Zoologist Dr Paul Yoxon said chemicals in everyday products are accumulating in fish and shellfish on which the mammals feed, weakening their immune systems.
The zoologist, who runs the International Otter Survival Fund (IOSF) on Skye with his biologist wife Grace, said hormone-disrupting chemicals, commonly found in shampoos and plastics, are also believed to be behind shrinking genitals of the male otter, affecting reproduction rates.
Research has shown Scottish otters are living only about five or six years, compared to 15-16 years in Germany and the Czech Republic.
Dr Yoxon said: “The problem is that our otters are not living long enough to significantly expand the population further.
“If you consider that a female in Scotland does not become sexually mature until she is 18 months, and has on average two cubs – only one of whom will survive to adulthood – and she is with them for 13-14 months, she will only have two litters in her short lifetime.
‘‘That is much less than those on the Continent where they have cleaned up their industrial pollution much better. Because otters in Scotland are not living past 5-6 years on average, there is a serious problem. Toxicology tests have shown that they have accumulated high levels of cadmium and mercury in their bodies from the fish they eat.
‘‘Those fish mainly originate in the North Sea, which traditionally has had high levels of industrial pollution.”
There are about 7,000 otters in Scotland out of a UK-wide population of 10,000. The IOSF has rescued more than 180 otters. Dr Yoxon said otters now faced their “biggest crisis” since Scottish naturalist and writer Gavin Maxwell helped save the species with his seminal book Ring of Bright Water, which was made into a much-loved film, starring Virginia McKenna.
Dr Yoxon said that we don’t yet know the effects of new chemicals, or the cocktail effect of different ones in the environment.
‘‘Another group of chemicals have now appeared in the environment – polybrominated diphenyl ethers (PBDEs), which are used as flame retardants in carpets, car seats and furnishings. These also accumulate in the environment and become concentrated in fish taken by otters, and can cause problems with the immune system.’’
Another potential threat is from personal care products, industrial chemicals and pharmaceutical drugs, which can have a serious effect on breeding.
Dr Yoxon said: “They appear to be reducing the size of the male otter’s penis – by about five per cent over the last decade – which obviously affects reproduction as well.
“The disappearance of the otter in the UK in the 1950s and 1960s went largely unnoticed until, suddenly, everyone began to ask where all our otters had gone. ‘‘We cannot afford to make the same mistake again.”