Disproportionate Relative Importance of a Terrestrial Beetle Family (Coleoptera: Scarabaeidae) as a Prey Source for Central Appalachian Brook Trout

-Brook trout Salvelinus fontinalis and other salmonids in Appalachia typically inhabit headwater watersheds, where food resources may limit growth. We monitored the feeding trends of a brook trout population in central Appalachia over the course of 2 years to determine variation in feeding intensity and important prey items. One terrestrial beetle family, Scarabaeidae, provided a disproportionate amount of energy during the only time of year when brook trout were feeding substantially above maintenance ration. Scarab beetles contributed 39.6% of all energy consumed during May and June of both years, though the number of fish with one or more scarabaeids present in the stomach varied by month (22.2-51.7%). The species composition of scarab beetles consumed suggested that four species are of particular importance. Our findings imply that scarabaeids represent a considerably important prey taxon for brook trout in the region. Considering the foraging habits of the scarabaeid species in question, the phenomenon we witnessed probably occurs throughout Appalachia. Lotic salmonids in low-productivity headwater watersheds typically experience poor feeding conditions, though the consumption of terrestrial organisms may improve energy intake. The most frequently cited source of nutrients in headwater streams is input of allochthonous forest material from the surrounding watershed, which provides energy to an invertebrate community (Vannote et al. 1980). This aquatic invertebrate community is the most commonly cited source of energy for top predators in streams, such as salmonids (Neveu 1999). However, recent examinations of salmonid diets in headwater watersheds reveal that terrestrial organisms may outweigh aquatic * Corresponding author: [email protected] Received March 7, 2006; accepted September 21, 2006 Published online January 29, 2007 organisms in energy provided to fish (Kawaguchi and Nakano 2001; Sweka and Hartman, in press; Utz and Hartman 2007). When taxonomic detail of terrestrial invertebrates is considered relative to nutrient input to streams, ecosystems, and salmonid diet, results suggest that certain organisms are of particular importance while others are of negligible importance (Allan 1981; Nielsen 1992; Wipfli and Gregovich 2002; Utz and Hartman 2007). Despite the notion that a variety of terrestrial organisms may be of critical importance to lotic salmonids, a large number of salmonid diet studies classify all terrestrial organisms into one broad category (Cada et al. 1987; Forrester et al. 1994; Bridcut and Giller 1995; Mookerji et al. 2004). The growing understanding that salmonids may be heavily dependent on certain terrestrial organisms merits more attention to the species composition of terrestrial organisms in their diets. In Appalachia, salmonids must cope with periodically poor feeding conditions (Cada et al. 1987; Ensign et al. 1990; Sweka 2003; Thome 2004) as well as occasional extreme environmental circumstances, such as drought and flooding (Carline and McCullough 2003; Hakala and Hartman 2004). The low productivity of Appalachian headwater watersheds, coupled with natural environmental variability, may affect the population dynamics and growth patterns of salmonids. The current study complements a 2-year observational analysis of temporal feeding trends of adult Appalachian brook trout Salvelinus fontinalis (Utz and Hartman 2006, 2007). These studies found that brook trout only exceed maintenance energy rations consistently and substantially during the spring (May and June). One family of terrestrial beetles, Scarabaeidae (hereafter, scarabaeids), emerged as one of the most important prey taxa for the population we studied