Migratory activity, refuge-seeking, and the sensory basis of light avoidance in spawning phase sea lampreys

This thesis combined statistical modeling, field studies, and laboratory experiments to better characterize migratory activity, refuge-seeking behaviour, and the sensory basis of light avoidance in spawning phase sea lampreys. Overall, my findings provide (i) a set of rules for predicting migratory activity, based on environmental cues, and (ii) new insights into the mechanism of light avoidance and refuge-seeking behaviour in spawning phase sea lampreys.;Water temperature was the most important environmental cue during the upstream migration---a finding that may distinguish Great Lakes sea lampreys from other lamprey populations. The seasonal distribution of migratory activity varied with stream temperature, peaking when mean temperature reached ∼15°C. Day-to-day increases in water temperature stimulated migratory activity. Decreases suppressed it. Discharge was a less important predictor of migratory activity, except in small streams. High discharge may stimulate migratory activity at the mouth of small streams by making streams more noticeable to searching lampreys. There was no apparent relationship between migratory activity and lunar cycle.;Light avoidance was also an important characteristic of upstream migration. Lampreys displayed abnormally high daytime activity and reduced nighttime activity when denied access to daytime refuge sites. Lampreys appear to begin searching for refuge sites before dawn. Daytime refuge-seeking probably only occurs when lampreys have not yet located a refuge site, or when refuge sites chosen at night provide inadequate cover during the day. Light avoidance is mediated primarily by dermal photoreceptors in the tail. Vision is not required for lampreys to locate refuge, nor was there evidence that lampreys used vision to locate refuge when the refuge was plainly visible.;Light avoidance behaviour was affected by water temperature. Near the end of the migration, sea lampreys lose their aversion to light and become active during the day. The proximate cause of this change in activity pattern is high temperatures near the end of the spawning season. The mechanism involves an inhibition of the dermal photoresponse and a reduction in motivation to seek out daytime refuge sites.