Use of a New Deep Water Electroshocking Platform to Identify Larval Lamprey Rearing Areas and Associated Habitat Characteristics: Field Validation and New Discoveries in the Columbia River Basin

A deepwater electroshocking platform (DEP) was developed to detect and measure larval lampreys (ammocoetes) within deep-water habitats up to 15 m.  The DEP provides habitat assessment and detection at a rate of 0.55 m²∙min^-1 without requiring ammocoetes to be transported to the surface.  Field tests at a known rearing location (mouth of the Wind River, WA) recently confirmed the efficacy of the device and assessed possible seasonal differences in sampling efficiency.  Ammocoetes ranging from 50 to 150 mm were found in water depths between 1.5 m to 4.5 m and were more common in sediments containing organic silt.  During summer, 74 ammocoetes were detected at 61% of locations sampled; during winter, 63 ammocoetes were detected at 50% of the locations.   Following field verification, the DEP was used to search for ammocoetes in four randomly selected regions of the lower Cowlitz River, WA, where lampreys had not previously been identified.  We found 41 ammocoetes in three of the search locations.  Ammocoetes were found in sediment dominated by silt containing organic material, often downstream of alluvial bars or other current breaks and along the shoreline in water depths ranging from 0.8 to 1.7 m.