Methods for Enumerating Upstream Passage of Pacific Lamprey at Dams and Diversion Structures

To assist in the management of decreasing populations, the enumeration and reporting of adult Pacific lamprey migrating past hydroelectric dams and diversion structures has become increasingly important. Passage counts are used to calculate relative abundance, reach escapement, run timing, passage efficiency, and to assess structural modifications and operational changes.  Systems and techniques that monitor upstream migrating lamprey are employed at several facilities in the Columbia River Basin and are typically modeled on those used in estimating the upstream passage of salmonids.  Visual techniques rely on human observers identifying and counting individuals at fishway windows or terminal collection traps.  Automated techniques such as pulse measurement, motion detection, electrical impedance, sonar, and optical methods have been used with varying levels of success.  Different approaches may be subject to over-counting, under-counting and system outages.  Further challenges to accurate lamprey enumeration are created by downstream movements, the ability to attach by oral disc, backclimbing, and anguilliform swimming style.  We will present case studies of lamprey counting systems and discuss the current state of applicable technologies.  The development of systems that provide reliable, cost effective, and accurate enumeration of upstream migrating lamprey at all routes of passage should be prioritized.