Push, pull, or push - pull? An alarm cue better guides sea lamprey towards capture devices than a mating pheromone during the reproductive migration.
Widespread interest in the development of environmentally safe management actions has prompted research into the use of sensory cues to manipulate the movements of invasive species. The push - pull approach, for which attractive and repellent semiochemicals operate synergistically to guide individuals toward traps, has proven successful in insect pest management applications. We examined the effectiveness of a natural repellent (an alarm cue) and a natural attractant (a partial sex pheromone) in push-only (repel), pull-only (attract), and push - pull configurations, to guide invasive sea lamprey (Petromyzon marinus) toward and into a target trap during spawning migration into rivers. Using PIT telemetry to monitor sea lamprey movement within the river, we found that the alarm cue was capable of strongly altering sea lamprey distribution, "pushing" them toward target areas and generating rates of encounter with trap entrances sufficient to achieve trapping-for-control targets. Encounter rate with trap entrances was not improved, but performed more consistently, with the addition of the attractant in the push - pull configuration. There was evidence this could stem from a transition in internal state of motivation, from migration to reproduction. Use of the attractant alone was ineffective. No odor combination improved trap captures. We conclude that push - pull strategies will prove effective in guiding sea lamprey movements and recommend two improvements for subsequent testing in management scenarios: (1) use of a superior attractant (e.g. a sea lamprey migratory cue derived from conspecific larvae), and (2) its subsequent application to a capture methodology based on the entrainment of individuals near trap entrances.