A significant decline in otter numbers in Wales is a “warning” over the state of the UK’s rivers, researchers have said.
Otter numbers have dropped 20 percentage points since 2010, according to a survey of more than 1,000 sites in the first Welsh national survey of the animals in more than a decade.
Once widespread in Britain, populations of otters were almost wiped out by the Sixties, a phenomenon blamed on organochlorine pesticides, as well as habitat destruction.
Since such pesticides were banned and the animals given protected status, their numbers have bounced back, with numbers in Wales reaching 90 per cent occupancy in the last survey in 2010.
However, this declined to 70 per cent during the latest survey work, researchers at Cardiff University and Natural Resources Wales found.
The reason for the decline is unclear, but could be related to the pollutants in the river ecosystem.
‘Forever chemicals’ present in otters
The survey came after researchers at the same university found that so-called toxic “forever chemicals” were present in otters across England and Wales.
This included a group of synthetic substances known as PFASs, which are found in many household items including food packaging, non-stick cookware and waterproof clothing.
The state of the UK’s rivers has come under intense scrutiny in recent months, with a report from the Commons environmental audit committee saying that England’s rivers contain a “cocktail” of sewage and chemicals.
Liz Halliwell, the team leader for terrestrial ecosystems and species at Natural Resources Wales, said: “Monitoring otter population status is important with respect to conservation of this much-loved mammal. As well as this, as top predator of our freshwaters, the otter can be an important biological indicator of the health of our rivers and wetlands.”
“The clear message coming out of this report is that we cannot be complacent about the ongoing recovery of the otter in the UK.”
She told the BBC: “We’re not back to situation we saw in the 70s but it is a warning to us that something may be going wrong.”
Researchers will now examine possible causes behind the decline, while the Environment Agency and Natural England have agreed to fund a national survey of otters.