Direct Measurement of Swimming Speeds and Depth of Blue Marlin

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Abstract
Acoustic telemetry was used to monitor the swimming speed, depth and water temperature of three blue marlin (60 kg, 70 kg, 125 kg) and 165 h of continuous swimming speed data containing both sustained and burst swimming events were collected. Measurements of swimming speed show that, while blue marlin are capable of high speeds, they spend most of their time swimming slowly. The fastest sustained swimming speeds (80–120 cms−1) occurred during a 4–6 h recovery period immediately after tagging when marlin consistently swim at depths greater than 50m. Short bursts of speeds up to 225 cms−1 were usually associated with changes in depth. Slower swimming (15–25 cms−1) occurred when fish were within 10 m of the surface. These velocities are similar to direct measurements of swimming speeds of free-swimming sharks, seals and sea lions, indicating that many large aquatic vertebrates swim slowly to minimize energetic costs of transport.