I quit using stinky prepared baits and chicken parts a long time ago here. Have had so much better luck using freshly cut up chunks of bluegill and other baitfish. In summer they feed later here and am not sure if it's because of warm temps or because that's just what they do. We are catching lots of cats after 10:00 PM on cut bait.
Jim

If the oxygen level is low in the pond they won't bite

I ran into the same thing on a pond just loaded with fish. Lady was tired of feeding all the cats and wanted some thinned out. Stink bait worked pretty well for me I was catching them about as fast as I could throw it in. I also had very good luck on nightcrawlers if I waited until just after a rain. I had thrown the book at them as well. I was surprised when you said shrimp didn't work. That's my bait of choice when something has been fished heavily and nothing else is working. On crowded bridges after rain here I tend to catch the cats as fast as I can cast using simple shrimp while others using the usual catfish bait don't do as well.

Might be a simple as keeping your bait further up the water column ,
sounds like these fish are trained to feed on the surface , the best
night I've ever had with channels(50 +) was in 15 feet of water with
a leach 18 in under a float .They also like woodchuck meat ,
but so do the turtles which might not be bad thing either .

( Bag or two of Walnut hulls at the pond intake,
If there is one ).

Disclaimer : "Rumor I have heard".

Saw a guy get tossed from a pay lake because he was using kibble and bits dog food. He would throw a hand full out then cast a bobber in the middle of it with a piece about 4 inches below. He was catching them as fast as it hit the water...

Great idea

Stretch a Gill Net out.. wont matter if they are biting lol

Worked for a man who had catfish ponds , before it was time to harvest them , he gave Us tackle and raisins to catch some to check the flavor on them before the truck came to pick them up.

Get somebody to tie a fly that looks just like their food.