Ghost fishing is a sad reality of the fishing industry, where abandoned, lost or discarded fishing gear continues to fish.
It can be particularly troublesome as smaller trapped animals entice larger predators, who themselves get tangled. A net, after all, can continue to work whether we're around to pull it in or not.
Recovering lost fishing gear is a challenging and often dangerous job. See, for example, ghostdiving.org
Also see:
Peripherally-related ideas:
Nurse shark drawn using How to draw a grey nurse shark