I. P. Smith

Digital electromagnetic telemetry system for studying behaviour of decapod crustaceans.

1 year and the receiving system batteries are replaced by divers at intervals of up to 4 weeks. In field tests, crab (Cancer pagurus L.) and lobster (Homarus gammarus (L.)) activity was monitored at an artificial reef for 14 months. Examples of the type of information acquired are presented to illustrate the capabilities of the system and potential applications are discussed. Limitations of digital electromagnetic telemetry stem mainly from the short range of detection, the need for cables on the seabed and the size and shape of the transmitting tag.

Electromagnetic telemetry of lobster (Homarus gammarus (L.)) movements and activity: preliminary results

Individual European lobsters were tracked on an artificial reef using an electromagnetic telemetry system, which detected movements between reef units and also recorded body movements (pitching and rolling) indicated by a tilt switch incorporated into the transmitting tag. Several environmental variables were recorded simultaneously by the telemetry system, which was self-contained on the seabed. To date, 26 lobsters (14 female, 12 male) have been tagged, up to seven have been monitored simultaneously and four individuals have been tracked for over 6 months. Movements between units of the artificial reef (over open seabed away from shelter) were predominantly nocturnal, although daytime movements occurred during periods of low light levels associated with increased turbidity resulting from wave action. A marked decline in the number of inter-reef movements from late summer to winter was most closely related to decreasing water temperature. Activity indicated by the tilt switch was greater at night for most lobsters, but there were moderate levels of activity during the day. As with inter-reef movements, activity declined as winter progressed and in addition the diel pattern diminished.