Factors that Affect Arctic Lampreys’ Ascent Behavior on Fishway Weirs

Abstract

We conducted laboratory experiments to clarify the weir designs suitable for Arctic lamprey (Lethenteron japonicum) ascent. Ascent experiments were conducted using three weir types (sharp-crested, inclined sharp-crested and broad-crested). The difference in water depth upstream and downstream of the weir and time period (daytime and night) were changed to determine their effects on ascent behavior. Our results indicated that the difference in water depth negatively and strongly affected ascent behavior and the weir type did not affect ascent behavior. No lamprey ascended the all types of fishway-weir when Δh was 24 cm. The inclined sharp-crested weir had a 45°incline upstream. However, it did not contribute to their ascent and gentler slope than 45°may be better for suitable weir design. The broad-crested weir served the attachment place for lamprey to suck by their mouth and was expected to be suitable for inherent ability of lamprey ascent. However, the ascent rate on the broad-crested weir was not better than the other two types. Additionally, video camera analysis revealed that lampreys attempted ascents more during the night than daytime. Our experiment result revealed unknown Arctic lamprey ascent behavior and can contribute to the conservation and modification in freshwater ecosystem.