Diel and density-related changes in food consumption and prey selection by brook charr in a New Hampshire stream

Abstract

SynopsisWe report the results of a field study testing influences of both density and changes over the diel cycle on food consumption and prey selection by brook charr, Salvelinus fontinalis. Charr density in replicate 35 m long sections of a New Hampshire stream was adjusted to either medium or high levels (relative to natural densities) . Diets of charr and the availability of drifting prey were then sampled every four hours for 24 hours .There were no significant diel changes in the weight of prey consumed by charr per four hours, though there was some indication of reduced feeding at night . Charr fed selectively on different prey taxa, showing most preference for cased caddis larvae . Several species of mayflies and stoneflies were selected more strongly during the day than at night . Charr fed selectively on larger prey during the daytime but showed no sizeselection at night . The density of charr had no significant effects on either their rate of food consumption or on selection for prey of different taxa or sizes .

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.…”

“…Besides Sweka (2003), we could locate only one other literature report of scarabaeids as important salmonid prey, and this was anecdotal (Ratcliffe and Ocampo 2002). Unfortunately, a typical approach in descriptive studies of salmonid diets has been to classify all terrestrial organisms into a single, broad category (Cada et al 1987;Forrester et al 1994;Bridcut and Giller 1995;Nakano et al 1999;Mookerji et al 2004). While we previously reported moderate terrestrial taxonomic analysis in a related study (Utz and Hartman 2007), the current study suggests that careful analysis of terrestrial taxonomic detail in fish diets reveals important ecological phenomena.…”

“…Individual parameters of the brook trout bioenergetics model can be found in Hartrnan and Sweka (2003). Though daily consumption typically requires estimates of feeding activity across a diel cycle (Bowen 1996), multiple studies of brook trout feeding trends revealed no significant diel pattern in multiple diet variables (Forrester et al 1994;Sweka 2003;Mookerji et al 2004). Further, the evacuation rate of brook trout has proven to be low relative to rates exhibited by other salmonids (Sweka et al 2004), which means that food items remain in the gut long after they have been ingested.…”

“…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.…”

The costs of becoming nocturnal: feeding efficiency in relation to light intensity in juvenile Atlantic Salmon

“…Elliott 1965Elliott , 1967Elliott , 1970Elliott , 1973Sagar & Glova 1988). From spring until autumn, when stream salmonids are active (and potentially able to feed) throughout the diel cycle, most studies of wild fish have found peaks in feeding at dawn and/or dusk (when light intensities are not constraining and drift abundance is higher than the daytime level) but rather little and less selective foraging during the night itself (Elliott 1970(Elliott , 1973Jenkins, Feldmeth & Elliott 1970;Sagar & Glova 1988;Angradi & Griffith 1990;Riehle & Griffith 1993;Forrester, Chace & McCarthy 1994).…”