Dales Otters doing well
Photo: Environment Agency

OTTER numbers are steadily increasing across the region - including along three Yorkshire Dales rivers - but more are falling victim to traffic on the region's roads.

That's the conclusion of a new Europe-wide study which has found Otter populations are healthy and continue to expand across England and Wales - thanks to decreasing levels of certain pesticides in the environment.

While sightings have increased in recent years in the region, there has also been a gradual increase in the number of Otters killed on the roads. Over the last four years there has been an increase from 2 deaths in 10 years to 7 deaths in the last 4 years in South, East and West Yorkshire.

The Environment Agency Science Department carried out a series of studies into the deaths of almost 1000 Otters between 1992 and 2003, which looked at the overall health of Otters, factors affecting their survival, the levels of chemicals in their bodies and the impacts these have on otter populations.

Experts believe that numbers have begun to expand again following the decline in numbers across England and Wales between the 1950s and 1980s. The results reinforce the view that one factor behind this recovery may be decreasing levels of Organochlorine chemicals (OCs), such as the insecticides Dieldrin and Aldrin, in the environment.

Dieldrin was progressively withdrawn from use from 1962 and banned by 1989. It was a very potent insecticide, used extensively by farmers, as it remained active for a long time after they applied it. It can take up to 25 years for 95% of Dieldrin in soil to disappear.

Otters are one of our biggest conservation success stories

Eleanor Andison - Environment Agency

North Yorkshire's Otter sightings continue to increase on three Dales Rivers - the Swale, the Ure, and the Wharfe - although they too are falling victim to the regions roads. Most road deaths occur in the Derwent catchment where the population is thought to be the largest in the county.

Over the last five years, West Yorkshire has seen a distinct increase in positive sightings along the River Aire from the upper reaches to where it meets the River Ouse.

Environment Agency biodiversity officer Eleanor Andison said: "Its great news that the Otter numbers are increasing on our rivers, but the road death increases indicate we need to be vigilant about where and how we locate new developments to ensure that the population growth of Otters on our rivers continue to thrive safely.

"Otters are one of our biggest conservation success stories, and a lot of work has been done to encourage the species back to our waterways."