The giant devil ray (Mobula mobular) is a large marine vertebrate and can reach up to 5.2 m in disc width (DW), although specimens of about 3 m DW are most common. This large epipelagic batoid fish inhabits the entire Mediterranean Sea and possibly the adjacent Atlantic waters. Due to its geographic distribution and rare records outside the Mediterranean, it is considered as an endemic elasmobranch in the region. Information on the biology of the giant devil ray is scarce. It mostly inhabits deep pelagic waters where it feeds on plankton, predominantly krill and small schooling fish. Giant devil rays are ovoviviparous, meaning that only one large egg is developed inside body of the female. After more than a year and a half, a young fish is “born”. At this time, young fish can have a DW of over a meter! Throughout its range, the giant devil ray is believed to live in low numbers although population estimates are unavailable. The giant devil ray is listed as Endangered (EN A4d) on the IUCN Red list.
Until research and surveys were carried out by the Blue World Institute, the presence of the giant devil ray in the Adriatic was relatively unknown and the species was considered as extremely rare. Analysis of the data indicated the existence of a temporal pattern of occurrence. The giant devil ray is generally considered to be a plankton feeder, feeding on pelagic crustaceans and small schooling fish. The earliest seasonal observations of the giant devil ray in the Adriatic are from the area of open waters in the central Adriatic in April and May while the majority of opportunistic sightings, however, are made in the areas closer to the coast late in the spring and throughout the summer. This distribution coincides with appearance of large quantities of sardines and anchovies. The increase in the number of sightings closer to the central Adriatic islands and along the western coast is likely to be connected with the migration of sardines along the eastern coast and anchovies on the western coast of the Adriatic Sea. The aerial surveys carried out in 2010 and 2013 provide the first overview of the summer distribution and abundance of the giant devil ray in the Adriatic Sea. Based on the results, it is estimated that over 3000 animals are present in central and southern Adriatic during summer months. In fall, giant devil rays move further south and possibly out of the Adriatic. New studies indicate that the area of Levantine basin could be an area of large winter aggregation of the species indicating that mating possibly occurs there. Our future work should help establish if there are migration corridors in the Eastern Mediterranean from the Adriatic towards the Levantine basin.