Intra- and interspecific competition for spawning space is a commonly observed interaction in salmonids that can result in progeny loss. This study examined the impacts of redd superimposition by kokanee Oncorhynchus nerka on the reproductive success of bull trout Salvelinus confluentus in the Deschutes River basin, Oregon. The activities of high-density spawning groups of kokanee were hypothesized to place the eggs and alevins of bull trout at risk of displacement and damage wherever the spawning habitats of these two species overlap. Bull trout egg pocket depths and kokanee scouring depths were measured. Fry emergence from redds, a proxy for bull trout reproductive success in the presence of kokanee, was compared between superimposed and undisturbed redds by using fry emergence traps. Our results indicate that groups of spawning kokanee did not scour the stream bed deeply enough to reach bull trout eggs. Data on bull trout fry emergence revealed that kokanee redd superimposition did not affect bull trout egg-to-fry survival rates.

Authors: 
M. A. Weeber, G. R. Giannico, and S. E. Jacobs
Short Description: 
This study examined the impacts of redd superimposition by kokanee Oncorhynchus nerka on the reproductive success of bull trout Salvelinus confluentus in the Deschutes River basin, Oregon.
Product Number: 
ORESU-R-10-013
Entry Date: 
Friday, January 1, 2010
Length: 
8 pp.
Source (Journal Article): 
North American Journal of Fisheries Management 30:47–54
DOI Number (Journal Article): 
10.1577/M08-038.1
Year of Publication: 
2010