N.C.S. acknowledges the financial support of the UK Natural Environment Research Council (NERC; GW4+ studentships NE/L002434/1), the Centre for Environment, Fisheries and Aquaculture Science (Cefas) and Willis Research Network. Three Cefas employees (S.C.M., J.K.P. and B.L.T.) are authors of this work. S.C.M., J.K.P. and B.L.T. acknowledge financial support from the Commonwealth Marine Economies Programme of the UK Foreign and Commonwealth Office (C7049). We thank the World Bank for comments on the draft manuscript.