Seasonal feeding specialization on snails by river darters (Percina shumardi) with a review of snail feeding by other darter species
We report food habits of River Darters (Percina shumardi) in Brushy Creek and the Sipsey Fork Black Warrior River, Alabama. River Darters preyed heavily on pleurocerid snails in both streams. Snail feeding varied widely among sample dates and was highest in October when snails represented nearly 100% of darter food items. Snail feeding declined through the spring, nearly ceasing by May, but increased to high levels again in July when hatchling snails composed about 80% of darter food items. Mean and maximum size of snails eaten increased with darter size, but minimum snail size was not related to darter size, indicating a broadening of prey size for larger darters. Non-snail food items were dominated by chironomid, trichopteran, and ephemeropteran insect larvae; these food items were most commonly eaten during periods of low snail feeding or feeding on hatchling snails. Specialization for snail feeding is suggested for all species in the subgenus Imostoma, including P. shumardi, but this feeding habit is well documented previously only for P. tanasi. Published diet studies for other species of Imostoma, including populations of P. shumardifrom elsewhere in its range, did not document snail feeding; most other observations of snail feeding for the group are anecdotal. Few other darters or other fish species are documented to prey heavily on riverine snails. Although the limited amount of published information makes it difficult to assess the degree to which Imostoma as a group relies on snails as a food source, P. shumardi and P. tanasi represent two of the few native fishes that exploit the abundant and diverse pleurocerid snail fauna of eastern North America.