Estimating Ghanaian purse seine and baitboat catch during 2006-2013 : input data for 2015 bigeye stock assessment

Ghanaian industrial tuna fisheries data covering the period 2006-2013 were analyzed following guidelines provided during the ICCAT preparatory meeting for the 2015 assessment of bigeye tuna (Thunnus obesus; BET). To account for differences in fishing strategy and quality of data sources available, the fleet was split between a component of large purse seiners and a component composed of baitboats and purse seiners that can collaborate at sea. First, the total Task I was derived from information on landings and logbooks for the first and second fleet components, respectively. Second, the monthly proportion of catch and spatial distribution on a 5°x5° grid were derived from logbook data with some necessary assumptions when data were missing. Third, species composition of the catch was estimated from the size samples collected onboard European purse seiners from fishing sets made on fish aggregating devices based on three processing areas. Bigeye represented about 15% in the ‘offshore’ area while its percentage in the catch was about 7-8% in areas closer to the shore during the same period. Size samples collected by MFRD during 2006-2013 showed that the distribution of bigeye caught by Ghanaian vessels differed from that of European purse seiners on FADs