An updated descriptive analysis of the toothfish (Dissostichus spp.) tagging program in Subareas 88.1 and 88.2 for 2006/07

The descriptive analyses of the toothfish tagging programme carried out in Subareas 88.1 and 88.2 since 2001 are updated, including data for the 2007 season for all vessels. This paper provides an update of the preliminary tag-release and tag-recapture data that were presented at the July 2007 meeting of WG-SAM by including revised data and data from non-New Zealand vessels that fished in 2007.
Overall, a total of 15 088 Antarctic toothfish have been reported as released and 458 recaptured, and 911 Patagonian toothfish released and 43 recaptured since 2001.
The number of tags recaptured in the Ross Sea in 2007 by New Zealand vessels was the highest annual recapture to date and double the number caught in 2006, although the nature of these recaptures suggests that assumptions of homogeneous mixing may need to be investigated. For the first time, long distance movements of Antarctic toothfish were observed from toothfish tagged by fishing vessels. Six fish moved 400–600 km from the slope fisheries in SSRUs 88.1H, 88.1I, and 88.1K to grounds off Terra Nova Bay and Ross Island in SSRU 88.1J. There was also some evidence that more fish are recaptured after a longer time at liberty on the slope than in the North. In addition, a Patagonian toothfish tagged near Macquarie Island was recaptured in the north of the Ross Sea, after 4 years at liberty.
Analysis of tag recapture rates suggested some evidence that rates between New Zealand and non-New Zealand vessels were different, and further, that the rate that tags were recaptured from vessels of different nations were different. The reason for these differences is unclear, but may related to different survival rates of fish tagged by different vessels, different detection rates of tagged fish on different vessels, and/or incomplete spatial mixing of the fish tagged by different vessels in different local regions. Further investigation is required.