The Effect of an Introduced Summer Steelhead Hatchery Stock on the Productivity of a Wild Winter Steelhead Population

Abstract

Abstract.-We investigated the effect of a hatchery program for summer steelhead Oncorhynchus mykiss on the productivity of a wild winter steelhead population in the Clackamas River, Oregon. We used a suite of Ricker and Beverton-Holt stock-recruitment models that incorporated species interaction variables to demonstrate that when high numbers of hatchery summer steelhead adults were present the production of wild winter steelhead smolts and adults was significantly decreased. We found that large releases of hatchery smolts also contributed to the decrease in wild adult productivity. Averaged over the results of our models, a 50% decline in the productivity parameter (the number of recruits per spawner at low densities) and a 22% decline in the maximum number of recruits produced in the basin were observed when high numbers of hatchery fish were present. We concluded that over the duration of the hatchery program, the number of hatchery steelhead in the upper Clackamas River basin regularly caused the total number of steelhead to exceed carrying capacity, triggering density-dependent mechanisms that impacted the wild population. The number of smolts and adults in the wild winter steelhead population declined until critically low levels were reached in the 1990s. Hatchery fish were removed from the system in 2000, and early results indicate that the declining trends have reversed.

Declining patterns of Pacific Northwest steelhead trout (Oncorhynchus mykiss) adult abundance and smolt survival in the ocean

“…1). For Oregon, we used Oregon Department of Fish and Wildlife unpublished data (J. Spangler, personal communication) and Kostow and Zhou (2006) to estimate SARs for five (one wild and four hatchery) populations. For BC, we used BC Ministry of Forests, Lands, and Natural Resource Operations unpublished data (T. Davies, personal communication) to estimate SARs for one wild population.…”

Factors that contribute to the ecological risks of salmon and steelhead hatchery programs and some mitigating strategies

“…The introduction of hatcheryproduced fish can be a major cause of ecological perturbation in salmon and steelhead populations (Fresh 1997). Recent research has demonstrated that the ecological effects of hatchery programs may significantly reduce wild population productivity and abundance even where genetic risks do not occur Kostow and Zhou 2006).…”

Structure of run, abundance and biological characteristics of hatchery and wild chum salmon in the basin of the Paratunka River (southeastern Kamchatka) in 2010-2015

“…Учёные подчёркивают, что значи-тельная доля заводских рыб может заметно снизить численность и продуктивность диких популяций (Reisenbichler, Rubin, 1999;Ford, 2002;Ford et аl., 2006;Araki et аl., 2008;Kostow, 2009Kostow, , 2012Zaporozhets, Zaporozhets, 2012;Hayes et аl., 2013). По мнению Костов и Жоу (Kostow, Zhou, 2006), искусственное воспроизводство оказывает менее заметное влияние на естественные популяции лососей, когда доля заводских рыб не превышает 10-12 %.…”