mink and otter predation, Fish caves?

I am building a new pond that will generate a fertile wetland as a filtration system. I plan to stock it with Koi etc,and have seen evidence of mink/otter predation in my other mud bottom ponds, and am planning to put in a fish cave as part of the construction.

 Knowing how capable mink and otter are in the water, I'm curious if anyone here has any advice /experience, at whether the typical fish cave approach will keep fish safe from  these predators..Or would some specialization of design be in order? IE  how small, long, tight bends in pipe cave construction, etc etc.

Mink will likely be the main issue, but some otter might show up in time.  

I haven't installed the liner yet and the pond construction could have all sorts of preventive measures built in.

Any ideas?

Hey there.

I have a big earth bottom pond and had big big koi successfully for about 10 years. I have mink, ermine and river otters and they never got a koi.  Raccoons either. I used An anchored barrel to accomplish a safe haven and anchored 2 large wood slabs to prevent bird predation.  I had overhanging boulders. I had lots of water plants.

Eventually it was not the 4 legged critters. It was the age of the big guys who I inherited and the osprey/eagles who out figured me.

What happened to your older koi , I never think of koi dying of old age, weren't there babies to carry on the tradition?

The barrel does sound like a good idea,  similar to a built in pipe "cave" I have in mind. how big are the holes in your barrel? how deep is the pond?  Is the water clear or murky?

How did the eagles defeat your defenses?

I have a bigger mud bottom catfish pond, and predation seems less problematic there, but for now the pond is young, and putting young  koi in there just ends up as bigger catfish.  The pond stays pretty murky all year, which may be why the mink didn't just clean it out

My koi never had babies.  I have no idea how old they were when I got them. They y were hand me down Koi from an elderly couple who moved.  They were huge..probably salmon size. The barrel had the top off no hole they just went onside.  It floated anchored with about 6 inches of head space on its side.

My pond has water in and water out.  It’s perfectly clear.

The eagles and he herons perched around the pond for years..but in the last couple years my husband caught one eagle on the bank with Lefty...who lived but lost his left eye.  And I lost another to an osprey.

My neighbors dirt bottom pond is over an acre; water in water out and he raised trout.  The Herons cleaned him out.

Much luck to you. I enjoyed them while they were here.

sorry to hear about your loss and the neighbor's, thanks for the good wishes.

With known mink and expected otter, both of whom are acrobats IN water, I would fear no sort of cave would be safe. Otters use scent/smell under water, so they would/could track them into a 'cave'.

The only true safety, IMO, would be unclimbable fencing; either solid metal or electrified.

Thanks, I tend to agree , except for the idea that any fencing is invincible forever, so at the least it would be good to have a backup or two.

I just found an old piece of pipe, 10inches across and 6 feet long which should defeat an otter, but I'm not sure about mink since they are so much smaller. everything I' m reading suggests dye in the water for mink, and a two strand electric fence for mink and otter-one strand at 4 inches the other at 8 inches. guess it's time to get the solar fence charger a new battery.