Diagnosis

A large (to over 300 cm) hammerhead shark with a broadly convex head measuring 26 to 29% of TL; its anterior margin arched and smooth, without any  median indentations. Tooth count (excluding small symphyseal tooth if present) 13-15 in each side of the upper jaw, 12 to 14 in lower jaw; teeth usually finely serrated. First dorsal fin moderately tall, measuring 12 to 15.4% of TL, with an acutely rounded apex and rather falcate in shape; its origin opposite the pectoral insertions and with its free rear tip not extending rearwards to above the pelvic fin origins. Posterior margins of pelvic fins essentially straight or very slightly concave. Second dorsal fin small and low, smaller than the anal fin height with its posterior margin roughly twice the fin height; free rear tip long but not extending to the precaudal pit. Pectoral fins moderate in size, their anterior edges equating to 15.4 - 18.0% of TL; their posterior margins only slightly falcate. Dorsal colour dark olive brown-grey, fading gradually to white ventrally. Ventral apices of pectoral fins dusky.

Size

Attains 370cm and possibly greater; mostly to 300cm; size at birth 50 to 60 cm.

Status and Distribution

Mediterranean Sea: Occasional; localised abundance apparently declining in some areas and may be in decline regionally. The most frequently-encountered hammerhead in the region. Cosmopolitan through the Mediterranean, from Gibraltar to the Bosphorus and Sea of Mamara but not the Black Sea; can be locally abundant at times, especially juveniles (e.g., within the Gulf of Tunis); only sporadically caught in recent years from some more northern areas such as the Ligurian Sea and upper reaches of the Adriatic; more frequent in the Aegean, especially the eastern (Turkish) side and Dodecanese Islands.

Biology

An active coastal and semi-oceanic pelagic shark of temperate and sometimes tropical waters, often occuring very close inshore including within small bays, estuaries and near tidal flats; ranging from the intertidal to depths of at least 50 metres based on diver sightings off Gozo, Malta; juveniles typically close inshore, particularly within sheltered, shallow bays and gulfs. These sharks may occur singly or in small groups; juveniles may be locally abundant and form large schools. Occasionally these sharks (both juveniles and adults) are seen swimming slowly at the surface, with dorsal fin exposed, especially in hot mid-summer weather.  Principaly piscivorous, they feed upon a wide variety of bony fish including clupeids and small scombrids, sea bass, mullet and flatfishes; also elasmobranchs including smaller sharks and especially batoids (stingrays); invertebrate prey includes especially cephalopods and some  benthic crustaceans.  They will readily scavenge from surface longlines and nets and have been encountered doing so at substantial distances offshore within the southern reaches of the Sicilian Channel.   Reproduction is viviparous, with litters of 29 to 50 young after a gestation period of 10 to 11 months. Parturition occurs within the Sicilian Channel and doubtless elsewhere in the region, apparently in the summer months with neonatal specimens occurring locally inchore through July, August and September. Females mature at about 265cm and males at 210 to 250cm.