Sad story:
I was talking with another guy at the garden center that had a bunch of koi for 30 years. I think he said he had 50 of them.
This Spring he couldn't find them.
They were all taken by something. All of them!
He thinks a mink swam under the ice and snatched them all. He said he didn't think it was a bird, due to the ice.
Very sad. 30 years. Those fish were basically family members.
I told him to get some cameras. Too late for those fish, but for the future it might help.
I had a trail camera out there in the past, but now I use the Blink wireless ones. It's much better and easier than downloading from an SD card in the trail camera. The Blink videos are right on my phone. Plus, you can talk through the Blink cameras. You do have to pay a $100 per year subscription for cloud service, but I think it's worth it. I currently have 8 cameras.
My daughter yells at bears through the cameras when they go after her chicken coop. It's kind of funny the way the bear turns and looks in the direction of the camera then walks away!
There are other brands out there that are just as good or maybe even better.