Population dynamics and fishery policy for migratory resources with two migration paths

Abstract

The population dynamics and fishery policy for a migratory resource with two migration paths are analyzed, based on the supposition that the resource separates into two groups, each migrating along and caught on a different path, after reproduction in a limited area. Two possible mechanisms determining individual migration paths are considered: (i) ``nongenetically controlled'' migration and (ii) ``genetically controlled'' migration. Initially, the relationships between the resource population dynamics and the fishery are analyzed for both these cases. Based on these results, the optimal fishery policy for each migration path is analyzed. Two criteria to be maximized were considered: (i) the ``game situation,'' which aims to maximize catches on each fishery path, and (ii) the ``cooperative situation,'' which aims to maximize the total, overall catch on both paths. In the case of genetically controlled migration, a fishery based on one path negatively affects recruitment on that path but positively affects recruitment on the alternative path. In both the nongenetically controlled and genetically controlled migration cases, the cooperative policy resulted in higher overall maximum catch, especially in the latter case. In the genetically controlled migration case, convergence to equilibrium is often slow, the rate being affected by density dependence of mortalities.