Abstract
ABSTRACTBrown trout (Salmo trutta) are commonly stocked in streams and rivers worldwide to enhance recreational fisheries, but this practice can adversely impact other organisms in these ecosystems. We used nonmetric multi-dimensional scaling ordinations to evaluate the response of the invertebrate community to trout stocking in two streams in New York State. Most importantly, we used estimates of trout population mortality (natural and harvest mortality rates) to inform the timeframe within which the invertebrate response was evaluated because the potential impact of trout stocking is highly dependent on the abundance of stocked trout. We found that although brown trout are stocked at greater densities than native brook trout (Salvelinus fontinalis) the mortality rate of stocked trout was high (0.15 daily mortality rate which corresponds to 99.9% annual mortality), thus predatory impacts of fish upon invertebrates were likely to be pulsed and could only occur within a short temporal period. Despite the high mortality rate of stocked brown trout, we found a significant multivariate divergence of invertebrate community structure within two months of trout stocking in both streams.
Highlights
For more than a century, the introduction of hatchery-reared salmonid fishes into streams and lakes has been used to enhance angling opportunities where natural trout populations were reduced, extirpated due to anthropogenic impacts, or naturally absent (Schramm & Mudrak 1994; Hanisch et al 2012)
Apparent mortality estimates conducted on the two study streams from 2011 to 2013 indicated that stocked trout had a mean daily mortality rate of approximately 0.15, which translates to approximately 99.9% annual mortality
Many studies have evaluated the effects of trout stocking on native salmonid populations, the direct and indirect effects on the food web and community structure have not been as thoroughly examined
Summary
For more than a century, the introduction of hatchery-reared salmonid fishes into streams and lakes has been used to enhance angling opportunities where natural trout populations were reduced, extirpated due to anthropogenic impacts, or naturally absent (Schramm & Mudrak 1994; Hanisch et al 2012). Stocked trout can impact native organisms through several mechanisms – including competition, predation, and displacement of wild fish (Kerr & Grant 2000; Zimmerman & Vondracek 2007) – and disruption of aquatic-terrestrial linkages (Epanchin et al 2010). Trout stocking can reduce the abundance and diversity of aquatic invertebrate species, alter trophic foodwebs (Flecker and Townsend 1994; Kerr & Grant 2000), and disrupt nutrient cycles (Schindler & Parker 2002; Eby et al 2006). Stocking streams with trout has introduced non-native predators into a wide variety of ecosystems throughout the world, yet evidence of ecological impacts from this practice is highly variable and continues to merit careful examination (Nasmith et al 2012)
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