Saturday, 6 June 2015

Disease hinders reintroduction of water voles

Many of you will know that I am a dyed in the wool conservationist. Wildlife is one of my lifelong interests. I was for many years a volunteer for the RSPB prior to spending more time on the boat. That's why I record what I have observed in our boat log postings whenever we move from place to place.  Such as Birds, Butterflies and Dragonflies. I also have a bat detector and frequently check for bats wherever we moor up the boat. The bats are reported into a central database and the information is used for plotting and estimating national numbers of bat species. 

Generally conservation is aimed at improving habitat to allow for the natural spread of flora and fauna. Also some protection of existing habitat such as ancient woodlands. However, there are times when work done in the name of conservation - for all the right reasons - can be misguided and counter productive. I have always wondered about CaRT reintroductions of water voles into the canal habitat - which because of all kinds of disturbance, through people on the towpath, dredging and sometimes even drastic scrub management. Can also be counter productive to maintaining a good habitat.  

The main threats to water voles
  • Predation – particularly by non-native American mink
  • Loss and fragmentation of habitats – particularly through inappropriate management and agricultural intensification (e.g. re-profiling, heavy grazing, drainage, vegetation control and extensive bankside tree-planting)
  • Disturbance of riparian habitats
  • Pollution of watercourses and poisoning by rodenticides
  • Persecution – sometimes in the mistaken belief that water voles are rats
  • Severe winters and droughts – these lead to significant water level fluctuations 

Much of the proactive managed canal habitat is not good for water voles. However, the biggest problem is Mink which are the top predator on our inland waterways. Water voles are just a light snack to the opportunist Mink. It is important to first of all control the Mink population before reintroduction of Water voles. One promising unintended consequence has been through the reintroduction and natural spread of Otters. Where Otters take over a section of waterways, the mink population actually falls. Water Voles and Otters seem to manage to live cheek by jowl as the main prey for otters are fish and eels. Otters are also known to take and reduce the populations of another pest - the American Signal Crayfish. 

Recently some research has highlighted a worrying concern about water vole reintroductions. Researchers have found evidence that diseases seem to be more prevalent amongst the rodents that have been released into the wild, as part of reintroduction projects. In some cases reintroduced water voles were found to be nearly seven times as susceptible to diseases such as leptospirosis than existing resident populations.

Biologists from the Wildlife Conservation Unit at Oxford University, who wrote the report for the People's Trust for Endangered Species, believe this extra burden of disease is hampering efforts to restore populations of water voles in parts of the country.
Professor David MacDonald, who co-wrote the report, said: "Wildlife diseases are a big issue in terms of conservation and management. In almost all of the endangered mammal species in Britain we have a disease aspect to their survival. We have been doing some work on water vole reintroductions recently and have found a prevalence of leptospirosis in 43% of reintroduced populations compared to 6.2% in wild populations. Probably what has happened is these reintroduced animals were living in high density and were somewhat stressed, so they became blighted. We have to consider disease as a factor in their survival."

The vulnerability of water voles, which were immortalised by Ratty in Kenneth Grahame's Wind in the Willows, was highlighted in a report written for the People's Trust for Endangered Species as part of their annual update on the health of Britain's wildlife.

Marking the 10th anniversary of the PTES' annual State of Britain's Mammals report, the authors state that while the country's mammals are in a better state than they were ten years ago, they still face significant challenges. Indeed, a number of species, including the hedgehog and red squirrel have continued to decline despite extensive conservation work.

Reintroduction projects have helped improve numbers of rare species such as the water vole, but they warn that without improved habitat and careful monitoring of disease they may never fully recover. The researchers point to the impact that squirrel pox, carried by grey squirrels, has had on red squirrel populations, which often die after being infected. The report also warns that the current row over tuberculosis in badgers threatens to have a significant impact on their populations as ministers consider implementing a cull of the animals to help prevent the disease from being passed to cattle.

Professor MacDonald added: "This is an opportunity for us to take stock of what has happened in mammal conservation over the past 10 years. We have seen otters come back, pole cats have come back and water voles are now being reintroduced and are on their way back. We have seen 600 dormice being restored to natural habitats, but there have been some downsides such as the red squirrel continues to be in decline while there has also been an apparent radical decline of numbers of hedgehogs on farmland. The fear is that the successes we have had are because we have tackled the low hanging fruit and we now face a far more difficult choices in the future."

As you move around the waterways on your boat - you might just want to help PTES to monitor the locations of Water Voles. You can find more information on how you can help here: The People's Trust for Endangered Species

About the People's Trust for Endangered Species
PTES is a UK conservation charity created in 1977 to ensure a future for endangered species throughout the world. Working to protect some of our most threatened wildlife species and habitats, it provides practical conservation support through funding research and internships; providing grant-aid for world-wide and native mammals species conservation; supporting education, training and outreach programmes; and driving public participation via wildlife monitoring surveys, publications, campaigns and events. Priority species and habitats include hazel dormice, hedgehogs, water voles, noble chafer and stag beetles and traditional orchards and native woodlands.

The National Water Vole Database and Mapping Project is managed by The Wildlife Trusts. It was established in 2008 by the UK Water Vole Steering Group, with funding provided by the Environment Agency, Royal Society of Wildlife Trusts (RSWT) and People’s Trust for Endangered Species, as a way to collate water vole survey records, map the distribution of this species and identify important areas for water vole conservation. The Project also collates and maps data on American mink.

Data gathered by the National Water Vole Monitoring Programme will be submitted to the National Water Vole Database and Mapping Project, so it can be included in the national distribution maps and alert and key area map.

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