MIGRATORY PATTERNS OF FEMALE SPIDER CRABS MAJA SQUINADO DETECTED USING ELECTRONIC TAGS AND TELEMETRY

Abstract

Migrations play a key role in the life history of the spider crab Maja squinado (Herbst, 1788) and affect fishery catches. Migrations involve important changes in depth and in the environment. Ultrasonic telemetry has a number of drawbacks due to the difficulties in the continuous tracking of crabs while they are moving to deep waters. The recent introduction of electronic data storage or archival tags permits continuous monitoring of depth and temperature in crab's habitat and reconstruction of the movement patterns using baseline data on habitat characteristics. On the Galician coast (NW Spain) we calibrated and used electronic tags as a tool to study spider crab migrations. In the summer of 1996, 17 crabs were tagged with both ultrasonic transmitters and electronic tags. Tracking was carried out discontinuously at intervals of approximately 1 wk. We obtained a recapture rate of approximately 70%. The information provided by telemetry and electronic tags indicates autumn migrations along the bathymetric gradients (from <10 m down to 100 m) within short periods (mean = 5.7 d, range = 1.3–13.6). During these movements crabs travel through habitats characterized by different temperatures and substrates. Bathymetric and oceanographic data as well as localisation records from the electronic tags make the reconstruction of the animal tracks possible.