Critically Endangered Species of the Week: the Ganges Shark!

     Its that time of the week again - here is the third critically endangered species of the week! This week I thought I would look at a better known group; sharks. Possibly suprisingly, the most famous sharks whose anthropogenic deaths make the news are not considered by the IUCN as critically endangered (although the majority of sharks are threatened). However, there is a reasonably long list of other shark species in imminent danger of extinction, including the Ganges Shark.

About:
      The Ganges Shark, Glyphis gangeticus, is a freshwater riverine, and possibly also inshore marine/estuarine, shark that is very poorly understood. The species is one of the 6 known species of river shark, all of which are very rare and likely endangered [3, 5]. It is known from a very small number of specimens, and is currently inadequately described. Maximum size is estimated as around 2m in length [1, 2, 3], and individuals have slender teeth and small eyes, suggesting the species has a fish-based diet and is adapted to the turbid waters in its geographical range. The species has a typical 'shark shape' (known as a requiem shark, belonging to the family Carcharhinidae); it is stocky with a rounded snout, and has a uniform grey to brownish colouration [2, 5, 6].

      The species has been implicated in numerous attacks on humans in the Ganges [1, 4...], however the infamous Bull Shark also occurs in the same river system with superficially similar characteristics, and therefore may be responsible for the attacks.

 

Diagrams of the Ganges Shark, Glyphis gangeticus. Confirmed photographs of the species appear

very rare and difficult to find! Image on top from Marine Species Identification Portal [6],

image on bottom from WWF India [5].

Number left in existence:

      The species was originally known from only 3 museum specimens, all collected in the nineteenth century [1, 3,...]. There are no records between 1867 and 1996, and the sightings in this last year are unconfirmed [1,...]. A specimen collected in 2001 has been identified as the Ganges Shark, however clearly the species is now extremely rare, with a likely decreasing population trend.

Geographical Range in the wild:

      The Ganges Shark is known only from the lower parts of the Ganges-Hooghli river system, West Bengal, India; it is endemic to India [1, 4, 5]. This likely includes the rivers rivers Hooghly, Ganges, Brahmaputra and Mahanadi [4, 5]. Wider ranges assigned, including marine areas, are likely based on other requiem shark species, such as the Bull Shark.

Geographical location of Glyphis gangeticus; the Ganges-Hooghli river system.

From IUCN [1].

Why they are endangered:

• Presumably confusion with the much more aggressive and dangerous to humans Bull Shark has lead to unfounded fear of the species, leading to preemptive attacks and killings of individuals by humans.
• The species has been traditionally and recently fished in the Ganges-Hooghli river system. It appears in the highly damaging oriental fin trade and is consumed locally - there are major fisheries for sharks in India, and large inshore requiem sharks are frequently targeted [1, 5]. Even low levels of exploitation by humans for resources can devastate populations due to their slow growth and small litter size [3].
• Individuals appear in the international curios trade of shark jaws [1].
• As with many species, overfishing, and habitat destruction and degradation from pollution, increasing river utilisation and management (e.g. construction of dams) are highly damaging to populations [1, 3, 5]. Furthermore, freshwater organisms cannot readily adapt to other conditions if their habitats are affected.

What can we do to help?

       Thankfully Glyphis gangeticus is now protected under the Indian Wildlife (Protection) Act of 1972 (Schedule I, Part II A) [1, 5]. However, only 10 Chondrichthyan species (the group including sharks and rays) are currently protected under this act, and the effectiveness of this measure is unknown and regulations are difficult to enforce - particularly due to the culture of local populations, and the prevelance of widespread fisheries for international trade [1].

       Furthermore, this act does not protect the species from population crashes due to habitat destruction - to prevent this locals need to be increasingly educated and informed about the danger to the species.
      The Ganges Shark, based on the fact that very little is known about the life-style or populations of this group, is a good species to illustrate the huge need for greater research and sampling of particular taxa and locations to protect ecosystem diversity.

References:
1. Compagno, L.J.V. 2007. Glyphis gangeticus. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Accessed 30 October 2012.
2. Wikipedia, 2012. Ganges Shark. <http://en.wikipedia.org/wiki/Ganges_shark>. Accessed 30 October 2012.
3. ReefQuest Centre for Shark Research. The Mysterious, Endangered River Sharks (Glyphis spp.). <http://www.elasmo-research.org/conservation/river_sharks.htm>. Accessed 30 October 2012.
4. Shark Foundation. Ganges Shark (Glyphis gangeticus). <http://www.shark.ch/Database/Search/species.html?sh_id=1079>. Accessed 30 October 2012.
5. WWF India. Ganges Shark. <http://www.wwfindia.org/about_wwf/priority_species/lesser_known_species/ganges_shark/>. Accessed 30 October 2012.
6. Marine Species Identification Portal. Ganges Shark (Glyphis gangeticus). <http://species-identification.org/species.php?species_group=sharks&menuentry=soorten&id=463&tab=beschrijving>. Accessed 30 October 2012.