Data from: Seasonal change in trophic niche of adfluvial arctic grayling (Thymallus arcticus) and coexisting fishes in a high-elevation lake system

Introduction of non-native species is a leading threat to global aquatic biodiversity. Competition between native and non-native species is often influenced by changes in food availability or suitable habitat conditions. We investigated diet breadth and degree of trophic niche overlap for a fish assemblage of native and non-native species inhabiting a shallow, high elevation lake system. This assemblage includes one of the last remaining post-glacial endemic populations of adfluvial Arctic grayling (Thymallus arcticus) in the contiguous United States. We examined gut contents and stable isotope values of fish taxa in fall and spring to assess both short- (within season) and long-term (between season) changes in trophic niches. We incorporated these data into a secondary isotopic analysis using a Bayesian statistical framework to estimate long-term trophic niche. Our data suggest that in this system, Arctic grayling share both a short- and long-term common food base with non-native trout of cutthroat x rainbow hybrid species (Oncorhynchus clarkia bouvieri x Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis). In addition, trophic niche overlap among Arctic grayling, hybrid trout, and brook trout appeared to be stronger during spring. In contrast, the native species of Arctic grayling, burbot (Lota lota), and suckers (Catostomus spp.) largely consumed different prey items. Our results suggest strong seasonal differences in trophic niche overlap among non-native trout and Arctic grayling, with a potential for greatest competition for food during spring. We suggest that conservation of endemic Arctic grayling in high-elevation lakes will require recognition of the potential for coexisting non-native taxa to impede well-intentioned recovery efforts.外来物种引入是全球水生生物多样性面临的主要威胁之一。本地物种与外来物种间的竞争通常受食物可获得性或适宜生境条件变化的影响。我们针对栖息于浅层高海拔湖泊系统的本土与外来鱼类类群，开展了食性广度与营养生态位重叠程度的调查研究。该类群包含美国本土现存为数不多的冰川后洄游性北极茴鱼（Thymallus arcticus）特有种群之一。我们于秋季和春季对鱼类类群的肠道内容物与稳定同位素值进行了检测，以评估营养生态位的短期（季节内）与长期（季节间）变化。我们将这些数据纳入贝叶斯统计框架下的二次同位素分析，以估算长期营养生态位。研究数据表明，在该湖泊系统中，北极茴鱼与外来的切喉鳟×虹鳟杂交种（Oncorhynchus clarkia bouvieri × Oncorhynchus mykiss）和溪鳟（Salvelinus fontinalis）共享短期与长期的共同食物基础。此外，北极茴鱼、杂交鳟与溪鳟之间的营养生态位重叠在春季更为显著。与之相反，本土的北极茴鱼、江鳕（Lota lota）和吸口鱼（Catostomus spp.）则主要摄食不同的猎物类群。研究结果显示，外来鳟类与北极茴鱼的营养生态位重叠存在显著季节差异，春季存在最强烈的食物竞争潜力。我们认为，对高海拔湖泊中特有北极茴鱼的保护工作，需要认识到共存的外来类群可能会阻碍旨在恢复种群的善意保护举措。