Australia’s Critically Endangered eastern gray nurse shark (Carcharias taurus) is showing early signs of recovery thanks to dedicated marine conservation efforts. Recent research combining genetic analysis, biopsy sampling, and advanced population modeling reveals that the shark population along the east coast is slowly increasing.
Shark Population Growth: A Positive Trend
Scientists from CSIRO and the NSW Department of Primary Industries and Regional Development (NSW DPIRD) collected DNA samples from over 300 gray nurse sharks across New South Wales. By analyzing family relationships through DNA profiling, they estimated the population trends between 2017 and 2023.
The findings show a 5% annual increase in adult sharks, growing from around 1,096 individuals in 2017 to 1,420 in 2023. While the breeding population remains small, this steady growth is an encouraging sign that conservation strategies are making an impact.
Why Recovery Is Challenging
According to Dr. David Harasti (NSW DPIRD), gray nurse sharks face significant reproductive challenges:
- They breed once every two years.
- Each breeding cycle produces only two pups after a year-long gestation.
- They are slow-growing and long-lived.
- The eastern population suffers from low genetic diversity, making them vulnerable to environmental changes and human activity.
These biological limitations make recovery fragile, emphasizing the importance of ongoing conservation.
Advanced Conservation Science: Close-Kin Mark-Recapture
The research team used a CSIRO-developed technique called “close-kin mark-recapture.” This method combines genetic sequencing with statistical modeling to estimate adult shark numbers.
- In smaller populations, more close-kin (siblings or half-siblings) are found in samples.
- In larger populations, fewer close-kin pairs are detected.
By analyzing 376 tissue samples, scientists could accurately estimate population size and age using a newly developed age-length growth model specific to Australian gray nurse sharks.
Protecting Shark Habitats in Australia
Many critical aggregation sites in New South Wales and Queensland—used for breeding, pupping, and feeding—are now under protection. Conservation actions include:
- Reducing fishing threats in shark hotspots.
- Collecting tissue samples via the NSW SMART drumline program and scuba surveys.
- Implementing the National Recovery Plan for the Gray Nurse Shark.
Divers trained in safe biopsy techniques collected samples using specialized spear tips, ensuring minimal impact on the animals.
A Priority in Australia’s Threatened Species Action Plan
The gray nurse shark is listed as one of 110 priority species in the Australian Government’s Threatened Species Action Plan (2022–2032).
Dr. Fiona Fraser, Threatened Species Commissioner, highlighted the significance of these findings:
“This early sign of recovery is great news for this long-lived species. But recovery takes time, consistent monitoring, and ongoing protection efforts. The eastern population remains Critically Endangered, so our work must continue.”
The Future of Eastern Gray Nurse Sharks
While challenges remain, this slow but steady population increase signals that conservation actions are working. Protecting critical habitats, advancing genetic monitoring, and reducing human threats are key to securing a sustainable future for this iconic Australian shark.