Juvenile 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.

Abstract:This study evaluated the use of ovarian fluid turbidity as a potential indicator of landlocked fall Chinook Salmon Oncorhynchus tshawytscha egg survival. A total of 21 females were spawned, with nine of the spawns containing between one and ten broken eggs per spawn. Ovarian fluid turbidity ranged from 55.1 to 159 nephelometric turbidity units (NTU), and egg survival to the eyed-stage of egg development ranged from 0 to 68%. There was no significant correlation between ovarian fluid turbidity and egg survival. Mean survival of eggs from the spawns containing broken eggs was 12.3%, which was significantly lower than the 32.9% mean survival from spawns without broken eggs. These results indicate ovarian fluid turbidity cannot be used to predict egg survival in spawns of landlocked fall Chinook Salmon, but the presence of even a small number of broken eggs may be indicative of poor survival to the eyed-egg stage of development.

The Lake Oahe, South Dakota, population of landlocked fall‐run Chinook salmon Oncorhynchus tshawytscha is maintained entirely by hatchery propagation and exhibits relatively poor egg survival during hatchery incubation. This study was undertaken to determine the influence of male gametes on embryo survival. Eggs from an individual female were subdivided and subsequently fertilized with milt from four discrete males. This was repeated with three additional females using the milt from the same four males. This entire procedure was then replicated three times, using four new females and four new males each time, for a total of 16 males and 16 females. The eggs from each unique cross were then incubated discretely. There was no significant effect of spawning males on subsequent embryo survival to the eyed stage of egg development. Swim‐up fry length and weight were also not significantly affected by male parentage. In contrast, there was a significant maternal effect on eyed egg survival, and swim‐up fry length and weight, which varied significantly among progeny from individual females. These results suggest that the relatively poor survival exhibited by Lake Oahe landlocked fall Chinook salmon eggs during hatchery incubation is largely a function of initial egg quality from spawning females.

This study examined 23 years of egg size data from a population entirely made up of hatchery-maintained fall Chinook Salmon Oncorhynchus tshawytschain Lake Oahe, South Dakota. Egg size data, obtained by water-displacement during hatchery egg inventories, ranged from 4.2 to 6.6 eggs/mL over the 23 years. However, linear regression of data from either pooled lots of eggs (y = 0.0035x -1.8116; P = 0.727) or individual spawns (y = 0.0003x + 5.3037; P = 0.907) indicated no significant change in mean egg size over time. The lack of change in egg size of Lake Oahe fall Chinook Salmon over the 23 years of this study indicates there was no hatcheryinduced evolutionary impacts on egg size.

Abstract:This study compared the survival of landlocked fall Chinook salmon Oncorhynchus tshawytscha eggs incubated in either upwelling jars, either with or without daily formalin treatments, or vertically-stacked trays treated daily with formalin in a production hatchery. In the first year of the study, survival to the eyed-egg stage was significantly greater in eggs incubated in jars without formalin compared to trays, but there was no significant difference in survival to hatch between the treatments. In the second year, there were no significant differences in eggs incubated in trays, in jars without formalin treatments, and in jars with formalin treatments. In the final year, there was no significant difference in eyed-egg survival between eggs incubated in trays and jars without formalin, but survival to hatch was significantly greater in the eggs incubated in jars. Jar incubation is recommended to maximize the survival of landlocked fall Chinook salmon eggs.