Distribution of Juvenile Pacific Lamprey in the Wenatchee River, WA

Pacific lamprey Lampetra tridentata were historically widespread and abundant throughout many Pacific coast watersheds from Mexico to Alaska. In recent years, the number of adult Pacific lamprey returning to the Columbia River has declined. This is most evident in the upper reaches of the Columbia River where spawning adults must navigate seven to nine main-stem dams to reach spawning tributaries. Reduced spawning and rearing habitat, dams and diversions, and contaminants are thought to be contributing to the decline. Efforts to conserve Pacific lamprey are underway but are hampered by a lack of basic life history information such as distribution. We conducted juvenile lamprey electrofishing surveys in 2010 and 2011 to provide information on the present distribution of Pacific lamprey in the Wenatchee River, a tributary to the upper Columbia River. Surveys were conducted using an ABP-2 backpack electro-shocker set at 125 volts (DC) with 3 pulses/second, a 25% duty cycle, and a 3:1 pulse train. Sampling was focused on near shore habitat in fine substrate with detritus. No juvenile Pacific lamprey were located upstream of Tumwater Dam at Rkm 49, which has an adult collection facility with a fish ladder, although ammocoetes were found downstream of the dam. Records from 1981 surveys confirm lamprey were present upstream of Tumwater Dam. The 2010 survey information combined with historic records of Pacific lamprey upstream of Tumwater Dam suggests that modifications to the ladder in 1987 or current operations at the adult collection facility may be impeding passage of adult Pacific lamprey.