In the tropical seas, main fishing grounds are shared with marine turtle's habitats and migration routes. As a result, while fishing species of commercial value with long-lines, other species, which are not fishing targets, unintentionally get caught as well. This is known as by-catch.
By-catch problem is directly tied to the use of J hooks in long-line fishing operations. Marine turtles are attracted by bates hanging from the line, by biting the hooks turtles usually suffer fatal injuries. If the hook is set deep in the water turtles cannot reach the surface to breath and can die by asphyxia. When fishermen find hooked turtles in the line, they can decide to unhook turtles, but lack of knowledge on how to do this properly can cause further damage, thus reducing the chance of survival of hooked turtles.