Current Distribution and Habitat Use of the Threatened Snail Darter (Percina tanasi) in Alabama

Abstract

The distribution of many fishes in larger rivers is poorly known, in part due to the difficulties of sampling them. This is especially true for small -bodied or rare species, such as the Snail Darter (Percina tanasi). This federally listed (threatened) species of darter has a limited distribution in the Tennessee River system in Alabama and Tennessee, where it is known from a few large tributaries or small rivers. The Snail Darter was previously known from only one locality in Alabama, but has recently been found in two additional, widely separated systems. These new distributional records raise questions regarding the accuracy of our current understanding of the range of this species. In particular, are Snail Darters present throughout the main stem Tennessee River, and is the species dispersing into new areas from source populations in the river? The occurrence of Snail Darters in the Tennessee River main stem would expand our knowledge of its range, and inform current conservation efforts for the species, such as habitat prioritization. To clarify the distribution of Snail Darter in Alabama, 61 unique sites were surveyed using environmental DNA for detection. This cost-effective detection tool eliminates the difficulty associated with empirically sampling large rivers for small fishes. Approximately 50% of sites sampled were positive for Snail Darter DNA. This study confirmed the known localities of Snail Darters in the Bear Creek, Elk River, and Paint Rock River. Several new localities were also discovered throughout the main stem Tennessee River and in Shoal Creek, near Florence, Al. Side scan sonar techniques were applied to compare habitat availability surrounding select negative and positive eDNA sites. Negative sites had a significantly higher proportion of fine sediment compared to the positive sites. These results determined critical localities and habitat types that sustain Snail Darter populations. These findings can inform biologists about where to prioritize conservation efforts and further, could lead to studies assessing movement and relatedness between populations in this system.