The water that flows from estuaries also influences the surrounding coastal and marine environment. Key problems arising here include dieback of seagrass and the loss of coastal saltmarshes and mangroves through land fill and reclamation. Declaring some of these areas as marine protected areas helps to reduce direct impacts on marine biodiversity but does not stop the flow of pollutants onto them with implications for habitat modification. A large percentage of marine activities centres around fishing, even though this industry only accounts for five per cent of gross income from economic activity associated with the oceans. Fishing is an exploitative activity and, although fish are a renewable resource, catch in a growing number of species has been declining5.
Commercial fishing is organised around target species and has a large impact on their populations.
Bycatch is inevitable and affects other fish, birds, mammals, turtles and marine organisms. Some fishing methods, such as trawling, have a lasting effect on the marine flora and ecosystem. Recreational fishing and indigenous fishing are concentrated in estuaries and on the shorelines. The major impact is on the populations of target fish species. Recreational fishing remains largely unmanaged despite its potentially large impact.