Headless fish in netted pond
 

I have a raised pond with small mesh netting resting on the surround, the water level some 6 ins below the net.
The pond is above ground level all the way round.
I have discovered 3 headless fish floating in the pond over the last month and I have one unaccounted for. They were all about 3 ins or so long. Has anyone any ideas please?

What kind of fish are these? Do you have cats ?

They are goldfish, shubunkins, orfe and one koi.
I dont have cats but they do visit the gardedn.
Since posting I have loosely laid another net over the other net and since then nothing has gone missing. So I think it might have been a bird that landed on the net at it was very taut across the pond and just managed to get its beak through to catch a fish but the holes in the net didnt allow for the whole fish to be pulled through.