Some young sharks pull an elaborate trick upon other ocean-going creatures.

They fake the way they look, making themselves appear similar to deadly sea snakes.

It is the first time any shark has been found to mimic something else.

Many fish are masters of disguise. Many will mimic dead leaves, plants, coral or other less palatable fish to avoid the attention of predators. But one group of fish, the elasmobranchs or cartilaginous fish that include sharks, rays, and skates, were not thought to mimic other species.

Now Australian scientists Dr William White at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Hobart, Tasmania, Australia and Dr Christine Dudgeon at the University of Queensland, in Brisbane, Australia think that young zebra or leopard sharks (Stegostoma fasciatum) mimic the appearance of sea snakes.

These sharks have two names for good reason. When this shark hatches from its egg, housed in a strange looking pouch sometimes called a mermaid's purse, the baby sharks are boldly striped. This is their zebra phase.

Gradually over time, starting at about one month of age, their stripes start to break up, leaving behind an ornate, mottled, spotty appearance completed about the time of their first birthday. Thus begins their leopard phase, one that lasts for the rest of their lives.

But this distinctive transformation from stripes to spots has long baffled marine scientists.

“This species of shark undergoes probably the most dramatic change in body patterning of any shark species,” says Dudgeon, surpassing the bamboo shark that changes from stripes to a uniform grey with age.

To investigate why, Dr White and Dr Dudgeon are working with sea snake doctoral researchers Vinay Udyawer and Blanche D'Anastasi at James Cook University, staff at the Reef HQ aquarium in Townsville, and Oceans IQ based in Cairns, Australia.

They believe the answer may lie in both the way the sharks look and move.

Not only are the young sharks striped like sea snakes, they have a slender, elongate appearance and unusually long tail. “Their tail is almost the same as the body length,” Dudgeon says. The only shark with a longer tail is the thresher shark (Alopias spp.), so named because it uses its tail to herd and whip fish for dinner, “but we don't think that leopard sharks do that at all,” says Dudgeon.

Zebra sharks are found in coastal tropical and subtropical waters of the Indo-West Pacific. Relatively rare, they spend their early days in shallow waters, often near seagrass or mangroves.

Pretending to be a sea snake could be a powerful way to deter predators lurking in shallow waters, where it can be hard to escape.

Sea snakes are very toxic to eat, due to their powerful venom, and most predators avoid them. Experiments in the 1970s confirmed that nurse sharks and grouper fish refused to eat sea snakes, even if sliced or skinned, and tiger sharks are among the few animals thought to take them in the wild. But a tiger shark, says Dudgeon, “eats just about anything.”

Not only do the young sharks resemble the snakes, they appear to swim like them too.

“When they swim it's very undulating,” explains Dudgeon, and their movements look more snake-like than shark-like.

They also swim near the surface, as do sea snakes, which “need to spend a lot of time on the surface because they have to breathe,” explains Dudgeon.

This behavior is unusual. Zebra sharks are carpet sharks, belonging to the Order Orectolobiformes. Almost all are bottom-dwellers, avoiding the surface. As zebra sharks age, becoming spotted, they also tend to swim in deeper waters, preferring deeper sandy areas near coral or rocky reefs.

“It definitely seems possible that juvenile zebra sharks mimic some species of sea snakes,” agrees Dr Sami Merilaita at the Åbo Akademi University in Turku, Finland, an expert on animal colouration and patterns.

But the idea needs to be tested, he adds.

Ideally, it should shown that predators of young zebra sharks are less likely to attack banded sea snakes than other prey, making the case for why the sharks would mimic the snakes.

Dudgeon agrees that testing their idea is necessary. As to how they will do it, she admits that, “we haven’t quite figured all that out yet.”