| Citation |
Welch, D.W.; Jacobs, M.J.; Lydersen, H.; Porter, A.D.; Williams, S.; Muirhead, Y. (2009) Acoustic Telemetry Measurements of Survival and Movements of Adult Steelhead (Oncorhynchus mykiss) within the Skeena and Bulkley Rivers, 2008, Kintama Research Corporation, Final Report to the B.C. Ministry of the Environment, 50 pages. |
| Abstract/Description or Keywords |
A pilot project using acoustic telemetry was designed and deployed in the Skeena and Bulkley River system in summer 2008 by Kintama Research, with the assistance of Ministry of Environment staff and local river guides. This project was intended to test the technical feasibility of using acoustic technology in the free-flowing Skeena River to answer several important questions about the survival and migratory behaviour of returning adult steelhead (Oncorhynchus mykiss). We deployed twelve acoustic receivers in the river 19-21 August 2008, and we subsequently tagged and released 84 returning wild steelhead from two collection sites in early September: (a) the Tyee sockeye test fishery near the Skeena River mouth and (b) a site located 300 m below the Moricetown Falls in the Bulkley River canyon. Individually identifiable Vemco acoustic tags (V9-2H or V13-1H) were externally attached just below the dorsal fin of 34 steelhead at Tyee and 50 steelhead at Moricetown. We recovered all receivers 24-26 November 2008 approximately three months later. Over the deployment period, a total of 118,159 detections were recorded from 61 individual steelhead. The data were compiled and we estimated survival and detection efficiency using two methods: 1) a simple division of the number detected by the number released (adjusted for detection efficiency [Jolly 1982] and 2) for the Tyee release group we were able to use a Cormack-Jolly-Seber model where survival, _, was constrained to be a function of distance _(distance)p(segment). This constrained model performed better than a model where survival was allowed to vary freely at each sub-array. Most steelhead released at Tyee travelled upstream in a unidirectional manner with the majority passing the lower Skeena receivers by 30 September. “Apparent survival” estimates of the rate of decline in fish numbers with distance followed a smooth curve of exponential decline (apparent survival/km = 0.992, 95% confidence interval: 0.988-0.997). We define “apparent survival” in its normal technical sense; that is, if all tags operate without premature failure, and no tag loss from the animal, emigration to side tributaries, or behavioural switches to cause the animal to take up residence in the river occurs, then the “apparent survival” measures the actual probability of survival for an animal migrating up the river. Although there were no receivers downstream of the Tyee release site, the relationship between survival and distance suggests that downstream movement was minimal after release. Nineteen of the 34 steelhead (estimated apparent survival 51% Ī 11%) tagged at Tyee reached the first sub-array (at RKm 109), and four of these nineteen were subsequently detected in the Bulkley River 270 km (RKm 285) upstream of the release site (estimated apparent survival 14% Ī 9%). Only four fish tagged at Tyee were detected on downstream receivers after first being detected at upstream locations. Owing to the configuration of the 2008 array, it is not possible to determine what proportion of the general decline in numbers with distance (“apparent survival”) represents losses due to mortality after release or due to migration into tributaries. Forty-two of 50 fish tagged and released in the Bulkley River at Moricetown (RKm 314) were subsequently detected on the array; the estimated apparent survival to the most upstream line (RKm 352) was 68%. Nine steelhead initially moved >11 km downstream to RKm 303 after release (four moved 21 km; two moved 29 km downstream); five of those nine then moved back upstream to the up-river Bulkley detection sites (8% of the fish released remained downstream). No steelhead released at Moricetown were detected on the Skeena River receivers. It is not possible to determine what proportion of the steelhead tagged and released at Moricetown moved downstream for less than 11 km based on the 2008 study design; however, the average travel rate between release and the first upstream array was extremely low (average of 12 days to move ten kilometres) which suggests that many fish did not move directly upriver after release. This evidence coupled with the extensive movements some steelhead made downstream and then upstream past the release site may be of importance for the interpretation of data from the Moricetown mark and recapture program which is used to estimate the abundance of steelhead in the Bulkley River. For both release groups, estimated steelhead abundance along the array route declined with upstream distance. Potential causes include: (1) movement into side tributaries; (2) overwintering in the mainstem river; (3) removal in fisheries; (4) mortality from other causes. To distinguish between mortality and emigration into lower river tributaries, future studies should include additional receiver sites below side tributaries known to support significant steelhead runs. The performance of the pilot array in the Skeena River was high with all units recovered and functional upon download. Although sample sizes for some sites were small, the estimated detection efficiencies were over 90% for four of five lines estimable for the Tyee release group (three lines were 100%) and were 100% for two of three lines estimable for the Moricetown fish. Overall acoustic conditions were poorer for two sites (RKm 325 and 118). Our results demonstrate that it is feasible to use acoustic telemetry with high detection efficiencies to measure survival post release of returning Skeena River steelhead. |
