Bigeye thresher shark
(Alopias superciliosus)

Alopias superciliosus (Lowe, 1839)

Diagnosis

Although superficially similar to A. vulpinus, this shark is very readily distinct upon closer inspection. Trunk rather stout, with the elongate caudal lobe nearly as long as rest of body; eyes distinctly large, dorsally-orientated with a prominent dorsal groove on the contours of the head above the gills. Snout short, laterally flattened between eyes; no labial furrows at corners of mouth. Anterior origin of 1st dorsal fin posterior to rear free tips of pectoral fins. Pectoral fins rather more broad-tipped than A. vulpinus.

Dorsal colour grey-brown, with a somewhat bronzy sheen on the flanks that may not always be distinct; ventrum shading to lighter grey -white, with demarcation or blotchiness not immediately apparent; no light pigment extending above the pectoral fin bases.


Size

To about 461cm TL; typically 270cm to 430cm but Mediterranean data scant; size at birth ca. 70 to 106cm.


Status and Distribution

Mediterranean Sea Rather infrequent or rare, with a limited identified range, but cannot be considered accidental; Western Mediterranean, from Gibraltar eastwards through the southern Alboran Sea and particularly Morocco; other recent records from the Sicilian Channel (landed at Mazara del Vallo); not yet reported from Tunisia but can be considered as frequenting those waters; off southern Malta towards Libya, the Central Ionian Sea and also Tyrrhenian Sea (Tropea; Eolie Islands); perhaps more cosmopolitan in deeper waters of the Central and Western Mediterranean.


Biology

An active epipelagic and epibenthic species, occurring from coastal neritic waters to well offshore in the great ocean basins; Mediterranean captures typically all over offshore continental shelf waters where it occurs from the surface down to circa. 250m; elsewhere recorded to at least 500m depth and considered a habitually deeper swimmer and feeder than A. vulpinus. Like its congener, the bigeye thresher is believed to utilise the elongate tail as a feeding tool. Reported diet consists of pelagic bony fishes including scombroids, clupeoids and small billfishes; hake and cephalopods; no Mediterranean data but anecdotal reports from Maltese fishermen suggest a strong association between these sharks and highly mobile scombroids such as Auxis rochei.

Ovoviviparous, with 2 - 4 young per litter; females mature between 355 - 430cm; males between 270 - 400cm.