Daggernose shark

The daggernose shark (Carcharhinus oxyrhynchus) is a little-known species of requiem shark, in the family Carcharhinidae. It inhabits shallow tropical waters off northeastern South America, from Trinidad to northern Brazil, favoring muddy habitats such as mangroves, estuaries, and river mouths, though it is intolerant of fresh water. A relatively small shark typically reaching 1.5 m (4.9 ft) in length, the daggernose shark is unmistakable for its elongated, flattened, and pointed snout, tiny eyes, and large paddle-shaped pectoral fins. Daggernose sharks are predators of small schooling fishes. Its reproduction is viviparous, with females giving birth to 2–8 pups every other year during the rainy season; this species is capable of shifting the timing of its reproductive cycle by several months in response to the environment. Harmless to humans, the daggernose shark is caught for food and as...

The daggernose shark is found along the northeastern coast of South America, off Trinidad, Guyana, Suriname, French Guiana, and northern Brazil. It reportedly occurs as far south as Valença in the central Brazilian state of Bahia, though fishery surveys have not detected this species in the area and it is apparently unknown to local fishermen. An inhabitant of coastal waters at a depth of 4–40 m (13–131 ft), the daggernose shark prefers highly turbid waters and decreases in number with increasing water clarity. Females tend to be found at greater depths than males. Its range encompasses a wide continental shelf with a humid tropical climate, extensive mangroves, and draining by numerous rivers including the Amazon. Water salinity in this area ranges from 20 to 34 ppt, while the tidal amplitude can measure up to 7 m (23 ft). Daggernose sharks are most common over shallow muddy banks and in estuaries and river mouths. It seems to be intolerant of low salinity, moving inshore during the dry season (June to November) and offshore during the rainy season (December to May). This species is not known to make long-distance movements, though some local seasonal movements are possible.

The daggernose shark is found along the northeastern coast of South America, off Trinidad, Guyana, Suriname, French Guiana, and northern Brazil. It reportedly occurs as far south as Valença in the central Brazilian state of Bahia, though fishery surveys have not detected this species in the area and it is apparently unknown to local fishermen. An inhabitant of coastal waters at a depth of 4–40 m (13–131 ft), the daggernose shark prefers highly turbid waters and decreases in number with increasing water clarity. Females tend to be found at greater depths than males. Its range encompasses a wide continental shelf with a humid tropical climate, extensive mangroves, and draining by numerous rivers including the Amazon. Water salinity in this area ranges from 20 to 34 ppt, while the tidal amplitude can measure up to 7 m (23 ft). Daggernose sharks are most common over shallow muddy banks and in estuaries and river mouths. It seems to be intolerant of low salinity, moving inshore during the dry season (June to November) and offshore during the rainy season (December to May). This species is not known to make long-distance movements, though some local seasonal movements are possible.

As its common name suggests, the daggernose shark has a very long, flattened snout with a pointed tip and an acutely triangular profile from above. The eyes are circular and minute in size, with nictitating membranes (a protective third eyelid). The nostrils are small, without prominent nasal skin flaps. There are short but deep furrows at the corners of the mouth on both jaws. The tooth rows number 49–60 and 49–56 in the upper and lower jaws respectively. Each tooth has a single narrow, upright cusp; the upper teeth are slightly broader and flatter than the lower teeth, with serrated rather than smooth edges. The body is robustly built, with large, broad, paddle-like pectoral fins that originate under the fifth gill slit. The first dorsal fin originates over the posterior half of the pectoral fin bases. The second dorsal fin is about half as tall as the first and located over or slightly ahead of the anal fin. The anal fin is smaller than the second dorsal fin and has a deep notch in the rear margin. The caudal fin has a well-developed lower lobe and is preceded by a crescent-shaped notch on the upper side of the caudal peduncle. The coloration is a plain gray above, sometimes with a brownish or yellowish cast, and lighter below. Males attain a length of 1.4 m (4.6 ft) and females 1.6 m (5.2 ft). There are unsubstantiated records of individuals 2.0–2.4 m (6.6–7.9 ft) long. The maximum known weight is 13 kg (29 lb).

The first scientific description of the daggernose shark, as Carcharias oxyrhynchus, was published by German biologists Johannes Peter Müller and Friedrich Gustav Jakob Henle in their 1839 Systematische Beschreibung der Plagiostomen. They chose the specific epithet oxyrhynchus, from the Greek oxys ("sharp" or "pointed") and rhynchos ("nose"). In 1862, American ichthyologist Theodore Gill coined the genus Isogomphodon for this species, from the Greek isos ("equal"), gomphos ("nail" or "peg"), and odous ("tooth"). However, Isogomphodon was subsequently relegated to being a synonym of Carcharhinus, until it was resurrected by shark authority Stewart Springer in 1950. In 2023, a phylogenetic study found the daggernose shark to be deeply nested within the genus Carcharhinus, as the sister species to the smalltail shark (C. porosus), another western Atlantic Carcharhinus species. The unusual elongated snout, which is shared by no other species within Carcharhinus, was found to be a derived trait adapted to living in the muddy, clouded waters produced by the plume of the Amazon River. For this reason, the species was reclassified as Carcharhinus oxyrhynchus. An extinct apparent relative, †Carcharhinus acuarius (Probst, 1879) (formerly Isogomphodon acuarius), has been identified from the Middle Eocene (45 Ma) of Germany on the basis of similar teeth. However, this clashes with phylogenetic estimates which have found the divergence of the daggernose and smalltail sharks to only date to the Middle Miocene.