Development and Validation of a Bioenergetics Model for Bull Trout

We conducted laboratory experiments to estimate the maximum consumption rates (C_max) and standard (SMR) and active (AMR) metabolic rates of wild bull trout to parameterize a bioenergetics model. C_max was significantly influenced by temperature, with mean values for fish with an average (± SD) mass of 87 (± 25) g being highest at 16°C (ca. 0.1 g·g^-1·d^-1), lowest at 3°C (ca. 0.01 g·g^-1·d^-1), and intermediate at 7, 10, 13, and 20°C (range = 0.04 – 0.09 g·g^-1·d^-1). Per capita C_max declined exponentially with fish size. Most fish showed some degree of hyperphagia on the first day of a feeding trial, with mean values of C_max for fish on day 1 being from 1.4 to 25 times higher than values for the same fish during days 2 – 4. The magnitude of hyperphagia on day 1 was highest at 3°C (25×), lowest at 20°C (1.4×), and intermediate at 7-16°C (2 – 6×). We are currently estimating the SMR of fish relative to size and temperature and will conduct some swimming respirometry trials to determine active metabolic rates. A validation experiment conducted for 40 d at 10°C using a model with our C_max parameters and some preliminary metabolic rate data showed that the model generally underestimated consumption by an average of 13% but predicted final mass within ± 3% of measured values. When finished, the model should be useful to those dealing with issues currently faced by bull trout, such as predicting the effects of climate change or alterations in prey availability. Further refinements of the model will come from user feedback and future experiments designed to reduce the uncertainty associated with some model parameters.