Rotary screw traps are used in rivers 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
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-sized fish (86–145 mm FL) and 14% of large-sized fish (146–230 mm FL) released during daylight
1.6 km upstream from the trap. We recaptured 33% of medium-sized fish and 17% of large-sized fish released
during daylight 4.8 km upstream from the trap. We recaptured 42% of medium-sized fish and 23% of large-sized
fish released at twilight 1.8 km upstream from the trap. A PIT tag 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 themedium-sized first-time migrants and 40% of the
large-sized first-time migrants. Although average capture efficiencies of first-time migrants were greater than those
from any of the recently trapped fish from the three release strategies, twilight releases of recently trapped fish were
the least negatively biased, especially for medium-sized fish.

I. A. Tattam, et al.
Short Description: 
This study examines the success of rotary screw traps for capturing fish in a variety of conditions.
Product Number: 
Entry Date: 
Friday, May 9, 2014
9 pp.
Size and Format: 
8 1/2 x 11, online
Source (Journal Article): 
North American Journal of Fisheries Management
DOI Number (Journal Article): 
Year of Publication: