Effects of hatchery supplementation on abundance and productivity of natural-origin Chinook salmon: two decades of evaluation and implications for conservation programs

Abstract

Hatchery supplementation has been developed to conserve salmonid populations and provide fisheries. We evaluated supplemented and reference Chinook salmon (Oncorhynchus tshawytscha) populations prior to, during, and after supplementation ceased for 22 years in two major drainages in Idaho, USA. Basin-level analyses showed supplementation increased abundance at some life stages, but effects did not persist into the postsupplementation phase and had no apparent influence on productivity. Natural-origin juvenile abundance increased during supplementation but results for adults were ambiguous. After supplementation ceased, abundance and productivity in supplemented and reference populations returned to their presupplementation relationships. Intensive analyses of supplemented populations with weirs showed abundance increased at some life stages with the addition of female spawners. However, the rate of increase varied with female origin (natural > supplementation ≥ nontreatment hatchery), and effects diminished through the life cycle. Based on these findings, we provide guidance for conservation programs. Supplementation alone is not a panacea because it does not correct limiting factors, which must be addressed to achieve population levels capable of sustaining ecological function and harvest.

Population variation in density‐dependent growth, mortality and their trade‐off in a stream fish

“…Furthermore, the effect of environmental variables on density‐dependent relationships may differ in natural systems: for example, habitat complexity may reduce growth if complex substrate positively covaries with fish density (Zorn & Nuhfer, ). Consequently, we emphasize the importance of considering population‐specific characteristics when devising conservation plans (Venditti et al, ), as even adjacent populations may exhibit different and unpredictable dynamics.…”

“…Consequently, we emphasize the importance of considering population-specific characteristics when devising conservation plans (Venditti et al, 2017), as even adjacent populations may exhibit different and unpredictable dynamics.…”

In‐Stream Egg Incubators Produce Hatchery Chinook Salmon with Similarities to and Differences from Natural Juveniles

“…The Tribes’ supplementation goals are to seed underoccupied habitat and to restore harvest opportunities for tribal members that are concurrent with population recovery and consistent with the most recent guidance for supplementation programs (Venditti et al. ).…”

“…; Venditti et al. ). Other concerns include the potential for disease transmission, genetic contamination, competition between hatchery and natural fish, predator attraction and the reduced population productivity that results from these and other mechanisms (Einum and Fleming ; Araki et al.…”

“…Despite its ubiquity, supplementation remains controversial because it does not address the underlying causes for population decline so it rarely achieves self-sustaining populations (Waples et al 2007;Venditti et al 2018). Other concerns include the potential for disease transmission, genetic contamination, competition between hatchery and natural fish, predator attraction and the reduced population productivity that results from these and other mechanisms (Einum and Fleming 2001;Araki et al 2007;Chilcote et al 2011).…”