A question that we’re often asked is from people who are losing fish from garden ponds and think they have a mink problem, but are worried it may be otters.
There are several very good sources of information on the differences between behaviour, tracks and droppings which will help you identify what’s been visiting your pond.
http://www.sussexotters.org/pdf/Mink%20Control%20for%20Wildlife%20Conservation.pdf
http://www.naturalengland.org.uk/images/ottersandstillwaterfisheries_tcm6-4592.pdf
http://publications.naturalengland.org.uk/publication/809095?category=41002