Thirty years ago, back in 1992, the first otter survey in Cambridgeshire was conducted by the Cambridgeshire Mammal Group; held every five years, this year the seventh survey is now underway, ending in February with results due in March (see below for results of the last survey which took place in 2017).
So where to find an otter and what are the clues to look for? One of the first places to look is under bridges – canny otters communicate and convey messages in their droppings, known as spraint. They have worked out that this lasts longer under cover, so bridges provide an ideal place for this calling card. With a distinctive smell (similar to jasmine tea but fishy when fresh) every spraint tells a story with a specific signature scent unique to each individual which contains and conveys information - whether male or female, if in season, etc. Prominent places generally make good places for spraint: on ledges, bricks or rocks, and sometimes they may scrape up earth to create their own platform.
Another clue is tracks - otter footprints are asymmetric, ranging in size between 40-80mm and normally showing only four toes even though they have five, and the webbing between the toes also doesn’t usually show. Those lucky enough to see them may also hear the distinctive series of squeaks and whistles they make, though these are more normally heard at night (video below from Paxton Pits).
Conducted by Trust staff and volunteers, along with members of the Cambridgeshire Mammal Group, the Environment Agency and the Middle Level Commissioners, last week Cambridge City Greenways Officer Iain Webb and Volunteer Officer Toby Humby surveyed a swathe of villages west of Peterborough, finding spraint evidence in eight out of 10 sites. Along the way Iain also found a belemnite, a hard bullet shaped fossil of the remains of part of an extinct mollusc, these squid-like animals belonged to the cephalopod family, and lived during the Jurassic and Cretaceous periods from 201 million to 66 million years ago.
Another element of this year's survey is the potential DNA testing of otter spraint at the Wellcome Sanger Institute, Cambridge; samples are being collected and frozen before being analysed. The Trust's Water for Wildlife Officer, Ruth Hawksley says: "The survey is going well – we’ve allocated all the sites and surveyed more than half of them and I've had more than a third of the survey forms, although my family is displeased by the amount of spraint in our rather small freezer! My impression so far is that this survey will be comparable to the previous one, but it’s too early to tell right now. I’m very excited about the possible spraint analysis and really hope it will help us estimate the number of otters present, rather than us just recording the number of signs."
