I was going to guess salmon, because studies have shown that catch and release, at least during the run, is not effective, the fish often die. Steelhead are basically a salmon, so this makes sense
The other species I know catch and release has been shown to be ineffective for is hammerhead sharks, IIRC the mortality rate was 50% even with careful handling. There are species that should not be fished with the intent to release them
However there are other species that do quite well when released, though I do think your uncle is wrong if he says any species of fish has a post relese mortality rate of 0%, it may be 0.1%, but never absolutely 0