Speed, Jet Pressure and Oxygen Consumption Relationships in Free-swimming Nautilus

1. Neutrally buoyant, ultrasonically telemetering, differential pressure transducers were attached to Nautilus pompilius L. to record mantle cavity pressures while the animals were induced to swim in a flume in response to food. 2. Synchronized videotapes and computer data files showed that jet pressures (p, Pa) increased linearly with swimming speed (M, ms"), p=1565u-8. 3. Because of their stereotyped responses to food, Nautilus could be induced to produce similar pressures in 51 respirometers, where oxygen consumption (VOv ml kg") increased as a power function of pressure, KO2=3.85/? '. 4. Combining these equations gave an oxygen consumption-speed relationship, VO2=283H' 8 4 . We used this equation to show that the cost of transport for Nautilus is dramatically lower than that for squid and, at speeds below 0.05 m s", even lower than that of an undulatory swimmer, the salmon. 5. Calculated power inputs and outputs suggest that squid have increased their power density (\Vkg~) 100-fold over their ectocochleate ancestors, and that Nautilus is very efficient in its low-speed, low-energy environment. 6. These laboratory 'calibrations' are a basis for field studies using telemetered pressure data to develop energy budgets for this unique living fossil as a reference for comparing the energetic requirements of ancient and modern seas.