Daggernose shark

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Not to be confused with the Goblin shark which has a similar snout.
Daggernose shark

Critically Endangered  (IUCN 3.1)[1]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Subdivision: Selachimorpha
Order: Carcharhiniformes
Family: Carcharhinidae
Genus: Isogomphodon
T. N. Gill, 1862
Species:
I. oxyrhynchus
Binomial name
Isogomphodon oxyrhynchus
Range of the daggernose shark
Synonyms

Carcharias oxyrhynchus Müller & Henle, 1839

The daggernose shark (Isogomphodon oxyrhynchus) is a little-known

pectoral fins
.

Daggernose sharks are

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]

Taxonomy and phylogeny

The illustration that accompanied Müller and Henle's original description.

The first scientific description of the daggernose shark, as Carcharias oxyrhynchus, was published by German biologists

Ma).[5]

Distribution and habitat

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.

rainy season (December to May).[7] This species is not known to make long-distance movements, though some local seasonal movements are possible.[1]

Description

Ventral view of head.

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

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]

Biology and ecology

The dominant shark species within the daggernose shark's range are the

schooling fishes that comprise most of its diet. Known prey taken include herring, anchovies, catfish, and croakers.[4]

The daggernose shark is

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.

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]

Human interactions

The daggernose shark poses little danger to humans due to its small size and teeth.

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]

See also

References

  1. ^
    doi:10.2305/IUCN.UK.2020-3.RLTS.T60218A3094144.en
    . Retrieved 19 November 2021.
  2. ^ Lessa, Rosangela, et al. “Close to Extinction? The Collapse of the Endemic Daggernose Shark (Isogomphodon Oxyrhynchus) off Brazil.” Global Ecology and Conservation, vol. 7, 2016, pp. 70–81., doi:10.1016/j.gecco.2016.04.003.
  3. ^ a b "The Daggernose Shark is Near Extinction".
  4. ^
    ISBN 92-5-101384-5
    .
  5. ISBN 0-8493-1514-X
    .
  6. ^
    ISBN 2-8317-0700-5
    .
  7. ISBN 978-0-691-12072-0
    .
  8. S2CID 23735874
    .
  9. doi:10.1071/MF99125
    .
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