SAM 2010 report paragraph 3.21), we revised the research plan to be concentrated in the two centered SSRUs, B and C. These centered SSRUs were selected due to increasing possibility of recapture for tagged fishes released throughout the four SSRUs in 2007/08 and 2009/10. Mean CPUE in weight in the 2009/10 season was significantly higher than that in the 2007/08 season (p = 0.02). The research hauls are revised to be allocated on more concentrated 7.5-minute latitude x 15-minute longitude grid points, taking into account the increase of the recaptures. A Trot line system will be employed for all hauls. To apply the mark-and-recapture studies, sufficient tagging rate of 5 fish/ton will be conducted. We calculated 77 tonnes of total allowable sample size for the 2010/11 survey, taking into account the need for completion of the survey and impact on the fish stock. However, this calculation contains several implicit assumptions as pointed out in WG-SAM 2010 (WG-SAM 2010 report paragraph 3.24). Thus we will take advices for the appropriate methods of estimations to overcome these problems in the WG-FSA-2010 meeting.

Preliminary studies on the age and growth of Dissostichus eleginoides sampled in the 2007/08 season in the Ob-Lena Bank were carried out. The ages of 214 of 3,013 fish sampled by Observers were estimated. The estimated ages ranged from 5 to 46 years for males and from 5 to 50 years for females. Five to eighteen years gave large contribution to the total age groups for both sexes. Females grew at a faster rate and reach a larger size than males. We took several advises and comments about the methods of otolith readings by experienced readers of AAD. One of these is that the first ring was generally identified within the primordium and thus many of age counts were overestimated. We would recount annuli for the present 214 otolith samples and count annuli for the newly added 300 samples referring these advices and comments.