10.1016/s0967-0653(97)88094-5

Abstract

Estimates of tag-shed­ ding and tag-reporting rates are re­ quired for an estimation of fishing and natural mortality rates from tagging data. For this purpose. double-tagging and tag-seeding experiments were un­ dertaken by the South Pacific Commis­ sion, in conjunction with a large-scale tuna tagging program, in the western tropical Pacific Ocean during 1989­ 1992. Estimates of tag-shedding rates indicated that 89% (95% confidence in­ terval of82%-94%) oftagged tuna still retained their tags after two years at liberty. Differences in shedding rates among skipjack, yellowfin. and bigeye tuna. and differences in shedding rates among taggers were found not to be sta­ tistically significant. Tag seeding car­ ried out on board purse seiners by ob­ servers resulted in 342 returns of the 532 tags seeded, for a return rate of64% (60%-68%l. The return rate of seeded tags varied significantly by unloading location (most tags were recovered dur­ ing unloading>. but not by species. The highest return rates of seeded tags oc­ curred from American Samoa, Philip­ pines, and Solomon Islands. whereas Korea and Thailand had the lowest re­ turn rates. The overall average report­ ing rate. weighted by the estimated numbers of tags recovered at each lo­ cation. was 0.59. Abootstrap procedure was used to estimate a 95% confidence interval of 0.49-0.67. These results implied that. of the 146.581 tags re­ leased during the large-scale tagging program, 31,166 (27,208-37,264) were recaptured, of which 18.266 were re­ turned to the South Pacific Commission.