Predation by hatchery yearling salmonids on wild subyearling salmonids in the freshwater environment: A review of studies, two case histories, and implications for management

Abstract

We conducted a literature review on predation by hatchery yearling salmonids on wild subyearling salmonids in the western United States. The review included 14 studies from the Pacific Northwest and California. In most instances, predation by hatchery yearling salmonids on wild subyearling salmonids occurred at low levels. However, when multiple factors contributing to the incidence of predation were met, localized areas of heavy predation were noted. Total prey consumed ranged from 456 to 111 000 subyearlings for the few studies in which enough information was gathered to make the estimate. We examined two of these studies in more detail: one detecting relatively low predation in four western Washington rivers and one detecting relatively high predation in the Trinity River in northern California. In the case of the rivers in western Washington, over 70% of wild subyearlings had migrated by the time hatchery steelhead were planted and those remaining had grown large enough to reduce their vulnerability to predation. In the case of the Trinity River, less than 20% of wild subyearlings had migrated by the time hatchery steelhead were planted and most were small enough to remain highly vulnerable to predation. We found that managers can effectively minimize the predation rate of hatchery yearling salmonids by reducing the spatial or temporal overlap of predator and prey. Unknown is the extent to which low predation rates, which likely occur in most places hatchery yearlings are released, might still negatively impact prey populations that are at low abundance because of other anthropogenic factors.

Development of natural growth regimes for hatchery-reared steelhead to reduce residualism, fitness loss, and negative ecological interactions

“…Regardless, the ecological implications of hatchery fish in the three Hood Canal streams will come primarily from fish greater than 200 mm, which were also more abundant than small residuals in each of the three streams. The incidence of predation by steelhead smolts and Proportion of population N=100 for each of three raceways (1-3) of age-1 smolts and each of two raceways (4 and 5) of S2 smolts summer residuals on juvenile salmon is typically very low (Sharpe et al 2008;Simpson et al 2009), but in rare cases can be a substantial source of mortality for juvenile salmon (Naman and Sharpe 2011). Interference competition between hatchery and wild juvenile salmonids is strongly determined by relative body size, and intraspecific competition appears to be more intense than interspecific competition (Tatara and Berejikian 2011).…”

Age at Release, Size, and Maturation Status Influence Residualism in Hatchery Steelhead

“…Residuals may compete for food and habitat with conspecifics and other native species (McMichael et al. , ; McMichael and Pearsons ; Huntingford ; Tatara and Berejikian ) and may prey on natural stocks (Hawkins and Tipping ; Naman and Sharpe ). Related to predation, large releases of hatchery steelhead and concomitant residuals may tend to increase and concentrate piscivorous fish, birds, and mammals in and around headwater rearing areas (Berejikian ; Collis et al.…”

Full Issue PDF, Volume 41, Issue 6

“…This is a difficult balancing act because of the clear contradiction between maintaining or increasing hatchery production to sustain near-term harvest and decreasing that production to reduce genetic, competitive, and other risks to wild populations. For example, improved understanding of the genetic consequences of hatchery fish straying to spawning grounds (e.g., Ford 2002;Araki et al 2007Araki et al , 2008 and of the potential for hatchery-origin salmonids to have ecological effects on their wild counterparts (e.g., Kostow and Zhou 2006;Buhle et al 2009;Naman and Sharpe 2012;Tatara and Berejikian 2012;Carmichael et al 2015) has clarified the need for substantial changes in hatchery programs to conserve wild fish.…”