Abstract
Conceptually, trophic niche overlap and species abundance can describe the strength and number of interspecific trophic interactions to determine the competitive impact on reintroduced species or other ecosystem changes. We use an example with young-of-year (YOY) Atlantic salmon (Salmo salar) reintroductions to determine whether trophic niche overlaps and abundances limit restoration success. Using seasonal stable isotopes and abundance estimates for invertivorous fishes in three Lake Ontario tributaries, we assessed community isotopic structure, trophic niche overlap, and the impact of the niche overlap by incorporating relative abundance. Brown trout (Salmo trutta) YOY could be a strong competitor with a high trophic niche overlap with Atlantic salmon YOY, but at lower abundances relative to Atlantic salmon there is minimal impact. Stream resident fish communities appeared to partition resources across seasons such that abundant species had low trophic niche overlap to minimize overall competition with Atlantic salmon YOY given available resources, indicating niche complementarity. Through joint consideration of trophic overlap and abundance using our conceptual model, the competitive impact of community composition on a reintroduced species could be assessed.
Highlights
In aquatic systems, stocking fish to supplement wild populations and enhance fisheries occurs globally, and it is important to determine any limitations to stocking success (Minckley 1995; Brown and Day 2002; Molony et al 2003)
We assessed the trophic niches of stocked Atlantic salmon YOY in multiple streams over seasons to determine whether potential competition with resident fishes may be occurring in Lake Ontario tributaries
Using conventional stable isotope analyses, brown trout YOY strongly overlapped with Atlantic salmon YOY; with the inclusion of their low abundance it would not be perceived to have a large impact on Atlantic salmon YOY population growth or survival, as seen in our conceptual model
Summary
In aquatic systems, stocking fish to supplement wild populations and enhance fisheries occurs globally, and it is important to determine any limitations to stocking success (Minckley 1995; Brown and Day 2002; Molony et al 2003). Removal of threats and having suitable habitat and food requirements are key factors to successful reintroductions (Harig et al 2000; Cochran-Biederman et al 2015). The composition of the resident fish community may influence the success of salmonid reintroductions (Harig et al 2000; Scott et al 2003; Cochran-Biederman et al 2015). Existing resident species may be strong competitors with stocked species for food resources and (or) habitat (Griffith et al 1989; Schooley and Marsh 2007; Ward et al 2008) and influence the outcome of the stocking
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