文摘
Lampreys are extremely efficient anguilliform swimmers, well–designed for long–distance travel, although they are frequently characterized as poor swimmers when compared to salmonids. We examine free–swimming adult Pacific Lamprey, Entosphenus tridentatus, in a raceway environment to approximate swim speeds and behaviors that may occur in the natural environment. Lampreys (mean Body Length 59.2 ± 3.0 cm, range 50–66 cm BL) traveled upstream at a mean groundspeed of 0.34 ± 0.188 BL/s (n=126, range 0.01–0.79 BL/s). Swimming activity was strongly nocturnal. Observed speeds in the lower range may have been the result of swimming in midwater against faster currents, indirect paths or rest periods. Lampreys generally took advantage of lower near–bottom current velocities by swimming within 6 cm of the bottom, where currents were substantially lower. Equivalent swim speeds, without currents, would be 0.49 ± 0.190 BL/s (range 0.17–0.96 BL/s). These speeds are in the high range of daily travel rates encountered in tagging studies of both Pacific Lamprey and Atlantic Sea Lamprey, Petromyzon marinus, but compare well when migration is limited to hours of darkness or tracking was continuous. Such rates suggest that, travelling only at night, lampreys would cover 1,000 km upriver in under four months. It is crucial that managers and designers incorporate the swimming capability, near–bottom association, utilization of boundary flow conditions, and nocturnal behavior of lampreys into their activities if we are to effectively manage in-stream facilities and conserve these key anadromous species.