A recent report by the Environment Agency and the Wildlife Trusts have indicated that the UK water vole population has decline by 20% this year: http://www.bbc.co.uk/news/science-environment-23975749
It certain matches what has been happening on the Ock, having done six water vole surveys this year (three on the Ock in Abingdon and three on Nor Brook to the west of Marcham Mill) there have been no positive signs of water voles - latrines or sightings.
Also, with regular trips down to the river there have been significantly fewer sightings in 2013 when compared to previous years - as illustrated in the chart below.
When in 2011 & 2012 there were multiple sightings during 2011 & 2012, I have only had 5 sightings this year and most of those were on the Lower Ock, such as this one taken back in April:
There are several possible explanations for this:
- Small mammal populations fluctuate and this could just be part of the natural population cycle (and 2011 could have been a population boom).
- The bad winter and the poor spring could have hindered the breeding season, possibly unlikely as other water vole populations in the area are doing very well.
- Despite control up stream a breeding population of mink could have established itself along the Ock.
- Or just plain bad luck, maybe the population of the Ock has not changed, but I have just been unfortunate with sightings this year (and this is far from a scientific study).
It is difficult to draw any conclusion from just one year, but as water voles (like most small mammals) are prolific breeders hopefully the population will re-establish itself next year.
If not, then there could be something seriously wrong with the river, especially as Abingdon and the Ock are important locations for an animal which has had a torrid time in recent years.