Ocean-Going Crocs Are Mean, Green Surfing Machines
Found and feared from India to China to Australia, the estuarine crocodile (Crocodylus porosus) is a renowned predator with an amazing geographical range of more than 3,861 square miles. But as the largest living reptile, this machine is not exactly built for long distance travel.
So, how exactly did this one species come to dominate such a large chunk of the world?
According to a new study in the Journal of Animal Ecology, the secret is surfing. When ocean currents are moving in a favorable direction, the crocodiles hop on for an express ride.
Generally estuarine crocodiles are territorial animals that predominantly live in rivers, mangrove swamps and brackish water estuaries.
Reports of crocodile sightings far off shore surprised scientists.
An Australian science team set off to uncover whether saltwater crocodiles regularly travel long distances or not, as well as how these cumbersome creatures managed such a marathon feat.
The researchers acoustically tagged 27 crocodiles from the Kennedy River in Australia. The team inserted small transmitters in the crocs and placed receptors along the river’s coastline.
Whenever a crocodile came within a quarter mile of the receptor, the movement was recorded. After a year of monitoring the reptiles along the river, the scientists discovered that they habitually travel from their home area to the river mouth, a distance upwards of 31 miles away.
Whenever the gigantic beasts traveled more than 6 miles a day, they surfed. The crocs always started their journey immediately after the tides turned, securing them a solid 6 to 8 hours of speedy travel.
Every time the tides changed to an unfavorable direction, the crocodiles took a rest stop. They retreated to the nearby shore for a period of hours to days.
As a short term solution to unfavorable tides, the animals would dive to the bottom of the river, where they can spend up to an hour lounging on the river floor, rather than moving back to land.
In a previous study, the researchers outfitted three crocodiles with satellite transmitters. This allowed the team to follow the “salties” — the Australian nickname for the predators — beyond the river mouth and into the ocean.
One of the crocodiles journeyed down the west Coast of Cape York Peninsula. The trip coincided with changes in seasonal currents. Over the course of 25 days, the salty moved a whooping 367 miles!
Similarly, two of its brethren also covered hundreds of miles in a few weeks.
Achieving these arduous journeys is made possible by the crocodiles’ acute sense of direction.
Estuarine crocodiles depend on an internal magnetic compass to reach their desired location, similar to birds and turtles.
Additionally, these reptiles can easily endure long trips and remain physically strong despite a lack of eating and drinking due to amazing internal engineering.
Aerial image croc Crystal Ck 1 Aug 2007Saltwater crocodiles only drink fresh water and rely on ambushing prey, a strategy difficult to maintain during sustained ocean travel.
But the creatures developed the ability to maintain nutrients from ingested food long after feeding. As a result, they can last up to 4 months in the ocean without regular eating or drinking.
Understanding the fierce crocodile’s ability to cross long stretches of water is important for safety reasons. Estuarine crocodiles are dangerous, powerful animals. Adult males regularly grow up to 23 feet long and weigh around 1,000 pounds.
These babies are called man-eaters for a reason.
They travel well past their home area on a routine basis, making them a serious threat to humans. Further monitoring of crocodiles and of current direction and strength could diminish human-crocodile interactions and consequently, trips to the ER.
Images: Australia Zoo, Geoff Keir