CCAMLR

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.

A survey of Patagonian toothfish, Dissostichus eleginoides,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 for the area of Division 58.5.2 to the west of 79 o 20’ E using standard CCAMLR methods. It presents a range of sensitivity analysis for the assessment based on deliberations at WG-FSA 2003 with respect to the surveys and ages included in the estimation of the recruitment series.

Tuck et al. (2003) describe an exact time of release and recapture stock assessment model and applied it to the stock of Patagonian Toothfish, Dissostichus eleginoides,at Macquarie Island that have been fished by Australian trawlers from November 1994. This work was previously presented to the Working Group on Fish Stock assessment in 2000 (Tuck et al. 2000; CAMLR-XIX, 2000 paragraphs 3.126, 3.127). The maximum likelihood estimation for this model has more recently been implemented in the AD Model Builder software by Dr Tuck. The AD Model Builder executable that implements Tuck et al. (2003) in order to estimate fish stocks where appropriate mark-recapture and catch data are available has kindly been made available to the Working Group by Dr Tuck. This paper describes the required inputs and the derived outputs for this implementation.

Assessments of long-term sustainable yield using the Generalised Yield Model (GYM) and the setting of total allowable catches (TAC) for Patagonian Toothfish, Dissostichus eleginoides, for the Heard Island Plateau region (Division 58.5.2) are based on data obtained from annual random stratified trawl surveys (RSTS) and from targeted commercial fishing operations via an observer program. Evaluation of both the current RSTS design for Division 58.5.2 and some options for future modifications of the design is carried out in a simulation environment using the program Fish Heaven with data analysis carried out using Splus. Fish Heaven is a simulation program that uses a spatially-explicit, age-structured fish population dynamics model. Recruitment, movement, mortality, growth, and fishing (both commercial and research) were simulated for the Patagonian Toothfish for the Heard Island Plateau region. Census of fish stocks by age class were compared to population estimates based on simulated RSTS hauls. For a series of 10 years of survey, age 4 recruitment was estimated using 111 RSTS stations, assuming the age of every fish caught in the surveys is known without error and assuming knife-edge fishing selectivity at age 4, using either (a) the age 4-alone RSTS results or (b) age 4 to 8 RSTS results using back-projections from each age to age 4 for each of 6 cohorts.