Use of Acoustic Telemetry to Reveal the Movements of Anadromous Coastal Cutthroat Trout in Hood Canal, Washington

Very little is known about the movements of individual salmonids as they enter marine waters, yet this is a critical life history transition for these species.  In particular, the movement patterns of cutthroat trout, Oncorhynchus clarkii clarkii, in marine waters have not been described.  This species differs from other members of the genus in distribution (being restricted to North America), and also in the spatially and temporally more limited marine migrations.  They were thus predicted to show limited movements, largely confined to shorelines, while in marine waters. We captured and surgically implanted acoustic tags into wild, downstream-migrating cutthroat trout at a weir in Big Beef Creek in 2006, 2007 and 2008.  We tracked their spring and summer movements within Hood Canal, Washington using an array of stationary receivers.  In all years, 93-96% migrated into Hood Canal, leaving the creek on the east side of the long narrow fjord, and dispersed both north and south along the shoreline.  However, a substantial fraction (33-55%) crossed ~ 2-4 km of deep, open water to the other side, though only one fish left the basin. Most fish remained within 10 km of Big Beef Creek, with a declining number at distances to 55 km.  There was considerable variation in movement patterns but overall the fish were most active near dawn with a lower level of activity all day and a reduction of movement at night.  Early season movements were evenly split between night and day but they became predominately day-active as summer progressed.   Some fish showed periods of little movement, as indicated by nearly continuous detection at one or more receivers, others showed relatively rapid movements to another location and re-establishment of stationary behavior.  There was a wide range of seasonal behaviors with highly mobile fish showing complex movements with some migrating greater than 400 km, some fish remained in localized shoreline areas for an entire year, and others occupied multiple sites over time.  There was no indication of entry and use of major rivers while 5-10% remained in Big Beef Creek.