Movements of juvenile and adult spider crab ("Maja squinado") in the Ría da Coruña (NW Spain)

Abstract

[Abstract] In August 2002, 12 juvenile and 12 adult (recently terminal moulted) spider crabs were tagged using ultrasonic pingers (Sonotronics, USA) in the Ría da Coruña (NW Spain). Both adults and juveniles were released in the same sandy shallow bottoms (5-10 m) in which they were caught. This area, as known from previous studies, is a typical juvenile area where juvenile spider crabs carry out their terminal moult before the autumn migration to deep bottoms. The tracking was carried out daily for a period of two weeks, although not all the crabs were located every day. Juvenile crabs were found to move small distances, performing non-directional movements near the coast, in protected areas up to 10 m deep. Two of the adult crabs performed small scale movements in the outer (more exposed) part of the estuary, at depths of up to 20 m. The rest of the adult crabs remained in the juvenile area, performing the same non-directional movements as the juveniles. Four male adult crabs were recaptured by commercial fisheries in the following months, three of them at more than 40 m deep, in the central channel of the estuary, probably while performing their seasonal descent migration. A female carrying eggs was recaptured in December near the coast, probably after carrying out both a descent and ascent migration.