Survival of Juvenile Chinook Salmon during Barge Transport

Abstract

Abstract To estimate survival during barge transport over a distance of 470 km from Lower Granite Dam on the Snake River to a release area downstream of Bonneville Dam (the lowermost dam on the Columbia River), we used a novel adaptation of a release–recapture model with 1,494 acoustic-tagged yearling Chinook salmon Oncorhynchus tshawytscha smolts. Smolts were collected at Lower Granite Dam, received surgically implanted acoustic transmitters, and were divided into three groups: (1) a barge group (RB) that was released into the raceway with fish that were later loaded into transportation barges (general barge population); (2) a control group (RA) that was held in a net-pen suspended within the barge hold containing the general barge population until 5–6 h prior to barge evacuation (i.e., fish release into the river), at which time they were confirmed to be alive and then released into the barge hold; and (3) a dead group (RD) that was euthanized and then released into the barge hold 5–6 h prior to barge evacuation in order to validate a model assumption. Six replicates of each group were loaded onto fish transport barges that departed from Lower Granite Dam between 29 April and 13 May 2010. Detections on acoustic receiver arrays between 70 and 220 km downstream of the barge evacuation site served as the basis for estimation of survival within the barge. The ratio of RB: RA survival from release to river kilometer 153 provided the estimate of within-barge survival. The replicate survival estimates ranged from 0.9503 ( = 0.0253) to 1.0003 ( = 0.0155). The weighted average of the replicate estimates of survival during the barge transportation experience was 0.9833 ( = 0.0062). This study provides the first active telemetry documentation that the assumed survival rate of 98% during the barge transportation experience appears to be justified for yearling Chinook salmon smolts. Received March 4, 2011; accepted August 30, 2011