Speartooth shark (Glyphis glyphis)

KingdomAnimalia
PhylumChordata
ClassChondrichthyes
OrderCarcharhiniformes
FamilyCarcharhinidae
GenusGlyphis (1)
SizeMale length: up to 157 cm (1)
Female length: up to 175 cm (1)

The speartooth shark is classified as Endangered (EN) on the IUCN Red List (1).

The rare and mysterious speartooth shark (Glyphis glyphis) is a rather stocky shark species with a broad, rounded snout and quite uniform colouration (2) (3). Its upperparts are grey and its underparts are white, with smaller individuals having a clearer colour difference between the upper and lower parts of the body (3). The mouth is white, and there is usually a pale ring around the black eye (3).

An identifying feature of the speartooth shark is the size of its second dorsal fin, which is relatively large in comparison to the triangular, slightly curved first dorsal fin. The tail of the speartooth shark has a longer upper than lower lobe, and the pectoral fins have dark tips on the underside, helping to distinguish this species from the closely related New Guinea river shark (Glyphis garricki) (3). Like other ‘river sharks’ of the genus Glyphis, the speartooth shark has very small eyes (2).

The spear-like teeth from which this shark gets its common name are situated at the front of the lower jaw, while the rest of the lower jaw has slender, unserrated teeth and the upper jaw has more broadly triangular, serrated teeth (2) (3).

No speartooth shark specimens have yet been caught that are fully grown and sexually mature. However, estimates based on knowledge of closely related species suggest that the speartooth shark could potentially grow to lengths of two to three metres (1) (3) (4).

The speartooth shark has only been found in a few locations in northern Australian, in the Northern Territory and Queensland, as well as Papua New Guinea (1) (3). There have also been photographs taken in parts of Western Australia of what was thought to be the speartooth shark, and various possible sightings of the speartooth shark in other areas have also been reported. However, these sightings were not confirmed by a specialist (4).

The speartooth shark has so far only been recorded in rivers and estuaries (5). Some of the shark species that are closely related to the speartooth shark are found in river systems as juveniles, but move to a marine environment when they reach adulthood. The speartooth shark is able to survive in more salty water than that of the estuaries it is found in as a juvenile, but as no adult specimens have been found it is uncertain whether this species is present in marine environments as an adult (4).

However, evidence from juvenile specimens of the speartooth shark suggests that it relies on these freshwater systems for longer periods of time than other species and perhaps throughout its entire life. The fact that it has not been captured in a marine environment despite much commercial fishing also suggests that this shark remains permanently in rivers and estuaries (4).

There is no data on the reproduction of the speartooth shark. However, information from a closely related species of shark, the New Guinea river shark (Glyphis garricki), suggests that members of the Glyphis genus give birth to around 9 pups of approximately 50 to 60 centimetres in length. The female gives birth to live young rather than laying eggs, and is likely to breed only once every two years. It is thought that the speartooth shark gives birth at river mouths, after which the young swim upstream to avoid predation (4).

The small eyes and slender teeth of the speartooth shark suggest that it feeds primarily on fish, which it catches in muddy river waters with poor visibility (1). It is likely to hunt close to or on the soft river bottom, using specialised sensors in its snout to detect tiny electric currents given off by its prey (3) (6).

There is no long-term information on the extent to which fishing has affected the speartooth shark, due to its natural rarity. However, recreational and commercial fishing, including gillnetting for barramundi (Lates calcarifer), is believed to be the most prominent threat to this species (1) (3) (4) (7).

The speartooth shark is also likely to be affected by habitat degradation (1) (3) (4). For example, a uranium mine in the Kakadu National Park may potentially impact on this species due to pollution contaminating the rivers in which it lives (4) (7). Shallow, inshore waters are also particularly vulnerable to habitat modification as a result of human developments (3).

Like many other sharks, the speartooth shark becomes sexually active relatively late in its life and has a low reproductive rate, making it more vulnerable to population declines. Freshwater sharks in particular are vulnerable to human disturbances as they have a restricted habitat, and so are less able than marine species to evade threats such as pollution, habitat modification or overfishing (1) (4) (7).

The speartooth shark is listed as ‘critically endangered’ by the Commonwealth Environmental Protection and Biodiversity Conservation Act of 1999 (1) (3). It occurs in rivers within the Kakadu National Park in the Northern Territory, Australia. This is likely to protect it to some extent from commercial fishing and habitat modification, but the effects of uranium mining in the park are unknown. The speartooth shark also occurs in Lakefield National Park in Queensland, but is not protected from commercial fishing there (3) (4).

In the Northern Territory of Australia, laws have been brought in to prevent commercial barramundi fishing in all the rivers in which the speartooth shark is known to occur (4) (3). Recreational fishing is still permitted in Kakadu National Park, but only lures with a lower chance of catching speartooth sharks can legally be used (4).

Between its initial discovery in 1982 and a conservation assessment in 2005, only 108 individual speartooth sharks were recorded (4). Further surveys are urgently needed to properly assess the populations, distribution and biology of this little-known species, as well as to determine the threats posed by fishing (1) (3) (4). A recovery plan has been drafted for the speartooth shark (1), but conservation plans are still hampered by a lack of information on this species, particularly in light of uncertainties over its identification (4).

More information on shark conservation:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk

  1. IUCN Red List (September, 2011) 
    http://www.iucnredlist.org/
  2. Compagno, L.J.V. (1984) Sharks of the World. An Annotated and Illustrated Catalogue of Shark Species Known to Date. Vol. 4: Part 2: Carcharhiniformes. Food and Agriculture Organization of the United Nations, Rome. Available at:
    ftp://ftp.fao.org/docrep/fao/009/ad123e/AD123e30.pdf
  3. Australian Government - Department of Sustainability, Environment, Water, Population and Communities (2011) Glyphis glyphis - Speartooth shark. In: Species Profile and Threats Database. Department of Sustainability, Environment, Water, Population and Communities, Canberra. Available at:
    http://www.environment.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=82453
  4. Stevens, J.D., Pillans, R.D. and Salini, J. (2005) Conservation Assessment of Glyphis sp. A (Speartooth Shark), Glyphis sp. C (Northern River Shark), Pristis microdon (Freshwater Sawfish) and Pristis zijsron (Green Sawfish). CSIRO Marine Research Department of the Environment and Heritage, Australia.
    http://www.environment.gov.au/coasts/publications/assessment-glyphis.html
  5. Thorburn, D.C., Peverell, S., Stevens, J.D., Last, P.R. and Rowland, A.J. (2003) Status of Freshwater and Estuarine Elasmobranchs in Northern Australia. Natural Heritage Trust, Canberra, Australia.
  6. Heuter, R.E., Mann, D.A., Maruska, K.P., Sisneros, J.A. and Demski, L.S. (2004) Sensory biology of elasmobranchs. In: Carrier, J.C., Musick, J.A. and Heithaus, M.R. (Eds.) Biology of Sharks and their Relatives. CRC Press, New York.
  7. Compagno, L.J.V. and Cook, S.F. (1995) The exploitation and conservation of freshwater elasmobranchs: status of taxa and prospects for the future. Journal of Aquaculture and Aquatic Sciences, 7: 62-89.