Monitoring the Metabolic Rate and Activity of Free-Swimming squid With Telemetered Jet Pressure

ABSTRACT Measurements of oxygen consumption and mantle cavity pressure (P, kPa) of squid, Illex illecebrosus, of various masses (M,kg), swimming at various speeds (U, ms−1) in a tunnel respirometer yielded two relationships: Both jet frequency and peak pressures increase with increasing speed. Patterns varied considerably between individuals, but total area under the pressure curve (P) was well correlated with oxygen consumption and speed. A differential pressure transducer linked to an ultrasonic transmitter carrying average pressure data encoded on impulse frequency was designed to be carried inside the mantle cavity. It was tested in both the swim-tunnel and in video-taped free-swimming animals. The relationships above held over a range of speeds from 0 to 1·4ms−1, the maximum speed observed, indicating that such transducers could provide direct estimates of both the metabolic rates and activities of these pelagic carnivores in nature; their use to test hypotheses about several energy-saving strategies is discussed. Average thrusts, calculated from pressure data, are consistent with rigid body drag predictions and with overall locomotor efficiencies of 5 %, which are also consistent with the relative costs of transport and efficiency estimates for fish.