Grey nurse shark (Photograph by C. Bansemer)
Scientific name: Carcharias taurus
Adult Size [1]: Generally range between 2.3-3.2 meters
Lifespan [2]: Male sharks are estimated to live for 30 years and female sharks for 40 years
Population size in Australia [3]: East coast population: 1146 -1662 individuals West coast population: Not available, but believed to be stable
Status [4]: East coast population: Critically endangered West coast population: Vulnerable Worldwide: Vulnerable
Discussed in this document: What is a grey nurse shark? Where do they live? What do they eat? Why are grey nurse sharks important? What are the key threats to their survival as a species? How long does this species take to mature? How does the research at Grey Nurse Shark Watch benefit this species? What is Australia doing to help the grey nurse shark? What can you do to help? References page
1 Written by GNS Watch Volunteer Project Officer Morgan Rubanow © GNS Watch, June 2016
What is a grey nurse shark?
Grey nurse shark with identifying features
The grey nurse shark (Carcharias taurus) is one of Australia's most endangered species. This shark is also known as the sand tiger shark or spotted ragged-tooth shark and are grey to grey-bronze in colouration. They have an off-white underbelly and brownish spots scattered on their bodies [5]. They are strong swimmers and are generally more active at night [6]. Despite their fierce appearance, these sharks are harmless. This being said, if you chase, touch or tease them they may defend themselves: they are wild animals and should be treated with respect. Every shark has lateral lines which run along the sides of their bodies (see below). These function as a sensory organ that help the shark detect vibrations, movements, and pressure changes in the water [7].
The lateral line is indicated by the red arrow of this female grey nurse shark (Photo by C. Bansemer)
Did you know… Sharks have an amazing ability to sense electrical pulses due to their ampullae of Lorenzini found along the shark’s face. The ampullae of Lorenzini help the shark detect electrical signals emmited by potential prey. (1b)
2 Written by GNS Watch Volunteer Project Officer Morgan Rubanow © GNS Watch, June 2016
Where do they live?
Grey nurse sharks can be found along the coastlines of many continents, including the east and west coast of Australia (see map below). This species can typically be seen in groups of up to 30 individuals and the sharks are thought to divide themselves based on age and sex. Groups of females also divide themselves between whether or not they are pregnant as well [8, 9]. Most of the time grey nurse sharks are found near the ocean floor around 15-25 m in depth. Reported sightings have also recorded grey nurse sharks in intertidal zones (less than 1 metre in depth) and near coral and rocky reefs down to depths of 191 meters [10]. Grey nurse sharks can also be found in the surf zone of sandy and rocky beaches, in shallow bays, and underwater caves. These sharks can swim thousands of kilometres [11], making it important to understand their seasonal movements and how these animals use different habitats in order to best protect this species.
Distribution map of grey nurse sharks indicated in dark blue (Last and Stevens 2009)
What do they eat?
The diet of grey nurse sharks has been determined by looking at the gut contents. Grey nurse sharks along the east coast of Australia have been found to eat bony fish, squid, and even other sharks. [12]
3 Written by GNS Watch Volunteer Project Officer Morgan Rubanow © GNS Watch, June 2016
Why are grey nurse sharks important?
Sharks are the top predators in many oceanic food chains and play a critical role in keeping their prey populations under control. This is called a ‘trophic cascade’ [13, 14]. Some sharks are also filter feeders (whale sharks) and smaller sharks can provide food for larger sharks, showing how these marine animals have varied roles within the ocean [15]. If we have too large of a decline in shark populations, including the grey nurse shark, our oceans will be greatly affected.
What are the key threats to their survival as a species?
Grey nurse sharks are believed to be in decline around the world [16]. Grey Nurse Shark Watch is currently focusing on the east coast subpopulation in Australia with hopes of expanding to the west coast population in the future. Historically, this species was hunted for its oil, flesh, skin and fins. Grey nurses were also killed by recreational spear and line fishers. They were also killed through shark control programs due to its fierce appearance and being mistaken for other shark species that were thought to pose a threat to humans [17].
List of current threats [18]: • Incidental capture by commercial and recreational fishing • Shark control activities such as culls, drumlines or shark nets • Illegal shark finning • Accidental or targeted killing by spear fishers
Did you know… There are different estimates for when this species may go extinct in Australia: • Worst-case: 13-16 years • Most Probable: 84-98 years • Best-case: 289-324 years (2b)
4 Written by GNS Watch Volunteer Project Officer Morgan Rubanow © GNS Watch, June 2016
How long do grey nurse sharks take to mature?
Grey nurse sharks, as well as most other shark species, take a long time to mature. Females mature in 9-10 years and males mature after about 6-7 years. Mature females have one or two pups per litter every two years, with some female sharks taking three years between litters [19]. Pups are born at 1 meter in length after a 9-12 month gestation period [20]. This species also has one of the lowest reproductive rates among elasmobranchs (cartilaginous fish). This means it will take a long time for populations to recover if there is a large decrease in population numbers [21].
Did you know... Mature females have two separate uterus. The largest embryo in each uterus will feed on the yolk sac within the uterus and then this embryo will eat all of the smaller embryos! Therefore, only two pups will be born. (3b)
How does the research at Grey Nurse Shark Watch benefit this species?
Grey nurse shark population numbers are constantly changing over time, therefore, long term monitoring programs are necessary to help researchers determine if the population sizes are stable, increasing, or decreasing. Such programs need to be at least 10 years long in order to establish trends and need to continue after the 10 years to properly monitor a species. Grey Nurse Shark Watch has established a long term monitoring program for the east coast population by using photographic identification of individual sharks. Each grey nurse shark has their own unique spot pattern on their sides that do not change over time [22]. This allows researchers to distinguish one shark from another without having to capture or tag sharks, which can be stressful for the animal. Since sharks can be identified and later re-identified by their spot patterns, other information can also be collected that tagging or genetic studies cannot provide. This includes information on interactions with fishing gear, survival, mating scars and pregnancy. Photographs are only limited by effort and access, for example Grey Nurse Shark Watch highly depends on photographs contributed by volunteers.
*If you have taken photographs of grey nurse sharks, please share them with us!*
5 Written by GNS Watch Volunteer Project Officer Morgan Rubanow © GNS Watch, June 2016
This is a female grey nurse shark with mating scars from a male during courtship. Mating scars would not be detected via genetic analyses since they are exterior scratches on the shark’s body. (Photograph by C. Bansemer)
Other research methods used to obtain information about sharks that are not used by Grey Nurse Shark Watch include external tagging (attaching a tag to a fin or other body part) or internal tags (a small device placed inside the animal). These methods are not ideal since they have limited lifespans, meaning the tags fall off or are no longer usable after a period of time. Internal tags are more commonly used, especially since external tags can lead to injuries or biofouling (attachment of organisms such as barnacles or algae to a surface, such as a tag) [23, 24]. Internal tagging can provide a large amount of information, however, battery life is currently limited to a maximum of 10 years. Ten years is not long enough for species such as many sharks that are slow to reproduce and live for a long time. Furthermore, internal tags cannot provide important visual information that photographs can, such as whether a female is pregnant or if an animal has sustained injuries due to fishing gear and survived. These are very important considerations for monitoring programs [25-26].
This is a male grey nurse shark due to the presence of claspers, which are used during reproduction. This male has been caught in fishing gear, which would not be known without a photograph. (Photograph by Peter Hitchens).
6 Written by GNS Watch Volunteer Project Officer Morgan Rubanow © GNS Watch, June 2016
What is Australia doing to help the grey nurse shark?
A recovery plan has been created by Federal government in Australia [27]. This plan aims to decrease the threats to this species (listed in ‘What are the key threats?’ section) and develop research programs to find out more information about this species. The more we know, the better we can protect them. The most recent management plan can be found here. Grey nurse sharks are protected from targeted fishing, meaning that any time a fisher catches a grey nurse it is considered bycatch (incidental). If the shark is found alive, it should be released. Interactions with grey nurse sharks must be reported to the relevant authorities [28] and if possible the deceased shark provided for necropsy. A necropsy can provide valuable information about the individual shark and the species as a whole.
What can you do to help?
The great thing is that anyone can help! First, it is important to be familiar with fishing regulations when you go fishing. If you are diving or snorkelling, keep a safe distance to avoid stressing the animal. You can also get involved in citizen science research, such as Grey Nurse Shark Watch. If you have any photographs of grey nurse sharks, please send them our way. Sometimes governments ask for the opinion of citizens on their policies- let your voice be heard when such opportunities arise. Lastly, there are a number of organisations that aim to gather important information and help to conserve sharks. Their ability to do so relies on donations from people like you who care about these creatures and want to protect them!
7 Written by GNS Watch Volunteer Project Officer Morgan Rubanow © GNS Watch, June 2016
Article References by Number 1 Cavanagh, R. (ed); Kyne, P. (ed); Fowler, S. (ed); Musick, J. (ed); Bennett, M, (ed). 2003. The Conservation Status of Australian Chondrichthyans: Report of the IUCN Shark Specialist Group Australia and Oceania Regional Red List Workshop. The University of Queensland, School of Biomedical Sciences, Brisbane, Australia. 2 Goldman, K. J., Branstetter, S., & Musick, J. A. 2006. A re-examination of the age and growth of sand tiger sharks, Carcharias taurus, in the western North Atlantic: the importance of ageing protocols and use of multiple back-calculation techniques. Developments in Environmental Biology of Fishes 25: 241–252. 3 Department of the Environment. 2016. Carcharias taurus (east coast population) in Species Profile and Threats Database, Department of the Environment, Canberra.
8 Written by GNS Watch Volunteer Project Officer Morgan Rubanow © GNS Watch, June 2016
22 Bansemer, C., and Bennett, M. 2008. Multi-year validation of photographic identification of grey nurse sharks, Carcharias taurus, and applications for non-invasive conservation research. Marine and Freshwater Research 59: 322-331. 23 Bansemer 2009 24 Bansemer and Bennett 2011 25 Bansemer and Bennett 2009 26 Bansemer and Bennett 2010 27 Department of the Environment. 2014. Recovery plan for the Grey Nurse Shark (Carcharias taurus). Australian Government.
References “Did you know” Inset Boxes 1b Department of the Environment. 2016. Carcharias taurus (east coast population) in Species Profile and Threats Database, Department of the Environment, Canberra.
9 Written by GNS Watch Volunteer Project Officer Morgan Rubanow © GNS Watch, June 2016