When temperatures drop below freezing good catch-and-release practices become critical. The fragile tissues of their gills can freeze in an instant when air temps are below freezing. They have no body temperature to stabilize their cells, so it happens quickly.
The solution is simple.
Don’t take fish out of the water when air temps are below freezing.
It’s a little cold on your hands but you can handle it. They can’t. If you don’t like the idea of putting your hands in cold water during winter but you want to fish, get yourself to Patagonia.