Daggernose shark | |
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Chondrichthyes |
Subclass: | Elasmobranchii |
Order: | Carcharhiniformes |
Family: | Carcharhinidae |
Genus: | Isogomphodon T. N. Gill, 1862 |
Species: | I. oxyrhynchus |
Binomial name | |
Isogomphodon oxyrhynchus (J. P. Müller & Henle, 1839) | |
Range of the daggernose shark | |
Synonyms | |
Carcharias oxyrhynchusMüller & Henle, 1839 |
The daggernose shark (Isogomphodon oxyrhynchus) is a little-known species of requiem shark, in the family Carcharhinidae, and the only extant member of its genus. 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 give 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 bycatch in artisanal and commercial fisheries. Limited in range and slow-reproducing, it has been assessed as Critically Endangered by International Union for Conservation of Nature in light of a steep population decline in recent years. The current population is believed to be extremely low, with no more than 250 individuals believed to be in existence as of 2023. [2] Indeed, it may even be in reproductive collapse, in which case it will likely become extinct in the near future. [3]
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 genius 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. [4] Regardless of its taxonomic validity, Isogomphodon, along with the genera Nasolamia and Prionace , is closely related to Carcharhinus. An extinct relative, I. acuarius, dates back to the Middle Eocene (45 Ma). [5]
The daggernose shark is found along the northeastern coast of South America, off Trinidad, Guyana, Suriname, French Guiana, and northern Brazil. [4] 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. [1]
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. [6] 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). [1] 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). [7] This species is not known to make long-distance movements, though some local seasonal movements are possible. [1]
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. [4]
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. [4] Males attain a length of 1.4 m (4.6 ft) and females 1.6 m (5.2 ft). [1] There are unsubstantiated records of individuals 2.0–2.4 m (6.6–7.9 ft) long. [4] The maximum known weight is 13 kg (29 lb). [6]
The dominant shark species within the daggernose shark's range are the smalltail shark (Carcharhinus porosus) and the bonnethead (Sphyrna tiburo). [1] Its elongated snout and tiny eyes are likely consequences of living in murky sediment-laden waters, reflecting an adaptive emphasis on electroreception and other rostral senses rather than vision. The snout bears a superficial similarity to the goblin shark (Mitsukurina owstoni), some Apristurus catsharks, and the long-nosed chimaeras, all found in the deep sea. [6] With long jaws and numerous small teeth, the daggernose shark is well-suited for capturing the small schooling fishes that comprise most of its diet. Known prey taken include herring, anchovies, catfish, and croakers. [4]
The daggernose shark is viviparous; once the developing embryos exhaust their supply of yolk, the depleted yolk sac is converted into a placental connection through which the mother delivers sustenance. Females give birth to litters of 2–8 pups every other year, following a year-long gestation period. There is no correlation between female size and number of offspring. [6] Mating and parturition take place over a roughly six-month period from the beginning to the end of the rainy season. However, the daggernose shark is capable of shifting the timing of its reproductive cycle by at least four months, possibly in response to varying environmental conditions. [8] Females move into shallow coastal nurseries to give birth; one important nursery exists off Brazilian state of Maranhão. [6]
Newly born daggernose sharks measure 38–43 cm (15–17 in) in length. [6] Males mature at 103 cm (41 in) long, corresponding to an age of 5–6 years, while females mature at 115 cm (45 in) long, corresponding to an age of 6–7 years. The lifespan of males has been measured at up to 7 years, and females 12 years; extrapolating from growth rates suggest that the largest known males and females may be 12 and 20 years old respectively. [9]
The daggernose shark poses little danger to humans due to its small size and teeth. [4] This shark is caught in small numbers by subsistence fishers in Trinidad, Guyana, Suriname, and French Guiana. [6] It also comprises about one-tenth of the catch of a northern Brazil floating gillnet fishery targeting Serra Spanish mackerel (Scomberomorus brasiliensis) and Acoupa weakfish (Cynoscion acoupa), which operates in estuaries during the dry season. This shark is often found in markets, but is not highly regarded as a food fish. The International Union for Conservation of Nature (IUCN) has assessed this species as Critically Endangered, as it has a limited distribution and is highly susceptible to overfishing due to its low reproductive rate. The daggernose shark has declined over 90% over the past decade off Brazil, and similar declines have likely also occurred elsewhere in its range as fishing pressure in the region continues to grow more intense. The IUCN has urgently recommended the implementation of conservation schemes and the expansion of fishery monitoring for this species. [1] Evidence also points to this species being on the verge of or already in reproductive collapse. [3]
The copper shark, bronze whaler, or narrowtooth shark is a species of requiem shark found mostly in temperate latitudes. It is distributed in a number of separate populations in the northeastern and southwestern Atlantic, off southern Africa, in the northwestern and eastern Pacific, and around Australia and New Zealand, with scattered reports from equatorial regions. The species can be found from brackish rivers and estuaries to shallow bays and harbors, to offshore waters 100 m (330 ft) deep or more. Females are found apart from males for most of the year, and conduct seasonal migrations. A large species reaching 3.3 m (11 ft) long, the copper shark is difficult to distinguish from other large requiem sharks. It is characterized by its narrow, hook-shaped upper teeth, lack of a prominent ridge between the dorsal fins, and plain bronze coloration.
The silvertip shark is a large species of requiem shark, in the family Carcharhinidae, with a fragmented distribution throughout the tropical Indian and Pacific Oceans. It is often encountered around offshore islands and coral reefs, and has been known to dive to a depth of 800 m (2,600 ft). The silvertip shark resembles a larger and bulkier grey reef shark, but can be easily identified by the prominent white margins on its fins. It attains a maximum length of 3 m (10 ft).
The blacktip shark is a species of requiem shark, and part of the family Carcharhinidae. It is common to coastal tropical and subtropical waters around the world, including brackish habitats. Genetic analyses have revealed substantial variation within this species, with populations from the western Atlantic Ocean isolated and distinct from those in the rest of its range. The blacktip shark has a stout, fusiform body with a pointed snout, long gill slits, and no ridge between the dorsal fins. Most individuals have black tips or edges on the pectoral, dorsal, pelvic, and caudal fins. It usually attains a length of 1.5 m (4.9 ft).
The Caribbean reef shark is a species of requiem shark, belonging to the family Carcharhinidae. It is found in the tropical waters of the western Atlantic Ocean from Florida to Brazil, and is the most commonly encountered reef shark in the Caribbean Sea. With a robust, streamlined body typical of the requiem sharks, this species is difficult to tell apart from other large members of its family such as the dusky shark and the silky shark. Distinguishing characteristics include dusky-colored fins without prominent markings, a short free rear tip on the second dorsal fin, and tooth shape and number.
The blacknose shark is a species of requiem shark, belonging to the family Carcharhinidae, common in the tropical and subtropical waters of the western Atlantic Ocean. This species generally inhabits coastal seagrass, sand, or rubble habitats, with adults preferring deeper water than juveniles. A small shark typically measuring 1.3 m (4.3 ft) long, the blacknose has a typical streamlined "requiem shark" shape with a long, rounded snout, large eyes, and a small first dorsal fin. Its common name comes from a characteristic black blotch on the tip of its snout, though this may be indistinct in older individuals.
The bignose shark is a species of requiem shark, in the family Carcharhinidae. Distributed worldwide in tropical and subtropical waters, this migratory shark frequents deep waters around the edges of the continental shelf. It is typically found at depths of 90–430 m (300–1,410 ft), though at night it may move towards the surface or into shallower water. The bignose shark is plain-colored and grows to at least 2.7–2.8 m (8.9–9.2 ft) in length. It has a long, broad snout with prominent nasal skin flaps, and tall, triangular upper teeth. Its pectoral fins are long and almost straight, and there is a ridge on its back between the two dorsal fins.
The graceful shark or Queensland shark is a species of requiem shark, in the family Carcharhinidae, found in the tropical Indo-Pacific, from the Gulf of Aden to northern Australia. It is a midwater species that has been recorded to a depth of 50 m (160 ft). A stoutly built shark growing up to 1.7 m (5.6 ft) long, the graceful shark has a short, wedge-shaped snout, large, sickle-shaped pectoral fins and first dorsal fin, and black tips on most fins.
The hardnose shark is a species of requiem shark, in the family Carcharhinidae, so named because of the heavily calcified cartilages in its snout. A small bronze-coloured shark reaching a length of 1.1 m (3.6 ft), it has a slender body and a long, pointed snout. Its two modestly sized dorsal fins have distinctively elongated rear tips. The hardnose shark is widely distributed in the western Indo-Pacific, from Kenya to southern China and northern Australia. It inhabits warm, shallow waters close to shore.
The creek whaler is a common species of requiem shark, and part of the family Carcharhinidae, endemic to northern Australia. It frequents shallow waters close to shore, including estuaries. This small, stocky shark usually grows to 1.0–1.3 m (3.3–4.3 ft) long and is brownish in color without conspicuous fin markings. It can be identified by its long snout, large, triangular pectoral fins, and large, anteriorly positioned first dorsal fin.
The spinner shark is a type of requiem shark, in the family Carcharhinidae, named for the spinning leaps it makes as a part of its feeding strategy. This species occurs in tropical and warm temperate waters worldwide, except for in the eastern Pacific Ocean. It is found from coastal to offshore habitats to a depth of 100 m (330 ft), though it prefers shallow water. The spinner shark resembles a larger version of the blacktip shark, with a slender body, long snout, and black-marked fins. This species can be distinguished from the blacktip shark by the first dorsal fin, which has a different shape and is placed further back, and by the black tip on the anal fin. It attains a maximum length of 3 m (9.8 ft).
The nervous shark is a species of requiem shark, and part of the family Carcharhinidae, so named because of its timid behavior in regard to humans. It is common in shallow, coastal waters off northern Australia, Papua New Guinea, and the Solomon Islands. A small brownish or grayish shark typically measuring 1.0–1.3 m (3.3–4.3 ft) long, this species has a short, blunt snout, oval eyes, and a relatively large second dorsal fin. The leading margins of most fins are finely edged with black, and the lower caudal fin lobe is black-tipped.
The whitecheek shark or widemouth blackspot shark is a requiem shark of the family Carcharhinidae, found in the Indo-West Pacific Ocean between latitudes 34°N and 25°S. It can reach a length of 1 m. It feeds mainly on fish, cephalopods, and crustaceans. It is a viviparous species, with the female giving birth to up to four live young.
The finetooth shark is a species of requiem shark, in the family Carcharhinidae, found in the western Atlantic Ocean, from North Carolina to Brazil. It forms large schools in shallow, coastal waters, and migrates seasonally following warm water. A relatively small, slender-bodied shark, the finetooth shark can be identified by its needle-like teeth, dark blue-gray dorsal coloration, and long gill slits. It attains a maximum length of 1.9 m (6.2 ft). The diet of this species consists primarily of small bony fishes, in particular menhaden. Like other members of its family, it is viviparous with females giving birth to two to six pups in estuarine nursery areas every other year.
The smoothtooth blacktip shark is a species of requiem shark in the family Carcharhinidae. It is known only from the type specimen caught from the Gulf of Aden, off eastern Yemen, and a handful of additional specimens caught from the Persian Gulf, off Kuwait. Reaching 1.3 m (4.3 ft) in length, this species has a stocky greenish-colored body, a short snout, and black-tipped fins. It can be distinguished from similar species by its teeth, which are narrow, erect, and smooth-edged.
The smalltail shark is a species of requiem shark, and part of the family Carcharhinidae. It is found in the western Atlantic Ocean, from the northern Gulf of Mexico to southern Brazil. It inhabits shallow waters close to shore, particularly over muddy bottoms around estuaries. It tends to swim low in the water column and forms large aggregations segregated by sex. A slim species generally not exceeding 1.1 m (3.6 ft) in length, the smalltail shark has a rather long, pointed snout, a broad, triangular first dorsal fin, and a second dorsal fin that originates over the midpoint of the anal fin base. It is plain gray in color, without prominent markings on its fins.
The night shark is a species of requiem shark, in the family Carcharhinidae, found in the temperate and tropical waters of the Atlantic Ocean. An inhabitant of the outer continental shelf and upper continental slope, this shark most commonly occurs at depths of 50–600 m (160–1,970 ft) and conducts a diel vertical migration, spending the day in deeper water and moving into shallower waters at night. Off northeastern Brazil, large numbers congregate around seamounts of varying depths. A slender, streamlined species, the night shark typically reaches a length of 2 m (6.6 ft). It can be identified by its long, pointed snout and large, green eyes, and is dark grayish blue or brown above and white below.
The milk shark is a species of requiem shark, and part of the family Carcharhinidae, whose common name comes from an Indian belief that consumption of its meat promotes lactation. The largest and most widely distributed member of its genus, the milk shark typically measures 1.1 m (3.6 ft) long, and can be found in coastal tropical waters throughout the eastern Atlantic and the Indo-Pacific regions. Occurring from the surface to a depth of 200 m (660 ft), this species is common near beaches and in estuaries, and has been recorded swimming up rivers in Cambodia. Juveniles are known to inhabit tidal pools and seagrass meadows. The milk shark has a slender body with a long, pointed snout and large eyes, and is a nondescript gray above and white below. This shark can be distinguished from similar species in its range by the long furrows at the corners of its mouth, and seven to 15 enlarged pores just above them.
The crested bullhead shark is an uncommon species of bullhead shark, in the family Heterodontidae. It lives off the coast of eastern Australia from the coast to a depth of 93 m (305 ft). This shark can be distinguished from other members of its family by the large size of the ridges above its eyes and by its color pattern of large dark blotches. It typically attains a length of 1.2 m (3.9 ft).
The spined pygmy shark is a species of squaliform shark in the family Dalatiidae found widely in all oceans. Growing no larger than roughly 28 cm (11 in), it is one of the smallest sharks alive, with this record beaten by the dwarf lanternshark. This shark has a slender, cigar-shaped body with a sizable conical snout, a long but low second dorsal fin, and an almost symmetrical caudal fin. Its sister species S. aliae and it are the only sharks with a spine on the first dorsal fin and not the second. Spined pygmy sharks are dark brown to black, with numerous bioluminescent organs called photophores on their ventral surface. The shark is believed to use these photophores to match ambient light conditions, which break up its silhouette and help the shark to avoid being seen by predators below.
The Colares stingray, Fontitrygon colarensis, is a species of stingray in the family Dasyatidae, native to the shallow brackish waters of the Amazon River estuary in northern Brazil. This species inhabits inshore bays during the dry season and moves away from the coast in the rainy season. It is characterized by a rhomboid pectoral fin disk, elongated snout, and a dark band on the lower lip. A fairly large species, males and females attain disk widths of 63 cm (25 in) and 91 cm (36 in) respectively. Females give birth to 1–4 young, possibly annually. Colares stingrays are both targeted and caught as bycatch by Brazilian artisanal and commercial fisheries; these pressures coupled with its small range and slow reproductive rate has led the International Union for Conservation of Nature (IUCN) to list this species as critically endangered.