Systems dynamics of North arctic cod

Systems dynamics of North arctic cod is a non-linear time varying dynamic process dependent on the ecology and the landings systems. In this dynamic system it is detected a dynamic process closely correlated to temperature cycles of 3*18.6=55.8 years, 18.6 years and 18.6/3=6.2 years. The temperature cycles is related to changes in the earth nutation and thus expected to be deterministic. The 6.2 year temperature cycle seems to have an important influence of cod recruitment, growth rate and landings. The temperature cycle of 18.6 years and 55.8 years seems to influence the growth rate and the maximum biomass. A delay in decision a level of landing, seems to introduce an instability in the biomass. In the paper it is suggested a control strategy to control the dynamics introduces by the temperature cycles. The deterministic dynamic properties of recruitment opens for a simplification of the dynamic modelling and forecasting of North arctic cod. In the paper it is identified a systems dynamics models that may be used for forecasting future biomass.