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A coypu. ABC
On the hunt for the coypu, the 'rat-nutria' that threatens Spanish rivers
Nature

On the hunt for the coypu, the 'rat-otter' that is posing a threat to rivers in Spain

The rodent is classified as one of the hundred most harmful invasive species in existence and it eats the equivalent of 25 per cent of its own body weight daily

Isabel Miranda

Madrid

Friday, 26 July 2024

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In 25 years as a Guardia Civil Seprona (nature and environment protection) officer, Martín Moreno had never come across a coypu, and even less so on the loose in Orihuela (Alicante). It makes no sense; it is a rodent from South America with prominent orange incisors and a long hairless tail. But after four days of searching following a tip-off from a member of the public, there they were.

Seven beautiful specimens, some weighing almost ten kilos, hiding in drainage pipes, eating native vegetation and colonising an irrigation canal in the Vega Baja. Weeks have passed since the discovery, but the officers are keeping a watchful eye on the area. "On social media networks people say that they have seen one or two.... We don't know if it's a hoax, but we keep an eye out in case one of them has wandered off," he said.

There shouldn't be a single one left in the southeast peninsular because the coypu (Myocastor coypus) is classified as one of the hundred most harmful invasive species in existence. Popularly known as the 'rat-otter', about 60 centimetres long and weighing six kilos, it moves along rivers. The problem comes with its voracity. It eats the equivalent of 25 per cent of its own body weight daily, threatening plants with local extinction. It also affects nesting birds - by destroying their habitat - and damages fish spawning grounds.

"We have had to catch up on genetics and learn about the damage they cause and what they eat," Moreno said. These rodents also make tunnels, change the water flow and destabilise riverbanks. In Orihuela they believe they have probably managed to slow down their spread. Luckily, they did not reach the Segura river. "Here we are on tenterhooks, everything is in balance. If another species arrives, it will finish us," the Seprona officer said.

They have not been so lucky in other parts of Spain. The coypu is established as an invasive species in Catalonia, Navarre and the Basque Country, after it spread from France - where it was used in fur farms. In France "there are a lot, and they don't control them there. They think it's too difficult", explained Belinda Gallardo, an expert in invasive species at the Pyrenean institute of ecology (IPE-CSIC).

Officers capture coypu in Catalonia.

This rodent "is not impossible to eradicate", Gallardo added, but it requires significant investment. "And if you have a country next door, like France, which has tens of thousands, you can control it, but it is frustrating. They are going to keep coming in from the neighbouring country."

Shock plan

In Catalonia, about 20 years ago, the coypu was eradicated from the Aran Valley, but in 2010, specimens were detected again in Catalan territory from France. Since then, it has grown exponentially and now occupies a third of Gerona. It is a species capable of breeding between two and three times a year, with litters of four or five offspring, although that can reach up to eight.

"They reach frightening densities," said Jordi Ruiz, head of invasive species at the department of climate action of the ministry of the environment of Catalonia. While it is usual to find one otter per kilometre, in the case of coypus, the figure rises to between 40 and 60 specimens. For this reason, the damage to crops, orchards and the natural environment in the counties of Gerona has been unbearable in recent years.

Last year, the Catalan government decided to design a 'shock plan' against the rodent. It commissioned the public company Forestal Catalana to create a specific unit, made up of five people, to work 365 days a year against the species: they set traps, track the coypu and look for their "expansion front". They have become specialists in finding them through their droppings, their footprints and the wide corridors in the vegetation they leave in their wake.

"It is more difficult for us to find their areas of expansion," Ruiz said. There, the clues are more tenuous. When there is a sighting in new areas, the tracking and search device is activated. They are usually male, but the great danger is that they are females. "You can't go to sleep," he adds.

1,600 caught

Since the unit was set up, catches have increased eightfold in Catalonia. In 2022, some 200 coypus were caught, while in 2023 there were 1,600, a figure that will be similar this year. According to Ruiz, without this action plan, the expansion of the coypu to the rest of Spain is practically assured. "We saw that the areas occupied by the coypu were becoming saturated and, when this happens, the young specimens go to other neighbouring areas and expand. If we don't act here now, Catalonia would fill up first and then they would go to Aragon, Valencia, etc."

However, the specialist knows that eradicating the species is "very complicated". For now, they have stopped the colonisation of new areas and have reduced the population by 40 per cent, but they know they cannot let their guard down. "If we stop working for a year, we will quickly be back to where we were." The objective in the future, Ruiz pointed out, "will be to work less" to provide a maintenance service that is limited to the border with France.

In Orihuela, the theory of the Seprona officer is that the colony was released by a private individual who had kept the species illegally. Sometimes, as often happens with exotic turtles, officers prefer to 'turn a blind eye' and not sanction the individuals who chose to hand in the animals. Otherwise the danger is the offender releases the species into irrigation channels and creates a major ecological problem.

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