Otters' reproductive organs may be affected by chemicals in our waterways, according to scientists.
Experts studying the reproductive health of the mammals in England and Wales were concerned to find a decrease in the weight of otters' penis bones.
Other health problems in males included an increase in undescended testicles and cysts on sperm-carrying tubes.
Experts suggest that, based on previous research, the changes could be linked to hormone-disrupting chemicals.
The study, funded by the Environment Agency, was co-authored by the Chemicals, Health and Environment (CHEM) Trust and the Cardiff University Otter Project, and features on BBC One series Countryfile.
"We were surprised to see the reduction in the baculum weight," said co-author Dr Elizabeth Chadwick, project manager at the Cardiff University Otter Project, referring to the bone found in males' penises.
"[It's] certainly something that needs further investigation."
During the 1970s, England's otter population plummeted, the decline attributed to high levels of Persistent Organic Pollutants (POPs) in rivers. However contaminants such as organochlorine pesticides have mostly since been banned, and otter populations have steadily increased.
Scientists examined hundreds of dead otters in a post-mortem laboratory to test if existing traces of POPs in rivers were still having an effect on the animals' health.
But they found no association between these old chemicals and the animals' penis bones becoming lighter over time.
Instead the report speculates that some modern contaminants could be causing the abnormalities. Previous studies have linked Endocrine Disrupting Chemicals (EDCs) to changes in animals' reproductive organs, such as male penis size.
"It's from that that we're drawing a possible inference that some of these Endocrine Disrupting Chemicals may be the reason that baculum weight has changed," Dr Chadwick explained.
EDCs are a range of synthetic and natural chemicals that can affect animals' hormone systems, according to the World Health Organisation (WHO).
Dr Chadwick said: "With many of these contaminants, there can be all sorts of different sources... so it might be things like drugs that we're taking and they flush through our sewerage systems and end up in the rivers."
She added that dust from industrial production travelling into the atmosphere could also carry contaminants that end up in rivers as rainfall, even travelling long distances between countries.
"Fantastic indicator species"The current report adds to some scientists' concern about the feminisation of male animals, according to CHEM Trust.
For example, previous studies in the UK have linked now-restricted POPs with male fish producing eggs in their testes and female egg-yolk protein.
As top predators in the UK's river systems, otters are a "fantastic indicator species", explained Countryfile director Anna Jones, who has been following urban otters in Bristol for the programme.
"The health of an otter can reveal a lot about the health of the environment they live in, and the health of the fish," she said.
Continue reading the main storyPENIS BONE FACTS
- Humans do not have bones in their penises but many other primates do, including gorillas and chimpanzees
- All male rodents have bones in their penises
- The fossilised baculum of an extinct walrus was discovered in 2007 and measured 1.2m
Dr Chadwick added that health problems found in otters "could be a warning for all mammals really, which include us humans".
"People are very quick to say: otters are in our rivers. That must mean rivers are perfect, they're so clean, everything's fine again? but it's not really that simple," said Ms Jones.
"It's not just a clear-cut, rosy picture that all is well for otters just because they're back. There are still challenges."
In order to prove the link, scientists will now need to measure the EDCs present in the otters and their habitat.
Countryfile airs on BBC One on Sunday 24 February at 1900 GMT.
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Source: http://www.bbc.co.uk/nature/21534742
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