Recent research has warned that liberalising trade in capture fish products originating from inefficiently managed fisheries might cause over-exploitation, reduced fish stocks and thereby a reduced steady-state of welfare. This paper qualifies the warning in a case study of the East Baltic cod market by developing an age-structured bio-economic supply model combined with basic theory of trade between two countries. Welfare effects of trade liberalisation are identified taking fishing quotas, input limitations, mesh-size regulations and shared ownership of stocks into account. It is shown that even though liberalising trade in products supplied by such a fishery might cause steady-state welfare reductions in the supplier countries, these welfare reductions are small compared to the welfare gains from a hypothetical change to optimal management. Hence, the introduction of better fisheries management is much more important than trying to meet potential negative consequences of trade liberalisation, since even small improvements in fisheries management may offset the negative effects of trade liberalisation. Keywords: EU enlargement, trade liberalisation, fisheries management, shared stock, backward-bending supply, welfare.