Variations in Vertical Location of Kootenai River White Sturgeon during the Prespawn and Spawning Periods

Abstract

AbstractOur objectives were to determine the general water column habitat use of Kootenai River white sturgeon Acipenser transmontanus during the prespawn and spawning periods and to determine the degree of their benthic existence. Depth‐sensitive radio transmitters were attached to five male and four female white sturgeon and were periodically monitored day and night from April through June 2001. A total of 297 radio contacts were made, of which 209 included the depth of the river. One fish was not used for statistical analysis because its behavior was often modified by the presence of our boat. Of the 209 contacts, 75% (156) were made within the bottom one‐third of the water column. Mean depth of the fish during the daytime prespawn and daytime spawning period was different (9.7 and 6.5 m, respectively), and the distribution between these two periods was significantly different. Some of the variation was likely due to the deeper habitat of the daytime prespawn staging reach compared with that of the daytime spawning period location (12.6 and 7.7 m, respectively). White sturgeon used a variety of locations throughout the water column, were closer to the river bottom during the spawning period, and were much more mobile during the spawning period than we previously believed. We were also able to chart some white sturgeon as they gradually cruised the contour of the river bottom several meters from the substrate yet paused momentarily. Although depth‐sensitive transmitters were well suited to further defining some white sturgeon behavioral characteristics, they lacked the precision to achieve instantaneous locations.