Effects of complete redd dewatering in salmonid egg hatching success and development of juveniles

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Transactions of the American Fisheries Society


The effects of prolonged stream desiccation on development of salmonid eggs were simulated for steelhead Salmo gairdneri and spring chinook salmon Oncorhynchus tshawytscha. Recently fertilized eggs were placed in artificial redds and subjected to controlled water flows in outdoor laboratory channels. Control redds were continuously submerged. 'Dewatered' redds were exposed to air; water flowed through the substrate 10 cm below the eggs. Eggs were dewatered 1-4 weeks (steelhead) or 1-5 weeks (chinook salmon) before they were returned to water in hatchery incubators, where hatching success and subsequent fry development were monitored. Several combinations of cobble, coarse sediment, and fine sediment used to cover eggs did not influence egg development, provided the mixtures retained at least 4% moisture by weight. Dewatered eggs hatched sooner than control eggs; faster hatch was associated with higher substrate temperature in exposed redds. Hatching success of dewatered eggs averaged 94% for steelhead (control: 88%) and 76% for chinook salmon (control: 56%) and was not affected by the time eggs had been dewatered. After 8 (chinook salmon) and 8.5 (steelhead) weeks of rearing, juveniles from dewatered and control eggs had grown equally well.





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