Otter populations have declined in Wales, according to a survey led by Cardiff University and Natural Resources Wales.
The first Welsh National Survey for Otters in more than a decade found fewer signs of the elusive mammals.
Cardiff University worked with NRW to organise the sixth national survey with the help of volunteer surveyors.
Dr Elizabeth Chadwick, who led the research for the Cardiff University Otter Project, said: "In the first survey since 2010 we noted a decline in signs of otters.
"Declines were not universal, with the worst affected regions in the Conwy, Loughor, and Teifi. Smaller declines were evident on most other catchments, while only a few, such as the Severn, seemed to have stable populations."
Using the same methods as previous surveys to ensure results were comparable, a total of 1,073 sites were visited, with signs of otters found at 756 sites, showing a substantive decline in their populations for the first time since the 1970s, from around 90% occupancy in 2010 to 70% in 2015 to 2018.
The reasons for this decline are unclear and further work is planned by NRW and the University to investigate the likely reasons.
Liz Halliwell, team leader for terrestrial ecosystems and species at NRW 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.
"In Wales as in much of the UK, the otter is a largely nocturnal animal and is rarely observed in the wild, but it is possible to detect its presence by searching for its distinctive droppings (spraints), and footprints.
"The clear message coming out of this report is that we cannot be complacent about the ongoing recovery of the otter in the UK."
You can find out more about the Cardiff University Otter Project here.
