CCAMLR

The icefish fishery on the Kerguelen shelf has been stopped after the1994/95 fishing season when 3889 tonnes of Champsocephalus gunnari were landed (see CCAMLR statistical bulletins) because yields were not enough high and the lucrative fishery of Patagonian toothfish Dissostichus eleginoides deverted fishermen from these specific shallow fishing grounds. However to follow the situation in the area the fishery licences for trawlers have been linked to the obligation of conducting some experimental cruises in the traditionnal area of fish aggregations. Such cruises occur regularly with two trawlers from 1996/97 to 2001/2002, the last season of trawling in the Kerguelen EZ. Preliminary results do not show an increasing of the icefish’s abundance in the surveyed area and biomass seems very low. It is a different situation comparitively to the Heard islands stock where biomass allows catches. This situation is not clearly explained and various hypothesis are proposed: no recovery in a too depleted stock, bad recruitement or emmigration in relation to the ENSO 1998 effect in the vicinity of the islands, increasing of predation by fur seals Arctocephalus gazella growing the population. Other analysis (total and species by species biomass, importance of the by -catch in the area) will follow this preliminary analysis.

Kirkwood and Agnew (2001, paper WG-FSA-01/48) proposed an ad hoc method for estimating selectivity curves for toothfish taken by longliners around South Georgia and Shag Rocks over the period 1995 – 1999. This method was applied by WG-FSA-01, with minor amendments, to estimate annual age-specific selectivities for the years 1995 – 2000 for input to the GYM assessment. In this paper, I propose a revised method for estimating the selectivities based on an assumption that the proportions of the total CPUE in an area for a particular length class that are taken in different depth zones are Beta-distributed. This removes some of the ad hoc nature of the former estimation method. The method is illustrated by application to data for 1995 – 2000.

This manual provides the documentation required for running the spatially-explicit population simulation software, Fish Heaven, which is available through the secretariat as well as the AAD.

This manual provides the documentation required for running the Generalised Yield Model (GYM) and its graphics user interface, which is available through the secretariat as well as the AAD.

This manual provides the documentation required for running the mixture program, CMIX, and its user interface through an Excel spreadsheet Add-In. This software is available through the secretariat as well as the AAD.

Thirty nine Dissostichus eleginoides were released in the vicinity of Heard Island carrying archival tags in April 2002. Since then seven have been recaptured and the depth and temperature data they recorded is analysed here. Most of the fish had periods of active vertical movement alternating with periods of relative inactivity, loosely correlated with moon phase. The direction of vertical movement was influenced by the bottom topography, with fish on the relatively shallow plateau or in the bottom of a valley only moving upwards from their resting depth, while those on the intervening escarpment moved both upwards and downwards. Major vertical movements took place between 0500 and 1100 local time.

In 2001/2002 Russian and UK vessels undertook surveys for icefish at South Georgia. Both used acoustic and trawl methods, and this paper uses both datasets to explore the similarities and differences between the surveys and discuss how much of the variation between the vessels was due to differences in the gear used and how much was due to natural spatial/temporal variability of the stock.
The acoustic surveys indicated that icefish were not only located near to the seabed, but that a significant portion of icefish biomass was located in the water column. Thus the traditional approach of using bottom trawls to assess icefish standing stock has resulted in biased estimates below the true value: acoustic estimates are ~ 1.5 times greater This should be taken into account in the forthcoming stock assessment during WG-FSA–2002.
These results show that the current observation system for the collection of data for icefish stock assessment should be changed to include regular acoustic surveys. This will improve the stock estimates of this species, and to achieve this we recommend the development of new survey designs and corresponding manuals.