CCAMLR

Over the last two years, discussions in WG-EMM, WG-FSA and the Scientific Committee have highlighted a need to develop an integrated work plan to develop and validate assessment methods.
WG-FSA noted (paragraph 11.3, WG-FSA 2001) that there are substantial difficulties added to the work of the assessment subgroup when new quantitative methodologies are introduced and incorporated into assessments undertaken during the time of a single meeting of WG-FSA. Issues related to the current procedures and new assessment techniques need to be introduced to the assessment subgroup and tested prior to WG-FSA. The Working Group suggested that the best way to achieve this is for the assessment subgroup to have intersessional communication to identify and discuss concerns, requirements and new methods. The activities of the assessment subgroup should be prioritised before the meeting to increase the efficiency and quality of the assessments.
This paper amalgamates the correspondence from during the year and the papers submitted to WG-FSA to provide draft points for discussion by WG-FSA on
1. materials available to WG-FSA for incorporating into assessments
2. a draft plan for assessments at WG-FSA this year, including reporting and archiving.
3. a proposed workplan for the future, including a timetable for work in the 2003 intersessional period.

Results of the inventory trawling survey of icefish carried out by Russian vessel STM-8390 Atlantida in February 2002 in Subarea 48.3 are presented. During this period, the fish were mainly foraging. Champsocephalus gunnary 22-28 cm in length at the age of 2-3 predominated on all grounds of the Subarea, except the north-eastern part. During the survey, specimens 15 cm in length at the age of 2 prevailed in pelagic catches. Peculiarity of Ch. gunnary biology in 2002 consisted in high internal fatness at low stomach fullness. On the eastern shelf part, a considerable number of pre-spawning specimens had already been detected, which was not characteristic of that month. .Total biomass near the bottom estimated by different methods is amounted to 38 – 45 thous. t.

Dynamic production models (DPM) have been proposed for D. eleginoides stock assessment in subarea 48.3. This type of the models differ from the models currently used by CCAMLR Working group on fish stock assessment as they do not require certain initial data and parameters (natural mortality, age selectivity, recruitment estimates, mean weight at age) In the calculations with DPM (with Schaefer and Fox production functions) were used: total yield for a series of years and abundance index describing interyear biomass dynamics (standardized catch per unit effort for 1986- 2001) and fishing effort estimates by years of fishing.
Both models showed that the D. eleginoides stock status at the initial period of intensive fishery was at the level of 22-24 thousand tons. In 1989-1990 stock size increased (to ~31 thousand tons) and then gradually declined, having reached the minimu m size of 12 thousand tons in recent years.
The trends in biomass dynamic estimated by DPM are very similar with trends from dynamic age-structured production model ( ASPM) (Gasiukov, Dorovskich, 2000): DPM and ASPM display more then twofold decline of total biomass since 1990 until now.

Samples of Chaenocephalus aceratus were collected during a trawl survey carried out around the South Shetland Islands in the austral summer 2002 (January-February). Fish were caught by commercial bottom trawl fishing down to 500 m depth, using a stratified randomized sampling design. As observed in other recent surveys within the same area, C. aceratus represented one of the predominant species. Overall, 357 specimens ranging from 13 and 67 cm (TL) were selected for the present study. Ages were estimated by counting annuli present in the sagittal otoliths, exposed by grinding and polishing along their sagittal plane. To estimate the precision of age data, we compared blind readings by readers from different institutions. The age range was 1-17 years for females and 1- 15 years for males. Von Bertalanffy growth curves were fitted to the estimated age-length data for each sex. The estimated values of asymptotic length L??(cm) and K (year-1) were respectively 79.8 and 0.07 for females and 60.0 and 0.09 for males. The growth performance index ranged between 2 and 2.5, similar to that reported in other icefish. Sexual maturity was attained by females and males at about 10 and 9 years old respectively, at about 60 % of their maximum estimated age. These results are compared with age and growth data available in the literature for C. aceratus, and discussed in the light of recent commercial exploitation.

The CPUE-based Age-Structured Production Model (ASPM) assessment of this resource by Brandão et al. (2001) is updated to take account of further catch and effort data that have become available over the past year. This leads to an improved picture of resource status compared to a year previously, but a spawning biomass nevertheless still estimated to be heavily depleted and at a level of only a few percent of its average pre-exploitation abundance. However, predictions from this assessment are at variance with the observed length frequency distributions for the fishery. It is important that the assessment model be refined to provide a consistent explanation of all the available data, as this might not only alter perceptions of the status of the Prince Edward Island resource, but also have important consequences for the assessments of other populations of toothfish in the CCAMLR region.

To provide an age-length key for use in modelling the age structure of the Patagonian toothfish stock around South Georgia, we used otoliths to estimate the age of a sample of 264 Patagonian toothfish (Dissostichus eleginoides) captured in the longline fishery. We used a thin section grinding machine to reveal a transverse plane through the otolith nucleus and between crenellations. A single reader undertook three readings of the sections, estimating age using criteria corresponding to those given by the CCAMLR Otolith Network for toothfish from South Georgia. Age estimates during the first two readings were significantly biased relative to reference ages but the third reading, after the reader had read more than 3000 otoliths, was not biased. For data pooled from this study and the South Georgia fisheries survey in 2000, estimates of the Von Bertalanffy parameters were L8 = 123.8, K = 0.10 and t0 = -2.1 for males; for females, L8 = 144.9, K = 0.085 and t0 = -2.0. Using these age data, we estimated total mortality to be Z = 0.054.

To provide an age-length key for use in modelling the age structure of the Patagonian toothfish stock around the Falkland Islands, we used otoliths to estimate the age of a sample of 1893 Patagonian toothfish (Dissostichus eleginoides) captured by trawl and in the longline fishery. We used a thin section grinding machine to reveal a transverse plane through the otolith nucleus and between crenellations. Two readers undertook one reading each of the sections, estimating age using criteria agreed at the CCAMLR Otolith Network. Age estimates by the experienced reader were unbiased relative to reference ages. However, the second trainee reader consistently over-estimated the age of younger fish, and her readings were not used in the analysis. Estimates of the Von Bertalanffy parameters were L8 = 129.3, K = 0.12 and t0 = -1.55 for females; for males, L8 = 110.9, K = 0.156 and t0 = -1.12. Using these age data, we estimated total mortality to be Z = 0.27.

Data on food and feeding of two icefish species, Champsocephalus gunnari and Chaenocephalus aceratus, were collected in the Elephant Island – South Shetland Islands region during the AMLR cruise in March 2001 with RV ‘Yuzhmorgeologiya’ and ANTXIX/3 in January – February 2002 with RV ‘Polarstern’. C. gunnari fed almost exclusively on krill (Euphausia superba) in both years. C. aceratus fed on krill and other crustaceans as well as on fish. C. aceratus smaller than 30 – 35 cm relied primarily on krill and other crustaceans while larger fish preyed predominantly on fish. They fed mainly on locally abundant fish species which were G. gibberifrons in 2001 and L. larseni and C. gunnari in 2002.

This paper reports on continuing exploration of conversion factors and the relationship between product weight & length frequency distribution in the exploratory fishery for Dissostichus spp. in sub-area 88.1 and more recently in sub-area 88.2.