What is thought to be the last of 12 otters released in Gelderland in 2002 has been run over by a car, local broadcaster Omroep Gelderland said on Wednesday.

The dead female was found last week on the highway between Duiven and Zevenaar, researcher Freek Niewold from the Niewold Wildlife Infocentre said.

Of the 12 otters released into the IJssel river near Doesburg in 2002, at least six have been run over and the others have never been seen again and may have drowned in traps, Niewold said.

The otter run over last week may have been forced onto the road because the wildlife tunnel under the motorway had been closed off to create a trap for muskrats, Niewold said. He wants this practice to be banned.

Cars

Ministers pledged earlier this year to take steps to improve the protection of the Netherlands tiny otter population after it emerged 31 were killed by cars in 2014.

The otter was officially declared extinct in the Netherlands in 1988. They were reintroduced from Lithuania and other eastern European countries between 2002 and 2008 in the north of the country and have since been spotted in the central belt.

Researchers at Wageningen University said last year the current population is around 140 but that there are signs of interbreeding and new blood is needed to freshen the genetic balance.

While the impact of inbreeding in otters remains unclear, in other animal populations it has led to a loss of fertility and resistance to disease.