A trotline is like a really big fishing line that people use to catch lots of fish at once. It's made of a long piece of string or rope, and it has hooks attached to it that hold the bait to catch the fish.
People attach one end of the trotline to a sturdy object like a tree or rock on the shore, and then they throw the other end into the water. The hooks with bait will be under the water hanging from the trotline.
When the fish come to eat the bait, they get hooked on the trotline and can't swim away. Then people come back later and collect all the fish that were caught on the trotline.
It's important for people to only catch the fish they need, because catching too many fish can harm the environment and the fish population. So, people need to be responsible when using a trotline and follow fishing regulations.