Fishes: A Guide to Their Diversity. Philip A. Hastings
to temperate; neritic to epipelagic to demersal over reefs and adjacent soft substrates
REMARKS: Requiem sharks are medium to large (up to 7.4 m) predators and are well known for their occasional migrations into freshwater (sometimes exceeding 1,000 km). Species in this family are among those most commonly encountered by divers and sport fishers, and several have been known to attack swimmers. The Bull Shark, Tiger Shark, and Oceanic Whitetip Shark are responsible for most human fatalities. Requiem sharks are generalist predators, taking a wide variety of prey. While some species are yolk-sac viviparous, most species are placental (Musick, 2011; Musick and Ellis, 2005). Some species are highly fecund: the Blue Shark (Prionace glauca) is known to have litters of up to 100 pups.
REFERENCES: Compagno, 1988, 2001, 2005; Compagno et al., 2005; Compagno et al., in Fischer et al., 1995; Compagno and Niem, in Carpenter and Niem, 1998; Garrick, 1982; Musick, 2011; Musick and Ellis, 2005; Naylor, 1992.
CARCHARHINID CHARACTERISTICS:
1) mouth large, subterminal
2) caudal peduncle with a precaudal pit
3) eyes with nictitating membrane
4) dorsal fin with lateral undulations along posterior margin
5) spiracles usually absent
6) nasal grooves and barbels absent
ILLUSTRATED SPECIMEN:
Galeocerdo cuvier, SIO 66–44, 1,310 mm TL
CARCHARHINIFORMES : SPHYRNIDAE—Hammerhead Sharks
DIVERSITY: 2 genera, 9 species
REPRESENTATIVE GENERA: Eusphyra, Sphyrna
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine; tropical to warm temperate; continental shelf and seamounts, neritic or demersal over reefs and soft bottoms
REMARKS: Their characteristic hammer-shaped heads distinguish these sharks from all other fishes. This unusual feature increases capabilities of both vision and the electromagnetic sense and also improves maneuverability. The phylogenetic relationships of hammerheads were studied by Naylor (1992) and Lim et al. (2010). Hammerheads are top predators that feed on bony fishes, sharks and rays, and squids and other invertebrates. Unlike most sharks, hammerheads often form large schools near seamounts during the day, likely dispersing to hunt individually at night. They are viviparous, with yolk-sac placentas (Musick, 2011; Musick and Ellis, 2005). Hammerheads are particularly vulnerable to overfishing and are often captured as bycatch in longline and net fisheries.
REFERENCES: Compagno, 1988, 2005; Compagno, in Carpenter, 2003; Compagno, in Carpenter and Niem, 1998; Compagno et al., in Fischer et al., 1995; Compagno et al., 2005; Gilbert, 1967; Lim et al., 2010; Musick, 2011; Musick and Ellis, 2005; Naylor, 1992.
SPHYRNID CHARACTERISTICS:
1) head flattened and broad, hammer-shaped
2) eyes and nostrils near ends of hammer-like extensions
3) mouth relatively small, subterminal
4) usually one or two gill slits above pectoral-fin base
5) spiracles absent
ILLUSTRATED SPECIMEN:
A) Sphyrna zygaena, SIO 64–528, 1,035 mm TL (dorsal view)
B) head of Sphyrna zygaena, SIO 64–528 (lateral view).
HEXANCHIFORMES—Six-gill Sharks
The hexanchiforms were once thought to be the most primitive extant shark group, but recent research (e.g., Naylor et al., 2005; Vélez-Zuazo and Agnarsson, 2011) has shown them to be allied with the squaliform and related sharks. This group is characterized by six or seven gill slits, a single, spineless dorsal fin originating posterior to the origin of the pelvic fins, a large mouth, and small spiracles, which are located above and well posterior of the eyes. The Hexanchiformes comprises two families, four genera, and six species. The two species of frill sharks (Chlamydoselachidae) have a terminal mouth and the first pair of gill slits meeting across the throat. The cow sharks (Hexanchidae) are described in more detail below.
REFERENCES: de Carvalho, 1996; Naylor et al., 2005; Shirai, 1996; Vélez-Zuazo and Agnarsson, 2011.
HEXANCHIFORMES : HEXANCHIDAE—Cow Sharks
DIVERSITY: 3 genera, 4 species
REPRESENTATIVE GENERA: Heptranchias, Hexanchus, Notorynchus
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine; tropical to temperate; continental shelf to slope, occasionally deeper, usually demersal over soft or rocky bottoms
REMARKS: The cow sharks are known for their numerous gill slits (six or seven), and each of the four species is found over a broad geographic range. These sharks are yolk-sac viviparous (Musick, 2011; Musick and Ellis, 2005) with two species known to have litters of over 100 pups. Hexanchids feed on a variety of prey, from squids, crustaceans, and small bony fishes to elasmobranchs, seals, and small cetaceans. Some species are utilized both for their meat and liver oil, and they often are displayed in public aquariums.
REFERENCES: Compagno, in Carpenter, 2003; Compagno and Niem, in Carpenter and Niem, 1998; Compagno et al., in Fischer et al., 1995; Compagno et al., 2005; Musick, 2011; Musick and Ellis, 2005; Shirai, 1992a, 1996.
HEXANCHID CHARACTERISTICS:
1) six to seven long gill slits, all anterior to the pectoral fins
2) teeth of lower jaw compressed, wide, and serrated
3) anal fin smaller than dorsal fin, originating posterior to origin of dorsal fin
4) mouth inferior
5) distinct, subterminal notch in caudal fin
6) pectoral fins larger than pelvic fins
ILLUSTRATED SPECIMEN:
Hexanchus griseus, SIO 74–176, 838 mm TL (dorsal and lateral views)
ECHINORHINIFORMES : ECHINORHINIDAE—Bramble Sharks
DIVERSITY: 1 family, 1 genus, 2 species
REPRESENTATIVE GENERA: Echinorhinus
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine; tropical to temperate; continental shelf to slope, benthic or demersal over soft bottoms
REMARKS: The bramble sharks, so-called because of their large denticles, were formerly placed in the Squaliformes, but recent authors have them independent of that group, and possibly closely related to the sawsharks (Vélez-Zuazo and Agnarsson, 2011). Both species have a broad geographic range, but they are rarely seen. These sharks are yolk-sac viviparous (Musick, 2011; Musick and Ellis, 2005), with one female E. cookei recorded with a litter of 114 pups; E. brucus is known to have up to 26 pups. Bramble sharks feed on bony fishes, small chondrichthyans, crustaceans, octopods, and squids, and E. brucus occasionally is utilized in fisheries.
REFERENCES: Compagno, in Carpenter, 2003; Compagno and Niem, in Carpenter and Niem, 1998; Compagno et al., in Fischer et al., 1995; Compagno et al., 2005; de Carvalho, 1996; Musick, 2011; Musick and Ellis, 2005; Vélez-Zuazo and Agnarsson, 2011.
ECHINORHINIFORM CHARACTERISTICS: