ABSTRACT
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.
Synchronized videotapes and computer data files showed that jet pressures (p, Pa) increased linearly with swimming speed (u, ms−1), p=1565 u – 8.
Because of their stereotyped responses to food, Nautilus could be induced to produce similar pressures in 51 respirometers, where oxygen consumption (
) increased as a power function of pressure, 
.Combining these equations gave an oxygen consumption-speed relationship,
. 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−1, even lower than that of an undulatory swimmer, the salmon.Calculated power inputs and outputs suggest that squid have increased their power density (W kg−1) 100-fold over their ectocochleate ancestors, and that Nautilus is very efficient in its low-speed, low-energy environment.
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.
