Publication Abstract

Preventing overexploitation of migratory fish stocks: the efficacy of marine protected areas in a stochastic environment

Christopher D. West*, Calvin Dytham, David Righton*, Jonathan W. Pitchford

Marine protected areas (MPAs) have been widely proposed as a method of protecting over-exploited fish populations. It has been suggested that fisheries may be enhanced by spillover of individuals from MPAs into fishing grounds. However, traditional spillover studies fail to account for seasonal migrations that occur in many fish populations. Most fisheries models also fail to include the stochasticity inherent in marine environments. In this paper we assess MPA efficacy using a simple population model which simulates the migration of fish populations between an MPA and fishery within a variable environment. Including stochasticity in our model allows the population to deviate from positive stable equilibria, something which is impossible in a deterministic analysis. This deviation may result in population collapse, especially with high levels of migration, in parameter space in which deterministic analysis predicts population persistence. We show that as migration increases, the ability of MPAs to protect stocks from collapse generally decreases. Despite this result, we argue that MPAs may still play a role in the protection of migratory species as, in comparison with a system without an MPA, they provide greater levels of protection. Additionally, combining MPAs with a harvest control rule further increases their level of protection.

Reference:

West*, C.D., C. Dytham, D. Righton*, J. W. Pitchford (2009) Preventing overexploitation of migratory fish stocks: the efficacy of marine protected areas in a stochastic environment. ICES Journal of Marine Science 66 (9) 1919-1930