Invasive snails threaten Salt River
Without intervention, species could overrun food chain
Israel Garcia paddled his kayak above underwater growth near cattail reeds along the banks of the Salt River. He scanned the waters, just below the surface, hunting for snails that didn’t belong. ❚ He was looking for apple snails, an invasive species that has spread along the Salt River and through connected waterways since its arrival around 2011. The snails easily adapt to new environments and seem to thrive in heat and drought. Once established, they are almost impossible to eradicate. They have no natural predators in Arizona and even eat other snails’ eggs. They threaten ecosystems and agriculture across the world, and host a parasite that causes meningitis.
Left unchecked, apple snails could overrun the food chain on the lower Salt River, leaving native fish and wildlife with little to eat.
So biologists like Garcia are hunting down the snails in an attempt to slow their spread.
Garcia pulled several apple snails from the Salt River backwaters, placing them on his kayak’s bow to for observation. He’s an aquatic invasive species specialist for the Arizona Game and Fish Department. And he embarked on the river with other biologists and volunteers to capture apple snails and drown their offspring before they hatch.
These South American snails were introduced to Arizona though the pet trade, said Jeff Sorensen, another biologist the department known as “the snail guy,” as he will tell you.
“Somebody’s unwanted aquarium pets were illegally introduced into the wild,” he said. “And now they become everybody’s problem.”
In calm backwaters and river banks on the Salt River apple snails climb above the water to lay bright pink egg clusters every couple of weeks. One female lays up to 15,000 eggs a year.
Garcia swiped his paddle through cattail reeds, knocking the pink clusters off the reeds and leaving the eggs to drown. The sides of his kayak were smeared with pink egg gel by the time he finished.
State and federal biologists are calling on the public to help them stop the spread of apple snails by doing the same on the Salt River.
Snail crews organized by the Arizona Game and Fish Department captured 642 snails from the Salt River and likely drowned 1.6 million eggs last week, Sorensen said.
He doesn’t know how many apple snails have invaded the Salt River, but it’s so many that eradication isn’t yet a realistic goal. At this point he hopes to chip away at their numbers so native pond snails can maintain a niche of the ecosystem to survive in.
The native snails make up a significant portion of the ecosystem’s food supply, which apple snails could eliminate if they displace the natives, Sorensen said. That’s because nothing will eat apple snails.
Sorensen hopes predators evolve to eat apple snails one day, but for now, crayfish will eat each other over the invasive snails.
Apple snails are among other highly adaptable invasive species in Arizona, Sorensen said, which may benefit from a hotter future with more frequent and intense droughts that climate change models predict.
Their numbers along the Salt River have increased in the past year. While Sorensen can’t pin it on one single factor, they’ve likely benefited from Arizona’s current drought, he said.
“With the drought, as long as there’s some kind of water they’ll do really well,” Garcia said. “Like much of the invasives they outcompete the native species.”
Apple snails could possibly take over a smaller habitat if the river loses enough water, Sorensen said. But he doesn’t know what the tipping point would be.
These snails would be a top species in stagnant or low-flowing rivers, with more warm, silky, shallow water, he said. “If we have periods where there is a lot less water flowing down that river … they are going to do very well.”
While invasive species and climate change threaten Arizona’s native snails, they have been on this planet long before humans and they’ll likely be here long after, Sorensen said. They have already survived several mass extinction events.
Species of apple snails have invaded countries around the world, but climate models show they have the potential to infest even more, like India and Australia, according to Columbia University’s Introduced Species Summary Project.
Apple snails invaded Mexico by way of the lower Colorado River in Yuma, according to apple snail researchers.
As far as Sorensen knows, the apple snails in the Colorado River are distinct from those in the Salt River, but he has yet to conduct an apple snail survey there.
The Global Invasive Species Database ranks the apple snail species in the Colorado River among the world’s 100 worst invasive species.
The California Department of Fish and Wildlife warns apple snails could threaten rice crops in the state’s Central Valley. The snails have already eaten rice in countries around the world, including China, the Philippines and Spain.
On the Salt River, apple snails have expanded their territory. Since a fisherman reported them to the Arizona Game and Fish Department in 2011, they’ve spread downstream and have infested connected waterways. They already glide along Tempe Town Lake, Sorensen said. And he’ll assess an infestation at the Tres Rios Wetlands in the coming months.
Sorensen encourages paddlers to knock down the apple snail eggs as they float the Salt River.
Fewer eggs will hatch as more people do it, he said. But wash your hands if you handle the snails.
Local kayaker Bea Valdez recently reached her paddle into a stand of cattails from her kayak, whacking the pink egg clusters into the water. She lives near the Salt River and paddles downstream about every two weeks.
She had noticed the eggs, but didn’t know they were invasive until about two months ago when she researched apple snails after her daughter found several in the water.
Since then she has been knocking the eggs into the water. She hopes it will help preserve the Salt River for her grandchildren and future generations.
“I wish everyone else would do the same,” she said.