The largest hammerhead, averaging 3.5 m (11.5 ft) and reaching 6 m (20 ft), separated from its smaller relatives by a head with a nearly straight front edge and a first dorsal fin that is absurdly tall, narrow and sickle-shaped. A large one in open water is among the most imposing animals a diver can meet.
The head is a tool for one job in particular. Stingrays bury themselves and defend with a barbed spine; this shark finds them by their electrical signature, pins them to the bottom with the flat of its head, and pivots to bite the wings off while the ray is held down. Great hammerheads are regularly found with ray barbs embedded in the head and jaws, apparently without ill effect.
It also swims on its side. Tracking work found these sharks rolled 50 to 90 degrees for most of their travel time, using that oversized dorsal fin as a lifting surface the way the pectoral fins would otherwise be used, which cuts the energy cost of covering distance by around ten percent. For an animal this size, that is a lot of tuna it does not have to catch.
Litters run to 50 pups, which is exceptional for a shark, and none of it is enough. Great hammerheads have among the highest at-vessel mortality of any shark - most die on the line before they are even landed - and the fins are the most valuable in the trade. The species is Critically Endangered.
The species.Sphyrna mokarran (Rüppell 1837) - Arabic name for this fish. ETYFish
How to recognise it
head with a nearly straight front edge, no central notch
first dorsal fin very tall, narrow and sickle-shaped
Mainly taken by drift gillnets, bottom gillnets and longlines, hook and line, pelagic and bottom trawls (Schneider 1990, Petersen et al. 2009). This species is a bycatch in both the industrial and artisanal fisheries but a specialised artisanal fishery for charcharhinid and sphyrnid species was introduced in Sierra Leone in 1975, and since then fishing pressure has not decreased (M. Seisay pers. obs. 2007). The Subregional workshop for sustainable management of sharks and rays in West Africa (Ducrocq 2002) noted the high threat to sharks in the West African region and a noticeable decline in the catch per unit effort of total sharks and rays.
Data are lacking as there are little species-specific data collection in the region, however this is a very distinctive species with a large dorsal fin which is highly valued for the shark fin trade. Increased targeting of sharks began in the 1970s, when a Ghanaian fishing community settled in the Gambia and established a commercial network throughout the region, encouraging local fishermen to target sharks for exportation to Ghana. By the 1980s many fishermen were specialising in catching sharks, resulting in a decline in overall shark populations (Walker et al. 2005). There has been rapid growth in the shark fin market in this region, for export to the Far East, and yearly production of dried fins exported from Guinea-Bissau alone is estimated at 250 tonnes dry weight (Walker et al. 2005). Sphyrna spp. combined represented 42% of bycatch in the European industrial pelagic trawl fishery off northwest Africa (Zeeberg et al. 2006).
Whilst there is little information on threats to the species within the European region, since the fish is highly mobile, impacts outside the Europe regional are relevant.
Threat classification from the IUCN Red List.
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