These Shrimp Leave the Safety of Water and Walk on Land. But Why?

The shrimp cease swimming at nightfall and collect close to the river’s edge. After sundown, they start to climb out of the water. Then they march. All night time lengthy, the inch-long crustaceans parade alongside the rocks.

The parading shrimp of northeastern Thailand have impressed legends, dances and even a statue. (Locals additionally eat them.) During the wet season, between late August and early October, vacationers crowd the riverbanks with flashlights to look at the shrimp stroll.

Watcharapong Hongjamrassilp first discovered about the parading shrimp, and the hundred thousand or extra vacationers who come annually to see them, about 20 years in the past. When he began learning biology, he returned to the matter. “I realized that we know nothing about this,” he stated: What species are they? Why and how do they depart the security of the water to stroll upstream on dry land? Where are they going?

Mr. Hongjamrassilp, a graduate pupil at the University of California, Los Angeles, determined to reply these questions himself. His findings appeared this month in the Journal of Zoology.

Working with wildlife heart workers members, Mr. Hongjamrassilp staked out 9 websites alongside a river in Thailand’s Ubon Ratchathani province. They discovered shrimp parading at two of the websites — a stretch of rapids, and a low dam.

The movies they recorded revealed that the shrimp paraded from sunset to sunup. They traveled as much as 65 toes upstream. Some particular person shrimp stayed out of the water for 10 minutes or extra.

“I was so surprised,” Mr. Hongjamrassilp stated, “because I never thought that a shrimp can walk that long.” Staying in the river’s splash zone could assist them hold their gills moist, to allow them to hold taking in oxygen. He additionally noticed that the shells of the shrimp appear to entice somewhat water round their gills, like a reverse dive helmet.

DNA evaluation from captured shrimp confirmed that almost all belonged to the species Macrobrachium dienbienphuense, half of a genus of shrimp that reside principally or totally in freshwater. Many Macrobrachium species spend half of their lives migrating upstream to their most well-liked habitats.

Most parading shrimp that Mr. Hongjamrassilp captured had been younger. Observations and lab experiments confirmed that these shrimp most likely depart the water when the movement turns into too robust for them. Larger grownup shrimp can deal with a stronger present with out washing away, so that they’re much less more likely to depart the water.

Walking on land is harmful for the little shrimp, even below cowl of darkness. Predators together with frogs, snakes and massive spiders lurk close by, Mr. Hongjamrassilp says. “Literally, they wait to eat them along the river.”

And the shrimp can survive on land for less than so lengthy. If the parading crustaceans lose their means, they could dry out and die earlier than they get again to the river. A number of occasions, Mr. Hongjamrassilp got here throughout teams of misplaced shrimp useless on the rocks, their once-translucent our bodies baked pink.

Yet most navigate upstream efficiently, and scientists have noticed different freshwater shrimp round the world performing comparable feats, scaling dams and even climbing waterfalls.

Leaving the water when the swimming will get robust could have helped these animals unfold to new habitats over their evolutionary historical past, Mr. Hongjamrassilp stated. Today, the quantity of parading shrimp in Thailand appears to be declining. He thinks vacationer exercise could also be an element, and studying extra about the shrimp would possibly assist shield them.

The examine’s authors made “some really excellent observations,” stated Alan Covich, an ecologist at the University of Georgia who was not concerned in the analysis. But understanding why the Ubon Ratchathani shrimp transfer upstream, and how far they journey, would require extra analysis, he stated.

“The most surprising thing to me was that it attracted so many tourists,” Dr. Covich stated. He doesn’t know of another instance of individuals gathering to understand a crustacean in fairly the identical means.

“We have crayfish festivals, we have all kinds of things,” Dr. Covich stated, “but generally it’s people eating them, not watching them move.”