The northern cod fishery was once one of the world’s largest capture fisheries. Using data from the fishery, this research calculated the economic value of a marine reserve using a stochastic optimal control model with a jump-diffusion process. The analysis shows that, an optimal-sized marine reserve in this fishery would have prevented the fishery’s collapse and generated a triple payoff. Even if harvesting had been ‘optimal’ the profits from fishing would have been raised. The recovery time would also have decreased for the biomass to return to its former state and smoothed fishers’ harvests and profits. Following a negative shock, the chance of a catastrophic collapse would have been lowered.