Movement and Habitat Use by Lake Whitefish during Spawningin a Boreal Lake: Integrating Acoustic Telemetry and Geographic Information Systems

Abstract

To quantify lake whitefish swimming behavior, substrate selection, and the influence of water level variation on spawning behavior and success, we tracked lake whitefish Coregonus clupeaformis during two consecutive spawning seasons (October–November) in a small boreal lake in northwestern Ontario, Canada. The lake was subjected to an experimental drawdown of 1.4 m in 1995 and 0.75 m in 1996 at the time tracking started. We used a radio‐linked, acoustic positioning system that produced positions every 100 s for 18 tagged lake whitefish, eight of which provided depth information. Fish position and depth were put into a geographic information system database with information on substratum, slope, and depth. Mean daily locomotor activity declined as the spawning season progressed. Two patterns of behavior occurred in both years. Offshore‐oriented fish spent their time along bottom contours, which increased in depth through the spawning season. Inshore‐oriented fish spent their time along the shoreline, and exhibited site fidelity during spawning before moving to deeper offshore areas, where movement was reduced. For inshore‐oriented fish, spawning positions were determined based on their presence in the littoral zone and a low instantaneous swimming speed of less than 6 cm/s. For these positions, only three substrata—boulder, cobble, and detritus—comprised 50% of these locations. Mean depth ranged from 2.7 m (±1.3, SD) to 3.5 m (±1.2) with mean slopes of 36% (±13.2%). We confirmed spawning by recapturing spent tagged fish; scuba divers also confirmed the presence of lake whitefish eggs at one site. Water level reductions apparently caused mortality of eggs laid at depths less than 3.5 m. Overall, lake whitefish displayed high fidelity toward specific substrate and slope characteristics, using new sites as water levels rose.