An approach for searching for bottom sediment environment that limits spawning ground of Micropterus salmoides

Abstract

In Lake Izunuma, a site survey by Side scan sonar in 2006 suggested spawning area of Micropterus salmoides corresponded to the location occupied by sandy sediments without ripple marks. In a 2007 survey, ripple marks were not confirmed, but soil sampling of bottom sediments and their grain size analyses showed fine sediments like silts and mud at the ripple mark location. It was also observed that reproduction season in 2006 had much stronger winds than 2007. This evidence indicates a possible mechanism for making ripple marks. They occur in areas with water depth of the lake between 1 meter or 1.5 meters; and very slow water current throughout the year. Then fine-grained bottom sediments move due to shear induced by wind over speeds of 5 meter-per-second to make the ripple mark. Wind direction is almost consistently from in the reproduction season, so the ripple marks form at nearly the same location according average wind strength of the season. This model helps in the aim of ecologic control of Micropterus salmoides. It would be useful to arrange a map of lake-bottom sediment type and of distribution of marks, whose are based on the Side scan sonar survey.