Developments towards an investigation of potential bias from the analysis of tag–release and recapture data in Ross Sea Antarctic toothfish abundance estimates

This report outlines developments towards evaluating bias in abundance estimates for the current tagrecapture programme for Antarctic toothfish in the Ross Sea. We present an initial approach that uses the current data on catch (C2 data), tag-recovery effort and tag-release data from Dunn et al. (2005c), but ignores movements of tagged and untagged fish.

The results suggest that as the spatial pattern of tag releases and recovery effort has changed over the years that the tagging programme has operated, these patterns can introduce different levels of bias into the estimates of total population abundance.