Swimming speeds and metabolic rates of semi-captive juvenile lemon sharks (Negaprion brevirostris, Poey) estimated with acceleration biologgers

Abstract

There is much interest in being able to quantify the swimming speeds and metabolic rates of wild aquatic animals such as sharks to develop bioenergetics models and evaluate the metabolic consequences of different stressors. This study sought to calibrate tri-axial acceleration biologgers (accelerometers) such that it would be possible to estimate swimming speeds and metabolic rates of semi-captive sharks in an enclosed natural mesocosm. Juvenile lemon sharks (Negaprion brevirostris, Poey; 60–75cm total length, 1–2kg) were equipped with accelerometers and swum at stepwise velocity increments in a Blazka-style swim tunnel respirometer using a critical swimming speed protocol. Metabolic rates and acceleration-derived metrics (overall dynamic body acceleration and tailbeat frequency) were measured concurrently during forced swimming, and accelerometer-equipped sharks were released to an enclosed mesocosm habitat to estimate average daily metabolic rate (ADMR) and swimming velocities across diel and tidal cycles. Acceleration-derived tailbeat frequency was a stronger predictor of metabolic rate than overall dynamic body action, and predicted an active metabolic rate of 249.7±1.9mg O2 kg−1h−1 and an ADMR of 88.7±0.7kJkg−1d−1 at 30°C. Following exhaustive exercise a maximum metabolic rate of 398.0±19.6mg O2 kg−1h−1 was achieved and over the subsequent 55-minute recovery period excess post-exercise oxygen consumption was 31.2mg O2 kg−1. The critical swimming speed of the sharks was 0.71±0.03 body lengths per second (BL s−1), and swimming speed in the mesocosm was 0.19±0.01 BL s−1. Locomotor activity levels of semi-captive sharks in the mesocosm were influenced by tide state and diel period, with sharks having highest swimming velocities during diurnal periods and flooding tides. Overall, accelerometry is a suitable means for estimating swimming speed and metabolic rate in this species, and additional research to address anaerobic energy expenditure of wild sharks is warranted.