Ecosystem model for evaluating potential cod production in a west Norwegian fjord

Abstract

Four age groups of Gadus morhua were represented as well as the main prey groups. These groups made up a near-shore compartment of the model, while nutrients, phytoplankton, herbivorous, carnivorous and gelatinous zooplankton comprised a pelagic compartment. The two compartments were coupled through water exchange. Cod production is sensitive to the amount of zooplankton advected into the fjord and to the availability of benthic preys. Under good environmental conditions maximal cod production is estimated to be 0.5 to 1.3 × 106 ind. yr-1, which is 7-8 times higher than the average levels of natural cod recruitment. Recruitment beyond 0.5 to 1.3 × 106 ind. yr-1 will reduce the overall cod production because of food shortage and cannibalism. Optimal cod production is obtained if the sum of released and wild recruits is within the range of the carrying capacity of juveniles. Releases of the same number of juveniles in several years gives dissimilar cod production due to interannual variations in the magnitude of advection, and its influence on zooplankton availability in Masfjorden. -from Authors