Comment on: "Managing fisheries from space: Google Earth improves estimates of distant fish catches" by Al-Abdulrazzak and Pauly

Abstract

This Comment was prompted by the substantial difference in weir catch estimates in the Gulf between (i) those reported by Al-Abdulrazzak and Pauly (2014. Managing fisheries from space: Google Earth improves estimates of distant fish catches. ICES Journal of Marine Science, 71(3), 450-454), who used Google Earth to count weir numbers, and (ii) those available from official national statistics provided by two major weir fishing countries (Bahrain and Iran). Satellite imageries, including Google Earth, are powerful tools for collecting data on visible structures when verified with adequate ground validation. However, an extension of their contribution to improving overall catch estimates is rather limited without having solid information on daily catch, which will substantially differ according to time and area, and fishing season lengths. It was noted that Al-Abdulrazzak and Pauly (2013) introduced positive biases through their interpretation of Google Earth images and data treatment. They included several assumptions, such as removing the impact of poor visibility, correcting grids of low resolutions, estimating number of unseenweirs, and applying daily catch rates higher than referenced observed values. The overall extent of such potential positive bias could be more than six times that whichwe considered reasonable. This Comment also corrects misconceptions about "FAO catch data", discusses other available national data, and introduces the existence of the Regional Commission for Fisheries (RECOFI), a mechanism for fisheries management in the Gulf region, and its recent activities to collect more complete catch and effort data separated by gear.