When I make a dive to the bottom of the Gulf of Maine in a research submersible, I can tell immediately whether an area has been recently trawled for fish or dredged for scallops. After trawling, the sponges and mussels, the tube-dwelling worms and the amphipod crustaceans that live in undisturbed areas are almost all gone. Boulders formerly covered with marine animals are almost lifeless from being rolled around by nets or dredges. And the mud has deep scars. It doesn't take a marine biologist to realize that these fishing methods are terrible for marine animals.
Nothing humans do to the sea has more physical impact.
Although laws exist that require resource managers to protect essential fish habitat from the adverse impacts of fishing gear and fishing practices, many regional fishery management councils have failed to comply.