Use of eDNA to estimate abundances of spawning Yellowstone cutthroat trout in Yellowstone National Part, Wyoming, USA

Abstract

Invasive Lake Trout Salvelinus namaycush and whirling disease have reduced the abundance of native Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri (YCT) in Yellowstone Lake, Yellowstone National Park, thereby disrupting the Yellowstone Lake ecosystem. One indication of the YCT population decline is the decrease in the number of adults returning to tributaries to spawn each spring. Yellowstone National Park implemented a gillnetting program to remove Lake Trout starting in 1995 to restore YCT abundance and size structure and thereby conserve the Yellowstone Lake ecosystem. An important metric for evaluating the success of the program is the number of YCT ascending spawning tributaries each year. Annually, 9 to 11 of these tributaries are visually surveyed on a weekly basis from May through July for the presence of spawners, but these surveys are time consuming. The use of environmental DNA (eDNA) has become increasingly common for determining presence of aquatic species and may provide managers with a more efficient tool for estimating abundances of YCT spawners. The primary objective of my study was to evaluate the efficacy and accuracy of using eDNA to detect the presence and estimate abundance of YCT spawners by collecting eDNA samples from spawning tributaries to Yellowstone Lake in conjunction with visual surveys of YCT spawners. A secondary objective was to evaluate whether terrestrial or semi-terrestrial species such as grizzly bear Ursus arctos horribilis and North American river otter Lontra canadensis could be detected in a water sample from YCT spawning tributaries. Environmental DNA quantities were more effective for determining presence of YCT spawners than for predicting their abundances, but eDNA quantities were positively related to spawner abundances. The difference between eDNA rates when spawners are present versus absent may provide managers with an efficient method for monitoring YCT in tributaries throughout Yellowstone Lake basin. I also demonstrated that DNA from a terrestrial species, grizzly bear, can be detected in water samples. Incorporation of eDNA sampling with existing methods for monitoring YCT spawners in Yellowstone Lake tributaries would facilitate an increased scale of assessment and allow for detection and quantification of multiple species of current and future interest from single samples.