A mystery solved

A few years ago we started to have the odd Koi go missing from our pond/mini lake at the same time of year each year. We knew Herons were about so we put it down to that. Then one year all but our 10" Koi dissappeared, again around the winter time so we just figured the Heron had had a field day again.
We restocked the pond for what felt like the tenth time and enjoyed the fish once again while puting up Heron deterrants.
Last Spring we waited for the Koi to resurface (this pond is huge) and we waited and waited - nothing! We were gutted as our 9 year old Gold Koi had been taken (the only one to survive all previous dissappearances). Thing is this time we didn't see the Heron once despite getting up before Dawn to spy and see if it came as it had other years - nothing!
So we figured it must be the Seagulls as we're so close to the beach, even though we'd never seen any evidence of them being interested.
Basically we went through every scenario before deciding we'd never re-stock the pond again.
A couple of weeks ago we let the dogs out and they began barking and growling at something. We called the Dane back but the GSD just wouldn't come to call so hubby grabbed a torch (it was dark) and set out to look for him.
It would seem the dogs had chased something into a pile of sleepers we have so he grabbed the GSD, bought him in and went back to look at what the victim was.
You can imagine hubbys surprise when he shined the torch and staring right back at him were the very alive eyes of an Otter. The Otter then ran away on to the garden and we left him alone to sort where he wanted to go.
Lightbulb moment:- It's the darned Otters that have been clearing the pond in what seems overnight each time. It's been the same time of year that fish have dissappeared each time so I guess it's the time when Otters are finding their own territory?
Guess we definitely won't be restocking that pond then.

Oh poor otters....they must know your pond is good for a good take away at this time of year!
When fish tend to stay deep where its slightly warmer ...
So your pond must be a regular winter feeding point......annoying, but, you can stop cursing the heron!
Trout in the pond for next year?

We're not putting anything in Dadie lol.
It's heartbreaking when the fish are all eaten literally overnight, especially the Koi.
Hmmm wonder if there's any way of making it Otter proof lol.