There are various ways to catch tuna and fishermen choose their fishing gear based on the following parameters: quality, quantity, affordability and infrastructure.
The best tuna for the sashimi market receives treatment as soon as it lands onboard. This treatment is to drain the blood and to remove the stomach. If it is destined for the fresh market it is iced, otherwise it has to be ultra-frozen (-60°C) to meet the high standards of the sashimi market.
The price difference between sashimi quality tuna and all other tuna does not justify that other tuna is caught and treated the same way. Hand Line-, Long Line and some Pole & Line caught tuna get a premium in the market for sashimi. Lately, you see the same for some purse seined Yellowfin tuna. However, it is only for the part which is first taken out of the purse seine net and treated the way as explained.
For less valued tuna, the only option to make it profitable is to catch sufficient quantities.
For this reason, the tuna purse seine sector has expanded over the years. In the beginning, the purse seiners were chasing free school tuna (Yellowfin Tuna and Skipjack). When there was so much tuna, it worked very well. Later by coincidence skippers found out that tuna assembled under natural logs and they applied this knowledge by making their own Fish Aggregating Devices (FAD’s). Initially they were equipped with radio beacons but today they can be monitored via satellite and receive signals from builtin echo beacons. The latter was a significant development in the setting up of FAD’s. Some fleets even use designated specialised supply vessels for it. This has became a common strategy to increase the size of catches to unimaginable levels.
Local fishermen also use FAD’s but they anchor them not too far away from their homes.
For a local fisherman, an angler and a hook are easy to make. A net is already a big step forward, but relatively expensive and they can not operate it alone. Some fishermen work with their net from the beach, but not as efficient as operating from a vessel. When it comes to the boat, it often a collective investment. With more owners, the decision-making process is harder, and therefore one boat is usually the maximum they achieve.
For the industrial fleet, it is different, the sector has proven itself, and many vessels belong nowadays to larger groups. Their buyers partly finance some fishermen, so they a guaranteed supply,
Tuna fishing is often in remote areas. Most of the ports have none or insufficient cold storage space and lacking tuna processing capacity. For fresh tuna export, it is essential to have airports with frequent and reliable flights.
The coastal community is in general not able to spend money on adequate fishing gear nor on seaworthy boats. Often they operate on small rank boats with an outboard engine.
They fish for their families, and the surplus they sell on the local market.
The principle of most gillnets is that the fish swims into the net. If the head is in, the fish tries to escape. This not possible, the twines of the net are behind the gill covers, which makes reversing impossible.
Other principles for gillnets, wedged (the mesh is tight around the body of the fish) and tangled (only with the teeth or spines stuck in the net)
A gillnet is often used in a less professional way along the coast, hanging down between buoys. In many countries, it is forbidden, because with the net is not only for fish, but also a lot of sea animals which get entangled in the net.
More professional ones go further out and set kilometres long nets, which are very destructive, as all kinds of fish sticks in the net.
It is getting worse when they use small-sized messes. Small messes nets are like vacuum cleaners and killing all the sea life in and around the net. Often the net is abandoned when it loses its functionality. However, it still floats underwater and remains destructive.
Since 1992 it is forbidden to use gillnets longer than 2,5 km. Before 1992 nets were often exceeding 100 km in length, used in the oceans to catch tuna.
The Indian Ocean is where most of the gillnet fishing takes place.
The purest way of fishing, as it says … a line with a hook operated by hand. The catch per person is limited, but fish with no value .. remains alive after being thrown back in the sea. Commercially not viable, unless in a school with valuable tuna. Pole and Line vessels switch to Handline fishing quite easily. They only need to ice on board to conserve the expensive tuna.
pole and line
A Pole and Line vessel is a boat with anglers, which is looking for schools of tuna. Before going looking for tuna, the boat is catching or stocked with live bait. Once the boat has found a school of tuna, they throw bait in the water … the tuna can’t see the difference between the hook and the bait and bites and bites. It is a method which works in areas with plentiful schools of tuna, because the Pole & Line boats are often made of wood and not equipped with sonar, computers with sophisticated software for i.e. biomass and water temperature images from satellites.
Most of the Pole & Line vessels do not have holds and tanks, so they can’t stay too long at sea if they want to land good quality tuna.
The main countries for Pole & Line fishing are:
The boats for trolling are mostly under 20 meters, equipped with powerful engines and booms on both sides. Via the booms, 5-8 lines, equipped with hooks with bait or lures, are towed through the sea. The targeted specie is often Albacore tuna, but swordfish and marlin are also well appreciated.
The total catch is neglectable, compared to the other fishing methods mentioned here.
Trolling takes place is in many countries in tropical and subtropical waters.
Longlining is fishing with a long mainline behind the vessel, on which evenly spaced hang branch lines between floats. The branch line is a line, with lead and hooks with bait. The length of the branch line is set for a specific dept, depending on the targeted tuna specie.
Depending on the targeted specie, the depth is adjusted.
If the branch lines are short (closer to the surface), Yellowfin Tuna will be likely the catch. With the depth set at 100-150 meters, target species are larger tuna species as Bigeye Tuna and Bluefin Tuna.
Setting the lines is a slow process because every hook needs will have bait.
Getting the catch onboard is also a time-consuming operation, as every tuna needs to bleed out and cleaned before frozen and put in the dry, refrigerated hold.
Longline fishing is not a selective fishing method and a major concern for the amount of by-catch. There is no real registration about by-catch, but it is not only marlin or swordfish but also sharks, turtles, sea birds, marine mammals.
For the longline vessels with ultra-low freezing capacity, the fuel price is a big issue. The whole Japanese longline fleet went alongside when the oil price went over the hill in 2006.
The annual catch for tuna longliners is not high, between 250-300 ton/year. Often they tranship their cargo at sea without control. There is no clear view of the reality of the reported catches.
The number of longliners has decreased tremendously in the last two decades, as fuel costs and rising labour costs were not compensated by the higher fish prices.
By far, tuna purse seining the most substantial activity for catching tuna. The vessels used are called tuna purse seiners. In Japan, it started in 1949 for tuna fishing. In Europe and the USA, It is originating from the sardines fisheries, which suffered from overfishing in the ’70s. The French fleet moved to West Africa and the West coast based US-fleet headed west to find tuna.
The basic principle for tuna purse seining has not changed over the years. It starts with the launch of an auxiliary vessel (skiff) from the stern of the vessel with the beginning of the purse seine net attached to the bow. The powerful skiff remains in the position. The purse seiner is circling round the school of tuna while shooting the net in the sea. If the circle is and once completed, the vessel picks up the end of the net from the skiff. The bottom of the net is closed by pulling, the so-called, purse line at the bottom of the net.
The tuna can now only escape under the tuna purse seiner, which the crews try to prevent with noises made with hammers on the ship’s steel. Also, a speedboat chases dolphins and mammals away before the net is closed. Heaving the net onboard is done with hydraulic power. Once the net comes alongside the vessel, the tuna is brailed in with a scoop net onboard. The catch goes via a hatch on transport belt to one of the tanks underdeck.
The tank contains chilled refrigerated seawater, so the tuna can chill till around 0º C. after that brine (seawater mixed with salt) replaces the seawater. Brine makes it possible to freeze the tune to minus 19°C. The tuna will remain frozen in the tanks for the remainder of the trip. To avoid the tuna is absorbing too much salt from the brine, the brine will be removed after several days. For discharging the tuna, brine is pumped in the tank to float the tuna out. Once out of the tank, the tuna moves on the transport belt under the hatch. Here the tuna leaves the vessel in a net.
A TUNA PURSE SEINER for tropical tuna fishing is between 60-115 meters long. The tanks can hold between 600 and 2.500 tons of tuna. Some massive vessels were vessels built in the period 2011-2015 the account of Spanish boat owners.
The size of purse seine nets is varying with the size of the vessels. The length varies between 1.200-2.000 meters with a depth of 200-380 meters (depending on the ocean)
An AUXILIARY VESSEL (SKIFF)l is between 10-14 meters long, with a very powerful engine
(900-1.300 hp). Such power enormous is necessary because the skiff keeps the beginning of the purse seine in the position of the launching of the skiff.
SPEED BOATS chase dolphins, sharks and mammals out of the net before it closes. After that, the speed boats help to keep the tuna in the net, while it is closing. They cruise alongside the tuna purse seiner, to avoid that tuna might escape when it dives deep or passes under the tuna purse seiner.
Fish Aggregating Devices or FADs are human-made floating objects or natural logs under which fish can assemble. Younger fish do tend to seek protection from their hunters under floating objects, to rest and eat.
About 40% of the TOTAL tuna catch comes from fishing on FAD’s
The human-made FAD’s are either of:
- Steel rings with a plastic bottom and covers with plastic jerry cans inside
- Bamboo with the use of webbing of an old fishing net
- A net filled with floaters hold together by a wooden construction
Nowadays, all FAD’s have buoys with a built-in echosounder. An echosounder can detect whether there is biomass or fish under the FAD. The buoy transmits on a very regular basis the findings of the echosounder to satellites. The information is forwarded to the vessel(s) and ashore.
The introduction of FAD’s changed the tuna industry. Purse seiners increased their catches year-on-year with FAD-fishing. On the other hand, the free school activity diminished. The focus is now to catch more fish, indifferent to many boat owners if the boats catch immature fish or not. They accept the risk they’re mightdestroying the stocks and with that their future.
More on this topic under SUSTAINABILITY.
Supply vessels (also known as support vessels) are vessels between 35 and 45 meters long, which do not carry fishing gear but well equipped with fish detecting equipment. The vessels do carry crewmembers to shore in case of casualties, but they also launch FAD’s and search for tuna for the tuna purse seiners. Basically, it is an extension of the tuna fleet and an efficient way to increase the catching effort of the tuna fleet.
The resistance against the use of supply vessels is increasing. The number of these vessels is in the Pacific Ocean very low (if today not zero), in the Indian Ocean the number decreases under a new tuna management resolution. Only in the Atlantic Ocean, the number of supply vessels has increased, due to lack of good regulations under ICCAT.
More on this topic under SUSTAINABILITY.