Recent advances in the understanding of cyclic behavior of Dungeness crab (Cancer magister) populations

By 1985, investigators of the cause(s) of cycles in Dungeness crab populations had: (1) discounted two predator-prey mechanisms involving salmon and humans as predators, (2) evaluated several density-dependent recruitment mechanisms using mathematical models, and (3) evaluated several potential environmental influences through statistical analyses of covariation. Since that time, substantial progress has been made. Analysis of the interaction between the egg-predator nemertean worm and the crab has shown that this interaction, by itself, cannot be the cause of the cycles, but that it may contribute synergistically. The evaluation of cannibalism field data presented here indicates most cannibalism is by females, and that the age specificity of cannibalism is consistent with the observed cycles. Analysis of five years of larval data has demonstrated that the effect of spring winds on vertically migrating larvae can explain their cross-shelf distribution, and hence may contribute to onshore transport of larvae to favorable settling areas. Recent research on mortality and growth rates has led to a sharper picture of population processes which increases the robustness of models used in the analyses of the causes of cycles. Currently, it appears that density-dependent recruitment, in the form of a combination of egg predation and post-settlement cannibalism, and environmental forcing, possibly involving onshore transport by spring winds, are involved in the observed cyclic variability in the Dungeness crab