Predicting Larval Pacific Lamprey Distribution and Abundance: Importance of Channel Gradient and Habitat-Related Detection Heterogeneity

Pacific lamprey Entosphenus tridentatus are a culturally valuable anadromous species that is endemic western North America, and which has experienced a significant population decline over the previous century. Sea lamprey Petromyzon marinus have similar spawning and larval habitat requirements as Pacific lamprey, but are an invasive species in the the Great Lakes region.  The ability to predict the larval distribution and abundance of both lamprey species would allow managers to prioritize locations for passage and habitat improvements, in the case of Pacific lamprey, and passage restrictions and lampricide treatments for sea lamprey. In this investigation, we constructed hierarchical models linking larval Pacific lamprey capture probability, occupancy, and abundance to habitat characteristics.  Model selection using deviance information criterion (DIC) revealed that lamprey catchability was negatively associated with an index of fine sediment volume, and that stream gradient was an important predictor of lamprey occupancy and abundance. Our findings suggest that larval lamprey catch rates do not directly reflect abundance and that lamprey managers across multiple regions would benefit from monitoring and research efforts that account for abundance- and habitat-related detection heterogeneity.