For many humans, the smell of a freshly opened can of fish can trigger a gag reflex, for a skunk it is the smell equivalent of a dinner bell. Canned fish like sardines or tuna emit a strong smell that skunks, seemingly, cannot resist. The scent of the fish oils creates a strong smell that the skunks will instantly recognize as food and head that way.
Sometimes, skunks can be cautious, especially when food is in an enclosed space with no discernable exit. This cautious nature means that often bait is not as effective as the skunk is not willing to take the risk. Not so with canned fish!

Canned sardines, tuna, or any other type of fish will override the fear of the skunk and they very rarely pass up the opportunity to gorge on a rare and delicious treat. Unfortunately for the skunk, this leads to them being trapped.