Scoophead Shark, Scoophead Hammerhead.
Hammer rounded with very subtle medial and central indentations. No inner-narial grooves. Broadly arched mouth is roughly 1/3rd of the hammer width. First dorsal fin high and falcate, second much lower. Free rear tip of first dorsal fin level with origin of pelvic fins. Anal fin long without significant tapering. Dorsal coloration grey-brown to golden-brown. Ventral surface pale. Fins mostly plain with slightly dusky tips.
Maximum length approximately 150cm but adult males/females are more commonly 100cm/130cm respectively. Average size at birth is probably around 30cm.
Inshore turbid bays, estuaries and rivers as well as continental shelves.
Present on both coasts of Central and South America. In the Atlantic, the scoophead ranges from Panama to southern Brazil including some Caribbean Islands. And in the Eastern Pacific from the Gulf of California to Peru and probably Ecuador.
The species exact range is difficult to determine due to its similarity to two other small hammerheads that share its range; the small-eye/golden hammerhead and the scalloped bonnethead.
Presumably taken with bottom longlines, gillnets and hook and line throughout its coastal range, but no information is available as to the extent of capture and fishing practices. It is however known to be a common bycatch in the mackerel gillnet fishery off Trinidad.
Personal note: I recovered and released a scoophead shark from a gillnet while accompanying artisanal fishermen in the Bay of Panama. The shark was moving very weakly and probably did not survive. Hammerheads are known to have a poor survival rate even if released soon after capture, due to lactic acid build up which they release as a stress response.
Citations and References
Casper, B.M. & Burgess, G.H. 2006. Sphyrna media. The IUCN Red List of Threatened Species 2006: e.T60201A12317805. https://dx.doi.org/10.2305/IUCN.UK.2006.RLTS.T60201A12317805.en.
A viviparous species with yolk-sac placenta. Litter size 1-8 (ref. Jose Castro).
Diet consists mainly of bony and cartilaginous fishes, squid, octopus and shrimps.
Reaction to divers
No known records of sightings by divers. Due to its small size, the scoophead shark is probably a very shy species which accounts for the lack of sightings. Also it appears to prefer turbid environments where divers are unlikely to venture.
Although this species is not seen by divers, it does occur in shallow water. Anyone wishing to encounter a scoophead shark should consider chumming with appropriate bait in the Bay of Panama.
When I encountered this species, I based myself in Chepo in eastern Panama and accompanied fishermen that were working near the mouth of the Chepo River.
Bonnethead Shark distinguished by very narrow rounded hammer without any noticeable scalloping or indentations.
Scalloped Bonnethead Very similar but more slender overall. Posterior margin of anal fin almost straight (less falcate). Confined to the eastern Pacific.
Smalleye/Golden Hammerhead Distinguished by a more pronounced medial notch in the hammer, a larger lower caudal lobe, and an overall golden hue.