CCAMLR

The rocks from stomachs of Dissostichus mawsoni were used as a source of geological information about sea bottom. Authors suggest toothfish picks up stones from the bottom randomly, and these stones may be used for geological description of the closed areas of Antarctic shelf and slope. In this respect, Dissostichus mawsoni may be considered as a «dredge» with a wide area of sampling. Preliminary analyses allow qualitative estimation of geological structure of Antarctic shelf and continental slope in different areas.

This is a preliminary report of the results of the 11th UK South Georgia groundfish survey, the first to be conducted during the austral winter since 1997. Preliminary biomass estimates are provided for C. gunnari whilst new information on the winter distribution and ecology of the demersal fish fauna at South Georgia is provided.

Analysis of recent commercial catch, research survey and larval data for mackerel icefish (Champsocephalus gunnari) recorded from CCAMLR Subarea 48.3 coupled with historical information indicates that they spawn inshore close to the bays and over the shelf to the northeast. There is also evidence that spawning is protracted and occurs from January through to July. The majority of commercial fishing activities for this species take place to the northwest of South Georgia over 12 nautical miles from the coast and do not overlap with important spawning areas. Therefore the current conservation measure restricting the total allowable catch during the assumed spawning period from March-May is unlikely to protect spawning aggregations of C. gunnari but could, inadvertently, increase the risk of brooding seabirds being caught as by-catch.

This document summarises the suggestions made by WG-EMM to address the requests made by the Scientific Committee in relation to Scientific Observer Manual. These are establishment and replacement of protocol for fish-larvae by-catch observation, review of priorities for scientific observation of krill fishery, and other minor revisions on the e-forms. This document also contains examples of the revisions made to the forms and is presented to the Working Group on Fish Stock Assessment for comment.

This paper further develops an integrated assessment for Patagonian toothfish in Division 58.5.2. It updates the model used at WG-FSA in 2006 using data from the 2007 season as well as 2006 data not available for WG-FSA in 2006. It also includes the following refinements: (i) estimation of the coefficient of variation (CV) for length given age, (ii) use of non-informative priors for year class strength parameters, (iii) separate selectivity parameters used for the pre-2006 compared to the 2006-2007 fishing seasons for the main trawl ground, (iv) separate selectivity parameters for the late (within-year) season compared to the combined early (within-year) seasons for the main trawl ground, and (v) the use of an improved method of determining effective sample size for commercial catch-at-length data. The estimated long-term yield was 2500 tonnes with depletion probability of 0.081 and escapement probability of 0.505. As expected, the assessment was sensitive to the inclusion of different datasets and to the choices of parameters used in both the stock assessment and projections. It is concluded that until the difficulties with the use of mark-recapture data are resolved, recruitment surveys provide the best means of establishing current stock status as an absolute index of abundance.

Fish samples collected through an overall period of 24 years at Potter Cove after the impact of the fishery in the area in 1978-80, allowed the comparison of the variations in mean annual lengths and density distributions of the commercially exploited species N. rossi and G. gibberrifrons with the ecologically similar but unexploited N. coriiceps. The sharp decline in the abundance of N. rossii reported for the period 1983 - 1991/2 is consistent with the increase in mean size observed between 1983 and 1986/7 and the duration of the inshore phase of the species, which is known to last for 6-7 years. In the following years, until 1991/92, the decreasing abundance is consistent with the entrance of low strength cohorts with the consequent reduction in mean size. The above interpretation is supported by the length distributions observed between 1982/83 and 1985/86, where the modal age changes from 2/3 to 6/7 years. After 1991/92 the densities, mean sizes and abundances do not depend on a single forcing event but on several interacting factors. The length data of G. gibberifrons, available from 1986, show a decrease until 1991/92, exhibiting a similar pattern to that of N. rossii. After a period of relative stability in mean sizes (1992-1994) a sharp increase is associated with a continuous decline in relative abundance suggesting that it is due to increasingly low recruitments. The length frequency distributions of N. coriiceps through the whole studied period do not show any definite change in modal size, nor a pattern in mean lengths as is the case with N. rossii and G. gibberifrons.

We analyzed data collected during 2005 seabird mitigation experiments on integrated weight longlines (IW) in a demersal longline fishery for effects on skate bycatch. Trials took place on two vessels targeting Pacific cod (Gadus macrocephalus) over a five-month period in the Bering Sea, Alaska, USA. The skate catch rate was 11% lower on the IW gear compared to unweighted gear. Location, month and depth were also significant predictors of skate catch rates. While results indicate IW shows potential to reduce skate catch rates, further evaluation and analysis by individual species should be performed in specific regions where skate bycatch is a problem.

Feeding of Antarctic toothfish Dissostichus mawsoni was studied in new fishing ground for this species in the Pacific sector of Antarctic: Amundsen Sea (Subarea 88.2). In terms of occurrence, the most important fish items in toothfish diet were: Whitson’s grenadier (Macrourus whitsoni), crocodile icefish (Chionobathyscus dewitti), antimora (Antimora rostrata), Antarctic jonasfish (Notolepis coatsi) and other species.
Cephalopod beaks were quite abundant in the stomachs of toothfish. These beaks were identified as belonging to large Antarctic squids: M.hamiltoni, P.glacialis ? K.longimana. Analysis of distribution and ecology of species prayed by Antarctic toothfish shows that D. mawsoni apparently represents a fast-swimming predator with wide feeding spectrum. Its diet includes bottom, bathy- and mesopelagic fishes as well as large squids.

The results of the histological analysis of the Antarctic toothfish (Dissostichus mawsoni) reproductive system, caught in December-March, 2004-2005 by the longliner VOLNA in subareas 88.1 and 88.2 in the Ross Sea are presented. The morphological parameters, indices of gonads have been described. The histological criteria of the assessment of the ovary maturity stages and cytological parameters of oocytes and type of the toothfish oogenesis have been determined. Under the maturing of toothfish ovaries from the stages II to IV show a slow increase in oocyte diameter. It was shown that for Antarctic toothfish during the fishing period the individuals with gonads of the III late stage of maturity were dominated. Their ovaries contained three size groups of oocytes: cytoplasmic group and two groups of vitellogenous oocytes. The type of the toothfish oogenesis has been defined as intermitted. The large oocytes of the nearest spawning season with average diameter 1000 - 1200?10-6 m have composed 5.4% of total cell number. The oocytes in the ovaries of analyzed fish did not reach the maximum size; consequently Antarctic toothfish was not matured for spawning in the Ross Sea during the investigation period.