Quantifying the Foodscape for Stream‐Dwelling Cutthroat Trout Reveals Spatial and Temporal Ranges of Resource Exploitation and Energy Intake

Abstract

Food availability is a primary factor limiting the abundance of wild populations, but quantifying it requires an understanding of when and where prey are vulnerable to predators. Salmonid fishes in streams are commonly thought to forage on drifting aquatic invertebrates during daylight hours. However, past studies also report benthic and nocturnal foraging despite the predominant view of salmonids as diurnal drift‐feeding predators. We used instream videography to assess foraging mode and energy intake for stream‐dwelling Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri. We recorded the foraging behavior of wild fish with a waterproof video camera and estimated energy intake based on fish size, foraging rate, retention rate, and caloric values of prey. Fish captured prey primarily from the water column and surface, targeting drifting invertebrates during daytime hours; however, they also foraged from the stream benthos and during nighttime. Yellowstone Cutthroat Trout foraging rate was most strongly related to foraging location in the stream, diel period, and month. Energy intake was highest from daytime drift‐foraging behavior and exceeded a modeled metabolic limit of food intake during October and November. Nocturnal and benthic foraging contributed the smallest proportion of total foraging attempts but was observed over all months of our study and sometimes comprised up to 30% of estimated energy intake. Our results indicate that Yellowstone Cutthroat Trout in streams acquire most of the food intake as daytime drift‐feeding predators.

Climate change impacts on native cutthroat trout habitat in Colorado streams

“…Heggenes et al (1991) reported that cutthroat trout larger than 9 cm total length selected stream habitats with depths >25 cm, and maximum channel depths are already or projected to be below this threshold in many study streams. Finally, slower velocity would reduce drift food availability, which is the primary food source for stream salmonids in summer (Owens & Keeley, 2022; Uthe et al, 2019). Optimal foraging velocity of stream salmonids during base flow conditions range between 20 and 40 cm/s (Morita, Sahashi, & Tsuboi, 2016; Nislow, Folt, & Parrish, 1999), which again fall within the velocity range projected in the current and future climate scenarios for the study sites.…”

Advances in biologging can identify nuanced energetic costs and gains in predators

“…Foodscapes, though developed for herbivores navigating immobile forage [49,55], can also be extended further up the food chain, as prey resource selection will shape the movements and selected hunting strategies of their predators [56].…”

Advances in biologging can identify nuanced energetic costs and gains in predators

“…These dynamics become more complicated in multi-predator systems where prey must contend with predators using different hunting strategies, resulting in complex landscapes of fear with varying levels of risk [ 52 ]. The concept of foodscapes, though developed for herbivores navigating immobile foraging resources [ 46 , 53 ], can also be extended further up the food chain, as prey resource selection will shape the movements and selected hunting strategies of their predators [ 54 ]. The landscape of disgust arises from parasite avoidance behaviour, with further consequences for predator–prey interactions and scavenging decisions [ 48 , 55 ].…”