Stock Assessment and Current Biological Viability of Small Pelagic Fish Stocks in Ghana

Abstract

Since 2000 landings of small pelagic fish species which provide employment, income and nutrition to over 2 million people have faced a sharp decline, evident from the decreased CPUE and increased average zero catch rate for fishing trips. To reverse the decline, a study was supported by USAID to assess the stocks of the four main pelagic fish species to ascertain their biological viability for sustainable management. Fish catch data was provided by the Fisheries Scientific Survey Division (FSSD) of the Fisheries Commission (FC). The assessment was carried out with the CEDA software package, applying the various production models that best fit the catch of the most dominant fishing gear (purse seines) and total standardized effort data of each pelagic stock. The best fit biomass production models for the species were the Fox Algorithm for anchovy and flat sardinella, Pella Tomlinson for mackerel, and the Schaeffer model for round sardinella. The intrinsic population growth rate r, tonnes/annum, and the carrying capacity K, tonnes, for the pelagic species were found to be, for anchovy 0.572 and 171,921, mackerel 0.147 and 147,417, round sardinella 0.693 and 245,659, and flat sardinella 0.194 and 83,312 respectively. Further a total biomass of 324,156 tonnes was required to restore the small pelagic stocks to the maximum sustainable yield (MSY) level whereas the present biomass, B_msy was only 44,771 tonnes; the current average fishing mortality was 0.72 while that required to manage the stocks at MSY was 0.2; and the current number of canoes fishing was 14,462 while that required at sustainable level was 9,000. Enforcement of size restriction regulations, alignment of the current level of effort and capacity with the maximum sustainable yield, institutionalization of closed seasons, introduction of supplementary or alternative livelihoods opportunities and a robust system for monitoring environmental parameters were recommended essential for sustainable management of the pelagic fishery.