GROUNDFISH SURVEY IN CCAMLR SUB-AREA 48.3 IN APRIL 2008 WITH PRELIMINARY ASSESSMENT OF MACKEREL ICEFISH

In April 2008 the UK undertook a bottom trawl survey of CCAMLR Sub-Area 48.3 on the FV Sil, with 70 bottom trawls undertaken giving good geographic coverage. Using 10 strata and the updated sea-floor areas and adjusting this for the low headline height of the UK trawl (see CCAMLR WG-FSA (2003), the biomass of mackerel icefish was estimated to be 80,426 tonnes, with a lower 1-sided 95% CI of 30,050. Catch-weighted length frequencies indicated that icefish population was dominated by 2+ and 3+ fish, with differences in the size between Shag Rocks and South Georgia and with few small fish in the NW South Georgia area. A preliminary short-term projection of the mackerel icefish stock was run using standard CCAMLR parameters in the GYM. Two scenarios were tested, both assumed that all the 2007/08 catch that remained after the survey (1709 tonnnes) will be taken. Scenario 1, which included the 1+ fish produced yield of 3445 tonnes in Year 1 (2008/09) and 2318 tonnes in Year 2 (2009/10). In Scenario 2, in which the 1+ fish were excluded and biomass adjusted accordingly, yields were 3372 and 2248 tonnes in Years 1 & 2 respectively. The Patagonian toothfish population was dominated by the same cohort that has been detected by surveys since 2003, with no evidence of new recruitment since. Biomass estimates and length frequencies are reported for other non-target species. Conducing the survey in April was successful. The icefish appeared to be dispersed, which is amenable to a random trawl survey. There was evidence that the September 2007 survey under sampled the 2+ fish, meaning that September is not an ideal time for a survey.