A Field Study to Investigate Repeat Homing in Pacific Lampreys
Douglas R. Hatch and John M. Whiteaker
Abstract.—In-season homing of Pacific lampreys Lampetra tridentata was investigated using radiotelemetry in the lower Columbia River from 1998 through 1999. A total of 50 Pacific lampreys were captured: 25 at Willamette Falls (river kilometer [rkm] 45 on the Willamette River, a tributary to the Columbia River, with its confluence at rkm 163) and 25 at Bonneville Dam (rkm 238 on the Columbia River). Each fish was fitted with a radio transmitter, transported, and released in the Columbia River approximately 26 km downstream from the confluence of the Willamette River. Movement of the radio-tagged Pacific lampreys was monitored for several months using mobile and fixed receiver stations to observe rates of homing towards the site of original capture. Results indicated that the lampreys exhibited nonsignificant in-season homing fidelity (p = 0.622) based on the null expectation that one-half of the total recoveries would home and the other half would stray. Final location classifications were 17 homed, 20 strayed, and 13 undetermined. The undetermined classification included individuals that were not detected upstream of the confluence of the Willamette River or in other Columbia River tributaries. Final location classifications were not influenced by fish length (p = 0.594). Although considered weak swimmers, Pacific lampreys were capable of traveling at velocities near 2.5 km/h and sustaining that activity for at least 24 h.