Data Envelopment Analysis (DEA) models are applied to the main French seaweed fleet to examine capacity output, capacity utilization, and scale inefficiency. Coastal seaweed vessels target only one output - kelp - with the same gear but with different input level combinations. The fishery is seasonal and subject mainly to input regulations, especially a one trip per day regulation implemented in 1987. The consequence was a decline in total observed output and a fall in capacity output and efficient output. Only the largest vessels and a few small vessels harvesting without this regulatory constraint operate at the optimal scale. The question of a change in regulation, especially a shift to an individual quota system, is raised.