Estimation of number of downstream migrating chum salmon fry in the Nishibetsu River in 2006 (short paper)

Marked chum salmon Oncorhynchus keta fry (n=104,200) with a clipped right pelvic fin were released in the upper reaches on 28 April, and were recaptured with a rotary screw trap in the lower reaches of the Nishibetsu River, eastern Hokkaido, northern Japan in 2006. A total of 23 marked fish were recaptured between 5 and 26 days after release. To assess the trap efficiency, chum salmon fry clipped upper the lobe of the caudal fin (n=5,970) were released at the 2 km upper the trap, and seven fish were recaptured; trap efficiency was estimated at 0.13%. Right pelvic fin clipped chum salmon fry that passed the trap site were estimated at 17,167; the rate of recaptured fish against released fish was estimated at 16.5%.