This week’s featured species is not well known, and likely never will be, because the Daggernose shark (Isogomphodon oxyrhynchus) is critically endangered and is likely facing extinction. The daggernose shark is so named for its elongated, flattened snout, that vaguely resembles the goblin shark’s, though the two sharks are not related. In fact its scientific name, Isogomphodon, is Greek for “equal nail tooth” and, oxyrhynchus, for “sharp” or “pointed nose” (Compagno, 1984).
The daggernose shark resides in turbid waters along the eastern coast of Brazil. Its small eyes and elongated snout suggest that it has adapted to use other electrosenses located in the sensitive rostrum to hunt, rather than rely on its vision in the murky waters (Compagno, 1984). Like other elasmobranch species, the snout of the daggernose shark is covered in little pores. These pores known as the ampullae of lorenzini, seen below as little black dots along the snout and mouth, allow the shark to detect electrical signals from its prey, even when visibility is low. Update: Following the publication of this post, a paper was published documenting the capture of a young‐of‐the‐year daggernose shark in a freshwater system in Northern Brazil—the first ever recorded in a non‐marine environment (Feitosa, Martins, Lessa, Barbieri, & Nunes, 2019).
The daggernose shark is under threat from commercial fisheries. They are sometimes taken as bycatch in gill nets targeting Spanish mackerel and King weakfish. Many species of elasmobranch are susceptible to fishing pressures. They are slow to reach sexual maturity, sometimes taking years or even decades depending on the species. In the case of the daggernose shark, it can take up to 7 years for females to reach sexual maturity. When they do, females will reproduce once a year, only having 2 to 8 pups per litter (Lessa, Charvet-Almeida, Santana, & Almeida, 2006). This low population growth rate leaves the daggernose shark in a highly vulnerable position when faced with pressures from the fisheries industry. A study published in 2016 estimated there were as few as 250 individuals remaining in the population and that the species could be headed towards a reproductive collapse (Lessa, Batista, & Santana, 2016). This means that sadly we may see the extinction of the daggernose shark within the coming years.
Authority: Müller & Henle,1839
Family: Carcharhinidae, 50+
Length: Maximum 5 feet (1.5 m)
Weight: Up to 29 lbs (13 kg)
Habitat: Turbid coastal waters; tropical coast lines with extensive mangroves, wide shelves and numerous rivers
Depth: Surface to 130 feet (40 m)
Gestation: 12 months
Litter Range: 2 – 8 pups
Home Range: Western Atlantic Ocean along the eastern coast of Brazil
Diet: Small schooling fishes
IUCN Status: Critically Endangered; in 2016 estimated 250 individuals left in the population, likely facing reproductive collapse and extinction
(Compagno, 1984; Lessa et al, 2006)
Thanks so much for checking out the daggernose shark! Remember to hope over to last week’s featured species: the Bat Ray. If there is a species of shark you’d love to know more about, leave me a comment or send me a message! I would love to do a feature on your favorite species.
The new Ocean For Sharks Shop is open! There’s handmade ocean inspired plush animals, canvas paintings, and of course my children’s book, Winifred the Wondrous Whale Shark, available in print and PDF. Be sure to stop by. Remember proceeds benefit shark research and conservation with a donation to Project AWARE!
Conservation legislation needs public support in order to become law and help protect the environment and wildlife. Tell your representatives that you care about environmental and wildlife conservation. It only takes a moment to make a change that will last a lifetime. Until next time finatics!
Featured Image Source
Müller & Henle (Authors). (1838 December 31). Systematische Beschreibung der Plagiostomen The illustration that accompanied Müller and Henle’s original description [Digital Image]. Retrieved from https://en.wikipedia.org/
Compagno, L. J. (1984). Sharks of the world: an annotated and illustrated catalogue of shark species known to date (No. QL 638.9. C65).
Feitosa, L. M., Martins, A. P. B., Lessa, R. P. T., Barbieri, R., & Nunes, J. L. S. (2019). Daggernose Shark: An Elusive Species from Northern South America. Fisheries, 44(3), 144–147.
Lessa, R., Batista, V., & Almeida, Z. (1999). Occurrence and biology of the daggernose shark Isogomphodon oxyrhynchus (Chondrichthyes: Carcharhinidae) off the Maranhão coast (Brazil). Bulletin of Marine Science, 64(1), 115-128.
Lessa, R., Batista, V. S., & Santana, F. M. (2016). Close to extinction? The collapse of the endemic daggernose shark (Isogomphodon oxyrhynchus) off Brazil. Global Ecology and Conservation, 7, 70-81.
Lessa, R., Charvet-Almeida, P., Santana, F.M. & Almeida, Z. (2006). Isogomphodon oxyrhynchus. The IUCN Red List of Threatened Species 2006. Retrieved from http://dx.doi.org/10.2305/IUCN.UK.2006.RLTS.T60218A12323498.en