Article published on the movements of the blue crab in the Guadiana

Published in the journal Estuaries and Coasts on September 4, 2025. More details here.

A study on the movements of the Atlantic blue crab in the Guadiana estuary, coordinated by the NEMA team, was recently published.

Twenty-four blue crabs were tagged with acoustic transmitters, which provided information about their movements in the estuary over a period of nine months. The main results indicate:

• A high degree of success for the study, as all 24 blue crabs initially tagged were detected regularly in the receiver network, with a total of 44,387 detections over the study period;

  
  

• The species was shown to take advantage of tidal currents to move down the estuary, then using the rising tide to quickly return to the middle estuary in the Foz de Odeleite area. In one case, a journey between the Azinhal area and Vila Real de Santo António, more than 9 kilometers, was recorded in just over 3 hours. The same crab also made a journey between Vila Real de Santo António and Foz de Odeleite, about 18 kilometers, in about 27 hours;

  
  

• Most trips along the estuary occurred at times of high tidal amplitude, showing that blue crabs actively and purposefully use this “means of transport,” most likely in search of food in other areas of the estuary.

  
  

• Many crabs end up returning to this area of the middle estuary, so there seems to be a longer residence time and preference for the middle or upper estuary;

  
  

• Although it was not possible to study many females, the three that were tagged showed a similar pattern of migration to the coastal area in the summer, since after being detected by the receivers in Vila Real de Santo António, they were not detected again. This is therefore a reflection of the seasonal migrations that females of this species usually make between estuaries and coastal areas to spawn.