The science behind the mysterious shrimp parade in Thailand

Research is beginning to unlock the secrets of a strange natural phenomenon in which thousands of freshwater crustaceans walk on land. 

Every year, during the rainy season, the north-east of Thailand hosts a special parade.

From late August to early October, thousands of tourists flock to the banks of the Lamdom River to watch the nightly procession, but this parade does not feature the intricately carved wax figures of the Ubon Ratchathani Candle Festival or the explosions of the Bun Bang Fai Rocket Festival.

It's more like a parade of shrimp.

For decades, locals have known that these shrimp emerge from the water and parade along the rocky shores.

There are statues, stories and even whole dances dedicated to crustaceans.

Fish biologist Watcharapong Hongjamrassilp heard about parading shrimp as a child in Bangkok, but as his research progressed, he began to wonder if scientists had really studied this captivating natural phenomenon.

"I realised that we didn't know anything about it," Hongjamrassilp, now a graduate student at the University of California, Los Angeles, tells Elizabeth Preston of the New York Times.

There was almost nothing in the scientific literature about the type of shrimp or why they left the water to go upstream.

As a scientist, Hongjamrassilp was motivated to get to the bottom of what was going on with these shrimp, but his connection to Thailand and its people also brought him back.

"I wanted to do a project that could help people in Thailand and at the same time help the environment," he told Jake Buehler of National Geographic.

Hongjamrassilp and his colleagues spent two seasons observing and documenting hundreds of thousands of freshwater shrimp emerging from the Lamdom River in Thailand to walk on land.

Now Hongjamrassilp is the lead author of a new paper published last month in the Journal of Zoology describing the phenomenon.

According to National Geographic, researchers believe that these shrimp make their perilous journey on land, where they risk becoming food for frogs, snakes and even spiders, to escape the river's strongest currents.

According to the Times, some of the shrimp travelled nearly 19 metres up river and spent more than 10 minutes out of the water.

"I was so surprised," Hongjamrassilp tells The Times. "I never thought a shrimp could walk for so long."

To study what caused the tiny shrimp to emerge from the water, the researchers brought the crustaceans into the laboratory.

After two years of developing the experiment, the team was finally able to get the shrimp out of the water, according to National Geographic.

It turned out that increasing the current velocity and using water directly from the river were essential to induce this unique behaviour in a laboratory setting.

The researchers also found that darkness and cooler temperatures were also important factors for shrimp to move to higher ground.

Finally, genetic analysis of the parading shrimp revealed them to be Macrobrachium dienbienphuense, according to The Times.

What remains a mystery is why exactly shrimp are willing to risk everything to go upstream.

Peter Novak, a freshwater ecologist with the Western Australian Department of Biodiversity, Conservation and Attractions who was not involved in the study, told National Geographic that the findings "raise interesting questions about why these animals are moving upstream if they don't have to be downstream in the first place".

In an interview with the Times, Alan Covich, an ecologist at the University of Georgia who was not involved in the study, says he is very surprised at the number of tourists the shrimp parade attracts.

"We have crayfish festivals, we have all sorts of things," he says, "but usually it's people eating them, not people watching them walk around.

Video : Parade of shrimps (Macrobrachium dienbienphuense)

Source: smithsonianmag.com