I thought so, but I couldnt find a reference in my books and the Otter tours website makes no mention of it.
(getting people to pay to see otters must be a licence to print money...from what I have heard its `not` comming across an otter that is the problem in Shetland...and my limited experience with otters seems to confirm this, they are mighty curious critters, and if you sit quiet, like as not they will come to watch you.)