Effects of Stocking Catchable‐Sized Hatchery Rainbow Trout on Wild Rainbow Trout Abundance, Survival, Growth, and Recruitment

Abstract

The Idaho Department of Fish and Game has proactively dealt with the potential adverse genetic effects of stocking catchable-sized hatchery trout in waters that support native salmonids by adopting a policy in 2001 whereby only sterile rainbow trout Oncorhynchus mykiss are stocked in flowing waters; however, concerns regarding the competitive effects of introducing hatchery trout into streams and rivers supporting wild trout have not been addressed. We stocked fish in the middle 3 years of a 5-year study to assess whether stocking hatchery rainbow trout of catchable size (hereafter, catchables) reduced the abundance, survival, growth, or recruitment of wild rainbow trout in streams. Catchables averaging 249 mm total length (TL) were stocked from 2006 to 2008 at an annual density of 4.2 fish/100 m 2 into 12 treatment reaches of stream that were paired with control reaches at least 3 km apart in the same stream in which no stocking occurred. Wild rainbow trout abundance (including all fish ≥75 mm TL), recruitment, survival, and growth were determined from population estimates and recaptures of fish tagged with passive integrated transponder (PIT) tags during mark-recapture electrofishing sampling. The abundance of wild rainbow trout averaged 13.2 fish/100 m 2 but varied substantially across sites and years, ranging from a low of 0.5 to a high of 131.3 fish/100 m 2 ; similar variability was observed in recruitment to age 1. Estimates of total annual survival averaged 0.53 based on the population abundance estimates (which allowed for emigration and immigration) and 0.26 based on the PIT-tag recaptures (which allowed for emigration but not immigration). Our paired study design demonstrated that the abundance, survival, growth, and recruitment to age 1 of wild rainbow trout were all unaffected by stocking catchables. The lack of population-level effects from stocking catchables was not surprising considering the high short-term mortality and the socially and physiologically naive behavior typically exhibited by hatchery catchables stocked in lotic systems.

How ecological processes shape the outcomes of stock enhancement and harvest regulations in recreational fisheries

“…, Meyer et al. ). Our model supports the trend seen in some countries to stock increasingly larger fish including catchable fish in stock‐enhancement efforts (Halverson ), which is likely a response to fry and small fingerlings rarely producing sustained outcomes for ecological reasons.…”

“…, Meyer et al. ). The recommendation to stock a nonnative species such as carp also assumes that one is not concerned with the possible negative ecological consequences of high carp biomasses (e.g., water quality impacts, habitat degradation, competition with other species, etc.…”

Effects of stocked trout on stream invertebrate communities

“…Most fishery resource managers are charged with the dual, often conflicting responsibility of providing and enhancing angling opportunities for the public while simultaneously protecting native organisms (Meyer et al 2012). This dual mandate suggests that stocking of non-native trout is likely to continue in the foreseeable future.…”

“…Results from studies examining the ecological impacts of stocked or introduced trout in streams and lakes at varying spatial scales have ranged from finding little or no effect (Allan 1982;Zimmerman & Vondracek 2007;Hanisch et al 2012;Meyer et al 2012) to observing large impacts on invertebrate abundances, biomass, or density (Flecker and Townsend 1994;Huryn 1998;Nakano 1999;Baxter et al 2004). For example, Baxter et al (2004) showed that stocked rainbow trout CONTACT Alexander V. Alexiades ava29@cornell.edu monopolized terrestrial invertebrates and caused native fish to shift their diet to insect grazers, thereby increasing algal biomass.…”

Release of hatchery adult steelhead for angler opportunity increases potential for interactions with endemic steelhead

“…To assess how programs balance providing harvest options of non-local animals through intentional releases, such as putand-take fisheries (Johnson et al 1995, Meyer et al 2012b, big game hunting preserves (Adams et al 2016), and upland bird introductions (Blanco-Aguiar et al 2008), with conservation of endemic populations, quantification of the proportion of Fig. Post-release fate may affect native conspecifics, similar species within the same guild or assemblage (i.e., other cold-water fishes), community dynamics via food web effects, or energy and nutrient flows within the recipient ecosystem.…”