If the technology in a multi-species fishery is such that there is jointness in inputs and non-separability between inputs and outputs, then management on a species-by-species basis may lead to unintended outcomes, including over-exploitation of the resource. This study investigates the nature of the technical and economic relationships underlying the 1989-1990 Mauritanian cephalopod fishery by estimating a system of dual output supply functions derived from a generalized Leontief revenue function. Model results indicate the existence of jointness in inputs and non-separability between inputs and outputs in the fishery. Cross-price elasticities indicated a number of substitute and complementary relationships, with these relationships changing in magnitude across years. Taken together, the results suggest that any attempts to economically manage the resource should be based on multi-product production theory, not single-species biological response functions. Besides ruling out single-species management, the dominance of substitute relationships in the Mauritanian cephalopod fishery precludes the use of "key species" management of the entire resource.