Invasive rodents called nutria could threaten the stability of aging levees and earthen dams in California鈥檚 Central valley region if the state fails to control their population.
鈥淲e are at a critical point in which we still have the opportunity to completely eradicate these animals from waterways in California,鈥� says at the California Department of Fish and Wildlife.
Nutria (Myocastor coypus), also known as coypu, were first introduced to the US from their native South America in 1899, and were farmed for their fur. But when the fur market collapsed in the 1940s, thousands escaped or were released into the wild. The rodents 鈥� which can grow up to 9 kilograms and have distinctive orange front teeth 鈥� spread to 20 states, most recently California.
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鈥淲e鈥檙e at the epicentre,鈥� says at the US Fish and Wildlife Service (USFWS). She works at a wildlife refuge south of Sacramento where nutria were first detected in the state in 2017. She says it is unclear how the nutria first got to California.
More than 3300 nutria have since been removed from the Central valley in an effort by state and federal agencies to prevent damage that could come with an established population. Barr says it is difficult to say exactly how large a California nutria population could get if left unchecked, but points to Louisiana, where more than 6 million nutria have been removed from the state since 2002. Takahashi says a small starting population of the rapid-breeding rodents could grow exponentially.
An established population could severely degrade wetland ecosystems and harm crops. The resulting erosion, as well as the rodents鈥� extensive, multi-level burrows, could also harm water infrastructure.
鈥淣utria can weaken levees to the point where even minor stresses or environmental changes can trigger a breach,鈥� says at Mississippi State University. He says the threat from nutria adds to other longstanding issues with the state鈥檚 ageing system of levees and earthen dams, particularly in the Sacramento-San Joaquin river delta, where century-old levees serve to protect farmland from encroaching seawater.
The state鈥檚 levees have been battered both by intense rains from atmospheric rivers and drought, as well as weakened by land subsidence caused by groundwater pumping. Meltwater from California鈥檚 record snowpack is also expected to strain water infrastructure later this year.
鈥淲hile nutria may not be the only contributing factor to levee failures, they can act as the final straw that breaks the camel鈥檚 back,鈥� says Vahedifard.
A spokesperson for the California Department of Water Resources said inspectors have noticed burrows and related erosion at levees in the state, but don鈥檛 usually identify what type of animal made a burrow.
US Congressman Josh Harder recently raised the growing concerns about nutria at a federal on 29 March in which he questioned the director of the USFWS about apparent funding cuts to nutria eradication.
鈥淲hen I came to Congress, I didn鈥檛 think I would be leading the charge to eradicate swamp rats,鈥� he said, speaking next to a taxidermic nutria he had brought as a prop. 鈥淏ut this is a real issue, and we have to act quickly before they fully invade our waterways.鈥�
According to Harder鈥檚 office, the current draft USFWS budget reduces funding for nutria eradication by 45 per cent. A USFWS spokesperson commented that this did not reflect a policy decision to reduce funding, and said the agency is 鈥渟till optimistic that nutria eradication is possible in the state鈥�.
