Dynamics of coastal cod populations: intra- and inter-cohort density-dependence and stochastic processes
Proceedings of the Royal Society of London Series B (1999) 266: 1645-1654.
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 have investigated 60 time series of 0-group juveniles sampled annually from 1945 to 1994. An age-structured model is developed which incorporates asymmetric interactions between the juvenile cohorts (0-group and 1-group) and stochastic reproduction. The model is expressed in delay-coordinates in order to estimate model-parameters directly from the time series, and thereby to test the model-predictions. The autocovariance structures of the time series are consistent with the delay-coordinate 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.