Nicholas M. Otway1
The Australian grey nurse shark, Carcharias taurus, is synonymous with the sand tiger and spotted ragged-tooth sharks of USA/Europe and South Africa, respectively. The species is one of the commonest and most sought-after elasmobranchs exhibited in public aquaria worldwide. Despite its popularity, the disjunct wild populations are extremely susceptible to fishing-related exploitation, require decades for recovery and are globally "Vulnerable" on the IUCN Red List of Threatened Species.1,2 In Australia, grey nurse sharks occur in two genetically isolated populations along the east and west coasts of the continent with the east-coast population extending from Yeppoon in Queensland (23.13°S, 150.75°E) to Eden in New South Wales (37.07°S, 149.90°E).2-4 A century of targeted fishing activities off eastern Australia has greatly reduced the total grey nurse shark population (1365–2049 individuals) and consequently the local population is listed as "Critically Endangered" by the State and Commonwealth governments, and the IUCN.2 In east coast waters, grey nurse sharks aggregate at known sites with rocky reefs and have been recorded to depths of 232 m whilst undertaking extensive, punctuated migratory movements of at least 3500 km linked to their reproductive cycle.4 They are piscivorous, have low fecundity with two pups born biennially after cannibalistic (adelophagous) and oviphagous phases, exhibit late onset of reproduction (males: 6–7 yr, females: 10–12 yr), and have a longevity of about 35 years.4,5 The Grey Nurse Shark National Recovery Plan describes a multifaceted research program that assists the direction of recovery initiatives. Research over the past decade has focussed on the species' demography, localized and migratory movements, and reproductive biology, and has also enabled the collection of clinically important data. Regular sampling has permitted observations of healthy, free-living sharks together with individuals with fishing-relating injuries including hook retention (n > 50), tail-roping (n = 15), gaffing (n = 6), and fining (n = 4). Smaller numbers of wild individuals have been observed with kyphoscoliosis (n = 10), presumptive vitiligo (n = 3) and permanent upper jaw protrusion (n = 2). Furthermore, 150 grey nurse sharks, comprising neonates to adults of both sexes, accidentally captured in the shark meshing program and/or by commercial/recreational fishers have been subjected to necropsy yielding additional information. With this in mind, this paper summarizes the current situation off eastern Australia by describing the shark's life history, human-induced threats, conservation initiatives and veterinary knowledge-base. Finally, similar research on a sympatric wobbegong shark has provided the basis for a "proof of concept" project examining the feasibility of using an artificial uterus for ex situ embryonic development to enhance the reproductive output of grey nurse sharks.6-10 The results of this experimental work are briefly summarized and its implications for future conservation initiatives discussed.
I thank numerous fishers, scuba divers, Mr. Trevor Long and Sea World staff, Mr. Rob Townsend, staff from public aquaria, and the technical and compliance staff of Fisheries NSW for logistical support. Discussions with Drs. David Blyde (Sea World), Sam Gilchrist (Sydney Aquarium), Karrie Rose (Taronga Wildlife Hospital), Rob Jones (Melbourne Aquarium), Megan Ellis (Gladstone Ports Corporation) and Geremy Cliff (Kwa-Zulu Natal Sharks Board) contributed to this research in various ways. The study was done under scientific research permit (P01/0059A), animal research authorities (99/14 and 03/04) and with grant funds from the Commonwealth and New South Wales governments, the Sea World Research and Rescue Foundation, and Coastal Catchment Management Authorities.
1. Otway NM, Bradshaw CJA, Harcourt RG. Estimating the rate of quasi-extinction of the Australian grey nurse shark (Carcharias taurus) population using deterministic age- and stage-classified models. Biol Conserv. 2004;119:341–350.
2. Cavanagh RD, Kyne PM, Fowler SL, Musick JA, Bennett MB, eds. 2003. The Conservation Status of Australasian Chondrichthyans. Report of the IUCN Shark Specialist Group Australia and Oceania Regional Red List Workshop. Queensland, Australia, 7–9 March 2003; University of Queensland, Brisbane, Australia; 2003: 170 p.
3. Stow A, Zenger K, Briscoe D, Gillings M, Peddemors V, Otway N, Harcourt R. Isolation and genetic diversity of endangered grey nurse shark (Carcharias taurus) populations. Biol Lett. 2006;2:308–311.
4. Otway NM, Ellis MT. Pop-up archival satellite tagging of Carcharias taurus: movements and depth/temperature-related use of south-east Australian waters. Mar Freshwat Res. 2011;62:607–620.
5. Gilmore RG, Dodrill JW, Linley PA. Reproduction and embryonic development of the sand tiger shark, Odontaspis taurus (Rafinesque). Fish Bull. 1983;81:201–225.
6. Huveneers C, Walker TI, Otway NM, Harcourt RG. Reproductive synchrony of three sympatric species of wobbegong shark (genus Orectolobus) in New South Wales, Australia: reproductive parameter estimates for population modelling. Mar Freshwat Res. 2007;58:765–777.
7. Huveneers C, Otway NM, Harcourt RG, Ellis MT. Quantification of the maternal-embryonal nutritional relationship of elasmobranchs: case study of wobbegong sharks (genus Orectolobus). J Fish Biol. 2011;78:1375–1389.
8. Otway NM, Ellis MT, Starr R. Serum biochemical reference values of wild dwarf ornate wobbegong sharks, Orectolobus ornatus. Vet Clin Path. 2011;40:361–367.
9. Ellis MT, Otway NM. Uterine fluid composition of the dwarf ornate wobbegong shark (Orectolobus ornatus) during gestation. Mar Freshwat Res. 2011;62:567–582.
10. Otway NM, Ellis MT. Construction and test of an artificial uterus for ex situ development of shark embryos. Zoo Biol. 2012;31:197–205.