Sea lamprey (Petromyzon marinus) transit of a ramp equipped with studded substrate: Implications for fish passage and invasive species control

Abstract Anguilliform-swimming fishes (eels, lampreys) are undergoing large and global declines due partly to an inability to pass dams via traditional fishways. The installation of “eel ladders” (wetted, studded/bristle substrates that permit these fishes to climb over obstructions) offer a potential solution. We examined the behaviour of migrating sub-adult sea lamprey (Petromyzon marinus) as they approached and attempted to ascend a 45° studded ramp in a mesocosm placed in a river. We also examined motivation to use the ramp in the presence of a conspecific alarm cue that signals predation risk. Entrance (75%) and attraction efficiency (85%) were high, but reduced by the presence of alarm cue. In total, 98% of sea lamprey attracted to the base of the ramp ascended, and alarm cue had no effect. Time to ascend the ramp (post-release) was variable (1–521 min) and on average was 119 min (50% probability = 35 min). Few sea lamprey required multiple attempts to ascend (19.8%) and was more likely during longer transit times, with multiple ramp attachments, and with higher body mass. Propensity to attach to the ramp increased with number of attempts. The high efficacy of this design, compared to poor-mediocre efficiencies of similar designs in previous studies, may be related to water velocity and depth, geometry of substrate studs, substrate presentation (horizontal/vertical, and incline), and length of studded substrate. Studded ramps represent a substantial opportunity for managers attempting to selectively pass anguilliform fishes over dams, aiding conservation efforts. Applications to the management of sea lamprey include removal in their non-native Great Lakes range, and fish passage in their native range.