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The best way to catch a big Channel is a big piece of freshly cut shad or any other bait-fish. Leave your rod out in the water for a long time, it takes longer for a big one to stumble upon your bait most of the time. Those scars could be other things like muskies, pike, etc or a fish diving into some sharp rocks after being hooked. Those big fish jumping are probably bass or carp, catfish don't generally jump.

I recently caught a 50+ pound blue cat using chicken gizzards soaked in chicken liver juice ( the chicken livers would work but they fall off too easily). Be sure to use a big hook and a sturdy rod, mine is an offshore deep sea rod. Change it up between using a bobber and bpttom fishing. But the key is- go at night.

sure fire way right here... Get ya some panty hose. And some liver. Let the chicken liver sit in the sun till it almost makes you puke smelling it. Put lil pieces in the pantyhose and tie a knot. Cut the extra off. Put a hook through it. Use a good catfish pole. I like a uglystick. Throw it as far as ya can and prop it up. Then put a plastic cup on the pole. When the cup falls off ya got one go ahead and bring it in. The rotten liver is like a piece of candy to them.

Maybe you and some friends are making noise in the boat or talking loud that scares them away.

Have you considered using a modified trout line?