Scientists have found major gaps in what is known about the movements of migratory sharks and rays around Australia, leaving conservation managers with little information about where many threatened species go when they cross national borders.
Shortfin mako (Isurus oxyrinchus) is a genuinely oceanic, highly mobile shark
Sharks can travel extraordinary distances. One white shark tracked from South Africa reached Western Australia before returning home—a journey of almost 11,000km. School sharks have crossed some 3,000km of the Tasman Sea, between Australia and New Zealand.
Yet, for most migratory shark and ray species found in Australian waters, scientists still know surprisingly little about where they actually go.
A new study has examined three decades of satellite and acoustic tracking, tagging and mark-recapture research to establish the first baseline of international movements by sharks and rays around Australia.
Most species remain a mystery
Researchers identified 29 species in Australian waters listed under the UN Convention on Migratory Species (CMS). Of these, 18 had no published movement data, while only 12 had any movement information available. Nearly two-thirds of the endangered or critically endangered species examined had been covered by only one study—or none at all.
Only five species—white sharks, whale sharks, shortfin makos, blue sharks and school sharks—had published evidence demonstrating movements between Australian waters and other national jurisdictions.
Those movements connected Australia with countries including Indonesia, Papua New Guinea, New Zealand, New Caledonia and Micronesia. White and whale sharks were among the comparatively well-studied species.
The absence of data does not mean the remaining species stay within Australian waters. Rather, researchers do not yet have enough published evidence to establish where they travel or which international boundaries they cross.
Protection ends at the border
That matters because a shark protected in one country can encounter very different conditions once it leaves national waters.
Whale sharks, for example, receive substantial protection in Australia, where interactions with them are regulated. Their migrations can nevertheless take them into Indonesian, Papua New Guinean and Micronesian waters and into the high seas, exposing them to different fisheries, shipping traffic and conservation regimes.
The researchers argue that effective conservation therefore requires countries to know which populations they share—and to cooperate in protecting them throughout their migrations.
Tracking these animals is neither simple nor cheap. Tags can fail or detach, animals may disappear beyond receiver networks, and maintaining long-term monitoring across remote ocean regions can be difficult.
But without better movement data, international agreements meant to protect migratory sharks and rays are being implemented with substantial knowledge gaps.
