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When it comes to large mammals living in the heart of UK cities, you might think the red fox is in a league of its own. But there's another top predator back in town: the Eurasian otter.
Discover facts about these mammals and their presence in urban areas including Sheffield, Birmingham and London.
Otters are often elusive, with large ranges and nocturnal behaviour making spotting them a rare and wonderful experience. But you can bank on the fact that there is an otter somewhere in a river near you if you live in Britain - a remarkable success story for a species driven to extinction in many parts of the country just decades ago.
Now that the tide is turning for otters, they are surfacing in some unexpected places, including large urban centres. But this isn't by chance: often the features that gave rise to some of Britain's industrial metropolises also make excellent habitats. And otters are settling into city living.
The Eurasian otter (Lutra lutra) is a large member of the weasel family that can reach nearly a metre in length and weigh up to 12 kilograms. It is the only wild otter species found in the UK. It is also known as the European otter and common otter.
Eurasian otters feed mainly on fish. They are well adapted to their riverine habitats, with webbed feet to help them swim and the ability to close their ears and nostrils underwater.
Eurasian otters will generally live anywhere that has a source of unpolluted fresh water with a sufficient food supply. This can include rivers, canals, lakes and wetland areas. They sometimes live along the coast, but they still require fresh water nearby.
Otters raise their young in underground dens known as holts, often with hidden underwater entrances on riverbanks well covered by vegetation. The cubs remain with their parents for just over a year before becoming independent.
Dr Jessica Wardlaw, Interim Citizen Science Manager at the Museum, explains that otters are generally shy creatures.
She says, 'You are more likely to see evidence of otters than otters themselves. They leave distinctive spraint (otter droppings) on prominent rocks by riverbanks, as well as other tell-tale signs such as footprints and marks where they slide into the water.'
Jessica has been lucky enough to observe otters at a river by her home in Dorset, using camera traps to record their behaviour.
It hasn't been plain sailing for otters in the UK in the last few decades. Populations suffered catastrophic declines in the 1950s and 1960s, a trend that was also seen across continental Europe.
The cause was the combined effects of water pollution, habitat destruction and persecution, including hunting. The situation was particularly serious in southern and central England, with otters vanishing from these areas completely, becoming locally extinct.
Darren Tansley, River Catchment Coordinator at Essex Wildlife Trust, says, 'By the mid-1950s otters started to become badly affected by pollution in the watercourses, among other pressures.
'This dire situation worsened through the 60s, with otters simply disappearing across tranches of lowland England, including here in East Anglia.'
Scotland, northern England and Wales also saw otter numbers crash, but populations clung on in isolated areas.
The 1980s were a turning point for otters. The Wildlife Countryside Act (1981) banned their persecution, efforts were made to improve the water quality of rivers and a programme of otter releases built numbers back up.
Darren says that the releases, while small, played their part in the recovery of otters in east England.
'Otters started to be released in East Anglia in 1983, and then in other parts of the country such as Dorset. These were very small numbers: perhaps 200 individuals UK-wide in the first ten years of the Otter Trust.
'As a result of the releases and natural recolonisation, UK otter populations recovered throughout the 1990s and we now have otters living in every county.'
As populations have steadily recovered, otters have been reported in more urban locations across Britain, from smaller cities such as Andover, Inverness and Exeter, to huge urban centres like Edinburgh, Manchester, Birmingham and London.
Darren says that large territories explain why otters are coming into UK cities as their numbers increase. A male otter needs a stretch of territory about 13 kilometres long, although it depends on the width of the waterway and the abundance of food available.
He explains, 'As otters have become more successful, they have naturally moved into urban habitats. These environments may not always be ideal, but any city or town with a river will have fish for otters to eat.
'They're being seen more frequently in Essex towns. Although most of their hunting behaviour happens between dusk and dawn, they can be seen foraging in the daytime and seem less worried about humans.
'In the last three years, people have regularly reported otters fishing and swimming in the River Colne right in Colchester town centre, especially at Castle Park - a popular public area with a heavily managed section of river.
'On the other side of town there are wilder places with more sightings near a large barrier that separates the fresh and salt water. You can stand on one bank and watch otters 30 feet [nine metres] away.'
Darren continues, 'There have been other sightings in urban Essex at Chelmsford city. Again, not a particularly great river for otters you might think - it's canalised with steep-sided artificial banks - and yet they are spotted swimming there frequently.'
Ken Hutchinson, Otter Co-ordinator for Dorset Mammal Group, estimates that around three quarters of otters in Dorset access a town or village as part of their territory.
He says, 'It appears more otters are moving into urban areas of Dorset to take advantage of benefits such as warmer temperatures and better-stocked rivers. This does depend on the level of human interference, but even this seems to be more widely tolerated by otters nowadays.'
It's not just in Essex and Dorset that wildlife groups are surveying otters in urban areas. Signs of the animals are being recorded elsewhere, including in central Sheffield.
Paul Richards, Ecological Monitoring Officer at Sheffield and Rotherham Wildlife Trust, recalls his astonishment at discovering that otters are thriving at heavily industrialised sites along the River Don.
He says, 'I worked on a project called Nature Counts in Sheffield in 2016. We were monitoring various species, but the otters really caught the imagination. No one had ever filmed otters in Sheffield before. Very few people even knew they were there. We managed to record over 60 clips of otters in the city centre. It was very special.'
Paul explains that the watercourses that otters call home were vital resources in the history of the city.
'The reason Sheffield is here is because its many waterways, rivers and trees for charcoal were the perfect environment for making steel. The industry built up along the rivers, which powered water wheels and acted as sewers to wash away pollutants.
'We know that salmon were abundant in the Don until the eighteenth century because apprentices working near the river had a clause in their contracts that stated they couldn't be fed salmon more than three times a week!
'But by 1760 there were 161 weirs along the Don. The weirs and pollutants prevented the movement of fish and killed them off. No fish, no otters.'
But the situation has improved, says Paul:
'Since the 1990s people have been creating fish passes around weirs to allow the movement of fish. There's now a nature reserve called Salmon Pastures right in the city centre, and in the last two years we've recorded salmon again in the heart of Sheffield.
'The presence of otters is a sign of a restored abundance of fish. The fact that there are now salmon, brown trout and grayling is a fantastic news story in itself. But more than that, the presence of this top predator proves the water is clean. It's testament to the work people have done over the years and it shows that the entire ecosystem is returning to something that's functioning.'
Surveying otters in any environment is a challenge but doing so in urban areas comes with a unique set of difficulties, as locations are often inaccessible. The Wildlife Trust teamed up with the University of Sheffield on the project.
Paul explains, 'It was a brilliant citizen science project. We had volunteers scouring the riverbanks and we recorded over 120 signs of otters - spraints, footprints, slide marks and half-eaten fish.'
'Dr Deborah Dawson at the University of Sheffield worked on DNA samples from the spraints to identify individuals and sex them,' continues Paul. 'From this research we knew we had at least three otters in our patch and possibly up to seven, with at least one male and one female.
'We put camera traps at strategic points and got regular footage of otters. It was brilliant to see.
'We were in one of the most urban areas you can imagine. There are steelworks, factories, trains going past, and yet we were getting footage of otters.'
More recently, signs of otters along the Birmingham canal network prompted the local Wildlife Trust to install motion sensor wildlife cameras. They were rewarded by a sighting of the elusive mammal near Birmingham's Mailbox shopping centre in November 2019.
As otters push into towns, there may well be features of the urban environment that they can use to their advantage.
David Wembridge, Mammal Surveys Coordinator at the People's Trust for Endangered Species (PTES), says that industrial areas can offer secluded habitats.
He explains, 'We often find otters in old industrial parts of towns. Otters are generally associated with large rivers, but they will use quiet outflow points and the canal network. I even had a contact who reported otters taking carp from his garden pond!'
But this new city lifestyle also brings downsides and new threats. David says, 'We've been seeing more otters run down on roads across the country, which is an unfortunate result of their expansion.'
This trend is also recorded in Essex. Darren from Essex Wildlife Trust says, 'In 2007 we might get four otters collected off Essex roads. Nowadays 15 in a year is standard. If you've got roads crossing rivers, then there's potential for otters to get hit by cars.'
Plastic pollution is also a concern. Darren says, 'We are starting to find small pieces of plastic in spraints which is worrying. These are the things that systematic surveys can uncover - things changing in the environment which we need to look at.'
Despite the challenges that come with the territory, growing otter populations in cities are a good sign for ecosystems and human inhabitants alike. Otters are a way to engage local communities and policymakers with the health of rivers and other urban habitats.
Paul explains that the work in Sheffield has brought about change in the city and made people care about conservation like never before.
'We've proved that otters are using the river. Now when developments and other disturbing activities are planned, the otters have to be taken into account. This is a really positive conservation outcome.
'The local community have shown such a real interest in the project: over 400 people came when we held an event to present the results. The otter story has been a massive success for raising the profile of conservation.’
David from PTES says that this picture is representative of urban conservation across the whole country.
'People are waking up to the benefits of more green space in cities: for wellbeing, cleaner air, cleaner water, reduced flood risk and for wildlife.
'Good cities can support a huge amount of biodiversity, including a surprising number of mammals at the top of the food chain. This is such a good indicator of healthy cities and towns, for wildlife and for people.'
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