Occupancy and Distribution of Larval Pacific Lamprey: Application of Survey Methods Across Multiple Habitats and Spatial Scales

Pacific Lamprey Entosphenus tridentatus in the Pacific Northwest are in decline and information on occupancy and distribution of these ecologically and culturally important fish is important for status assessment.  We adopted a statistically robust approach to efficiently assess the probability of occupancy of larval lampreys.  This approach is appropriate for assessing occupancy regardless of sampling gear, habitat type, or spatial scale.  Estimates of detection probability coupled with a generalized random tessellated survey framework were used to guide sampling effort.  We demonstrate the use of this approach to meet various occupancy-related objectives including: 1) a large-scale riverine study (Columbia River) using a deepwater electrofisher to evaluate occupancy for entire impoundments and specific tributary input areas; and 2) smaller-scale studies to assess occupancy or changes in occupancy as a result of habitat alterations (i.e., evaluation of passage barriers) in wadeable streams using backpack electrofishing.  Estimated detection probabilities ranged from 0 to 0.34 with deepwater electrofishing and over 0.95 with backpack electrofishing.  This approach allowed us to design studies that efficiently answered questions regarding the probability of larval lamprey occupancy, which could produce the distribution information needed to guide Pacific Lamprey conservation.