Utility of molt data for linking life stages and estimating abundance of Dungeness crab (Metacarcinus magister) in Puget Sound

Abstract

The Puget Sound Dungeness crab fishery in Washington state is culturally, economically, and recreationally valuable. Despite the importance of the fishery, large data gaps often render abundance estimates of Dungeness crabs highly uncertain; no demographic data are typically available for the several-year period between larval and adult stages. Since crabs molt in regular intervals like all arthropods, shed molts may provide a useful index of population abundance during these intermediate years, at relatively low effort and cost. While these molt data are indirect evidence of a Dungeness crab, they nevertheless provide information that a crab was once present. When paired with other datasets, molt data could increase confidence in abundance estimates and determine size class distribution of Dungeness crab in intermediate life stages across space and time in Puget Sound. My analysis using Bayesian hierarchical models shows spatial, but not temporal, variation in predicted mean molt count. Predicted mean counts of Dungeness crab megalopae are positively correlated with predicted mean counts of Dungeness crab molts. This positive relationship varies across space with Northern Hood Canal as a notable outlier.