Maximum Yield Fishing and Optimal Fleet Composition. A Stage Structured Model Analysis With an Example From the Norwegian North-East Arctic Cod Fishery

A stage structured fishery model with three stages; recruits, immature fish and mature fish is formulated and utilized to analyse maximum sustainable yield (MSY) and optimal harvesting composition in a fishery with two heterogeneous fleets. The stage structured model developed bundles the age classes found in age structured models into stage classes based on their level of maturity, but also the pattern according to which they are harvested. Two fleets, high sea and coastal vessels, harvest respectively the immature and mature stages. The maximum sustainable yield (MSY) is studied in light of both perfect and imperfect fishing selectivity. In addition, we analyse the biomass loss of a sharing rule where the high sea trawler fleet is granted a certain share of the harvested biomass. The paper provides a theoretical extension to the literature on age structured models, and presents several new analytical results related to stage structured models which are supported by a numerical illustration inspired by the North-East Arctic cod fishery.