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 ¢xed 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 timeseries 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.

Competition among fishermen and fish causes the collapse of Barents Sea capelin

“…The recruitment rate log(N t 1 ͞N tϪ2 mat ) is typically (16,17) assumed to be either a linear or a log-linear function of abundance, i.e., either a linear function of N tϪ2 mat [called the Ricker model (18)] or of log(N tϪ2 mat ) [ Fig. 2e; called the Gompertz model (19)(20)(21)]. As can be seen from Fig.…”

Food web dynamics affect Northeast Arctic cod recruitment

“…We assume a Gompertz relationship (Gompertz 1825; see also Stenseth et al 1999) between the abundance at age five months and at 3 years, with the cod-capelin ratio as a proxy for cannibalism. We also included temperature (Temp) in the cod's spawning year as a proxy for the cod's spatial distribution; cod larvae are transported far east in warm years, which will affect the spatial distribution of this cohort for at least the first year of the cod's life (Helle et al 2002).…”

How effective are maternal effects at having effects?

“…Recent theoretical and empirical studies suggest that intrinsic, delayed, density-dependent processes (such as created by maternal effects) may be a substantial source of variation in population dynamics by introducing a lag into the dynamics (Ginzburg & Taneyhill 1994;Rossiter 1994;Bjornstad et al 1998;Ginzburg 1998;Inchausti & Ginzburg 1998;Stenseth et al 1999;Benton et al 2001;Coulson et al 2001;Dennis et al 2001;Beckerman et al 2003). In the case of a lag introduced by maternal effects, offspring performance is influenced by past environments through changes in investment patterns by mothers: either directly through changing the per capita investment in the offspring, or the associated change in fecundity changing the offspring's competitive environment.…”