Invasion Of River Rats In California Prompts Declaration Of Emergency

For the first time in history, 20-pound river rats called nutria have been found west of Stockton, California, near a delta. Greg Gerstenberg, wildlife biologist for the California Department of Fish and Wildlife, says that if the river rats get into the delta, the population will become very difficult to manage. The rats are originally from South America but were released in California in the early 1900s with the intent of them being raised for the fur trade. The rodent is very destructive, however, and in the 1970s, California tried to eradicate them in order to bring an end to the damage they were doing to the environment.

The river rats can eat 25 percent of their weight in a day. They live near water and can burrow into the sides of levees and canals. Their burrows can be 50 to 70 or more feet long. They are now being sighted around the San Joaquin River. If the rodents begin targeting levees and canals, there is great concern that they will trigger erosion, causing a collapse of the structures followed by flooding. An emergency eradication program has begun in Merced County, California. CBS San Francisco Bay Area reports that Peter Tira with the California Department of Fish and Wildlife describes efforts to eradicate the rodent as very serious.

“Its an emergency response very similar to what we do in a wildfire or earthquake or flood. That just gives you a sense of the severity that we believe this is a threat to California.”

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Two factors that pose a challenge to the eradication are the rate at which the river rats reproduce and the difficulties that even a team of biologists have in distinguishing between them from other rodents like otters and beavers. WKYC3 reports that nutria can produce 13 offspring every 130 days. They can become pregnant 48 hours after giving birth. A single litter can include a dozen babies. Full-grown, the river rats are described as being about two-and-a-half feet long with a 12-inch tail, white whiskers, and webbed hind feet. A grid has been created for the search for nutria. Teams of biologists are searching each cell of that grid that covers 40 acres. As of May 1, 50 of the river rats had been trapped or reported dead.

Maryland was also invaded by river rats at one time. The problem became so severe that in 2001, President Bush granted the state $20 million dollars to assist in their eradication efforts.