Quantifying vessel performance in the CCAMLR tagging program: spatially and temporally controlled measures of tag-detection rates
A reliable commercial fish tagging program is critical to the successful management of a number of toothfish fisheries in Antarctica. In particular, tag-detection rates are directly linked to stock size estimated from the tag data in an integrated stock assessment. Previous attempts to assess the relative reliability of vessels in detecting tagged fish have been inconclusive due to low numbers of recaptures after controlling for spatial and temporal confounding. This paper presents a method that utilised most of the data while also controlling for spatial and temporal variables using a case-control study design, and uses this method to develop relative indices for detection rate performance for vessels involved in the Antarctic toothfish tagging in CCAMLR Subareas 88.1 and 88.2.
The index derived provides evidence of significant differences in the relative performance of vessels in the Antarctic toothfish fishery in CCAMLR Subareas 88.1 and 88.2, as well as changes in the performance of some vessels over time. Further investigations show that these indices appear robust to the assumptions made, in particular the choice of the control group and the maximum distance between fishing events compared. The results suggest that the method can be useful for assessing the relative vessel tagging performance across all CCAMLR fisheries, and may potentially be developed as a more general method for comparing relative performance of spatially and temporally heterogeneous datasets.