Grey nurse shark - Carcharias taurus

By David Pollard

Threatened Fish Profile – In Newsletter 29_2, December 1999

(Drawing by Jack Hannan)

Conservation status:

Vulnerable (ASFB, IUCN, NSW, Commonwealth).

Description:

The grey nurse shark is a large, stocky shark that grows to 3.2 m and up to 300 kg. The dorsal surface is grey to grey-brown, merging to off-white on the belly. Dark blotches or spots may occur on the upper two thirds of the body.

Distribution and abundance:

Grey nurse sharks have a broad inshore distribution in sub-tropical to cool temperate waters around the main continental land masses, except in the eastern Pacific Ocean off North and South America. They are relatively common in Australia, South Africa and south-eastern USA, although there has been a significant decline in abundance in these regions since the 1960’s (Dudley and Cliff, 1993; Pollard et al., 1996). Throughout the rest of their range, they are relatively uncommon.

Habitat and feeding:

Grey nurse sharks are often observed hovering motionless above the seabed at depths of 15-25 m, usually in or near sand gutters or rock caves in the vicinity of inshore reefs. They are also occasionally found in the surf zone, around coral reefs, and on the continental shelf at depths of up to 200 m. Grey nurse sharks usually occur alone or in small to medium sized groups (possibly breeding aggregations). Migration patterns are poorly understood, although there appears to be a northwards migration in autumn and winter and a southwards migration in summer. Grey nurse sharks feed on a wide range of bony fishes, sharks, rays, crabs and lobsters (Compagno, 1984). Groups of grey nurse sharks have been reported to feed co-operatively, surrounding and herding schooling fish before preying upon them (Compagno, 1984).

Life history:

Males and females mature at approximately 2 m length. In South Africa, mating occurs between October and November, with pregnant females moving southwards each year during July and August to give birth in early spring. The gestation period lasts from 9-12 months and size at birth is relatively large at 1 m. Mature females generally produce litters of one or two pups once every two years. Grey nurse sharks are embryonic cannibal livebearers, with the largest and most advanced embryo in each horn of the uterus eating less advanced eggs and embryos (Gilmore et al., 1983).

Threats:

In the past, grey nurse sharks were fished commercially throughout their range, although they are of variable economic importance regionally (Compagno, 1984). Although now protected in many areas, it is susceptible to bycatch from commercial fishing and beach shark protective meshing activities (Smith and Pollard, in press).

Conservation/management:

Smith and Pollard (in press) made the following recommendations regarding the conservation of the species: 1) the species should be totally protected within its range; 2) live sharks captured as bycatch should be tagged and released; 3) information on shark behaviour and ecology should be recorded by SCUBA divers; 4) further taxonomic research should be undertaken to determine the status of populations of the species throughout its range; 5) the effectiveness of Marine Protected Areas at breeding and nursery sites should be investigated; 6) the impact of SCUBA divers on shark behaviour should be investigated and a code of conduct developed.

References:

Compagno, L.J.V. 1984. FAO species catalogue, Vol. 4, Sharks of the world. An annotated and illustrated catalogue of shark species known to date. FAO Fisheries Synopsis 125, 1-250.

Dudley, S.F.J., and Cliff, G. 1993. Some effects of shark nets in the Natal nearshore environment. Env. Biol. Fish. 36, 243-55.

Gilmore, R.G.D., Dodrill, J.W., and Linley, P.A. 1983. Reproduction and embryonic sand tiger shark, Odontaspis taurus (Rafinesque). U.S. Fish. Bull. 81, 201-25.

Pollard, D.A., Lincoln-Smith, M.P., and Smith, A. 1996. The biology and conservation status of the grey nurse shark (Carcharias taurus, Rafinesque 1810) in New South Wales, Australia. Aq. Conserv. 6, 1-20.

Smith, A.K., and Pollard, D.A. in press. Threatened fishes of the world: Carcharias taurus (Rafinesque, 1810). Env. Biol. Fish.

Further information:

Dr Nick Otway,
NSW Fisheries Port Stephens Research Centre,
Taylors Beach Rd, Taylors Beach, NSW 2316.
Ph (02) 49821232