CCAMLR

New length-at – age data for South Georgia toothfish are presented from a range of sources. Data from the commercial fishery, research trawl surveys and pelagic plankton tows are combined to generate new von Bertalanffy parameters. The new parameters (L(inf) 150cm, K= 0.073 and t0 = -0.792 are similar to values obtained in previous studies at South Georgia and other sub-Antarctic islands. Evidence for the separation of early year classes is presented along with mean sizes for each age class.
Age length keys indicate that fish enter the fishery at 7 years and are fully recruited at between 10 and 11 years.

This report describes the activities and preliminary results of the 9th UK fish stock assessment survey within CCAMLR Statistical subarea 48.3 (South Georgia) which was carried our by MRAG and British Antarctic Survey scientists during January and February 2004. In addition to the random stratified bottom trawl survey the research was extended by a week in order that further investigations into the use of acoustic methods for the determination of icefish biomass could be undertaken. Following the recommendations of the CCAMLR subgroup on fisheries acoustics (WG –SFA) emphasis was to be put on obtaining information on the target strength and length composition of the pelagic component of the icefish biomass. A continued emphasis on providing information on bycatch species gave a further key aim to the survey.

This report presents results of an exploratory fishery for Antarctic toothfish (D. mawsoni) conducted by the Russian vessels “Yantar” and “Volna” for two seasons of 2002/03 and 2003/04.
The analysis of data collected relates to catch composition, effort , CPUE, and biological characteristics in different SSRU, month and depth of sets longlines. The comparison of these resultants showed that in the general fishery effort (quantity of sets and hooks) in those two seasons were similar (233 sets and 1,55 mln. hooks in 2002/03, and 222 sets and 1,79 mln. hooks in 2003/04 ). But the total catch of D.mawsoni was very different:703 t in 2002/03, and 276 t in 2003/04. CPUE what were comparing in different SSRU has been also much smaller in 2003/04 season. The analysis of the length composition fish from the catches by longlines at different depth shows a tendency toward an increase in the modal length on the deeper ground .The modal length of toothfish caught in the different seasons and month did not change so strong. Meanwhile, the modal length of fish catches in the 2003/04 season was slightly lower than in the previous season. This trend is clearly seen when comparing the length frequencies of fish in different seasons among the largest individuals. It was very interesting that in the both seasons we had two modal classes: between 120-130sm, and second-near 145-150sm. The more detailed consideration of the length composition from the different SSRU catches showed that the individuals of the smaller size were caught closer to the shore while the larger ones of the second modal group were captured in the northern off-shore zone of the Ross Sea.

At WG-EMM in Siena, 2004, the UK reported on the bycatch of fur seals in the krill fishery around South Georgia, and on mitigation methods that were being developed and deployed to avoid fur seal deaths in the fishery. WG-EMM requested the UK to provide further details of the methods employed for consideration of IMAF. Observers recorded mitigation measures for fur seal (Arctocephalus gazella) entanglements on krill vessels fishing around South Georgia in the 2004 fishing season. The measures implemented were based on 4 themes: Physical barrier, barrier plus escape hatch, manufactured seal exclusion devices and gear configuration. Those vessels initially without mitigation measures were able to introduce them without further cost and minimal disruption to fishing activity.

We conducted several different assessments of toothfish in Subarea 48.3 using four different methods, one fishery dependent and three fishery-independent. Survey-generated recruitment is apparently not sufficient to generate realistic estimates of current biomass using GYM. ASPM runs coded in AD Modelbuilder failed to fit satisfactorily to CPUE trends and catch length composition. The most consistent results were provided by tag-recapture data adjusted for initial tag mortality, natural mortality, tag loss rates and fishery age-based selectivity. Estimations based on local depletions of toothfish generated results essentially similar to the tagging data. Based on these results, we conclude that the most likely current exploitable biomass of toothfish in Subarea 48.3 is between 45,000 and 62,000 t. GYM was run to generate these levels of exploitable biomass at the start of 2004. This generated estimates of yield between 3240 and 4150 tonnes.

A preliminary assessment of mackerel icefish, Champsocephalus gunnari, was undertaken for South Georgia (Subarea 48.3) using the standard CCAMLR methodology. This was based on the results of a UK bottom trawl survey during January 2004. Using CCAMLR decision rules, an estimate of the one-sided 95% confidence bound for the total biomass for 2003/04 was obtained using the bootstrap method for age 2+ fish only (age 1+ were not available from UK acoustic data in 2004). Estimates of short-term yield estimated within the GYM for 2004/05 and 2005/06 were 4,270 tonnes and 2,357 tonnes respectively.

A survey of Mackerel Icefish, Champsocephalus gunnari,was undertaken in Division 58.5.2 in the vicinity of Heard Island in May 2004 to provide the information for an assessment of short-term annual yield in the 2004/2005 CCAMLR season. This paper provides a preliminary assessment of yield using the assessment methods of CCAMLR for SAFAG 21.