Possible culprit for taking fish from pond

Two very large fish have disappeared from our garden pond in the last week. Today my partner has seen what we believe to be a black kite over the garden. We have been puzzled as there were no obvious culprits, other than a bird, that would be strong enough to remove them. Cats usually leave a trail, of which there was none. Our garden is enclosed and he has now netted the pond, which was very exposed. We live in south west Norfolk, in the Brecks. Are we seeing things ? Any information would be welcome.