Hemiscyllium dudgeonae, n. sp., male paratype, UPNG E0534, 610 mm TL, Nubwageta, Milne Bay Province, Papua New Guinea at 2 m.

M.V. Erdmann

Imagine wading through a shallow tropical reef, small fish darting between coral heads. Crabs scuttle across the seafloor as water ripples around your feet. Then something unusual catches your eye. A shark, no longer than your arm, appears to be walking across the reef on its fins. It sounds like a fantasy, right? A shark, walking? Yet walking sharks are very real and among the most remarkable sharks on Earth. Unlike the fast-swimming predators that often dominate popular imagination, these small bottom-dwelling sharks spend much of their time moving across reefs, seagrass beds and mangroves using their muscular fins. They are masters of their local neighborhoods, rarely venturing far from home. Yet despite their fame among shark enthusiasts, scientists are still uncovering just how many species exist and where they live. Now, a new study from eastern Papua New Guinea has added another individual to that story. After extensive field surveys and genetic analyses, researchers have identified a tenth species of walking shark, Hemiscyllium dudgeonae, while also revealing a surprisingly complex patchwork of distributions among several other species.

Walking sharks belong to the genus Hemiscyllium, a group found nowhere else in the world except Australia and the island of New Guinea. They typically grow to around 28 to 32 inches (70 to 80 centimeters) long and inhabit shallow coastal habitats, often less than 32 feet (ten meters) deep. Their limited mobility is one of their defining characteristics, and individual sharks may spend their entire lives within an area measuring only a few hundred square meters. Unlike many marine animals whose larvae or young can drift long distances on ocean currents, walking sharks lay egg cases directly on the seafloor, so their offspring hatch close to where their parents lived. Over millions of years, this lifestyle can isolate populations from one another, especially in regions filled with islands, deep channels and shifting coastlines.

Few places fit that description better than Papua New Guinea. The country sits within the Coral Triangle, one of the most biodiverse marine regions on Earth. Over millions of years, tectonic plate collisions, volcanic activity and dramatic sea-level fluctuations have continually reshaped the landscape. Islands emerged and disappeared, shallow reefs became separated by deep water. Populations that were once connected became isolated. And for species with limited dispersal abilities, these geological changes can act like giant evolutionary experiments. Thus, to investigate how walking sharks are distributed across eastern Papua New Guinea, researchers conducted 70 surveys between 2023 and 2025 searching coral reefs, mangroves and seagrass habitats by diving, snorkeling and even walking across reefs at low tide. Captured sharks were photographed, measured and sampled for genetic analysis before being released.

What they found was unexpected. The team documented expanded ranges for two previously known species, Hemiscyllium michaeli and Hemiscyllium hallstromi; yet despite occurring in the same broader region, the two species never appeared together at any surveyed location. Instead, their ranges formed what researchers describe as a mosaic of separate, non-overlapping distributions. Even more intriguing was a distinctive population found in the Amphlett Islands — these sharks possessed a unique pattern of brown freckles, white spots and bold markings unlike those of any known walking shark species and genetic analyses confirmed that they represented a separate evolutionary lineage! The result was the description of Hemiscyllium dudgeonae, or Dudgeon’s epaulette shark, named in honor of shark geneticist Dr. Christine Dudgeon, whose work has helped unravel the evolutionary history of walking sharks.

This raises fascinating questions about how biodiversity develops. The known range of H. dudgeonae currently covers only about 7,000 square kilometers, making it the most geographically restricted walking shark known. Nearby islands separated by relatively modest stretches of water appear to host entirely different species. In fact, in some cases, populations just a few hundred kilometers apart show clear genetic differences despite looking nearly identical. At first glance, this may seem surprising. Afterall, the ocean often feels like an open, connected environment where animals can move freely from one place to another. Yet for walking sharks, the sea can be every bit as fragmented as a mountain range or desert is for land animals. Deep-water channels, stretches of unsuitable habitat and even strong currents can act as barriers that these small, reef-associated sharks rarely cross. Over time, populations become isolated from one another, each following its own evolutionary trajectory. We often think of speciation as a process that requires vast distances or dramatic geographic separations. Here, however, entire evolutionary lineages may be emerging across archipelagos separated by distances that seem relatively minor on a map.

Because of their tiny rangs and limited ability to disperse, walking sharks are especially vulnerable; habitat degradation from coastal development, pollution and coral reef decline can affect entire populations because unlike wide-ranging sharks that can move elsewhere, walking sharks often have nowhere to go. And the newly described H. dudgeonae may face the greatest risk of all. Researchers observed signs of fishing pressure within its already restricted range, and some localities where walking sharks were reportedly once common no longer appear to support populations. Based on current evidence, the species may already qualify as Endangered.

While an exciting discovery, it does make one wonder how much biodiversity remains unrecognized in other marine organisms with similarly restricted movements. Walking sharks are relatively charismatic and well-studied compared to many reef fishes and invertebrates. If scientists are still uncovering previously unknown species and distinct populations within this group, it suggests that the true scale of marine diversity in regions like Papua New Guinea may be far greater than current estimates indicate.