Fisheries in Guinea Bissau contribute greatly to the economy and food security of its people. Yet, as the ability of the country to monitor its fisheries is at most weak, and confronted with a heavy foreign fleet presence, the impact of industrial foreign fleets on fisheries catches is unaccounted for in the region. However, their footprint in terms of catch and value on the small-scale sector is heavily felt, through declining availability of fish. Fisheries in Guinea Bissau are operated by both legal (small-scale and industrial), and illegal (foreign unauthorized) fleets, whose catches are barely recorded. In this paper, we assess catches by both the legal and illegal sector, and the economic loss generated by illegal fisheries in the country, then attempt to evaluate the effectiveness of Monitoring Control and Surveillance (MCS) of Guinea Bissau’s fisheries.