Regarding boat tools, very sorry to report this two edged sword. If the magnet doesn't work, maybe they're stainless? But I think the magnet SHOULD work!
They look like stainless, but automotive tools are RARELY made of SS (maybe never?). So the bad news is that most automotive tools DO rust in the salty atmosphere.

The good news is, your magnet was the right bait, just didn't get close enough to catch them.
Maybe they don't use SS because it's too brittle for hand tools? While trying to turn a rusty screw, I actually snapped-off the tip of a straight-edged screwdriver last week (Craftsman!). Sometimes tools are marked 'chrome vanadium' (not sure exactly what that means) and usually they're marked 'hardened'. Anyhow, the magnet works.