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EVALUATION OF LIGHT AS A NON-PHYSICAL CUE TO GUIDE DOWNSTREAM-MIGRATING LAMPREY TRANSFORMERS INTO TRAPS
2U.S. Geological Survey, Leetown Science Center, S.O. Conte Anadromous Fish Research Laboratory, 1 Migratory Way, Turners Falls, MA USA 01376.
3 U.S. Geological Survey, Great Lakes Science Center, Hammond Bay Biological Station, 11188 Ray Road, Millersburg, MI USA 49759.
Trapping downstream migrating metamorphosed sea lamprey (Petromyzon marinus; transformers) is a largely unexploited opportunity to limit damage to the fishery for the sea lamprey control program. Currently, the high cost of trap operation is not justified by the number of transformers captured. The GLFC and fishery managers have expressed interest in expending control efforts to this life stage but first tools must be developed that can allow for maintenance-free fishing. One possible solution is the use of non-physical cues to direct downstream migrants to traps in areas where debris and ice fouling are manageable. Here, to determine how speed and direction of juvenile sea lamprey downstream movement was influenced by exposure to light, recently metamorphosed downstream migrating sea lamprey (Petromyzon marinus) were exposed to light cues in several orientations and intensities at night under controlled flowing water conditions in a laboratory flume. Then, a follow-up study evaluated how sea lamprey chemosensory alarm cue and combinations of light and alarm cue influence downstream migration in the same bioassay. When exposed to low intensity white light, sea lamprey were more likely to be captured in a net closest to the light cue array compared to a dark control condition, suggesting some attraction to light. At higher light intensities, sea lamprey progressed downstream at a slower rate. Reduction in downstream movement rates in response to higher light intensities may be representative of a photonegative behavior where juvenile lamprey in strong light (> ~100 lux) suspend downstream migratory behavior to remain stationary or burrow, possibly to avoid detection by predators. When exposed to alarm cue, sea lamprey arrived downstream faster, but did not avoid the alarm cue plume by moving perpendicular to flow. When alarm cue and light was applied simultaneously in a push-pull configuration, alarm cue still triggered enhanced downstream movement (push) and more sea lamprey were still captured in the net nearest the light (pull), so more lamprey were captured in the lighted net. These studies show that juvenile sea lamprey detect and behaviorally respond to light and alarm cues and these cues may be useful in management when used independently or integrated. Additional systematic experiments are needed to understand how responses are influenced by context and the presentation of the stimulus.