The influence of release strategy and migration history on capture rate of Oncorhynchus mykiss in a rotary screw trap Public Deposited

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  • Rotary screw traps are used throughout the West Coast of North America to capture emigrating juvenile salmonids. Calibrating the capture efficiency of each trap is essential for valid estimates of fish passage. We released Passive Integrated Transponder (PIT) tagged Oncorhynchus mykiss upstream of a rotary screw trap in the South Fork John Day River, Oregon to estimate capture efficiency. We used three strategies for release of fish recently captured in the trap. We recaptured 28% of medium-size fish (86–145 mm fork length) and 14% of large-size fish (146–230 mm fork length) released during daylight 1.6 km upstream of the trap. We recaptured 33% of medium-size fish and 17% of large-size fish released during daylight 4.8 km upstream of the trap. We recaptured 42% of medium-size fish and 23% of large-size fish released at twilight 1.8 km upstream of the trap. A PIT antenna detected summer tagged parr (which were PIT tagged upstream 1–5 months before migration) as they approached the trap to evaluate potential bias from reduced recapture of recently trapped fish. We captured 53% of the medium-size first-time migrants and 40% of the large-size first-time migrants. Although average capture efficiencies of first-time migrants were greater than any of the three recently trapped fish strategies, twilight releases of recently trapped fish were least negatively biased, especially for medium-size fish.
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  • Tattam, I. A., Ruzycki, J. R., Bayley, P. B., Li, H. W., & Giannico, G. R. (2013). The influence of release strategy and migration history on capture rate of Oncorhynchus mykiss in a rotary screw trap. North American Journal of Fisheries Management, 33(2), 237-244. doi:10.1080/02755947.2012.758202
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  • 33
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  • 2
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  • The work of I. Tattam, P. Bayley, H. Li, and G. Giannico was funded by the U.S. Bureau of Reclamation, Pacific Northwest Region through M. Newsom. The involvement of J. Ruzycki and other Oregon Department of Fish & Wildlife employees was supported by the Bonneville Power Administration (Project Number 1998-016-356 00) through J. Baugher and J. Karnezis.
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