Otter hunting was finally banned in Britain in 1978, and that, combined with the banning of organochlorine pesticides and a general improvement in river quality, has led to a resurgence in otter numbers in England and Wales.
Hence the surprise and concern over the recent findings, which emerged after researchers from the Cardiff University Otter Project and the Chemicals, Health and Environment Monitoring Trust, studied 755 otters found dead between 1992 and 2009 across England. and Wales.
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They looked to see if residuals organochlorine pollutants might be responsible, but found no evidence they were to blame, suggesting that "other factors (potentially including newer pollutants that are not measured here) are driving the observed changes"
The initial suspects, say the scientists are Endochrine Disrupting Chemicals (EDCs), which as their name suggests are known to affect the hormonal and reproductive systems in mammals.
Such chemicals are found in a wide range of products, and if they are responsible for affecting the otters, said Dr Elisabeth Chadwick of Cardiff University Otter project, "it might be things like drugs that we're taking and they flush through our sewage systems and end up in the rivers."