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Since the advent of the human race, every type of device imaginable has been used to capture tuna, from spears or harpoons, to dynamite. Probably the first commercial harvests of tuna were made using hand hauled nets and fish traps. These first commercial captures of tuna probably took place in the Mediterranean Sea. The Phoenicians used fish traps more than three millenia ago to capture bluefin tuna, which they traded throughout their empire. Though such traps are still used to harvest tuna in the Mediterranean Sea, and Japan too, nearly all of the present-day harvest of tuna is made from fishing vessels. The vessels represent a variety of gear types and sizes.

4.1 Gear Types

4.1.1 Purse Seines

Purse-seine nets are set vertically in the water, with floats attached to the upper edge, while along the lower edge is a chain, for weight, and a series of rings, through which the pursing cable passes. Purse-seine nets can be as long as 1.5 km and more than 150 m deep. On sighting a school of tuna, a large skiff with the end of the net attached is released from the stern of the fishing vessel. The vessel encircles the school with the net. The cable is hauled aboard the vessel, causing the bottom of the net to close, and the fish are trapped inside the pursed net. Most of the net is then pulled aboard the vessel, confining the fish in a “sack,” from which they are transferred to the deck of the vessel. Tuna purse-seiners vary in length between about 30 to 115 meters, and can pack on board up to 4 000 tonnes of frozen fish. However, most high-seas tuna seiners average about 70 to 80 meters in length and can carry about 1 000 to 1 500 tonnes of frozen tuna. Such vessels can fish throughout the oceans of the world, and make trips that last up to several months before returning to port. Many carry helicopters to improve their efficiency in finding and catching fish.

Purse seiners target mostly yellowfin tuna and skipjack, and on a world scale account for roughly 60% of all the tuna landed. In recent years the purse-seine catch of bigeye tuna has been increasing rapidly, mostly due to the increased use of FADs.

4.1.2 Longlines

This type of gear involves the use of a mainline which can be more than 100 km in length and from which as many as 3 000 branch lines, each with a baited hook, are dangled in the water column. The mainline is kept afloat by a series of buoys attached at intervals. It can take up to 8 hours to set the net and 12 to retrieve it. The gear is passive, in that it captures whatever fish happen to take the bait. One set of the net can capture several species of tunas, plus other types of fish, particularly swordfish and marlins. The gear fishes mostly at depths between 100 and 150 meters, where temperatures are cool and the largest tuna are most often encountered. These large tunas, especially bigeye and bluefin, fetch very high prices in the sashimi markets of Japan. The majority of large longline vessels target bigeye tuna. The smaller longline vessels use shorter mainlines and fewer hooks than do the larger vessels. They operate mostly in nearshore waters, whereas the larger vessels fish throughout the world. These larger vessels are often supplied by tender vessels, and can stay at sea for extended periods. The largest longline fleets are those of Japan, followed by those of Taiwan, Province of China and Republic of Korea.

In terms of tonnage of tuna captured, longlining captures about 14% of the world catch of tunas.

4.1.3 Pole and Line

Pole-and-line fishing, which was developed in several separate regions of the world, involves use of a hook and line attached to the end of a pole, improving both leverage and reach. This general method of fishing has been used for centuries in the South Pacific, Japan, and the Maldives. However, what could be called modern pole and line fishing developed during the early twentieth century. At that time the Japanese developed larger pole-and-line vessels capable of travelling to any ocean where tuna occurred in fishable quantities. The vessels, which carry live bait in tanks of circulating seawater, can freeze their catches and stay at sea for three or four months. In some cases, when bait from cooler waters is carried into tropical areas in pursuit of tuna, the water in the bait tank is refrigerated in order to maintain a temperature similar to that of the water where the bait was captured thereby increasing the survival of the baitfish.

The greatest growth in pole-and-line fishing occurred in Southern California in response to a growing demand for tuna following the introduction of tuna canning in the early Twentieth century. It was in this fishery that the “tuna clipper,” originated. These pole-and-line vessels were capable of packing up to 600 tonnes of frozen tuna, carrying large quantities of live bait, and staying at sea for many months. Pole-and-line fishing is a two-mode type of fishing. Live bait must first be caught before the tuna, which are most often skipjack and yellowfin, can be captured. The live bait was used to attract the tuna to the vessel where they where caught by pole-and-line gear. If the tuna were feeding well, and the “chummer” could keep the fish along side the vessel, several tonnes could be captured in a short time. Though pole-and-line fishing was at one time the major type of tuna fishing in terms of catch, because of improvements in purse-seine gear and methods it has diminished in importance.

In terms of tonnage of tuna captured, pole-and-line fishing, like longlining, captures about 14% of the world catch.

4.1.4 Trolling

Trolling consists of towing from a vessel, generally less than 20 meters in length, several lines with bait or lures attached. Most troll fisheries target albacore tuna (Thunnus alalunga), but several other species are also taken. Trolling accounts for only a very small percentage of the world catch of tunas.

4.1.5 Gillnets

Gillnets consist of a panel of fine, nearly invisible webbing suspended vertically in the water column by a series of floats along the top and a series of weights along the bottom. The fish become entangled when they try to pass through the net. Drift gillnets, which are generally used to capture tunas in the open ocean, consist of a series of individual nets connected together, often-exceeding 100 km in length. Because of the high incidental capture of other species, the use of drift gillnets longer than 2.5 km, was banned on the high seas by the United Nations. Nevertheless, such nets continue to be used inside the juridical waters of several states. Only a small percentage of the world catch of tunas is taken with gillnets.

4.2 Present-day Tuna Fleets

The ability of these different types of vessels to catch fish varies with the type of gear used, and the size of the vessels, and other factors. Their relative differences can be measured in economic and/or biological terms.

With respect to economic terms, a large purse-seine vessel might, on the average, be able to catch 20 tonnes of fish per day fishing (some high-line vessels can average much more than that), all of that is normally destined for canning. During one day of fishing a distant-water longline vessel might catch 2 tonnes of fish much of which is normally sold in the sashimi market, perhaps fetching 10 to 20 times the value per ton of the purse-seine caught fish. The economic success of fishing for each of the vessel types would, of course, depend on the costs of production, which depend on the cost of capital, amount of fuel used, crew size, etc. With respect to biological terms, catch is important because it represents mortality of the stock of fish being harvested. Because of their characteristics, such as speed, size, characteristics of the gear deployed, type of fish-finding equipment available (e.g. sonar, radar, aircraft), etc., the efficiency (measured in terms of how much fish is caught during a given period of time) may be quite different for two vessels fishing side by side. Estimating this efficiency, or fishing power, and how it changes with time, for the different types of vessels involved in a fishery is essential to the evaluation of the impact of fishing on the stocks of fish being exploited, and therefore to the study of methods to limit fishing capacity.

The FAO definition of fishing capacity, given in the introductory section of this document represents the maximum amount of fish that can be produced by a fully utilized fleet or vessel during a time period, given the size of the stock being fished and the level of fishing technology being employed. The vessel’s fishing capacity represents some maximum level of fishing mortality that it can generate. Throughout this study the term “vessel or fleet carrying capacity” is used to represent the capacity of a vessel or fleet to carry fish, and though not equivalent to the FAO definition, this carrying capacity (hold capacity) is assumed to be related to the ability of a vessel to catch fish under normal fishing conditions, and hence to the fishing mortality it can theoretically generate. Also throughout this document when vessel and fleet sizes are being referred to, carrying capacity is used. The two definitions can be equivalent when a fleet of vessels is fully utilized, but for most tuna fisheries, carrying capacity for a fleet of vessels is probably most often less than fishing capacity. Fish carrying capacity is measured for most tuna fishing vessels as the tonnage of fish that can be stored on the vessel when it is fully loaded, or the storage area measured in cubic meters. Of course there is some variability in this, depending on the size of fish being stored. A 1 000-ton vessel can store slightly more than that amount if the fish are small, and slightly less if they are large. Carrying capacity can be calculated for a vessel by examining its history of unloadings, and then taking some average of the maximum amounts unloaded. In the case of volumetric measures the shipyard-rated capacity of the fish holds are used. There is, of course, a correlation between the two measures, and one can be estimated from the other. For example, for the purse seine fleet operating in the eastern Pacific Ocean one cubic meter of storage capacity is equivalent to approximately 0.8 tonnes of carrying capacity, averaged over all sizes of tuna captured. Similar relationships can be defined for net tonnage, gross registered tonnage, displacement tonnage, etc., versus carrying capacity. The relationship among these variables is different for different countries, areas, fleets, shipyards etc., depending upon how the variables are defined. It will be essential to standardize the definitions if these relationships for large fleets from a variety of areas and nations are to be defined. In this report, carrying capacity will, in most cases, be used when discussing fleet size.

4.2.1 Purse-seine fleets

As already mentioned purse-seine vessels account for the majority of the commercial landings of tuna, taking about 60% of the nearly 4 million tonnes landed each year. The world fleet of purse-seine vessels consists of a variety of sizes, ranging in carrying capacity to a maximum of about 4 000 tonnes. Smaller vessels with less than about 200 to 250 tonnes capacity, generally fish within one or two days of the coastline, while the large vessels roam throughout the oceans of the world. In terms of the total carrying capacity of the world purse-seine fleet, the majority is comprised of large vessels, and these vessels account for most of the purse-seine catch.

There is no single source from which to obtain a listing of all purse-seine vessels. Most international organizations attempt to keep lists of vessels fishing in their areas, but for many tuna fisheries good records are not maintained.

The most complete data set available is that for the eastern Pacific Ocean, which is maintained by the IATTC. This data set, extending back for about forty years, includes all purse-seine vessels that have captured tuna in the EPO, and characteristics such as length, breadth, gross registered tonnage (GRT), net registered tonnage (NRT), carrying capacity, cubic meters of fish hold capacity, aircraft use, fish-finding electronics, net dimensions, etc. Much of this information is confidential, but in recent years the Commission has been making available to the public a list of the vessels, by name, flag, and fish carrying capacity or cubic meters of hold capacity.

The next most complete listing of vessels, for the western tropical Pacific, is maintained by the Forum Fisheries Agency (FFA) and the Oceanic Fisheries Programme of the Secretariat of the Pacific Community (SPC). The FFA includes in its list all vessels, by flag and size, which are licensed to fish in the waters of the nations belonging to the Agency, which covers much of the region of the western-central tropical Pacific. Although some purse-seine vessels without licences fish in the region, and are not included in the FFA list, the majority are so included. The SPC maintains a similar list of vessels which fish in its convention waters, but this list does not include all of them. In addition to the vessels that have fished in SPC waters, that organization includes some vessels from outside the region, particularly those of the Philippines. There is a great deal of overlap in the FFA and SPC lists, as would be expected, since the geographic areas of responsibility for the two organizations overlap a great deal. Both the FFA and the SPC have recently made their lists available to the public. Beyond the areas of these three international organizations, there or no detailed lists or registers of vessels available from public institutions for the Pacific Ocean in general. Such a lack of available information is important for any studies related to world fleet capacities. Data from industry sources and government reports were used to obtain information for vessels not included in the three lists. All of this information was utilized to estimate the size of the current fleet of large purse seiners operating in the Pacific Ocean. These estimates are shown in Table 1, as number and tonnage of high-seas purse-seine vessels by intervals of 400 tonnes of carrying capacity for the eastern Pacific (EPO) and the western Pacific (WPO). It is believed that these vessels account for at least 95% of the tuna catch from the Pacific Ocean made by purse-seine vessels. Small purse-seine vessels that make their catch mostly near shore make the remaining 5%. In the case of Japan, for example, there are approximately 25 purse seine vessels of about 200 tonnes of carrying capacity each that fish intermittently for tunas around Japan during June to September.

The majority of purse-seine vessels operating in the Indian Ocean fish in the western part of that ocean, and mostly in the region near the Seychelles. The Seychelles Fishing Authority (SFA) has licensed such vessels to fish in its waters since the mid-1980s. Between 1985 and 1995 the SFA maintained and published, on a quarterly basis, lists of purse-seine vessels authorized to fish in its EEZ. During that time the vessels listed in the quarterly reports accounted for most of the catch of tuna made in the Indian Ocean by purse-seine vessels.

Table 1: Estimates for the year 2000 of the numbers and carrying capacities of the world’s high-seas tuna purse seine fleet, by 400 ton intervals







<401 (mt)

Vessel #






Capacity (mt)



11 274

6 215

17 889

401-800 (mt)

Vessel #






Capacity (mt)

26 265


19 802

21 909

68 720

801-1 200 (mt)

Vessel #






Capacity (mt)

11 467

16 213

72 867

162 833

263 380

1 201-1600 (mt)

Vessel #






Capacity (mt)

8 030

13 204

44 745

33 033

99 012

1 601-2000 (mt)

Vessel #






Capacity (mt)

1 902

16 343

10 699

6 909

35 653

>2000 (mt)

Vessel #






Capacity (mt)


80 050

25 558

2 234

107 842


Vessel #






Capacity (mt)

48 064

126 554

184 945

233 133

592 696

A few purse-seine vessels that do not fish in the western Indian Ocean, and therefore are not included in the SFA data, catch small quantities of tuna in the eastern Indian Ocean. Recently the staff of the Indian Ocean Tuna Commission (IOTC) began to collect statistics on the number and characteristics of vessels fishing for tunas in the Indian Ocean, and it has made these statistics available for this study. The IOTC data, along with data from SFA, and supplemented by industry data, were used to estimate the number of high-seas purse-seine vessels fishing in the Indian Ocean (IND) during 2000 (Table 1).

Of the approximately 500,000 tonnes of tuna taken annually in the Atlantic Ocean nearly 45% is reported by ICCAT to be taken by purse seine vessels. Most of the purse seine catch is made in the eastern Atlantic by vessels flying the flags of France or Spain. Though the staff of ICCAT does not at the present time maintain a register or list of purse seine vessels operating in the Atlantic Ocean, it is currently in the process of formulating such a list. The tonnage and number of vessels presented in Table 1 for the Atlantic, by size intervals of 400 tonnes, is therefore comprised of information obtained from a variety of sources, mostly industry, and is not considered to be as complete as that for the other oceans.

The world fleet of high-seas purse-seine vessels currently stands at about 570 vessels. The total carrying capacity of this fleet is estimated to be nearly 600 000 tons, and if it were completely loaded with tuna this would represent nearly 600 000 tonnes of fish. The mean size of a purse-seine vessel is approximately 1 040 tons.

4.2.2 Longline fleets

Longline vessels account for approximately 14% of the world production of tuna. They are not usually referred to in terms of tonnage capacity, but rather as to whether they are distant-water vessels, which are capable of operating in all the world’s oceans and staying at sea for extended periods of time, or coastal vessels that normally are smaller and usually fish within the EEZ of the flag state. The former class of vessels accounts for the majority of the longline catch. The various international organizations are in the process of creating databases for the numbers of longline vessels fishing in their areas of competence, but such lists are generally not as far advanced as those for purse-seine vessels. Therefore, not as much detail will be presented for the longline fleets of the world. However, industry organizations, particularly Japan Tuna (Nikatsuren), maintain records of longline fleets throughout the world. In a recent document presented at the 2000 Commission Meeting of ICCAT, Document 019, the world fleet of large distant-water longline vessels was listed as follows: Japan, 532 vessels; Chinese Taipei, 600 vessels; Republic of Korea, 198 vessels; and approximately 236 vessels categorized under Illegal, Unregulated and Unreported (IUU) status. These 1 566 longline vessels are most likely an underestimate of the world longline fleet as the list does not include vessels from several nations, nor does it include smaller longline vessels that fish in the more inshore areas, but which land significant quantities of tuna.

4.2.3 Baitboat fleets

Baitboats, like purse-seine vessels are usually classified in terms of fish-carrying capacity. At one time, prior to 1950, baitboats were the dominant type of gear used to capture tuna. Once the modern purse-seine vessels were brought onto the scene in the late 1950s, they quickly overtook baitboats in terms of tonnage of tuna landed on a global basis. As the number of baitboats declined, the proportion of the world catch taken by longliners increased. Currently global catches of longliners and baitboats are almost the same, with baitboats also taking about 14% of the world catch of tunas. In the Pacific and Indian Ocean baitboats account for about 12% of the catch, while in the Atlantic Ocean, baitboats account for about 26% of the catch. In this study no estimate will be made of the number and total capacity of baitboats operating in the world tuna fishery, but because they account for nearly the same amount of catch as do the longline fleets, it is imperative that a concerted effort be made to create a world register of baitboats.

4.2.4 Other fleets

About 12% of the world catch is taken with gear other than purse seine, longline, and pole and line. About one-half of this remaining 12% is taken by trolling vessels that fish for albacore and the rest by a variety of other fishing gears, such as anchored and drifting gillnets, harpoons, and traps. No estimate will be made in this study of the amount of these gears operating in the world tuna fishery.

4.3 Fleet Statistics for the Future

It is obvious from the foregoing discussion that detailed information on the numbers and characteristics of tuna fishing vessels is limited, and not adequate for sophisticated quantitative analyses of fishing capacity on a global scale. It is also obvious that before the problems of global fleet capacity can be addressed in a comprehensive way there must be adequate information on the numbers and kinds of vessels fishing for tunas. The fact that it should be collected has been recognized in many international and national fora, so the only question is how this information can be collected. Most notably, the FAO Agreement to Promote Compliance and the U.N. Agreement on Straddling Fish Stocks and Highly Migratory Fish Stocks call on nations to work together within regional organizations to maintain lists of vessels operating in their areas of competence. Accordingly several of the regional tuna bodies have taken initiatives to create and maintain databases that will include all vessels fishing for tuna in their areas of competence. A world list of tuna fishing vessels and gear must include all types and sizes of vessels used to catch tunas, rather than just large purse-seine and distant-water longline vessels.

Currently, regional tuna bodies cover most waters of the globe where tuna are taken. ICCAT, which has responsibility for the Atlantic Ocean and adjacent seas, has initiated steps to compile a vessel list. The IOTC, which has responsibility for the Indian Ocean, has compiled a list of vessels currently fishing in the Indian Ocean, is working to improve the list and collect historical data on vessels that had previously fished in the area. The SPC, similarly, has compiled a list of vessels fishing in its region, and is working to update that list and compile historical information. The IATTC and FFA maintain databases for vessels that are currently and have previously operated in their respective regions. There are, however, areas that fall outside the jurisdiction of these various bodies, for which data is lacking. Most notably these areas represent parts of the west-central Pacific. The information that is collected by the various organizations is not uniform. Some organizations include detailed data and specifications for individual vessels, but others compile only statistics on the numbers of vessels fishing for tunas. Because the problems of tuna management are quite similar throughout all fisheries and areas, and because the vessels move from region to region, there is a strong need to collect detailed information by individual vessel that is comparable among regional organizations. The type of data that should be collected has been clearly identified in the FAO Agreement to Promote Compliance and by some of the regional tuna bodies, and such lists can serve as useful guidelines for collecting and maintaining a vessel database. The kind of information which would be useful to include in any international registry of tuna fishing vessels to be compiled by the regional tuna bodies includes:

In addition to the need to standardize the collection of vessel data, there is an urgent need to compile similar information for areas lying beyond the jurisdictions of the regional bodies. There are several possible means of accomplishing this, but two appear to be most practical. The first would be for the regional bodies to establish an inter-regional council or committee to standardize the collection of data and create a global register of tuna-fishing vessels. This committee or council would need to extend its investigations to include the collection of vessel information from areas outside the geographical areas of responsibility of its members. Because of matters related to jurisdiction and sovereignty, however, it could prove difficult for the regional bodies to collect such data. Therefore, a second possibility might be to call on the FAO to work with the proposed committee or council or to serve as the coordinating mechanism among the regional bodies. This latter approach would ameliorate the problems of jurisdiction and sovereignty that would be associated with the first approach. Both of these approaches are envisioned in the U.N. Stocks Agreement, Annex I, Article 7. It is interesting to note that the secretariats of the regional tuna commissions met in July 1999 at the offices of Eurostat in Luxembourg to consider the need to formulate a mechanism for the collection and exchange of information. Such an initiative could provide a mechanism for collecting and exchanging vessel data.

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