Nursing Grey Nurse Shark populations back to health

By Natalie Kikken

19 November 2018

3 minute read

Gnarly gnashes: in South Africa the grey nurse shark is known as “ragged tooth” for the rows of pointy teeth. Photo credit: David Harasti

Gnarly gnashes: in South Africa the grey nurse shark is known as “ragged tooth” for the rows of pointy teeth. Photo credit: David Harasti

Globally, the Grey Nurse Shark is listed as vulnerable. 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.

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 this innovative genetic approach, we estimate that the eastern Grey Nurse Shark adult abundance is about 1,700 to 2,200 individuals, a slight increase in population size since 2010. These results indicate that protective measures are working.

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

A SCUBA diver approaches a Grey Nurse Shark to obtain a tissue sample. Photo credit: David Harasti.

A SCUBA diver approaches a Grey Nurse Shark to obtain a tissue sample. Photo credit: David Harasti.

This new population result aims to assist with the ongoing and effective management of Grey Nurse Sharks. We are partnering with government and universities to do this including the National Environmental Science Program Marine Biodiversity Hub, Office of the Threatened Species Commissioner, Department of Environment and Energy, New South Wales Department of Primary Industries and University of Queensland.