Effects of trap funnel and finger design on Sea Lamprey entrance and retention

Traps are used to catch adult sea lampreys during their upstream migration to estimate their abundance in streams and, in turn, provide a measure of the Sea Lamprey Control Program’s effectiveness. During 2015 and 2016, we experimentally compared two components of sea lamprey trap design: trap entrance funnel type and the presence of retention devices, using side-by-side instream test chambers as well as laboratory flumes. We modeled how likelihoods of entrance and retention were influenced by funnel type, retention fingers, water temperature, and lamprey sex. Likelihood of entrance was highest with bottom-oriented funnels and no retention fingers. As water temperature increased, the likelihood of entrance generally increased, but funnel type and retention fingers determined the magnitude of the increase. Likelihood of retention was highest with bottom-oriented funnels and retention fingers and was also influenced by water temperature. Overall, the likelihood of capture (result of entrance + retention) was highest for bottom-oriented funnels and varied by water temperature and lamprey sex but not retention fingers. Further testing on other components of trap design is needed. This type of controlled experimental design can help guide future work to improve trap exploitation rates.