Remote telemetry of daily vertical and horizontal movement of Nautilus in Palau

Abstract

Vertical depth migrations, by the chambered cephalopod Nautilus when moving into shallower waters at night, were first documented by Wiley¹. Although unsupported by quantitative data, this observation strongly influenced the interpretation of the mode of life of Nautilus and of the palaeoecology of fossil chambered cephalopods^2–4. To determine whether these migrations do occur, we mounted ultrasonic transmitters on four Nautilus belauensis in Palau. The transmitters contained a strain-gauge depth sensor that caused the transmitters to emit sonic pulses at intervals that varied with depth, so that geographical position and depth could be ascertained. Our results indicate that at least in this population or geographical area, vertical depth changes of up to 200 m per day are common. Although too soon to make generalizations about other populations of Nautilus in the Pacific, it has been suggested that the morphological position of the siphuncle within the phragmocone of the chambered shell would increase the efficiency of vertical migrations m Nautilus, if such migrations were found to occur^5,6. As similar siphuncle configurations are common in most post-Triassic nautiloids, and some ammonoids^6,7, it could be that vertical migration was common in many fossil forms as well.