Trawling perspectives
Dr Floor Anthoni, director of the Seafriends Marine Education Centre in Leigh

Should we ban trawling from the Hauraki Gulf? Trawling is one of the most efficient ways of catching fish, particularly those fish that don't want to take the bait. Trawling provides society with an affordable supply of necessary proteins. Why then, do we now think that trawling is bad and should be banned from the Hauraki Gulf? Isn't the sea bottom just a huge sand pit with fish on top, that can be plowed and scraped without causing any lasting damage? Let's look more closely at how trawling is done.

trawler drawing

The drawing shows a single bottom-trawler with its net. The net is towed by one rope that splits somewhere deeper down, or by two ropes and two boats (pair-trawling). On each side of the net is an otterboard, a heavy door-like paddle that is pulled on an angle. It scrapes over the sea bottom while pulling the ends apart. Between the otterboards extends a chain to weigh the entrance down onto the bottom so that no fish escapes from underneath. The top of the net overlaps the bottom chain if possible, so that few fish escape over the top. The entrance of the net is wide so that it is most effective, while allowing only few fish to escape sideways. The whole contraption is dragged forward as fast as possible so that fish cannot out-swim the net and also to cover a large area in as short a time as possible.

The drawing also shows (with arrows) that by pulling a net over the bottom, a considerable force attempts to lift it off the bottom, counter-balanced by heavy weights in otterboards and chains. The faster the boat goes, the heavier the fishing gear must be. As the fish becomes scarcer, trawlers must go faster and work longer in order to remain effective, while nets must become larger, resulting in ever increasing amounts of damage to our sea bottom.

One doesn't need to be a fisheries scientist to see that this activity, exercised on its present scale, MUST result in massive damage to long-lived organisms that are rigid, like fan shells, sponges, corals and tubeworms. But it also causes damage to what appears just sand or mud. Because the bottom is inhabited by scores of species that burrow and glue the loose particles together, they provide a living habitat where our table fish finds its food. Ploughing this field is like ripping the sand dunes with fourwheel drive vehicles, resulting in massive blow-outs after storms. Trawling not only threatens its own existence but unfortunately also catches a lot of young fish of all kinds and because the fish get crushed in the cod-end, its flesh is of low quality.

To be able to continue trawling in a sustainable way, we need to improve the trawling method considerably, for instance, by rolling the gear over the bottom rather than ploughing it. We must also set aside vast areas as marine reserves, to enable scientific study and also as an insurance policy for our children. The Hauraki Gulf with its uniqueness and many spawning sites, may well be needed in its entirety.

Field of tubeworms
Carpet tubeworms have disappeared from many places.