Sphyrna zygaena

Body elongated and later ally compressed. Head hammer-shaped, its anterior con- tour strongly arched in young but moderately rounded in adults, without a median indentation but with a deep rounded depression opposite each nostril; lateral expansions of head very prominent, broad transversely and narrow from front to back; eyes large (their horizontal diameter almost equal to length of shortest (fifth) gill sl its, their posterior margins about opposite mouth or just anterior to it; nostrils with strong prenarial grooves; eyes large, their horizontal diameter greater than length of shortest (fifth) gill sl its; mouth broadly arched, with sm all labial furrows on lower jaw only, corners of mouth anterior or about opposite to outer corners of head; teeth triangular, deeply notched posteriorly, with smooth or weakly serrated edges, mostly cuspidate, and with posterior teeth not keeled and molari form. Fifth gill sl its shorter than the 4 preceding ones, and located posterior to pectoral-fin origins. First dorsal fin high, moderately falcate, with its origin above or just behind level of pectoral-fin insertions with its free rear tip not very slender and ending well anterior to the pelvic-fin origins and its inner margin less than 1/3 the length of its base; second dorsal fin sm all, with a very long inner margin almost twice the length of its anterior margin, a free rear tip ending well anterior to upper precaudal pit, and a nearly straight to sh allowly concave posterior margin; anal fin falcate, with base slightly longer than second dorsal-fin base and a deeply notched posterior margin; pectoral fins short, broad, and slightly falcate, with weakly concave or nearly straight posterior margins; pelvic fins with straight to sh allowly concave posterior margins. Colour: brownish olive or plain grey above, white or grey-white below; fins nearly plain, dusky, or blackish-tipped.

Body shape: elongated. A large hammerhead without a notch at the center of the curved headhead (Ref. 58085); but with prominent lateral indentations; prenarial grooves well-developed; snout short, 1/5 to less than a third of head width; mouth broadly arched (Ref. 114967); the first dorsal fin is moderately high, the second dorsal and pelvic fins are low. Colour olive-grey or dark grey above, white below, and the undersides of the pectoral fin tips dusky (Ref. 58085).

Essenti ally circumglobal in tem- perate and tropical seas; in the area, Nova Scotia to Florida and the Virgin Isl ands; also nor theast- ern Brazil to Argentina. Not recorded in the Gulf of Mexico. Possibly more wide-ranging in the area. BATOID FISHES by J. D. Mc Eachran, Texas A & M University, USA and M. R. de Carvalho, Ameri can Museum of Natural History, New York, USA 508 Batoid Fishes TECHNICAL TERMS AND MEASUREMENTS (straight-line distances) pectoral fin alar spines (or thorns) of males pelvic fin, anterior lobe spiracle pelvic fin, posterior lobe thorns of clasper of males 1st dorsal 2nd dorsal orbit median row fin fin caudal fin lateral tail axil of fold inner margin pectoral of pelvic fin fin upper side of a typical skate (family Rajidae) length of snout, preorbital tail spine (sting) dorsal cutaneous fold length of disc ventral cutaneous fold length of base of tail in stingrays (family Dasyatidae) snout, preoral anus mouth width of disc nasal apertures length of tail gill sl its lower side of typical skate total 41 rows snout angle in front of level of spiracles anterior part of disc of a skate teeth of a stingray (arrows indicate method of counting pavement pattern in batoids) General Remarks 509 GENERAL REMARKS Batoid fishes are moderately to greatly flattened and are distinguished from the o ther elamsobranchs (sharks) by their ventral gill sl its, their lack of an anal fin, and by having the pectoral fins connected to the sides of the head and trunk to form a disc. The eyes and well-developed spiracles are usu ally located on the dorsal surface of the head, these are secondarily located on the sides of the head in the more pelagic rays, and eyes are vestigial in a few electric rays. Sawfishes and guitarfishes are shark-like, in being only moderately flat- tened and later ally exp anded, with pectoral fins uniting anteriorly to the sides of the head. They possess rela- tively stout tails that are not clearly demarcated from the disc, and well-developed caudal fins. These forms, like sharks, swim by later ally undulating their trunk musculature. Electric rays, skates, and stingrays are greatly flattened and later ally exp anded, with the pectoral fins united anteriorly with the sides of the snout. They pos- sess a slender tail that is clearly demarcated from the disc, so the head and trunk thus form a circular, ovate, or rhombic disc. These forms swim by vertic ally undulating or oscillating their discs. The mouth and nostrils are ventr ally or subtermin ally located in all batoids except they are terminal in Manta. The majority of the batoids have 2 dorsal fins, but some electric rays, skates, and stingrays have ei ther a single dorsal fin or no dorsal fins. Jaw teeth are arranged in transverse rows, and like sharks are constantly replaced from inside the mouth; teeth are later ally fused to form large tooth plates in some of the more pelagic rays. Batoids vary from being more or less evenly c overed with tooth-like placoid scales or dermal denticles (occasion ally enlarged into thorns, bucklers, or spines) to completely lacking scales and scale-like structures. Batoids, like sharks, have cylindrical copulatory organs or claspers derived from pelvic girdle cartilages that are used for internal fertilization of eggs in females. All batoids, except skates, are viviparous without placen- tas. Fetuses of sawfishes and guitarfishes are nourished by contents of the yolk sacs but fetuses of stingrays are furnished with histotroph or uterine milk after they exhaust the contents of their yolk sacs. Skates, on the o ther h and, are oviparous, and deposit the fertilized eggs in rectangular, horn-like egg capsules that are de- posited on the bottom. Batoids vary greatly in size, ranging in total length from about 13 to 20 cm, in some electric rays (Narcinidae) and skates, to over 7 m in sawfishes; some species may reach a disc width of about 6.1 m (manta rays); and ranging in weight from 10 to 20 g to between 1 and 3 t. Most batoids are sm all to moderate in size, below 1 m and 60 cm wide. Most batoids are generalized benthic predators that lack specialized food capturing and processing struc- tures. These generalists consume a wide variety of infaunal and epifaunal benthic organisms ranging from polychaetes and o ther soft-bodied invertebrates to relatively sm all ray-finned fishes. Some electric rays (Torpedinidae) use their electric organs to stun large fishes that are sw allowed whole; sawfishes use their rostral saws to disable or kill schooling fishes; and eagle rays and cownose rays use their plate-like teeth to crush hard-shelled organisms such as oysters and clams. Manta rays have specialized filter plates associated with their gill arches and feed on zooplankton and nekton. Although primarily marine animals, batoids are also found in brackish estuaries and lagoons or rivers, but only 1 family of rays, the Potamotrygonidae, is confined to fresh waters (South Ameri can rivers draining into the Atlantic Ocean). Batoids are widely distri buted in all oceans, from the Arctic to the Antarctic and from sh allow coastal waters to great depths. Skates have the greatest latitude and depth ranges, with representatives at most latitudes and depths to about 2 000 m, but are r are in tropical sh allow waters and coral reef areas. Some electric rays (Torpedinidae) are also abundant in temperate latitudes; but all remaining batoid families are restricted to tropical and warm-temperate areas, and show a p

Common to abundant coastal and semi-oceanic, living close inshore (espe- ci ally the young) and near surface in deep water not far offshore. A strong-swimming shark, migrating north- ward in summer; young often found in large schools of hundreds of individuals. Number of young 29 to 37 per litter. Feeds on bony fishes, o ther sharks, rays, crustaceans, and squids. Caught with pelagic longlines, h and- lines, and even pelagic and bottom trawls. Utilized fresh, dried-salted, and possibly smoked; hides are pro- cessed for lea ther; liver oil is extracted for vitamins; fins are processed into shark-fin soup base; and carcasses utilized for fish meal. It is uncertain if this shark figures in shark viewing within the area.

Maximum total length probably between 3.7 and 4 m, commonly between 2.75 and 3.35 m; size at birth between 50 and 60 cm; adults maturing at about 210 to 240 cm.

Occurs inshore and well offshore (Ref. 5578), over continental and insular shelves (Ref. 244). Coastal, pelagic, and semi-oceanic, but often bottom associated at 1-139 m (Ref. 58302). Migrates northward in summer; young often in large aggregations of hundreds of individuals (Ref. 13562). Prefers to feed on small sharks, skates and stingrays, but also preys on bony fishes, shrimps, crabs, barnacles and cephalopods (Ref. 244). Viviparous (Ref. 50449). Regarded as being dangerous to people, though only few can be tentatively attributed to this species due to its occurrence in temperate waters (Ref. 244). Reported to cause poisoning (Ref. 4690). Caught occasionally by shark and tuna longline fisheries (Ref.58048). Meat utilized fresh, dried-salted, and possibly smoked for human consumption; liver oil for vitamins, fins for soup, hide for leather, and carcasses for fishmeal (Ref. 244). Used in Chinese medicine (Ref. 12166). Become sexually mature when 250 to 300 cm long. The female gives birth to 30 - 40 young (Ref. 35388).

Reproductive mode: dioecism; fertilization: internal (oviduct); bearers (internal live bearers). Viviparous, placental (Ref. 50449), with 20 to 50 young per litter (Ref. 6871)after a gestation period of 10-11 months (Ref.58048). Size at birth between 50-60 cm TL (Ref. 13562).

IUCN Red List Status: Vulnerable (VU), assessed 2018-11-08. Resilience: Low (tmax=21; tm=8.8; Fec=20-40).