Scalloped hammerhead (Sphyrna lewini): An important bycatch of in gillnet fisheries of Pakistan
Presently there is no aimed fisheries for scalloped hammerhead, however, it is mainly landed as bycatch of tuna gillnet fisheries that operates in coastal and offshore waters including Exclusive Economic Zone and Areas Beyond National Jurisdiction (ABNJ). In addition, small quantities of scalloped hammerhead are caught by coastal gillnet fisheries and coastal longline fisheries. Juveniles that are known to inhabit coastal waters, bays and lagoon are mainly caught by coastal gillnet fisheries, as well as from coastal waters by tuna gillnet vessels as bycatch. An aim shark fisheries was established in Pakistan in 1988 and hammerhead sharks used to a preferred species contributing about 25 % of the total shark catches. This fisheries started to dwindle by 1999 and by 2003 it collapsed. Since then no aimed shark fisheries is being practiced in Pakistan and sharks including scalloped hammerhead are landed as bycatch of other fisheries. At present it is contributing about 7 % of total landings of pelagic sharks of Pakistan. Along Pakistan coast maximum size recorded for this species was 270 cm TL, however, most of Sphyrna lewini recorded were 65 and 185 cm TL. Small specimens of scalloped hammerhead sharks are caught in coastal waters and continental shelf area by coastal gillnetters whereas larger specimens (150-400 cm ) are mainly caught as bycatch by tuna gillnetters. In Pakistan, Sphyrna lewini feeds upon bony fishes small sharks, rays, crustaceans and cephalopods whereas juveniles were observed to feed on mantis shrimp, portunid crabs, shrimp, cephalopods and small fishes. Study on fecundity in Pakistan revealed that female may have 18-34 pups (44 to 47 cm TL) mainly during April and June. Although national legislations provide protection to scalloped hammerhead, however, there is no implementation of these laws. Considering that the stocks of scalloped hammerhead are dwindling in Pakistan, therefore, there is a need for implementation on the existing legislations as well as creating awareness among the coastal communities for protection of this iconic species.