While I am not familiar with the Austin area, I can promise you probably have a huge group of predators that know all about your pond. I am an insomniac so I get to see a population of critters that would horrify my neighbors. There are many birds that could be the culprit. Hawks, eagles, owls, kingfishers and of course the herons are starting or ending their hunts at sunrise or sunset when the fishies won't see them as easily. Then you have raccoons, coyotes, turtles and other 4 legged hunters and snakes. About the only thing that does the job well is a net. Many ponders resist it thinking it is too noticeable but it is the most effective against birds. The least noticeable is bird netting. For the larger critters a Fido Fence or similar device works well. Or you can sit by the pond at night as I do and scare the heck out of them with a good shot from a water hose at full force. If you need the sleep, a water cannon such as a Scarecrow works well for me. Sandy

If plants were disturbed as well, most likely a raccoon. I can assure you that they are there even if you never see them.

If plants are still pristine then a heron is the next most likely culprit. Something could have scared him off before he ate the fish. Usually they grab and swallow in one motion but if the fish is big they do stab them and leave them on the outside of the pond.

If you want to see them, get up really early just before sunrise and wait quietly. My husband has to get up at 4:30 for work and he sees the raccoons in our yard at least once a week....