Identification of critical prey items to Appalachian brook trout (Salvelinus fontinalis) with emphasis on terrestrial organisms

Abstract

Brook trout (Salvelinus fontinalis) in Appalachia experience prolonged periods of poor feeding conditions, particularly during summer and fall. To determine which prey organisms are important in sustaining brook trout populations, we monitored the feeding patterns of a population of brook trout over the course of 2 years with an emphasis on seasonal change. We employed a bioenergetics model to estimate whether or not each fish had obtained enough energy to meet daily metabolic demand. As a result, qualitative comparisons between fish feeding above maintenance ration (successfully feeding fish) and fish feeding below maintenance ration (unsuccessfully feeding fish) were possible. With the exception of winter, brook trout derived significantly more energy from terrestrial organisms than aquatic organisms. During each season, successfully feeding brook trout fed on greater proportions of specific prey types.Terrestrial Coleoptera and Lepidoptera consistently proved to be important prey during warmer seasons, while large organisms such as vertebrates and crayfish appeared to be important during winter. Our findings suggest that terrestrial organisms are more important than aquatic organisms in sustaining brook trout populations. Further, certain large and abundant terrestrial taxa are critical in providing energy to brook trout.

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

“…For all months (except May 2004), no single scarabaeid species was ranked as the most important prey item, but the entire family ranked very high in both frequency of occurrence in brook trout stomachs and in mean energy provided per capture. As a family, guchi and Nakano 2001; Kawaguchi et al 2003), Alaskan (Wipfli 1997) and eastern United States streams (Forrester et al 1994;Utz and Hartman 2007;Sweka and Hartman, in press). However, few researchers have identified a specific family or species of terrestrial organism that provides a large amount of energy as consistently as do the scarabaeids in the Middle Fork River watershed.…”

“…However, few researchers have identified a specific family or species of terrestrial organism that provides a large amount of energy as consistently as do the scarabaeids in the Middle Fork River watershed. When taxonomic detail has been applied to terrestrial organisms in salmonid diets, terrestrial beetles usually emerge as very important (Allan 1981;Wipfli 1997;Kawaguchi and Nakano 2001;Utz and Hartman 2007). In a nearby watershed, Sweka (2003: Appendix A) found that scarabaeids contributed as much as 63% of the total ingested prey weight for brook trout populations.…”

“…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 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).…”

“…However, recent examinations of salmonid diets in headwater watersheds reveal that terrestrial organisms may outweigh aquatic 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).…”

Ontogenetic shifts in terrestrial reliance of stream-dwelling brown trout

“…In fact, inputs of terrestrial invertebrates from riparian canopy cover may represent an important food resource for stream-dwelling fish species (Kawaguchi and Nakano, 2001;Utz and Hartman, 2007;Syrjänen et al, 2011). Therefore, the importance of terrestrial invertebrates in riverine systems is unquestionable, such importance has been identified in different ways; that is, in terms of energy subsidy for fish species (Edwards and Huryn, 1996;Nakano et al, 1999b;Utz and Hartman, 2007), annual fish production (Edwards and Huryn, 1995), food resource partitioning between sympatric fish species (Dineen et al, 2007; or ecosystem functioning (Nakano et al, 1999c). That said, it should be kept in mind that the terrestrial invertebrate input to the riverine systems greatly depends on riparian canopy cover (Edwards and Huryn, 1996;Kawaguchi and Nakano, 2001;Ryan and KellyQuinn, 2015), but this allochthonous prey supply occurs primarily during summer, when aquatic invertebrate biomass is usually low (Nakano and Murakami, 2001).…”