Movements by Adfluvial Bull Trout during the Spawning Season between Lake and River Habitats

摘要

Movements of adfluvial Bull Trout Salvelinus confluentus were evaluated with acoustic telemetry during spawning seasons 2006-2011 in Chester Morse Lake, Washington. Ninety-six percent of the individuals made multiple trips between the lake and river habitat during the spawning season, which lasted from less than 1 day to more than a month. Male Bull Trout took an average 13.2 (± 8.7 SD) trips, while females averaged 18.0 (± 14.0 SD) trips. Directional movement between the lake and a river occurredthroughout the day; however, the distribution of movement activity was bimodal, peaking from 0600 to 0900 hours (downstream movement) and from 1700 to 2000 hours (upstream movement). The majority of time spent in the river per trip occurred during nighttime hours for female (mean = 74%) and male Bull Trout (mean = 72%). While spawning activity was not confirmed for each trip, this study illustrates an as-yet unreported movement pattern of adfluvial Bull Trout during the spawning season. These results are relevant to managers considering monitoring population trends by way of redd count surveys because multiple redd sites per spawning season are possible, a situation that could lead to overestimating population numbers. Additional research to determinewhether spawning occurs on individual trips would help assess whether population numbers could be overestimated by simply using redd counts in systems similar to the one studied.