Western Coastal Cutthroat Colition Study

Draft Study Plan Summary: Association Between Cutthroat and Shellfish Aquaculture in Samish Bay Background

Knowledge of cutthroat movement patterns as they transition from residency at nearshore beaches to spawning in freshwater is growing; however, limited information exists for more exposed beaches like those in Samish Bay, and there is a lack of information for areas outside South Puget Sound. This leaves numerous unanswered questions important for the management of this native salmonid and for those using the nearshore habitat for commercial purposes, such as shellfish aquaculture.  

Emerging science suggests that Coastal Cutthroat Trout (Oncorhynchus clarkii clarkii) lend themselves to studies of spatio-temporal movement patterns in the nearshore marine environment.  Relative to other salmonids native to Washington and British Columbia, juvenile coastal cutthroat trout spend a significant amount of time in estuaries (Quinn 2024), exhibit high site fidelity for nearshore beaches (Losee et al. 2018), and can be considered an indicator species of nearshore habitat quality. 

Study Goals

Over 1 year, this study will compare the movement behaviors of individual fish in bays with and without shellfish aquaculture using surgically implanted tags in the saltwater form of Coastal Cutthroat Trout. Each tag will emit a unique high-frequency sound (69khz) that can be detected and recorded by nearby acoustic receivers. The aims of this study are to 1) describe marine movement patterns of coastal Cutthroat trout in and around shellfish aquculture sites of Samish Bay and 2) describe temporal patterns of inter-habitat (freshwater, estuarine, nearshore) movements to inform best practices for commercial shellfish growing.  

Study Area and Fish Collection

We will capture and acoustically tag 30 adult cutthroat trout in Samish Bay, using a beach seine and/or hook and line. Exact beach locations and timing of collections will be informed by local anglers, fish biologists or shellfish farm staff. Acoustic receivers will be deployed across the study area to detect movement patterns across divert habitat types and shellfish growing methods. In addition to fish movements, each receiver will collect temperature data from the surrounding environment to better understand how temperature influences cutthroat movements and habitat use.  

Tagging Methods 

Cutthroat greater than 180 mm fork length will be tagged in the field in April through October of 2026 with Vemco V9-6L acoustic tags (high power, 210 s delay, battery life 569 days). Specifically, they will be anesthetized with MS-222 (0.07 g/L) and supported upside down by a closed-cell foam block during surgery or held with electronarcosis gloves during the procedure. After an incision is made in the abdomen forward of the pelvic girdle muscle, a tag will be inserted, and the incision will be sutured with 2 stitches (4-0 RB-1 Taper antibacterial Ethicon Vicryl Plus violet braided). Weight and length will be recorded, and fin clip and scale samples will be collected.  

Pictures of equipment used in acoustic telemetry study; Acoustic transmitters (e.g. tags), VRT2x acoustic receiver and example of on-site surgery station.

Figure 2. Map of Samish Bay, in North Puget Sound, Washington State. Colored polygons represent diverse shellfish growing operations and areas of interest for Cutthroat Tracking Project.

Figure 3. Photo of a sea-run cutthroat trout tagged with an acoustic transmitter with visible incision posterior to the pectoral fin.