Analysing otter spraint

Guest blog post by Community Science volunteer Barry Soames.

Moors for the Future have a new Community Science Project, looking for signs of mammals in the uplands, the Tails of the Uplands Survey. (Follow the link for details of how to get involved and training courses available.)

Barry analysing a spraint sample

A key target species is the otter, one of our most attractive and endearing mammals, which nearly disappeared from England in the 1960s and 1970s, but which is now starting to recover across much of the animal's former range.

As I have had an interest in looking for signs of otters for over 20 years (when working in Scotland), I decided that I would like to get involved.


Evidence for otter presence is indicated by a number of signs, one of which is their droppings, known as spraint. As well as indicating presence, analysis of spraint can help us find out what the otters are eating. Traditionally this was done by examining spraint under a low power microscope, and identifying bones (and other undigested material, such as fur and feathers).

However, nowadays, more sophisticated methods are available using DNA analysis. It is interesting to compare results of both techniques, and I have been examining samples from which DNA has been extracted and sequenced to identify prey items. The genetic analyses were performed at the Molecular Ecology Laboratory at the University of Sheffield as part of the Otterly Amazing project run by the Sheffield and Rotherham Wildlife Trust.

The first step in identifying prey remains involves cleaning the spraint. Otter spraint tend to be surprisingly sweet smelling, with the remains embedded in a sort of oily matrix. To dissolve the matrix and leave the cleaned bones, I used denture cleaning tablets. The spraint is dropped in an inch or two of hot water in a beaker, a denture tablet added and then left overnight. After the spraint has been cleaned in this way, it is then filtered to leave just the bones, and any fur.

Sample '119' contained mainly fish bones

Not all the droppings collected were otter spraint, for instance at least one specimen seems to be mink. I found out that my cleaning method only really works well with otter spraint, other droppings often had to be teased apart using tweezers.


Once this is done, the harder part comes in - identifying a small pile of assorted bones. To do this, I started with a very useful Mammal Society publication, "A Guide to the Identification of Prey Remains in Otter Spraint" This small booklet is mainly aimed at identifying fish bones, and concentrates on those bones which have the clearest differences between species. Much of the booklet deals with caudal vertebrae (the parts of the backbone in the tail), with additional clues coming from parts of the jaw, particularly pharyngeal teeth (teeth found on the gill arches).

This sample was probably mink scat, with mammal remains, in particular field vole, having been identified from the teeth and jaw remains.

So far I have identified bones from minnow and bullhead, as well as crayfish shell. It is noticeable that the prey identified so far has been of small fish, compared to the larger fish found when, several years ago, I examined spraint from rivers in Scotland. Not all the material examined was from otters, with one sample consisting mainly of fur with a few bones. Parts of jaw and teeth found in this sample enabled identification of field vole. (This dropping would seem to be mink).

If you would like to see some of the results, I have a page on my website for results.