The otter population in the Netherlands has gone up to 185, according to researchers at Wageningen University who have been monitoring efforts to re-introduce the otter to Dutch rivers since 2002.

However, 49 were run over on the roads last year, and several others died in fish traps, the researchers said.

‘The increase in road deaths is proportional to the increase in the population but shows that solving traffic issues must have the highest priority,’ they said in a new report.

By reducing the number of otters killed on the roads, the population will spread more easily into other parts of the country, the researchers say. The otter population is currently centred on Friesland and Overijssel.

Ministers pledged last 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.