ESTIMATES OF TAG-REPORTING AND TAG-SHEDDING RATES IN A LARGE-SCALE TUNA TAGGING EXPERIMENT IN THE WESTERN TROPICAL PACIFIC-OCEAN

Estimates of tag-shedding and tag-reporting rates are required for an estimation of fishing and natural mortality rates from tagging data. F or this purpose, double-tagging and tag-seeding experiments were under taken by the South Pacific Commission, in conjunction with a large-sca le tuna tagging program, in the western tropical Pacific Ocean during 1989-1992. Estimates of tag-shedding rates indicated that 89% (95% con fidence interval of 82%-94%) of tagged tuna still retained their tags after two years at liberty. Differences in shedding rates among skipja ck, yellowfin, and bigeye tuna, and differences in shedding rates amon g taggers were found not to be statistically significant. Tag seeding carried out on board purse seiners by observers resulted in 342 return s of the 532 tags seeded, for a return rate of 64% (60%-68%). The retu rn rate of seeded tags varied significantly by unloading location (mos t tags were recovered during unloading), but not by species. The highe st return rates of seeded tags occurred from American Samoa, Philippin es, and Solomon Islands, whereas Korea and Thailand had the lowest ret urn rates. The overall average reporting rate, weighted by the estimat ed numbers of tags recovered at each location, was 0.59. A bootstrap p rocedure was used to estimate a 95% confidence interval of 0.49-0.67. These results implied that, of the 146,581 tags released during the la rge-scale tagging program, 31,166 (27,208-37,264) were recaptured, of which 18,266 were returned to the South Pacific Commission.