Rhizoprionodon terraenovae

Body slender and fusi form. Eyes large, internal nictitating lower eyelids present. Snout long and depressed, preoral length 1.5 to 1.7 times internarial width, tip narrowly rounded; labial folds well developed, the upper pair about equal in length to eye diameter and ending well behind eyes. Teeth strongly oblique, their edges smooth to finely serrated in adults; anteroposterior tooth row counts 11 to 13/12 to 13 on each side, total tooth row counts 24 to 27/24 to 27. Spiracles absent; gill sl its short, height of third gill slit about 2.2 to 2.5% of total length; gill arches without papillae. First dorsal fin moderate-sized, height 7.4 to 9.2% of total length, with a narrowly rounded apex, an origin opposite the pectoral-fin inner mar- gins, and the midlength of its base slightly closer to the pectoral-fin insertions than the pelvic-fin origins; sec- ond dorsal fin low and much sm aller than first dorsal fin, height 1.9 to 2.5% of total length; second dorsal fin with a sh allowly concave posterior margin, an origin opposite the space between the midpoint of the anal-fin base and the anal-fin insertion, an attenuated free rear tip, and an inner margin over twice the fin height; anal fin with a sh allowly concave posterior margin and long paired preanal ridges; pectoral fins relatively short, broad and not falcate, extending to below midpoint of first dorsal-fin base when adpressed. A low interdorsal ridge present between dorsal fins; no keels on caudal peduncle. Precaudal vertebral centra 56 to 66, usu ally below 66, and equal or less in number than caudal centra, total vertebral centra 126 to 144. Colour: grey or grey-brown above, large specimens with sm all light spots on the dorsal surface, white below; pectoral fins with white margins, dorsal fins with dusky tips.

Body shape: fusiform / normal. Small, generally gray, streamlined shark, with long pointed snout. Posterior margin of anal fin straight or slightly concave. Second dorsal fin origin well behind anal fin origin (Ref. 26938).

Western North Atlantic: Canada (New Brunswick), Canada, USA (New Engl and to Florida and the Gulf of Mexico), Mexico, and Honduras. SPHYRNIDAE Hammerhead and bonne thead sharks Diagnostic characters: Sm all- to large-sized sharks. Body elongate and moderately slender, cylindrical or somewhat compressed. Anterior portion of head much flattened dorsoventr ally and widely ex- p anded later ally in hammer or shovel form, with the eyes at its outer edges; eyes with well-developed in- ternal nictitating lower eyelids; anterolateral teeth blade-like, with a single cusp; posterior teeth similar to anterolateral teeth or modified into keeled, molari form crushing teeth without cusps. Two dorsal fins, the first dorsal fin high and pointed, its base much shorter than caudal fin and wholly anterior to origins of pel- vic fins; second dorsal and anal fins much sm aller than the first dorsal fin and ei ther equal-sized or with the anal fin somewhat larger than the second dorsal fin; caudal fin much less than half of total length and strongly asymmetrical, with a well-marked subterminal notch and a sm all, but well-defined ventral lobe. Cau- dal peduncle slightly compressed, not strongly flattened dorsoventr ally or widely exp anded later ally, without lateral keels but with upper and lower precaudal p its present. Intestine with a scroll valve. Colour: back pre- dominantly grey or brassy, sometimes yellow or very dark grey, no prominent markings except dark fin tips in young of some species; underside white or light grey. anterior portion of head dorsoventr ally flattened and exp anded ventral view of head Habitat, biology, and fisheries: Hammerhead sharks inhabit all tropical and warm-temperate seas, from the surface, surf-line, and intertidal down to at least 275 m in waters near continents, continental isl ands, and oce- anic isl ands. Sm all species are confined to coastal continental waters; juveniles of large species are coastal off continents and isl ands, while adults are primarily semi-oceanic although they often approach coasts in search of food. All species are viviparous (placental viviparous, with a yolk-sac placenta), and have 4 to 42 young per litter. Hammerheads feed on a wide variety of bony fishes, o ther sharks (including batoids), cephalopods (squids, octopi, and cuttlefish), gastropods, bivalves, and crustaceans (shrimp, mantis shrimp, brachyurid crabs, lobsters, barnacles, and isopods), but do not feed on marine mammals or o ther very large marine verte- brates. Hammerhead sharks are important for fisheries in the area and are used as food and also for the prepa- ration of various subproducts, especi ally Vitamin A from the liver and fins for the oriental soupfin market. A few species have been reported to occasion ally bite people, but large species are gener ally timid when ap- proached by divers. Hammerheads (particularly Sphyrna lewini and S. mokarran) are popular subjects for ecotouristic diving worldwide and are viewed by divers in Area 31. Sphyrna lewini and S. tiburo are popular fish for large public aquaria, including a number of aquaria along the eastern and Gulf coast of the USA. The conservation status of hammerheads is problematical because of heavy bycatch and targeted fisheries that catch them wherever they occur (including fisheries on nursery grounds which may be decimating the young), the high value of their fins (particularly from large species), their vulnerability to gill nets because of their head-shape (which helps to sn are them in net-meshes), the high activity level of some species which means that they perish quickly when caught in nets or on longlines, and often poor or nonexistent species-specific or even family-specific fisheries statistics for most species. Catches of large hammerheads (S. lewini, S. mokarran) have declined markedly off the USA in Area 31, and catches are now regulated in USA waters. 498 Sharks Similar families occurring in the area No o ther shark family has the characteristic hammer- or shovel-shaped head of the Sphyrnidae. Key to the species of Sphyrnidae occurring in the area 1a. Head shovel-shaped and narrow, its width usu ally less than 3 times the preoral length (Fig. 1); posterior teeth formed as broad, keeled, molari form crushers . . . . . . . . . . Sphyrna tiburo 1b. Head hammer- or m allet-shaped and wider, its width over 3 times the preoral length (Fig. 2); posterior teeth not molari form crushers . . . . . . . . . . . . . . . . . . . . . . . .(cid:1) 2 Fig. 1 Sphyrna tiburo (underside of head) Fig. 2 Sphyrna lewini (underside of head) 2a. Free rear tip of first dorsal fin over or posterior to pelvic fin-origins (Fig. 3); posterior margin of anal fin straight or weakly concave; size sm aller, adults less than 2 m . . . . . . . . . . . .(cid:1) 3 2b. Free rear tip of first dorsal fin well ahead of pelvic-fin origins (Fig. 4); posterior margin of anal fin deeply notched; size larger, adults to 3 m or more . . . . . . . . . . . . . . . . . .(cid:1) 4 Fig. 3 Sphyrna tudes Fig. 4 Sphyrna mokarran 3a. Prenarial grooves well developed; head broader, with a well-developed medial indentation on snout (Fig. 5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sphyrna tudes 3b. Prenarial grooves poorly developed; head narrower, without a strong medial indentation on snout (Fig. 6) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sphyrna media prenarial grooves prenarial grooves Fig. 5 underside of head (Sphyrna tudes) Fig. 6 underside of head (Sphyrna media) 4a. Anterior margin of head nearly straight in adults, moderately convex in young; prenarial grooves hardly developed; teeth strongly serrated at all sizes; first dorsal fin markedly falcate; second dorsal about a third as high as first dorsal fin, with a short inner margin; posterior margins of second dorsal and pelvic fins deeply concave (Fig. 4) . . . . Sphyrna mokarran 4b. Anterior margin of head moderately convex in adults, strongly so in young; prenarial grooves well developed; teeth smooth in young, weakly serrated in large individuals; first dorsal fin erect or slightly falcate; second dorsal-fin less than a third the height of first dorsal fin, with a long inner margin; posterior margins of second dorsal and pelvic fins slightly con- cave to nearly straight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (cid:1) 5 5a. Median indentation present on anterior margin of head; free rear tip of second dorsal fin nearly reaching upper caudal-fin origin; anal-fin base noticeably larger than that of second dorsal fin (Fig. 7). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sphyrna lewini 5b. Median indentation absent from anterior margin of head; free rear tip of second dorsal fin well ahead of upper caudal-fin origin; anal-fin base about as large as that of second dorsal fin (Fig. 8). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sphyrna zygaena Fig. 7 Sphyrna lewini Fig. 8 Sphyrna zygaena List of spec(cid:1)ies occurring in the area T(cid:1)he symbol is given when species accounts are included. (cid:1)Sphyrna lewini (Griffith and Smith, 1834). (cid:1)Sphyrna media Springer, 1940. (cid:1)Sphyrna mokarran (Rüppell, 1837). (cid:1)Sphyrna tiburo (Linnaeus, 1758). (cid:1)Sphyrna tudes (Valenciennes, 1822). Sphyrna zygaena (Linnaeus, 1758).

Inhab its waters from the intertidal to possibly 280 m deep, but usu ally in wa- ter less than 10 m deep. Often occurring in the surf zone off s andy beaches, and in enclosed bays, sounds, har- bors, estuaries, and river mouths. Tolerates reduced salinities but does not penetrate far into fresh water. A common to abundant shark where it occurs. Mi- gratory, moving inshore in summer and offshore in winter. Number of young 1 to 7 per litter. Feeds primarily on sm all bony fishes, shrimps, crabs, worms, and molluscs. Fished wherever it occurs, caught commerci ally in Mexico. Caught in gill nets and targeted by sports anglers using rod- and-reel; and a major bycatch of the USA shrimp trawling fishery. Despite heavy fishing pressure numbers in the Gulf of Mexico seem to be stable.

Maximum total length at least 110 cm, common to 90 cm; size at birth about 29 to 37 cm; males maturing between 65 and 80 cm and females at 85 to 90 cm.

Reaches at least 103 cm TL (Ref. 244). Abundant in the continental shelves, from the intertidal to deeper waters. Often occurs close to the surf zone off sandy beaches, and also enclosed bays, sounds, and harbors, in estuaries and river mouths. Feeds on small bony fishes, shrimps, crabs, segmented worms and mollusks (gastropod feet). Viviparous, with 1 to 7 young in a litter (Ref. 27549). Size at birth about 29 to 37 cm. Utilized for human consumption. Minimum depth from Ref. 055195.

Reproductive mode: dioecism; fertilization: internal (oviduct); bearers (internal live bearers). Distinct pairing with embrace (Ref. 205). Viviparous, placental (Ref. 50449). 1 to 7 young per litter. Larger females carry more young. Size at birth 29-37 cm. Gestation period is 10 to 11 months in the northern Gulf of Mexico. Sex ratio of near term fetuses is 1:1 (Ref. 244).

IUCN Red List Status: Least Concern (LC), assessed 2019-06-20. Resilience: Very low (K=0.19-0.45(?); tmax=10; tm=4; Fec 1-7).