ReSharking the Ocean

During the warmer months, the waters off south-east Queensland and northern New South Wales become a significant aggregation site for leopard sharks (Stegostoma tigrinum). Notably, Manta Bommie near Minjerribah (North Stradbroke Island) and Nguthungulli (Julian Rocks) in the Cape Byron Marine Park host over 500 mature individuals annually, representing the largest known leopard shark population worldwide. While this species inhabits coastal waters across the western Pacific and Indian Oceans, overfishing has drastically reduced its numbers, leading to an Endangered global status on the IUCN Red List in 2015 and a Critically Endangered designation for the western population in 2024. 

This status starkly contrasts with the thriving populations observed in large public aquariums globally, where leopard sharks readily breed in captivity and  are known as the largest oviparous shark species, laying upwards of 80 eggs each year. This paradox between the precarious wild populations and successful captive breeding sparked the idea of a tertiary conservation program centred on ex situ breeding – a novel approach for shark conservation. 
 

International collaboration 

The concept of ex situ breeding materialised in 2019 during a workshop hosted by Georgia Aquarium in the US. The workshop brought together representatives from major public aquariums, Dr Mark Erdmann from Conservation International, and myself from The University of Queensland, contributing expertise on wild leopard shark populations. This collaboration led to the establishment of the StAR project (Stegostoma tigrinum Augmentation and Recovery). The initial proposed location for StAR was Raja Ampat in eastern Indonesia. This site was selected due to several key factors: (1) it falls within the species’ natural distribution; (2) the wild population had experienced a severe decline (fewer than 20 individuals observed in the preceding decade); and (3) the recent establishment of an extensive marine protected area network, including Southeast Asia's first shark and ray sanctuary, offered crucial protection for released animals. 

Furthermore, the project garnered significant support from local communities to the regional government of West Papua, with two local conservation foundations willing to construct and manage hatcheries. 

A high-level meeting with the Indonesian federal government in Jakarta addressed two primary concerns – first, the necessity of the intervention, questioning why the population couldn't recover naturally now that threats were presumably reduced and, second, the source of the animals. To address the first concern, we conducted a population viability analysis (PVA) in collaboration with the IUCN Conservation Strategy Planning Group. This analysis heavily relied on data from my PhD and postdoctoral research in eastern Australian waters, providing crucial insights into wild population demographics and ecology. The PVA modelling indicated that under a business-as-usual scenario, population recovery could take up to a century with a substantial risk of extinction. However, various augmentation scenarios projected the potential for recovery into a genetically diverse and self-sustaining population within a couple of decades. 

Genetics and husbandry 

The second concern revolved around the potential for genetic pollution. My PhD research had identified two distinct major populations globally, separated by the deep-water barrier of the Indonesian Throughflow Current, aligning with the Wallace Line biogeographic boundary. Leopard sharks exhibit clear genetic differentiation on either side of this feature, with Raja Ampat situated on the eastern side. Consequently, potential breeders from eastern populations, including those in Australian waters, were deemed genetically appropriate for the Raja Ampat project. 

With the Indonesian government's approval, the StAR project moved forward rapidly. An Indonesian program manager, Nesha Ichida, was appointed. Two hatcheries with sea pens were constructed: one at Kri Island in the Dampier Strait (associated with Raja Ampat Research and Conservation Centre) and another in southern Misool (Misool Foundation). Twelve young Indonesian aquarists, affectionately known as “shark nannies”, received training in leopard shark pup husbandry. To establish a genetically diverse breeding stock, 164 potential breeding animals from aquariums in the US, Australia and Asia were genotyped. 

Wild release 

In August 2022, the first leopard shark eggs were shipped to Raja Ampat from Sea Life Sydney Aquarium, and the first pup hatched six weeks later. To date, 90 eggs have been transported, resulting in the release of 22 pups to the wild. Local school groups have actively participated by collecting live food, primarily snails, to nourish the developing pups before their release. We are meticulously monitoring the pups' diet and growth. Each released pup is equipped with radio frequency identification and acoustic telemetry tags for post-release tracking. 

A citizen science initiative, an extension of the Spot the Leopard Shark program initiated in Thailand in 2013, has been launched to monitor both released pups and other wild leopard sharks in the region. Research in Australia has shown that adult leopard sharks possess unique and stable body patterns for up to 20 years, facilitating individual identification. 

However, juvenile leopard sharks undergo significant transformations from striped hatchlings to various spotted patterns in adulthood, and the point at which these patterns stabilise for reliable individual tracking remains unknown. 

Enter ReShark 

Our ongoing work with wild Australian populations aims to address critical knowledge gaps, including diet and reproductive cycles, such as mating and egg-laying sites. In November 2024, we conducted an ambitious expedition off Minjerriba (North Stradbroke Island) (GASSE: Great Aussie Stegostoma Semen Expedition) to collect sperm from wild male leopard sharks for artificial insemination, while on SCUBA. This endeavour combined our expertise in handling wild sharks with the specialised skills of veterinary colleagues from Hong Kong Ocean Park, who had developed techniques for
blood and semen collection underwater. We successfully sampled 17 males and artificially inseminated six female leopard sharks in aquariums across Australia and Singapore. The first potential artificially inseminated pups have recently hatched, and we will soon conduct genetic analysis to confirm the success of the artificial insemination. 

The success of the StAR project has spurred the development of an overarching program: ReShark. This initiative aims to expand ex situ conservation efforts to more locations (StAR Thailand has recently commenced) and encompass other threatened shark and ray species. Given that sharks and rays are the second-most threatened vertebrate group after amphibians, immediate conservation action is crucial. As a tertiary conservation project, StAR complements and reinforces effective primary and secondary conservation measures, while also inspiring them, such as the full protection of leopard sharks enacted in Thailand in 2024. The ReShark global coalition has rapidly grown to 105 partners across 19 countries in 2025, encompassing government agencies, NGOs, zoos and aquariums, academic institutions and businesses, signifying a unified global effort towards shark and ray conservation. 

Learn more about the program at reshark.org 

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