Shark and ray migrations span entire ocean basins, yet nearly two-thirds of threatened species lack published tracking data across international borders, according to a 30-year review of marine movement studies. Researchers found that while iconic journeys—such as a white shark swimming nearly 11,000 kilometres from South Africa to Western Australia and back—capture public attention, critical management gaps leave highly mobile marine life vulnerable to vessel strikes and accidental catches once they leave nationally protected waters.
Tracking Gaps Leave Migratory Sharks Vulnerable
Scientists analyzed three decades of research utilizing satellite tracking, acoustic tags, and catch-mark-recapture methods. The review identified 29 shark and ray species known to cross international boundaries. However, only five species—white sharks, whale sharks, shortfin makos, blue sharks, and school sharks—had documented movements connecting Australian waters with other countries, including Indonesia, New Zealand, Papua New Guinea, Micronesia, and New Caledonia.
Worryingly, the study revealed that 18 species had no published information whatsoever regarding their movement patterns. Nearly two-thirds of the threatened species examined lacked baseline tracking data, making it impossible for conservationists to determine whether these populations travel across vulnerable high-seas corridors or remain within localized estuaries.
Why Sharks and Rays Cross International Borders
Sharks and rays migrate for fundamental biological needs, including foraging, giving birth, and seeking out specific water temperatures or salinity levels. Body size and maturity heavily influence these journeys, with older and larger animals consistently traveling greater distances. Ocean depth, currents, and habitat availability further shape their migration paths.
Whale sharks offer a clear example of these transnational movements. While tourists and researchers regularly gather to watch whale sharks aggregate seasonally at Ningaloo Reef in Western Australia—where the species enjoys strict state and federal protection—tracking data shows these animals routinely swim thousands of kilometres beyond Australian jurisdiction into Indonesian waters, where national protections no longer apply.
Australia’s Role in Cross-Border Marine Conservation
To meet international commitments under the United Nations Convention on the Conservation of Migratory Species of Wild Animals, the study recommends three primary conservation strategies for Australia:
- Shared expertise: Australia should bolster marine science ties with Indonesia, Timor-Leste, Papua New Guinea, and the wider Pacific, sharing expensive tracking technology to assist remote monitoring efforts.
- Targeted research: Researchers must prioritize tracking the 18 data-deficient species. Additionally, Australia and New Zealand should coordinate research around the Lord Howe Rise in the Tasman Sea, a region currently evaluated for protection under the High Seas Biodiversity Treaty.
- Strategic tracking: Scientists should combine movement data with oceanographic variables like currents and temperature to predict migration corridors, optimizing where governments deploy acoustic receivers and satellite tags.
The authors argue that Australia must align its domestic species classifications with scientific evidence. While the UN convention lists hammerhead sharks as migratory, Australian management frameworks do not, a discrepancy researchers attribute to pressure from commercial and recreational fishers.
School sharks swim to New Zealand from Australia
School sharks in southern Australia can cover up to 3,000 kilometres while crossing the Tasman Sea to reach New Zealand waters.
Frequently Asked Questions About Shark Migrations
Why do sharks migrate across international waters?
Sharks travel thousands of kilometres to find food, give birth, and seek out favorable water temperatures and salinity levels.
How many shark and ray species are known to cross borders?
The 30-year review identified 29 shark and ray species known to migrate across international borders, though many more lack sufficient research.
What threats do whale sharks face outside Australian waters?
Once whale sharks leave strictly regulated Australian zones, they face risks such as accidental capture by fisheries and vessel strikes from cargo ships.
Which species have the biggest gaps in tracking research?
Researchers found 18 species had no published movement data at all, with nearly two-thirds of all threatened species examined lacking any movement studies.
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