CCAMLR

Application of lead-radium dating was attempted as a feasibility study for otoliths of blackfin icefish (Chaenocephalus aceratus) and ocellated icefish (Chionodraco rastrospinosus). Because otoliths from these fishes were small and the number of otoliths available low, a whole otolith application was necessary as a first look at lead-radium levels. The application was successful as a first step in determining the parameters of future applications that would lead to a validation of age. In the current study, sample mass for the pooled otolith samples was low (~0.4 g). This finding, coupled with low radium-226 levels, led to age determinations that had a high margin of uncertainty; however, the findings led to an educated recommendation for future lead-radium dating studies for these species. Based on the measured lead-radium levels, the future direction may include further exploration of the whole otolith approach. This approach has some disadvantages, such as the circularity associated with developing a mass-growth model, but would provide the opportunity to make an age determination that does not reply on growth zone counting. Furthermore, a follow-up lead-radium dating study using cored otoliths (extraction of the first few years of growth) is possible for these species, provided there is enough sample mass and perhaps an application of micromilling. This approach would require ~150 otoliths per sample, given an arbitrary target core weight of 0.01 g, near the low end of the range used in this study. It is recommended that the collection of otoliths from these species be given a priority whenever possible to facilitate future age and growth studies and potential applications of lead-radium dating.

We asked whether silverfish (Pleuragramma antarcticum) are distributed in independent, discrete populations along the Western Antarctic Peninsula (WAP), or whether the shelf circulation leads to connectivity, by testing between rival hypotheses of population segregation and linkage. If independent, reduction in sea-ice along the WAP may lead to extinction of local populations through drastic mortality of early stages which are ice-dependent. Alternatively, if linked by the large-scale circulation, abundance in areas subsidized by migration may be more robust to declining sea ice coverage. We provide preliminary data from sampling along the WAP on board the R/V Nathaniel B. Palmer, including initial simulations using a circulation model. Differences in length distributions and maturity suggested two discrete populations at 1) the north tip of the Peninsula, and 2) the southern WAP encompassing Charcot Island and Marguerite Bay, with no mixing between. The presence of a single length mode at Charcot Island and Marguerite Bay corresponding to the year class found during GLOBEC 2001 suggested a dominant cohort and no local recruitment since 2001. The collapse in silverfish abundances previously found off Anvers and Renaud Islands, without similar collapses to the north and south, suggest a third population in the central WAP. Analyses of otolith chemistry are scheduled over the next year.

At the 2000 Fish Stock Assessment Working Group Meeting (WG-FSA-2000), differences were noted in the growth parameters being used for assessments of toothfish. To assess whether these differences were real or else due to methods of otolith preparation and reading, scientists from CCAMLR member nations participated in a Workshop in 2001 at Old Dominion Unversity with the primary aim of seeking conformity in estimating age of Patagonian toothfish (Dissostichus eleginoides). Arising from the workshop, the Center for Quantitative Fisheries Ecology at Old Dominion University has developed a manual to address recommendations for: the use of otoliths for estimating age; key features to be taken into account in reading otoliths; quality assurance and control; and the use of reference sets to monitor precision.

Presented some data for Dissostichus eleginoides fishery in the southwestern Atlantic Ocean beyond EEZ in statistical divisions 41.3.1 and 41.3.2.

For the determination of the age of Dissostichus mawsoni used otoliths and scales. All samples were collected in the Indian Ocean sector of the Southern Ocean. Methods are described. Otoliths were measured and weighed. All major life periods in corresponding ecological conditions are reflected well in the sections of otoliths as certain groups of the annual rings.

A survey of mackerel icefish, Champsocephalus gunnari, was undertaken in Division 58.5.2 in the vicinity of Heard Island in March-April 2010 to provide the information for an assessment of short-term annual yield in the 2010/2011 CCAMLR season. This paper provides a preliminary assessment of yield for the area of Division 58.5.2 to the west of 79°20’ E using standard CCAMLR methods. The strong year class detected in the last three years’ surveys is now fully recruited as the 4+ cohort, and dominates the population, however it is assumed this cohort will be unavailable to the fishery in 2010/11. A new 2+ cohort has been detected, and it is expected that the fishery in 2010/11 will focus on this cohort. A new growth model is also estimated which shows an improved fit to observed sizes at age of icefish from recent surveys.

For the first time the study of diet composition of deepwater icefish Chionobathyscus dewitti was conducted through Antarctic toothfish Dissostichus mawsoni acted as an “agent”, i.e., all analyzed icefish individuals were taken from stomachs of toothfish caught in the Ross Sea in 2010 from board the longliner “No. 1 IN SUNG”.

Patagonian toothfish (Dissostichus eleginoides) is the target species of a bottom longline fishery occurring in the Southern Indian Ocean off Kerguelen and Crozet islands. This fishery is exposed to high levels of interactions with cetaceans removing fish from the fishing gear and to accidental bird mortality. In order to find a solution to these issues a 25-day pot trial cruise was conducted on board vessel Austral Leader II from January 22nd to February 17th 2010 with a period of comparison with longliners. This paper describes the trial and the results obtained with different pot models. The catch rate of Patagonian toothfish with pot was lower than when using longline but direct comparison are not straightforward due to the large number of pot model tested and the large differences in fishing techniques and further investigations are needed to be in position to asses the economic viability of such fishery. One of the aim of the study was to test different pot models to assess differences in fishing efficiency and in their by catch. Crab by-catch was identified as a major issue which still needs to be solved. Furthermore the operational, safety and social issues should also be taken into consideration before planning to implement such fishery. Bird by-catch and depredation was eliminated using pot.

This paper summarises recent, fishery-related scientific research notified in accordance with Conservation Measure 24-01. Four notifications were received by the Secretariat for research in 2009/10, and five notifications have been received to date for research in 2010/11. Details of the notifications for 2010/11 are appended.

This paper summarises the information collected by observers for the 2009/10 season relating to compliance with Conservation Measures 24-02 (2008), 25-02 (2009), 25-03 (2009) and 26-01 (2009).