Scalloped Hammerhead

Scalloped Hammerhead is taken as both a target and bycatch by trawls, purse seines, gillnets, fixed bottom longlines, pelagic longlines and inshore artisanal fisheries. The latter catch large numbers of pups and juveniles in some regions. The species’ aggregating habit makes it susceptible to capture in large schools. This also means that they may appear more abundant in landings, where they are caught in high, localised concentrations. Intense fishing pressure can deplete regional stocks rapidly, and re-colonization of depleted areas from neighboring regions is expected to be a slow and complex process. This species is expected to have a low resilience to exploitation because of its life-history characteristics (Maguire et al. 2006).

Eastern Atlantic

As longline fleets in in the Northeast and Eastern Central Atlantic exert comparable fishing effort to those in the Northwest Atlantic, and effort is seen to shift from western to eastern Atlantic waters (Buencuerpo et al. 1998, Serafy et al. 2004, Zeeberg et al. 2006), population trends for hammerheads (Sphyrna spp.) are likely to be similar in these regions (Zeeberg et al. 2006). European industrial freezer trawlers targeting small pelagic fish (sardinella, sardine, and horsemackerel) operate on the northwest African shelf nearly year-round with five to ten large vessels (9,000-18,000 horse power). A study of bycatch rates in more than 1,400 trawl sets off Mauritania from 2001 - 2005, showed that hammerheads combined represented 42% of total bycatch during this period (Zeeberg et al. 2006).

Scalloped Hammerhead occurs in purse seine catches of Spanish and French fleets fishing off West Africa. It accounts for 3.2 and 5% in number and weight respectively of the shark bycatch recorded by these fisheries (that translates to 0.2 tonnes of bycatch in the period 2003-2007) (Amandè et al. 2010). It is also taken by the Japanese longline fishery operating in the Eastern Central Atlantic. Nominal catch rate in 1995 was 0.13 per thousand hooks (Matsushita and Matsunaga 2002).

Hammerheads are caught by both inshore artisanal fisheries and offshore European fisheries operating along the coast of West Africa. The Subregional workshop for sustainable management of sharks and rays in West Africa, 26-28 April 2000 in St Louis, Senegal 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. Walker et al. (2005) also noted that there is concern for this species off Mauritania, with catches comprised exclusively of juveniles, often newborn. 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 t (dry weight) (Walker et al. 2005).

This species is frequently caught along the West African coast and is heavily targeted by driftnets and fixed gillnets from Mauritania to Sierra Leone (M. Ducrocq pers. comm. 2006). Juveniles are very susceptible to coastal fisheries using drift or fixed gill nets such as sole, sciaenid and Sepia spp. fisheries (M. Ducrocq pers. comm. 2006). They were taken as bycatch in the milk shark fishery and in the Banc d'Aguin national park, Mauritania, until the fishery was stopped in 2003 and they are still caught in large quantities in the sciaenid fishery. A specialized artisanal fishery for carcharhinid and sphyrnid species was introduced in Sierra Leone in 1975, and since then fishing pressure has been continuous (M. Seisay pers. obs. 2006).