The Variability among Populations of Coho Salmon in the Maximum Reproductive Rate and Depensation

Estimating parameters for population-dynamics models is a critical component in assessing extinction probabilities of populations. For many individual populations, key parameters will be poorly defined, and meta-analysis would provide a basis for estimating the parameters. Here, we introduce meta-analytical techniques to estimate the maximum reproductive rate, carrying capacity, and depensation in coho salmon on the west coast of North America. We used both nonlinear mixed-effects models and Bayesian techniques to estimate several population-dynamics models, including the Beverton-Holt and hockey-stick models, for 14 spawner-recruitment time series. The Beverton-Holt and hockey-stick mixed-effects models yielded equivalent fits to the data but gave very different estimates of α (the maximum rate at which female spawners can produce female smolts at low population sizes). The mean a for the Beverton-Holt mixed-effect model was 71.5 (1 SE = 1.2) female smolts per spawning female, whereas the hockey-stick estimate was 53.0 (1 SE = 1.14). We found little evidence for a general effect of depensation in coho salmon, unless fewer than one female per kilometer of river returned to spawn.