Testing a model of drift-feeding using three-dimensional videography of wild brown trout, Salmo trutta, in a New Zealand river

• Published in: Canadian journal of fisheries and aquatic sciences Vol. 60; no. 12; pp. 1462 - 1476
• Main Authors: Hughes, Nicholas F, Hayes, John W, Shearer, Karen A, Young, Roger G
• Format: Journal Article
• Language: English
• Published: Ottawa, Canada NRC Research Press 01.12.2003; National Research Council of Canada; Canadian Science Publishing NRC Research Press
• Subjects: Agnatha and pisces; Agnatha. Pisces; Animal and plant ecology; Animal behavior; Animal ethology; Animal populations; Animal, plant and microbial ecology; Animals; Autoecology; Biological and medical sciences; Fish; Fisheries management; Foraging behavior; Freshwater; Fundamental and applied biological sciences. Psychology; Habitats; Interception; Natural environment; Prey; Psychology. Psychoanalysis. Psychiatry; Rivers; Salmo trutta; Salmon; Scientific models; Streambeds; Swimming; Trout; Upstream; Velocity; Vertebrata; Water depth; New Zealand; Oceania; New Zealand, South I., Travers R; Feeding behavior; Predatory behavior; Video technique; Wild animal; Foraging behavior; Feeding; Prey; Aquatic environment; Capture rate; Vertebrata; Salmo trutta; Pisces; Drift; Models
• ISSN: 0706-652X; 1205-7533
• DOI: 10.1139/f03-126

We tested the assumptions and predictions of a foraging model for drift-feeding fish. We used three-dimensional videography to describe the foraging behavior of brown trout, Salmo trutta, mapped water depth and velocity in their foraging area, sampled invertebrate drift to determine length class specific drift densities, and captured trout to determine the size composition of their diet. The model overestimated the fish's prey capture rate and gross energy intake rate by a factor of two. Most of this error resulted from the fact that prey detection probabilities within the fish's foraging area averaged only half the expected value. This was the result of a rapid decrease in capture probability with increasing lateral distance from the fish's focal point. Some of the model's assumptions were accurate: equations for predicting reaction distance and minimum prey size supported reliable predictions of the shape and size of the fish's foraging area and the size composition of the diet. Other assumptions were incorrect: fish detected prey within the predicted reaction volume, not on its upstream surface as expected, fish intercepted prey more slowly than the expected maximum sustainable swimming speed, and fish captured about two-thirds of their prey downstream of their focal point, rather than upstream.