What killed our Koi?

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We've heard of several cases where pondfish have been eaten by otters. Image by Shutterstock.

Yesterday we woke to find 10 very large Koi up to 50cm/20in length dead and half eaten, spread around the garden. Our pond is 48in/4ft deep with no shelf. It has an overflow drain that drains into a culvert and we noticed the cover was off. 

We live just outside Much Wenlock in Shropshire and we have no idea what could have done this. Any ideas?
DIANE CLIFTON, EMAIL

Sorry to hear you’ve had this problem. I spoke to a carp angling, carp keeper and he had this to say when I asked him if it was an otter: 

“Half eaten is classic otter.  I have seen carp on my lake with just the stomachs eaten.

“This is a massive problem with otters being introduced into areas.  They eat nesting birds, rare amphibians too. 
 
“They are an apex predator, like a wolf in a field of sheep. People can’t shoot them as they are protected.”

So it’s an otter. Standard netting won’t keep them out and they can and will come back. I’d rather otter roamed the UK’s waterways than introduced mink, and one could argue that there are plenty carp to go around, both in ornamental ponds and fishing lakes.

Not you want to hear though and you must be absolutely gutted. As mentioned above you can’t touch them so your only way is to try to prevent them entering the pond, and that probably means strong wire mesh or a metal grid system.    
JEREMY GAY