abstract:Bigeye tuna has been the second largest catch species of the Taiwanese longline fishery in the Atlantic Ocean since 1990. In 2004, there were 98 bigeye vessels, but the number decreased to 15 in 2006 to implement the ICCAT Recommendation 05-02. The data from VMS has been used to verify the logbook information to improve the data quality. More than 95% of the differences between logbook position and VMS position were within 2 degrees in both longitude and latitude, and the percentages have increased by years. Observer data are being used as a reference when analyzing logbook catch and effort information to improve research quality. In 2006, the 15 bigeye vessels authorized to fish in Atlantic Ocean were 100% observed by observers. The size sample of bigeye tuna has been widely distributed in time and ICCAT statistical area and only 1% substitutions were needed in the development of catch-at-size data for stock assessment purposes.