Globally, the grey nurse shark is listed as vulnerable, due to its susceptibility to fishing pressure, historical overfishing, and low reproductive rates.
Two populations exist in Australia : an eastern population (critically endangered) and a western population (vulnerable).
Our scientists are playing a key role to derive a population estimate for the eastern population to assist ongoing management and recovery of the species, and determine if protective measures are working.
In good news, our recent findings show the grey nurse shark eastern population has been slowly increasing.
DNA the secret to population estimates
Grey nurse sharks are known to form large groups at specific sites along the east coast of Australia. It is from these groups that we have taken DNA tissue samples and applied a technique called close-kin mark-recapture to identify the parents and genetic relationships between the sampled individuals to help us estimate how many there are.
A large number of related individuals' means there are fewer adults, translating to a smaller population. Conversely, fewer related individuals' means there are more adults, and a larger population.
Using an innovative and refined genetic approach, we estimate that the eastern grey nurse shark adult abundance is about 1,420 individuals, an increase of 5 per cent in population size per annum since 2018. These results indicate that protective measures are working.
This work also looked at juvenile survival rates. Initial results show juveniles up to the age of four have an 85 per cent chance of survival.
Close-kin mark-recapture has also been used to estimate white shark numbers and southern bluefin tuna too.
Some interesting facts about grey nurse sharks Grey nurse sharks can reach a length of 3.2m and like to cruise around sandy bottoms and rocky caves, and close to reefs and islands, to a depth of at least 230m.Grey nurse sharks have rows of ragged, haphazard teeth that are razor sharp. However, even though they are well-equipped with an abundance of teeth, they aren't a threat to you if you are in the ocean swimming, diving or surfing as they are not aggressive in nature and will only attack if provoked.They aren't fussy on diet with a preference for a smorgasbord of fish, smaller sharks, octopus, rays, squids and crustaceans like lobsters.Grey nurse sharks become most active at night. They are slow moving but strong swimmers. It is thought that male sharks may live for up to 30 years and female sharks for 40 years.Male sharks reach sexual maturity between 6-7 years of age, and females at 9-10 years. The gestational period is 9-12 months and the dominant embryo can eat the other pups/eggs when in the womb, resulting in a maximum of two pups per birth.It is thought that grey nurse sharks breed only once every two years. This means they are slow to recover from population loss. Data drive to understand age and survival rates
Along with population estimates, we're looking to expand this research by using genetic data to estimate the age of the sampled sharks. This will in turn provide more robust data on abundance.
From our current research, age estimates of the grey nurse sharks sampled range from 1 to 19.
We are also obtaining accurate length measurements. This will increase certainty in age estimates. We are also looking at how best to determine survival rates using acoustic tags and telemetry. This helps us better understand shark movements too.
This new population result aims to continue to build our understanding of the eastern populations and assist with the ongoing and effective management of grey nurse sharks.
This research was undertaken with the NSW Department of Primary Industries and Regional Development, Department of Energy, Environment and Climate Change and WA Department of Primary Industries and Regional Development, supported through funding from the Australian Government's National Environmental Science Program (NESP) Marine and Coastal Hub.
This article was originally published in November 2018, and was updated in September 2025.
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