Why ‘walking’ sharks are at greater risk of extinction than we thought

Hemiscyllium halmahera), one of nine species of walking shark

The Halmahera bamboo shark (Hemiscyllium halmahera), one of nine species of walking shark known to inhabit the waters around Australia and the island of New Guinea. (© Conservation International/photo by Mark Erdmann)

Editor’s note: Conservation International (CI) Vice President of Asia Pacific Marine Programs Mark Erdmann is a pioneer in the study of walking sharks, having discovered three of the nine total species over the past 10 years. New research reveals that the species’ ranges are significantly smaller than previously thought, which could put their survival more in doubt. 

My fascination with walking sharks began a decade ago, when I first encountered one of these strikingly colored animals on a night dive while conducting a CI-led marine Rapid Assessment Program survey of Cendrawasih Bay in Indonesia’s Bird’s Head Seascape.

Also known as bamboo or epaulette sharks, these curious little bottom sharks are only active at night, when they emerge from hiding places to “walk” about the reef in search of food. Though seemingly a peculiar mode of locomotion for a shark, they are adapted for poking their heads under corals and into nooks and crannies in search of crabs, shrimps, small fishes and various mollusks; they can even use this skill to crawl above water between isolated tide pools.

As it turned out, that first walking shark I ran into was a species new to science (subsequently named Hemiscyllium galei), and video of its unique walking behavior was broadcast around the world. The sharks’ newfound celebrity status was the driving impetus for the Blue Auction, where CI and partners auctioned the naming rights to 11 fish species discovered in the Bird’s Head. The walking shark was the star of that event, fetching $500,000 that was immediately used to launch the Kalabia, a shrimp trawler turned marine conservation education vessel in the Raja Ampat archipelago. The brightly painted ship now travels from village to village delivering a customized conservation education curriculum to primary school children — often giving them their first look at the marine life in their own backyards.

Kalabia is the local name for the walking shark, which is the much-loved mascot of the program. Indeed, over the years we’ve found that the walking shark is a great conservation ambassador for its “toothier” cousins, allowing us to start important discussions with communities and government about shark and ray conservation, and leading to the declaration of Southeast Asia’s first shark and ray sanctuary in Raja Ampat in 2012!

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New findings

In the seven years following that first discovery in Cendrawasih Bay, we’ve uncovered three more new species of walking shark, bringing the total to nine species in the genus Hemiscyllium. Our studies on these enigmatic creatures over the past decade have revealed a host of unusual aspects to their ecology and distribution that we’ve just published in a major review of the genus along with colleagues from the Indonesian Institute of Sciences, University of Queensland and Australia’s CSIRO.

Previous studies on walking sharks have indicated relatively wide-ranging and overlapping distributions for the initially known five species, most being reported from either the coast of the northern half of Australia and/or the circumference of the island of New Guinea. However, in reality we have found that each of the nine species has highly restricted, non-overlapping ranges that form a ring around northern Australia, New Guinea and the satellite Indonesian islands of Raja Ampat, Aru and Halmahera.

Map of the Australia-New Guinea region showing distributions of the nine species of Hemiscyllium walking shark

Map of the Australia-New Guinea region showing distributions of the nine species of Hemiscyllium walking shark. (Map courtesy of Gerry Allen)

The reason for these relatively tiny geographic distributions of each walking shark species appears to be related to their unusual form of reproduction.

Most coral reef fishes “broadcast spawn” in the water column, with the resulting fertilized eggs (and tiny larvae which hatch within a few days’ time) then drifting in the currents for days or weeks. This method provides a great mode of dispersal which can result in distributions spanning entire ocean basins.

By comparison, the walking sharks are oviparous, laying specialized egg cases which hatch into juveniles that are essentially miniature adults — with very little chance of long-distance movements. This extremely limited dispersal potential has resulted in highly-restricted ranges for each of the species.

Hemiscyllium galei, the first walking shark species discovered by Mark Erdmann

Hemiscyllium galei, the first walking shark species discovered by Mark Erdmann. (© Gerry Allen)

Our new understanding suggests a more complicated conservation road ahead for walking sharks, as isolated species with smaller ranges are often more vulnerable to localized threats such as pollution or overfishing. The discovery may lead to increased calls for specific protections for walking sharks, as did a similar finding on giraffes earlier this year.

Fortunately, many of the walking sharks are already at least partly protected through inclusion of significant parts of their ranges in marine protected areas; the Bird’s Head Seascape marine protected area network, for instance, covers habitat occupied by three of the walking shark species, with one of these (Hemiscyllium freycineti) completely protected by the Raja Ampat Shark and Ray Sanctuary. Nonetheless, several species currently have no specific protections, so we hope the results of this study will spur further conservation efforts on behalf of these most endearing elasmobranchs — not only for their benefit, but for the wider ocean and all who depend on it.

Mark Erdmann is a marine scientist and the vice president of CI’s Asia Pacific marine programs.

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