CCAMLR

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.

Distribution, relationship between sizes and depths, sex ratio, size composition and maturity condition for Dissostichus eleginoides and D. mawsoni were investigated on Banzare Bank, using the biological data sampled by a Japanese commercial fishing vessel during austral summer from 2006/07 to 2008/09 fishing season. D. eleginoides was mainly caught in the shallower bank <1000 m, while D. mawsoni was mainly caught in the deeper slope >1500 m. The separation of the two species by depths may be related to the physical intolerance to the cooler temperature by the lack of antifreeze for the former species. The mean total length (TL) of females was significantly larger than that of males for both species. The proportion of males to the total adults decreased significantly with the depths with gradual slope for both species. Male D. mawsoni showed a significant correlation between depth and the TL with gradual slope. The size structure varied among the fishing seasons and showed the polymodal distribution in D. eleginoids, while the size structure was very similar among fishing seasons and showed the unimodal distribution in D. mawsoni. D. eleginoides showed resting stage in sexual maturity, while D. mawsoni was in running ripe condition. In both species, small fish contributed low proportion in abundance, which suggest that substantial recruitment does not take place on Banzare Bank and the population may consist primarily of adults migrating from other area

A survey was conducted in order to collect information for the stock status and various biological information on toothfish in Division 58.4.4a & b (Ob Lena Bank) by using a commercial bottom longline vessel, Shinsei Maru No. 3, from April 30 to June 20. The survey was undertaken according to the decision in the 28th CCAMLR Meeting of the Commission (28th CCAMLR report paragraph 4.43). This report described the results preliminarily during the survey in four SSRUs of Ob Lena Bank. The catch amounted the total allowable catch of 60 tonnes in 94 longline sets, which corresponded to 83 % to the total allocated fishable 113 sets. D. eleginoides contributed 80.1 % in numerical number and 96.1 % in weight to the total samples in SSRUs. Mean CPUEs of D. eleginoides for 71 hauls where only Trot line system was adopted were 13.1 indiv. / 1,000 hooks in number and 138.9 kg / 1,000 hooks in weight. These values were larger than mean CPUEs of 11.0 indiv. / 1,000 hooks and 108.0 kg / 1,000 hooks in the same Division in the 2007/08 season. D. eleginoides caught showed a broad polymodal composition for each SSRU, but the proportion of smaller fish caught in eastern SSRUs tended to be lower than that caught in the western SSRUs, as observed in the previous 2007/08 survey.

In accordance with the Conservation Measure 41-07 (2009), a survey was conducted in order to collect information for the stock status and biological information on toothfish in the southeast sector (24 allocated points) of Division 58.4.3b (Banzare Bank), using a commercial bottom longline vessel Shinsei Maru No. 3, from December 1 to 13, 2009. Shinsei Maru Trot line system was used as fishing gear. Total catch (excluding released weight) of Dissostichus spp. And the other by-catch species was 15.9 tonnes in the SE sector, where the catch limit of 18 tonnes was set. Dissostichus spp. Made up 16 % in number and 87.5 % in weight of the whole fish caught, while Macrourus spp. Made up 81% in number but only 11 % in weight to the total. Among two species of toothfish, Dissostichus mawsoni was dominant (82 % in number and 88 % in weight to the total). Mean CPUE of D. mawsoni was 3.4 indiv. / 1,000 hooks in number and 111 kg / 1,000 hooks in weight. D. mawsoni showed a broad modal composition at approximately 130-150 cm. Total of 60 individuals of toothfish were tagged and released during the survey. One male D. eleginoides was recaptured.