Tuna Fishing

Types of Tuna Fishing

The difference between Purse Seine, Long Line & Pole and Line tuna fishing methods

Our appetite for canned tuna creates a huge tuna fishery that scours the ocean looking for wild tuna to catch.  It is a game of cat and mouse between the wild tuna and the fishing fleets and in most circumstances the tuna is losing.  There are many different ways to catch tuna and the prevalence of one method over another can make a huge difference in this world.  Unsustainable and illegal fishing can cause quick and substantial depletion to fish stocks and can cause major ecological problems.  Understanding some of the harvesting techniques is important if you strive to ensure you eat sustainably caught tuna.  The four most common methods are listed below along with some of their benefits and problems.

Pole and Line Fishing

Pole and line tuna fishing is the most sustainable method for commercial tuna harvesting.  This fishing technique uses a multitude of fisherman using hand held fishing poles to catch the tuna.  The pole does not contain a reel and has only a small line connected at the tip of the pole.  The end of the line contains a lure or bait on a hook that is typically non-barbed for quick and easy release of the tuna.  The fishers will search for a fleet of tuna and use bait to bring them up to the ocean surface. As the tuna grab the hook the fishermen will bring them to the boat and detach the fish from the hook before quickly bringing the pole back to the ocean to resume fishing.

The method will target only the tuna being sought and therefore will have little to no bycatch.  It is recommended to try and buy canned tuna from a pole and line caught fishery for sustainability purposes.

Surface Trolling

Tuna trolling boats will use many different rigs with lines that drag lures and hooks through the water at varying depths.  The trolling boat will travel at a fairly slow but brisk speed and will seek to find a school of tuna before dropping the rigs. Once the school is located the boat will usually make wide circles around the tuna.  The hooks and lures are very durable and will be used many times.  Once a tuna is caught it is brought in, released from the hook and the line will be dropped back into the water as quickly as possible.

Longline Fishing

Longline fishing uses a strong rope that is set into the ocean that runs for many miles.  The rope is weighted and can get fairly deep into the water.  This rope has attached to it many different lines all set at different lengths and buoyed with floats.   After the line has been in the water for a set amount of time the entire rope is reeled in and all fish caught are removed from the hooks.  Sometimes a fishing boat will work with a few longlines at once.

Because of the indiscriminate nature of longline fishing many other species of fish other than tuna are caught on the hooks.  This can include other large predator fish and sharks.  These fish will either die on the line or will be discarded as by catch. Long line fishing is not considered a sustainable tuna fishing method.

Purse Seine Fishing

Purse Seine fishing is the most indiscriminate and most unsustainable fishing method listed here.  It uses a giant net to encircle a school of tuna and catches all sorts of other fish and animals in the process.  Purse Seine netting works by having a large main ship haul a big net to a located tuna school.  Smaller boats are deployed and bring the net in a circle around the tuna fish.  As the tuna are enclosed the main ship gets the other end of the net back and a line (purse line) is pulled through rings in the net.  As the net tightens around the bottom the fish are trapped and the net is mechanically wound back into the main boat and the tuna and other bycatch are taken out.

In previous times purse seine fishing boats used dolphins to find tuna schools and then circled the dolphins and tuna all at once.  This resulted in a huge amount of dolphin kills.  Now, in order to be dolphin friendly fishing fleets are using fish aggregation devices.  FAD’s attract fish and make it easier for the fishing boat to catch a large amount tuna.  Unfortunately all sorts of different fish (other than tuna) and marine animals such as sharks and turtles are also attracted to the FAD and the fish that come to it.  When the purse seine net is deployed all these species are trapped and killed.  Purse seine fishing is though to be highly unsustainable and results in the unnecessary deaths of all sorts of marine animals.  We recommend trying to avoid canned tuna products that were sourced using purse seine fishing methods.