Covariates of release mortality and tag loss in large-scale tuna taggingexperiments

tThe data from tag-recapture experiments, which are used to help understand animal behaviour anddynamics, and to provide input data for population models such as stock assessments, are affected bymortality associated with tagging and by tag shedding. These processes introduce bias and uncertaintyinto parameters estimated in population models such as tuna stock assessments. The causes and magni-tudes of tag shedding and post-release mortality in tuna tagging experiments are not well understood.We analysed data from tuna tagging experiments in the Western Pacific (330,000 releases) and IndianOceans (168,000 releases) to investigate factors affecting post-release mortality and tag shedding. Tagreturn rates were modelled as functions of the tagger identity, tagger experience, tagging assistant, tag-ging station, treatment of the fish, use of oxytetracycline, tuna species, and size at release.