CROATIAN FAUNA - GIANT DEVIL RAYS

GIANT DEVIL RAYS The giant devil rays (Mobula mobular) are a group of cartilaginous fishes in the family of eagle rays (Myliobatidae). They are also known as „devil fish“, for their two cephalic fins that extrude in front of the head and look like horns. The giant devil ray may have a disk width greater than three meters and may weigh up to 300 kg. It inhabits the pelagic zone of the open sea, and feeds on planktonic organisms, small crustaceans, and small schooling fish which they speed through with a wide-open mouth, filtering the food out of the water. The giant devil ray is easily recognizable: its back is dark grey to brown in colour, while its belly is almost completely white, and a dark band stretches from eye-to-eye on its head. The giant devil ray’s very long and narrow tail has a serrated barb connected with a poison gland. Until recently, it was thought the giant devil ray is an endemic species of the Mediterranean Sea, but new taxonomic and genetic studies have found it to be a widely distributed species that can be found in almost all seas in tropical and temperate regions. However, the giant devil ray is a special fish. This is an ovoviviparous species, meaning that, even though it is a fish, it does not lay eggs, but a single large egg grows inside the female. After a year and a half, a young fish is hatched, and at that point it may already have a disk width of one meter! Since it inhabits the pelagic zone, the giant devil ray is rarely spotted, and its presence in the Adriatic Sea is almost unknown. The Blue World Institute scientists’ studies have determined that the giant devil ray frequently appears in the open waters of the Adriatic Sea during the warmer parts of the year, when the organic production increases, as does the growth of the planktonic organisms it feeds on. With colder weather and the disappearance of prey, the giant devil ray migrates towards the warmer parts of the Mediterranean Sea in search of food. New studies estimate that over 3000 rays enter the Adriatic from the Mediterranean Sea during summer. Even though there is no estimate of the abundance of its population in the Mediterranean, it is assumed that the giant devil ray is present in small quantities. The giant devil ray is not, fortunately, a commercially fished species as the quality of its meat is not particularly high, but bycatches in pelagic trawls and longlines have quite a negative impact on the species, especially considering its very low reproductive capacity.