They're caught from the same lakes and rivers everyone catches walleyes, cats, etc. from. They eat the same kinds of foods those other fish eat. They even drink the same kind of water, if you haven't noticed that. If they are trashes, then so are those. You guys are eating more of other fish that the Mev have eaten sheepsheads.
I caught a huge one 20 years ago. At first, it felt like my line was stuck on some underground rock. I gave up reeling and was about to cut the line off. Then it moved again. I now realized it was a huge fish on the line. So, I carefully reeled that in not to break the 8-pound line. When the fish was finally at the edge, I had to use both hands to lift it up to shore like lifting a toddler from the ground.
I removed the hook and took a good look at it before letting it back into the water.