Dynamics of coastal cod populations: intra- and intercohort density dependence and stochastic processes

Abstract

Skagerrak populations of Atlantic cod (Gadus morhua L.) have been surveyed at several fixed stations since 1919. These coastal populations consist of local stocks with a low age of maturity and a short life span. We investigated 60 time–series of 0–group juveniles (i.e. young of the year) sampled annually from 1945 to 1994. An age–structured model was developed which incorporates asymmetrical interactions between the juvenile cohorts (0–group and 1–group; i.e. one–year–old juveniles) and stochastic reproduction. The model was expressed in delay coordinates in order to estimate model parameters directly from the time–series and thereby test the model predictions. The autocovariance structure of the time–series was consistent with the delay coordinates model superimposed upon a long–term trend. The model illustrates how both regulatory (density–dependent) and disruptive (stochastic) forces are crucial in shaping the dynamics of the coastal cod populations. The age–structured life cycle acts to resonance the stochasticity inherent in the recruitment process.