Macroinvertebrate prey availability and food web dynamics of nonnative trout in a Colorado River tributary, Grand Canyon

Abstract

Abstract.-We examined the influence of water temperature, diet, and feeding sites on growth differences of brown trout Salmo trutta in southeast Minnesota streams. Streams were classified as having either fast or slow growth based on back-calculated lengths at age and incremental growth measurements from scales collected in 2002 and 2003. Mean back-calculated lengths at age in fast-growth streams exceeded 141 mm at age 1, 229 mm at age 2, and 289 mm at age 3. In slowgrowth streams, mean back-calculated lengths did not exceed 127 mm at age 1, 208 mm at age 2, and 268 mm at age 3. The frequency of feeding sites was low in both stream groups, although possibly higher in the fast-growth streams. Water temperatures were significantly warmer in the fast-growth streams in summer and somewhat cooler in winter. We used a Wisconsin-style bioenergetics model for brown trout to independently test the effects of water temperature and diet, holding other parameters constant. Differences in temperature regime alone were not sufficient to explain differences in growth, and, in fact, predicted slower growth in the fast-growth streams in summer. Different diets resulted in differing predicted weight gains when temperature was held constant; diets with the highest energy densities always resulted in the greatest predicted weight gains. For younger cohorts, diet items with high energy densities included amphipods and mayflies (Ephemeroptera). Estimated consumption rates increased with summer temperatures. Our data suggested that growth differences among streams were likely due to differences in diet and prey availability, with more energy-rich diets available in fast-growth streams. We hypothesize that differences in diet and prey availability are mediated by water temperatures.

Establishment of a Reproducing Population of Endangered Humpback Chub through Translocations to a Colorado River Tributary in Grand Canyon, Arizona

“…The large-magnitude monsoonal floods that were frequent during our study period did not appear to limit the survival of translocated fishes, but they may have provided an advantage for native fishes that evolved under frequent disturbance regimes (e.g., see Meffe and Minckley 1987;Poff and Ward 1989). Salmonids that are present in the Colorado River and are known to prey upon or potentially compete with Humpback Chub (Marsh and Douglas 1997;Yard et al 2011;Whiting et al 2014;Spurgeon et al 2015a) may be sensitive to tributary flow regimes that differ from those in their native range (see Fausch et al 2001;Cattanéo et al 2002;Dibble et al 2015). The successful establishment of Humpback Chub in Havasu Creek may be partially attributed to the rarity of invasive fishes, as newly translocated fish and offspring would face less competition or predation pressure (Olden et al 2008;Whiting et al 2014;Spurgeon et al 2015a).…”

“…; Whiting et al. ; Spurgeon et al. 2015a) may be sensitive to tributary flow regimes that differ from those in their native range (see Fausch et al.…”

“…Salmonids that are present in the Colorado River and are known to prey upon or potentially compete with Humpback Chub (Marsh and Douglas 1997;Yard et al 2011;Whiting et al 2014;Spurgeon et al 2015a) may be sensitive to tributary flow regimes that differ from those in their native range (see Fausch et al 2001;Cattanéo et al 2002;Dibble et al 2015). The successful establishment of Humpback Chub in Havasu Creek may be partially attributed to the rarity of invasive fishes, as newly translocated fish and offspring would face less competition or predation pressure (Olden et al 2008;Whiting et al 2014;Spurgeon et al 2015a). Indeed, the presence of nonnative fishes in translocation sites is a common cause of failure (Al-Chokhachy et al 2009;Cochran-Biederman et al 2015).…”

Pulsed flows, tributary inputs and food‐web structure in a highly regulated river

“…Creek. Finally, previous work suggests that tributary food webs-especially Bright Angel Creek-are unique and fundamentally different than simplified mainstem food webs (Whiting, Paukert, Healy, & Spurgeon, 2014) and may, therefore, contribute to enhanced diversity of potential trophic pathways connecting resources to consumers near the Bright Angel Creek confluence. Pulse flows through tributaries during the monsoon reset the food web-increasing FCL and increasing niche width and trophic diversity.…”

Can translocated native fishes retain their trophic niche when confronted with a resident invasive?

“…A carrying capacity for small tributary streams within Grand Canyon National Park based on food availability has not been estimated; however, tributary streams may support high invertebrate densities (Whiting et al. ). Before translocation, humpback chub were not recorded in surveys above the waterfall separating Shinumo Creek from the mainstem Colorado River.…”