Comment: Natural Productivity in Steelhead Populations of Natural and Hatchery Origin—Assessing Hatchery Spawner Influence

Abstract

Interactions between hatchery-origin and wild anadromous salmonids, and their potential influence on the productivity of wild fish, are often a concern of those trying to maintain or recover natural populations. The concern stems from the large size and broad geographic scope of existing hatchery programs, increased emphasis on the use of hatcheries to enhance natural production for recovery, and recognition that the programs may be having consequential effects on wild salmonids. Answers to questions about the magnitude of such effects on individual programs or populations are often pursued but frequently unavailable. This makes it important in the instances in which answers are developed that they be reliable.The purpose of Lister (2014) was "to determine the influence of hatchery steelhead [Oncorhynchus mykiss] spawners on productivity of natural steelhead spawners in mixed populations that included adults of hatchery and natural origin." In pursuit of this, the paper presents results that are dependent on confounded methods and unsupported assumptions as a basis for suggesting that hatchery-origin spawners (S h ) have not negatively influenced the natural productivity of multiple steelhead populations in the interior Columbia River basin. The paper has at least three critical flaws: the analytic approach, the use of a measure of productivity for natural fish that is inherently flawed, and the drawing of erroneous conclusions from irresolute data.The paper has additional technical shortcomings that we have chosen not to address here, particularly with regard to how specific data estimation errors and biases (other than those of the flawed productivity metric) have or have not been addressed. ANALYTIC APPROACHPast analyses of spawner-recruit data that examined the influences of hatchery-origin salmonids on the productivity of naturally spawning populations have typically relied on meta-analytic techniques, multivariate modeling approaches, or both (Chilcote 2003;Nickelson 2003;Kostow and Zhou 2006;Buhle et al. 2009;Chilcote et al. 2011Chilcote et al. , 2013. A key reason such approaches were taken is their statistical power to discern patterns in data that exhibit high variability.Lister (2014) takes an alternate analytic approach. The paper focuses on the presence or absence of statistically discernable differences in productivity between three specific pairs of hatchery-affected (mixed-treated) and littleaffected (reference) steelhead populations. However, there are no before-and-after statistical evaluations of the influence of S h on the mixed populations, as are performed under before-after control-impact paired study designs (Stewart-Oaten et al. 1986) and no true experimental controls. The paper's pairwise comparisons are instead dependent on an unverified assumption that populations within the selected pairs would have similar productivities (identical or very nearly so) absent hatchery influence. This assumption is suspect because the productivities of steelhead populations are affected by a variety of ...

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.…”

Natural Productivity in Steelhead Populations of Natural and Hatchery Origin—Assessing Hatchery Spawner Influence: Response to Comment

“…This response to the comment by Carmichael et al (2015, this issue) makes reference to the natural productivity of steelhead Oncorhynchus mykiss expressed as either (1) the number of natural-origin adult recruits per parent of natural origin (R nat /S nat ) or (2) the number of natural-origin adult recruits per total spawners of natural and hatchery origin (R nat /S tot ). The purpose of the Lister (2014) study was to determine the influence of hatchery-origin steelhead spawners on the natural productivity of natural-origin steelhead spawners in mixed populations that include adults of both hatchery and natural origin.…”