I appreciate all the replies. I have contacted TWRA. The gentleman was very knowledgeable. He confirmed that it's most likely otters and didn't have another explanation. He gave me guidance on how to control them with traps and said it would be completely lawful.

I plan to catch as many as I can. I'll probably kill the fish left and start over in the fall. I'd like to drop the water and do some maintenance anyway.

Thanks for all the replies. I'll be watching closer in the future.