Seasonal Movement Patterns of Smallmouth Bass and Northern Pikeminnow in the Lake Washington Ship Canal, Seattle, WA

We investigated the seasonal movement patterns of adult smallmouth bass and northern pikeminnow in the Lake Washington Ship Canal (LWSC), a long, narrow water body that connects Lake Washington with Puget Sound.  Both species can be important predators of juvenile salmonids.  Fishery managers have been concerned about predation in the LWSC because all juvenile salmonids must emigrate through it to reach the marine environment.  The movement of predatory fish species between the LWSC and Lake Washington is not well known.  We determined the seasonal movement patterns through acoustic telemetry.  Vemco fixed receivers were placed at multiple locations in LWSC and Lake Washington.  We also conducted mobile surveys to supplement information from the fixed receivers.  We implanted Vemco tags in a total of 72 smallmouth bass and 34 northern pikeminnow.  All fish were released at their capture site.  Eighty-two percent of tagged smallmouth bass migrated to Lake Washington sometime between June and October.  Smallmouth bass < 350 mm were more likely to overwinter in the LWSC than larger bass and if they did migrate to Lake Washington, they migrated later in August-October.  Smallmouth bass that migrated to Lake Washington were found throughout the entire lake. After overwintering in Lake Washington, smallmouth bass moved back into the LWSC sometime from March to mid-April. Timing of their return to the LWSC was shortly before the initial spring warming period and was likely related to spawning activity.  Smallmouth bass often showed some degree of site fidelity between years for both spring/summer locations in the LWSC and summer/fall/winter locations in Lake Washington.