Density Effects on Subyearling Fall Chinook Salmon During Hatchery Rearing in Raceways with Oxygen Supplementation and After Release

Abstract

AbstractTo determine the effects of hatchery rearing density on fall Chinook Salmon Oncorhynchus tshawytscha released as age‐0 subyearlings, we experimentally reared fish at densities of 200,000, 300,000 and 400,000 fish per raceway in Michigan‐style raceways that employ oxygen supplementation to achieve high density rearing. The study was conducted for two release years at a maximum raceway density of 52.3 kg/m3 and a maximum loading of 0.92 kg·L−1·min−1. At the end of hatchery rearing there was no significant difference in weight in either release year and Fulton's condition factor was similar in the first year. In the second release year condition factors were significantly different; the low‐density group had significantly lower values and the high‐density group had significantly higher values. Following release into the Umatilla River, Oregon, out‐migration survival and travel time to John Day Dam on the Columbia River was monitored by using passive integrated transponder tags in a subsample of each release group. We found no significant difference in either out‐migration survival or travel time between density groups. We used recoveries of coded wire tags to estimate smolt‐to‐adult survival (SAS) and straying. There was no significant difference in SAS, consequently the high‐density treatment produced nearly twice as many adults as the low‐density and 27% more adults than the medium density. Straying rates ranged between 61% and 66% for each density group and were not significantly different. Rearing density had no effect on the gender or age distribution of returning adults. Our results indicate that high‐density rearing of subyearling fall Chinook Salmon in Michigan‐style raceways is useful for increasing adult production.