Assessment of the Maximum Sustainable Yield (MSY) of the Tuna Fishery in Ghana and its Application in Management

Abstract

The Ghanaian tuna fishery is a thriving industry employing more than 15,000 people. Three major tuna species, Skipjack (Katsuwonus pelamis), Yellowfin (Thunnus albacares) and the Bigeye (Thunnus obesus) form the base of the fishery. High fishing effort, use of modern technologies, fish aggregating devices and increased number of vessels have increased total landings, largely composed of juveniles. This study assessed the catch trends and sustainability of the fishery in Ghana. The results indicated that total tuna landings declined from 94,180 MT in 2010 to 79,447 MT in 2013. K. pelamis dominated the landings from 1987 to 2013 with an average component of 71 % of current landings. T. obesus contributed least of the three species, with 12.13 % composition of current landings. Catch per unit effort, (CPUE), of the fishery declined from 29.49 MT/fishermanday in 2001 to 17.12 MT/fishermanday in 2013, symptomatic of overfishing. Using the equilibrium assumptions of the Schaefer’s Surplus Production Model, 187.38 MT, 20,091.59 MT, 60,274.38 MT and 2,091.56 MT were the MSY estimates for T. obesus, T. albacares. K. pelamis and the artisanal fishery, respectively, making a total of 82,644.91 MT with average FMSY of 3,076 fishermandays. The total MSY for the tuna fishery, 82,644.91 MT, compared favourably with the range of sustainable yield of the resource estimated to be in the Ghanaian waters. The current average total landings, 86,477.2 MT, is in excess of the estimated MSY. Current landings of both T. obesus and K. pelamis are also in excess of the MSY estimated. The CPUE and MSY coupled with information on size composition of landings of the fishery provided evidence that the tunas in the Ghanaian waters are fully exploited and being overfished. With the stocks of K. pelamis viscous, local management actions would be very useful in managing the stock. The MSY and average FMSY estimated can be useful in setting catch quotas and implementing input controls for the Ghanaian tuna fishery. Although regulations by the International Commission for the Conservation of Atlantic Tunas (ICCAT) have been helpful, national management actions are needed to keep the tuna stocks at sustainable levels to save the highly profitable tuna fishery and industry in Ghana from collapse in the near future. To this end, the cooperation of all stakeholders in the Ghanaian fisheries is needed to plan and enforce practical precautionary management actions including setting restrictive quotas and regulation of inputs of the fishery to moderate Fcurrent and regulate landings. This would not only ensure the sustainability of the fishery but increase its profitability too.