Decreased Hatchery Rearing Density Improves Poststocking Harvest and Return to Spawning of Landlocked Fall Chinook Salmon

Abstract

AbstractJuvenile landlocked fall Chinook Salmon Oncorhynchus tshawytscha were coded‐wire‐tagged and reared in 1.8‐m‐diameter circular tanks at a low or high density for up to 52 d prior to stocking in Lake Oahe, South Dakota, during late May of 1999, 2003, and 2004. Final hatchery rearing densities ranged from 7.29 to 11.72 kg/m3 for the low‐density tanks and from 15.02 to 25.22 kg/m3 for the high‐density tanks, with the higher densities being at least double the lower densities in each year. Flows were adjusted to maintain similar loadings (kg·L−1·min−1) between the treatments each year. The fish used in this study came from spawns collected during the October prior to stocking; TL at the end of hatchery rearing ranged from 103 mm in 1999 to 124 mm in 2004. In each year‐class, the percentage of fish that were harvested by anglers or that returned to spawn was significantly greater for the lower‐density treatment than for the higher‐density treatment. Angler harvest primarily consisted of age‐3 fish, with a small number of age‐4 fish harvested as well. Feed conversion ratios were significantly improved in the lower‐density tanks relative to the higher‐density tanks in 1999 and 2003, and fish from the lower‐density tanks were also significantly longer just prior to stocking in 1999 and heavier prior to stocking in 2003. To maximize poststocking survival for landlocked fall Chinook Salmon, lower rearing densities are recommended.