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Northern Speartooth Shark - Glyphis sp. C

By Helen Larson

Threatened Fish Profile – In Newsletter 30_1, May 2000

(Photograph courtesy of the Museum and Art Gallery of the Northern Territory)

Conservation Status: Currently listed as Uncertain; considered Endangered at Albury workshop (ASFB; not yet IUCN listed).

Description: Speartooth Sharks look rather like the common Bull Shark, Carcharhinus leucas, but have a taller second dorsal fin (about 2/3 the height of the first dorsal), the first dorsal fin is more triangular, the upper jaw teeth triangular, but with “shoulders”, and the eye is small, and placed on the grey-shaded part of the head, not the white counter-shaded part. They are a steely grey rather than the yellowish grey of the Bull Shark when alive. These sharks probably reach 2m total length as adults, with the largest found so far being 1.47m.

Life History: Virtually nothing is known. Parks Australia North staff, who caught the Alligator Rivers specimens, noted that a 1.47m TL specimen survived far longer out of water, strongly flexing its body, than did Carcharhinus leucas and C. amboinensis from the same river. Tanaka (1997) estimated that the 1.3m TL female from the Adelaide River was four years old, based on the vertebral centra. Research on these sharks has been hampered by a lack of specimens.

Distribution and Habitat: Only nine specimens have ever been collected - an immature female taken about 100km up the Adelaide River in 1989, an adult male taken some 60km up the South Alligator River in 1996, and in 1999, five females and two males from the East, West and South Alligator Rivers, in brackish water, with salinity ranging from 6 to 26 ppt. All these rivers are turbid and seasonally fast-flowing (during the monsoon rains from December to April). Despite considerable fishing and collecting activity in the Northern Territory, no specimens have ever been found in coastal marine habitats. Glyphis sp. C apparently co-occurs with Glyphis sp. A in the Alligator Rivers, according to early results of study of these specimens by Peter Last (at least one specimen shares vertebral count with sp. A). Glyphis sp. A was previously known only from the Bizant River in north Queesland.

Threats: The main threat is from commercial (and also illegal) gill nets set for barramundi and threadfin in northern rivers. Any speartooth sharks caught in these nets would be dumped or used as bycatch.

Conservation/management: This species should be protected, although it has not yet been formally listed by the ASFB or IUCN.

References:

Last, P.R. and Stevens, J.D. 1994. Sharks and rays of Australia. CSIRO Australia.

Tanaka, S. 1991. Age estimation of freshwater sawfish and sharks in northern Australia and Papua New Guinea. The University Museum, the University of Tokyo, Nature and Culture 3: 71-82.

Stevens, J.R. In press. A new record of the river shark Glyphis sp. from northern Australia. Chondros.

Taniuchi, T. and Shimizu, M. 1991. Elasmobranchs collected from seven river systems in northern Australia and Papua New Guinea. The University Museum, the University of Tokyo, Nature and Culture 3: 3-10.

Watabe, S. 1991. Electrophoretic analyses of freshwater elasmobranchs from northern Australia and Papua New Guinea. The University Museum, the University of Tokyo, Nature and Culture 3: 103-109.

Further information:
Dr Peter Last,
CSIRO Marine Research,
PO Box 1538, Hobart, Tasmania 7001.
Ph.: (03) 6232 5222.
E-mail: Peter.Last@marine.csiro.au.