Effects of hatchery fish density on emigration, growth, survival, and predation risk of natural steelhead parr in an experimental stream channel

North American Journal of Fisheries Management
By: , and 

Links

Abstract

Hatchery supplementation of steelhead Oncorhynchus mykiss raises concerns about the impacts on natural populations, including reduced growth and survival, displacement, and increased predation. The potential risks may be density dependent.We examined how hatchery stocking density and the opportunity to emigrate affect the responses of natural steelhead parr in an experimental stream channel and after 15 d found no density-dependent effects on growth, emigration, or survival at densities ranging from 1-6 hatchery parr/m2. The opportunity for steelhead parr to emigrate reduced predation by coastal cutthroat trout O. clarkii clarkii on both hatchery and natural steelhead parr. The cutthroat trout exhibited a type-I functional response (constant predation rate with increased prey density) for the hatchery and composite populations. In contrast, the predation rate on natural parr decreased as hatchery stocking density increased. Supplementation with hatchery parr at any experimental stocking density reduced the final natural parr density. This decline was explained by increased emigration fromthe supplemented groups. Natural parr had higher mean instantaneous growth rates than hatchery parr. The proportion of parr emigrating decreased as parr size increased over successive experimental trials. Smaller parr had lower survival and suffered higher predation. The final density of the composite population, a measure of supplementation effectiveness, increased with the hatchery steelhead stocking rate. Our results indicate that stocking larger hatchery parr (over 50 d postemergence) at densities within the carrying capacity would have low short-term impact on the growth, survival, and emigration of natural parr while increasing the density of the composite population; in addition, a stocking density greater than 3 fish/m2 might be a good starting point for the evaluation of parr stocking in natural streams.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Effects of hatchery fish density on emigration, growth, survival, and predation risk of natural steelhead parr in an experimental stream channel
Series title North American Journal of Fisheries Management
DOI 10.1080/02755947.2011.571503
Volume 31
Issue 2
Year Published 2011
Language English
Publisher Taylor & Francis
Publisher location London, UK
Contributing office(s) Great Lakes Science Center
Description 12 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title North American Journal of Fisheries Management
First page 224
Last page 235
Google Analytic Metrics Metrics page
Additional metadata about this publication, not found in other parts of the page is in this table