Multi-species and multi-gear tuna fisheries in the Atlantic and possible interactions between gears and species

Peter M. Miyake and Papa Kebe
International Commission for the Conservation of Atlantic Tunas
C. Estebanez Calderon, 3, Octauo
28020 Madrid, Spain

ABSTRACT

Most of the tuna fisheries in the Atlantic Ocean (including the Mediterranean Sea) often target more than one species, with additional species being taken as bycatch. These multi-species fisheries are very complicated; one species is targeted by various fisheries simultaneously or consecutively, while the same species is also caught by a third fishery as bycatch. Also, the Atlantic tuna stocks are quite heavily exploited; gear interactions are possibly more significant than for those stocks which are less exploited. In this report, the type and magnitude of possible gear interactions on Atlantic (and Mediterranean) tunas and related species are briefly discussed. The fisheries are considered in terms of longline and surface gears, with some reference to the probable interaction among surface gears. This report analyses possible fishery interactions on size-specific tuna catches as well as in terms of area. As far as yellowfin, skipjack and swordfish are concerned, the interactions between longline and surface gears do not appear to be as significant as has been believed. On the other hand, for albacore and bluefin tuna, fishing mortality by surface and longline fisheries seems to occur in different size categories of fish, suggesting possible significant interaction.

1. ATLANTIC TUNA FISHERIES

The following are the major tunas and tuna-like species that are targeted commercially by the Atlantic¹ tuna fisheries: bluefin tuna (Thunnus thynnus), southern bluefin tuna (T. maccoyii), yellowfin tuna (T. albacares), bigeye tuna (T. obesus), albacore (T. alalunga), skipjack (Katsuwonus pelamis) and swordfish (Xiphias gladius). In addition to these species, many small tunas and tuna-like fishes are of importance to coastal fishermen, from the point of view of economy as well as diet. These species are mainly blackfin tuna (T. atlanticus), various king mackerel species (Scomberomorus spp.), bonito (Sarda sarda) and frigate tunas (Auxis thazard). Among billfishes, sailfish (Istiophorus albicans) are targeted by many east Atlantic coastal fisheries but other large billfishes are either bycatch species to the commercial fisheries or targeted by recreational fishermen. Atlantic (including the Mediterranean Sea) catches of tunas and tuna-like species are summarized in Table 1.

¹ According to the Convention on which the International Commission for the Conservation of Atlantic Tunas (ICCAT) was established, the Atlantic Ocean includes all the adjacent seas including the Mediterranean. Some stocks are common between the Atlantic and the Mediterranean Sea and, hence, in this report the Mediterranean Sea is considered to be a part of the Atlantic Ocean.

	1983	1984	1985	1986	1987	1988	1989	1990	1991	1992	1993
Bluefin tuna	24202	26716	26836	22828	20668	27280	24874	24890	27051	27264	29674
Southern bluefin tuna	522	1636	1493	426	1193	612	700	1257	1344	525	1576
Yellowfin tuna	162315	113166	149110	134539	135326	127964	155287	177134	158586	148442	142874
Albacore	67320	57661	75978	88469	82707	67866	63365	67195	53723	66442	72985
Bigeye tuna	60339	69208	74093	59412	48868	58512	69295	71415	71702	77497	89645
Blackfin tuna	1738	1908	1403	1875	2130	3134	2918	3715	3542	4103	3460
Atlantic black skipjack	20881	19829	11699	13426	14439	22916	24272	25050	20014	16507	4667
Skipjack	133681	126786	118670	124473	116577	139888	115386	139639	195439	145702	180434
Bonito	42874	22505	25433	21990	30229	40886	26164	28049	33832	21944	29021
Frigate tuna	20221	25343	22460	17907	19578	20724	17473	16169	10639	7755	4251
Bullet tuna	0	0	0	2	0	357	723	3634	2171	814	70
Plain bonito	38	49	133	87	564	1482	1116	335	408	363	344
Wahoo	2366	2159	920	1150	1235	1616	1546	1460	1641	1912	2281
Spotted Spanish mackerel	16206	19491	15091	20666	20743	19518	21860	16960	17757	18326	20006
Serra Spanish mackerel	0	0	0	0	0	2704	2864	2471	2749	0	0
King mackerel	14607	13182	9964	12187	11890	13041	10841	10171	10122	10536	8994
W. African Spanish Mackerel	4716	4498	3989	3292	1799	3772	2684	4248	3581	1433	1788
Cero	677	680	574	500	392	219	234	225	375	389	360
King mackerel, unclassified	20	485	22	11	102	159	37	80	176	305	265
Sailfish	3780	3121	2925	2709	3112	2485	1967	2407	1994	2403	2877
Spearfishes	0	0	0	54	75	10	40	1	0	0	0
Black marlin	1	6	2	16	++	0	26	2	5	0	7
Blue marlin	1801	2227	2694	1954	1870	2497	3743	3293	3045	3060	2826
White marlin	1694	1089	1531	1630	1466	1283	1672	1035	1745	1451	1137
Swordfish	26702	35540	39104	41021	43730	51693	51671	42866	38742	40279	43689
Billfish, unclassified	21	161	156	138	252	178	127	35	28	43	5
Mixed tuna	0	0	0	0	0	0	0	0	0	0	3
Others & unclassified	11870	7554	7411	6728	14722	12435	14807	16832	16433	23808	7645
Total	618592	555000	591691	577490	573667	623231	615692	660568	676844	621303	650884

There is no fishing gear which catches one of the above species exclusively. In other words, all the tuna fishing gears also catch various tuna-like fishes in addition to their target species. At the same time, there is no tuna species which is the exclusive target of a single fishery (or fishing gear). Therefore, when considering fishing effort and abundance indices, the possibility of the existence of species interaction as well as gear interaction must always be taken into consideration. This situation is very similar to that of any other ocean in the world, but since the tuna resources in the Atlantic have been extensively exploited by European, African, American and Asian nations, and by the local subsistence fisheries as much as by the distant water high seas fishing nations, gear interaction is probably more complicated and significant.

Table 2 shows the catches of the commercially important tunas and tuna-like species, by major fishing gears in the Atlantic, in 1993. This table explicitly shows the complications of tuna fisheries in the Atlantic. What is not shown in the table is the catch of minor species such as frigate tuna, bonito, etc. As a matter of fact, these species are often discarded at sea and are never reflected in the catch statistics; this is particularly true of large industrialized fleets. On the other hand, as indicated above, the catches of such minor species are still very important for subsistence fishermen who catch these species with very small boats (e.g., dugout canoes).

Table 2. Catches, by species, of the major fisheries and areas in the Atlantic Ocean, 1993, in thousands of metric tons.(BFT=bluefin tuna, ALB=albacore, YFT=yellowfin tuna, BET= bigeye tuna, SKJ=skipjack tuna, SWO=swordfish)

Major gears	Area	BFT	ALB	YFT	BET	SKJ	SWO
Purse seine	E. Tropical Atl.		0.4	100.8	17.0	80.5
Baitboat	E. Tropical Atl.		++	13.3	12.3	40.3
Longline	E. Tropical Atl.			4.3	24.6
Purse seine	W. Tropical Atl.		0.2	11.2	0.1	3.3
Baitboat	W. Tropical Atl.			5.2	0.0	21.4
Longline	W. Tropical Atl.			9.4	16.0
Baitboat	Northeast Temperate	2.4	13.6
Longline	Northeast Temperate	2.6
Troll	Northeast Temperate	0.3	8.7
Drift net+Pelagic trawl	Northeast Temperate	2.7	5.9				0.9
Longline	Northeast Temperate	4.6	1.9	1.8	7.3		7.5
Purse seine	Mediterranean	11.8
Baitboat + other surf.	Southeast Temperate		4.6				0.4
Longline	Southeast Temperate		10.9	2.5	17.3		6.5
Rod and reel	Northwest Temperate	0.6
Purse seine	Northwest Temperate	0.3
Other surface	Northwest Temperate	0.8					0.4
Longline	Northwest Temperate	0.8	2.0	3.4	8.0		7.1
Baitboat + other surf.	Southwest Temperate		0.8				0.1
Longline	Southwest Temperate		11.0	6.0	8.0		7.6

2. STOCK UNITS OF MAJOR SPECIES OF TUNA AND THEIR EXPLOITATION

Figures 1-10 show average catches (in weight) of bluefin, yellowfin, albacore, bigeye and swordfish for the period of 1983 through 1993, by 5° × 5° area, by quarter, and by surface and longline gears. The size of the circles is proportional to catch and the same scale was used for longline and surface gears, so that these figures can be used to compare catches directly. However, different scales are used among species and, therefore, the circle sizes between species can not be compared directly. Efforts with nil catch are not shown in the figures. When catches were reported only in number of fish, they were converted into weight using constant conversion factors. No consideration was given to the variability of sizes between seasons, years and areas for this analysis, since the figures only show the indication of catch levels on a large scale basis. A few minor fisheries, for which information on area-time distributions of catches is not available, are excluded.

The surface gears contain all gears other than longline. Therefore, many gears (fisheries) are combined in this category. Although comparisons of average catches by longline and surface gears show a possible existence of gear interactions, gear interactions may also exist among various surface gears. On the other hand, the catches in the same area by surface and longline gears do not necessarily indicate the presence of simultaneous gear interactions, since these could be on different stocks or different age classes. The reverse is also true, i.e., the non-overlapping fisheries could have interactions.

These figures are prepared on a quarterly basis, since some of the overlapping between longline and surface fisheries on an annual basis may not show the true overlapping which takes place on a seasonal basis.

A general overview of the consideration of stock structure and fisheries interactions is provided below for major commercial tunas and tuna-like species in the Atlantic.

2.1 Bluefin tuna (Figures 1 and 2)

The ICCAT has adopted a two-stock hypothesis for Atlantic bluefin tuna, one stock in the east (including the Mediterranean) and one in the west, with some unknown (but of not very significant) magnitude of annual mixing between the two. These stocks are harvested at age 0 to 1 by handline (Spain and Italy), trap (Spain and Morocco), drift gillnet (Italy) and purse seine (Spain); at age 2-4 by baitboat (Spain), purse seine (France, Spain and USA), troll lines (Spain and considerably less by France), rod and reel (Spain, USA and France), handline, drift gillnet and trap; at age 6 and above, by longliners (Asian, USA, Canada and many other boats flying flags of convenience), harpoon (Italy, Canada), tended line (Canada), trap (Spain, Morocco and Canada), purse seine (France, Italy and Spain), handline (Spain, Morocco, Portugal) and rod and reel (USA).

Figures 1 and 2 demonstrate very little overlapping in the geographical distribution of bluefin catches between longline and surface gears. However, both are definitely fishing on the same stock directed at different age groups, and the geographical distributions of bluefin tuna change according to ages. The interactions between surface gears and longline alone could be complex, since most of the surface gears catch juveniles and, hence, will probably have an effect on longline catches a few years later, while the same size is caught by both trap and longline which are, therefore, directly competitive.

For the eastern stock, interactions among surface gears alone could be significant, since each fishery takes specific age groups in specific areas from age 0 to 10+, although quantifying the interactions would be very difficult due to the lack of fundamental data.

On the other hand, fishing by various surface gears for the same age groups also occurs almost in the same area and at the same time (e.g., troll and baitboat for age 2-4). The situation is further complicated by many of these gears catching tunas other than bluefin (e.g., Spanish trollers catch albacore as the target species; Asian longliners also target bigeye and most of the other tunas and Spanish longliners target swordfish).

2.2 Yellowfin tuna (Figures 3 and 4)

In the past, ICCAT has based its stock assessments on a two-stock hypothesis, i.e., one stock in the east and one in the west. However, due to the large number of recoveries of yellowfin tagged in the west and recovered in the east, the Commission is now inclined to adopt a one-stock hypothesis. However, further tagging and its analysis would be needed in order to draw any conclusions, since the fishing mortality rate seems much lower in the west, which may explain the lack of recoveries of tags in the west. The size of the fish being tagged should also be taken into account in such an analysis.

Small yellowfin tuna (age 0 to age 1) are caught mainly in the east tropical Atlantic by purse seine (mostly France, Spain, Morocco and vessels flying flags of convenience) and baitboats (Spain, Senegal, Ghana, etc.).

Medium to large size yellowfin are caught in both the east and west by longline (Cuba and Asian countries, particularly Korea), purse seine (France, Spain, Venezuela), baitboat (Portugal, Spain, Cape Verde, Venezuela). Most of the surface fisheries (baitboat and purse seine) also target skipjack, while the longliners target other major species of tuna.

As shown in Figures 3 and 4, the longline catches have declined in recent years. Although the major reason for this decline is the change in target species of longliners from yellowfin to bigeye, the surface catches can have an impact on the yellowfin population available for longline fisheries but not the other way around, particularly given that no spawner-recruitment relation has been recognized (also see the discussion in Section IV).

2.3 Albacore (Figures 5 and 6)

Two stocks, one in the north and one in the south, have been hypothesized based on the distribution and spawning areas. South Atlantic albacore may have some mixing with the Indian Ocean stocks.

The northern stock is harvested by surface gears and longline, while the catch by the latter has been much less important. The fishing area does not overlap significantly between these two types of gears due to the fact that the surface gears catch mostly young fish while the longline catches spawning stock (or mature fish). The surface gears consist of troll (Spain and France), baitboat (Spain, France), drift gillnet (France, Ireland and the UK) and mid-water trawl (France), and the areas of their operations are almost identical. In recent years, there has been significant conflict between the countries using drift gillnets and those which prohibit the use of this gear, since it seems that the drift gillnet is a more efficient fishing method (see Section 3.3 for explanation). Yield-per-recruit studies suggest that some increase in yield could be expected if the size of the first capture is increased.

The southern stock has been taken by purse seine (South Africa) as a target species as well as bycatch to yellowfin tuna (France and Spain), during the juvenile stage. However, the major exploitation is by longline (Taiwan) on the spawning stock. This is a rather unique tuna stock, on which both gear and species interactions are suspected to be minor, since most of the catches of southern albacore are taken by Taiwanese longliners strictly targeting albacore.

2.4 Bigeye Tuna (Figures 7 and 8)

A single stock in the total Atlantic is assumed. The young fish (0 to 2 years) are caught in eastern tropical waters by purse seine (France and Spain) and baitboat (Ghana). Medium to large bigeye continue to be caught by purse seine (France and Spain), but more specifically by the longliners (Japan, Korea and Taiwan) targeting this species. The purse seine and baitboat fisheries for juveniles actually catch a mixture of yellowfin, skipjack and bigeye, and report them together as skipjack or small tunas. Therefore, the total catches by species are not reported. The species breakdown of these mixed catches of small fish have been estimated by the intensive sampling of catches.

Since the magnitude of the longline catches has been much greater than those of surface gears, the recent increase in catches of small bigeye by surface gears may have a strong impact on the longline catches in the future, particularly in light of the results of the yield per recruit analysis, i.e., a substantial increase in yield is expected if the age of first capture is increased. It should be noted that the fishing areas significantly overlap between these two categories of gears in eastern tropical waters. However, the effect of longline fishery on surface gears would be minimal, unless the longliners were to deplete the spawning stock and so affect the abundance of juveniles, which has not been the case.

2.5 Skipjack Tuna

The two-stock hypothesis, east and west, has been adopted by ICCAT. Gear interaction is probably minor and less complex for this species, since longline gears are not involved. Also the fisheries harvesting this stock are limited to baitboat and purse seine.

In the southwest Atlantic, skipjack are almost entirely harvested by baitboat (Brazil). Occasional purse seine fisheries took place in the past but they have not been very successful. In the northeast Atlantic, baitboat and purse seiners (both Venezuelan) harvest this species together with yellowfin tuna.

In the east Atlantic, both purse seiners and baitboats (Ghana, France and Spain) catch large quantities of skipjack tuna. However, it is very difficult to evaluate the effort exerted on skipjack since this fishing effort is generally directed towards yellowfin tuna. This is particularly obvious for the purse seine fleets, except for certain years and areas when some purse seine fleets (particularly that of Spain) gave priority to skipjack. Hence, the situation is quite complicated.

2.6 Swordfish (Figures 9 and 10)

Stock structure is not yet very well defined. For the time being, the stock assessments are carried out under various hypotheses, North Atlantic, South Atlantic, and Mediterranean, or the entire Atlantic and Mediterranean. The majority of the catches are taken by longline targeting swordfish (Spain, Canada, Brazil, Portugal, Italy and many other Mediterranean countries), while some drift gillnet (Italy) and harpoon (Italy) fisheries also take place (particularly in the Mediterranean).

The Asian longliners (Japan and Taiwan) consider swordfish to be bycatch. However, in terms of quantity, the catch of this species is too large to be considered as bycatch. Swordfish catches comprise close to, or sometimes exceed, 10% of the total catches of longline fishery targeting bigeye. This is because the geographical distribution areas of bigeye and swordfish coincide, although vertically the bigeye is fished at a depth while swordfish are caught nearer the surface.

3. HISTORICAL CHANGES IN GEAR INTERACTION

As the fisheries develop, there can be considerable changes in gear interactions on tuna stocks. These changes have been seen for almost all the tuna species. The extreme cases of bluefin, yellowfin and albacore tunas are briefly discussed below:

3.1 Bluefin Tuna

For the eastern stock, the major catches have been in surface gears. The interactions among surface gears should have been significant as described briefly in Section 2.1, but the magnitudes may vary historically, depending on the catches by each gear. Figure 11 shows the historical catches by various gears. The trap fishery used to be the most important fishery on large bluefin (over 6 years old), while the catches by purse seine and baitboat which concentrate on juveniles (age 2-4) have been increasing significantly in recent years. At the same time, as the price has increased for bluefin tuna in the sashimi market, many longliners have been attracted to operate on this stock in recent years and these catches have also been increasing. Therefore, the pattern of interactions among the fisheries must have undergone significant change.

Several bluefin fisheries have disappeared in recent years, namely Norwegian purse seine fishery and Canadian trap fishery. The latter sometimes show signs of recovery from time to time. They are both large-fish fisheries operating at the marginal area of distribution. Therefore, their decline may be an indication of a depletion of stock size or merely of changes in the environment.

In the western Atlantic, there have been many regulatory measures taken since the early 1980s, including strict catch quotas and various size regulations. Those regulations have definitely affected the type of interactions among various gears. At present the purse seine catches of small bluefin tuna, which used to be the biggest portion of the total catches, have practically disappeared.

3.2 Yellowfin Tuna

Asian longliners used to target yellowfin tuna in equatorial waters, in the 1960s and early 1970s. At that time, the surface fisheries (baitboat and purse seine) were developing very quickly in the eastern tropical waters. In consequence, baitboats and purse seine gears were exploiting yellowfin tuna in the same area, while longline effort was very widespread.

In recent years, most of the longliners no longer target yellowfin tuna but are deploying deep longline gears to catch bigeye tuna. Therefore, the current longline fishing grounds do not coincide as much with the surface fishing grounds for yellowfin, although the surface grounds have extended much further west, which were historically the longliners’ yellowfin fishing grounds.

3.3 Albacore

In the Bay of Biscay, traditional fisheries of baitboat and trollers mostly harvesting albacore and some bluefin have been operated out by Spain and France for many years. Since the late 1980s, France developed new albacore fisheries using drift gillnets and pelagic trawls. Since the new fishing methods have been much more effective, most of the French traditional trollers have adopted new gears. However, drift gillnet fishing is illegal for the Spanish fishermen.

This has been causing very serious conflict between the fisheries of the two countries, since both French new fisheries and Spanish traditional fisheries are fishing in the same area and on the same stock, and one is more efficient than the other. While part of the conflict may be due to gear interaction, the major cause is the mere gear competition and the socio-economic problems shared by these countries.

4. INTERACTIONS WITH RESPECT TO SIZE OF FISH

As it is well known, gear interactions can take place in many different ways, such as consecutive and simultaneous interactions.

4.1 Consecutive Gear Interaction

Figures 12, 14 and 16 show size frequencies of Atlantic bluefin, yellowfin and albacore catches, respectively, by surface and longline gears, averaged over a nine-year period. Figures 13, 15 and 17 show catches shared between the surface and longline gears, by size categories of fish. These figures illustrate the location and the size of fish where gear interactions may be taking place.

From these figures, as has been already discussed in the previous sections of this report, it can be concluded that the longline gears catch relatively large tunas while the surface gears catch relatively small tunas. Therefore, if there is an interaction between surface and longline gears, it will occur more consecutively than simultaneously. Surface fishing reduces the stock size of juveniles and thus, like the longline fishery, affects the adult spawning stocks. For most of the tunas, the spawner vs. recruit relationship is not yet well established and thus the catches by longline may not affect the young tuna populations exploited by the surface gears. However, if such a relation exists, as has been assumed in the bluefin tuna assessments, the possible interactions of these two types of gears are mutual.

However, these same figures also show that in the area where the surface fisheries are developed (North Atlantic for albacore, east Atlantic for yellowfin, and east Atlantic and Mediterranean for bluefin), the absolute number of fish taken by surface gears surpasses the longline catch (Figures 12A and 14A). In many cases, even though surface gears catch relatively small tunas, the actual number of large fish caught by surface gears is greater than that caught by longline. In this sense, both fisheries can be interactive simultaneously as well as consecutively at different life stages of the fish.

Within the surface gears, several gears are exploiting fish stocks at the same stage, area and time, as discussed in the previous sections. Good examples are the purse seine and baitboat fisheries for tropical species (yellowfin, skipjack and bigeye), and the troll vs. drift gillnet and pelagic trawls for albacore in the North Atlantic.

5. MANAGEMENT OF MULTI-SPECIES FISHERIES WHICH HAVE INTERACTIONS AMONG GEARS

The management of tuna stocks which are caught by many gears at different life stages in different waters is very complicated and it is not the objective of this paper to address management issues. However, it should at least be recognized that the management measures aiming to obtain the best biological or economical yield is often not very realistic (see the following paragraphs for real examples). For example, for most tuna stocks, the biological yield per recruit would be increased by increasing the current age of recruitment (or age of first capture) considerably, and increasing fishing mortality of older fish. If the fish price according to the size category is taken into consideration, the economical yield would be increased substantially by restricting the catch to only the very large fish. However, this may result in prohibiting the taking of all small fish, a condition which would penalize usually coastal (often artisanal) fishermen and generally benefit the large industrialized fisheries.

In the case of ICCAT regulatory measures taken for west Atlantic bluefin tuna, the stock of which has been in a very serious condition, the best economical and biological yields have been sought and regulations have been set up to reach those objectives. Besides, in this case only three developed countries (Canada, Japan and USA) are involved in the fishery. However, for the yellowfin tuna and east Atlantic and Mediterranean bluefin tuna, the ICCAT management policy is more flexible, giving consideration to the African and Mediterranean coastal fishermen. The stock condition is, of course, not as serious as that of the west bluefin tuna stock.

Good examples of the above is the minimum size regulations for yellowfin and bigeye (both 3.2 kg), and for bluefin tuna (6.4 kg). This would increase the yield per recruit of these species. However, they are not really implemented. In all these cases, the catch of undersized fish are well over 50% of the total catches, in terms of number of fish and exceeded to a great extent the legal limit of 15% allowance. It is very difficult to implement the regulations since those small fish are mostly caught by local artisanal fisheries or by developing countries fisheries. Socio-economically those fisheries are very important for these countries.

Nevertheless, management policy should be made with a clear understanding of the fisheries’ interactions in order to avoid creating feelings of injustice on the part of the fishermen.

Figure 1. Geographical distribution of bluefin tuna catches by longline fishery, average for 1983-93.

1st quarter

2nd quarter

3rd quarter

4th quarter

Figure 2. Geographical distribution of bluefin tuna catches by surface fisheries, average for 1983-93.

1st quarter

2nd quarter

3rd quarter

4th quarter

Figure 3. Geographical distribution of yellowfin catches by longline fishery, average for 1983-93.

1st quarter

2nd quarter

3rd quarter

4th quarter

Figure 4. Geographical distribution of yellowfin catches by surface fisheries, average for 1983-93.

1st quarter

2nd quarter

3rd quarter

4th quarter

Figure 5. Geographical distribution of albacore catches by longline fishery, average for 1983-93.

1st quarter

2nd quarter

3rd quarter

4th quarter

Figure 6. Geographical distribution of albacore catches by surface fisheries, average for 1983-93.

1st quarter

2nd quarter

3rd quarter

4th quarter

Figure 7. Geographical distribution of bigeye tuna catches by longline fishery, average for 1983-93.

1st quarter

2nd quarter

3rd quarter

4th quarter

Figure 8. Geographical distribution of bigeye tuna catches by surface fisheries, average for 1983-93.

1st quarter

2nd quarter

3rd quarter

4th quarter

Figure 9. Geographical distribution of swordfish catches by longline fishery, avenge for 1983-93.

1st quarter

2nd quarter

3rd quarter

4th quarter

Figure 10. Geographical distribution of swordfish catches by surface fisheries, average for 1983-93.

1st quarter

2nd quarter

3rd quarter

4th quarter

Figure 11. Cumulative bluefin catches (in metric tons) in the east Atlantic (including Mediterranean), by various fishing gears. BB = bartboat, LL = longline, PS = purse seine, UNCL SURF = unclassified surface gear.

Figure 12. Average size frequencies of bluefin tana catches for the east and west Atlantic stocks, by surface and loogline gears, 1985-93.

A) E. Atlantic (& Med.) bluefin tuna. Longline and surface plotted on a same scale.

B) E. Atlantic (& Med.) bluefin tuna. Longline and surface plotted on different scale.

C) W. Atlantic bluefin tuna. Longline and surface plotted on a same scale.

Figure 13. Percentage of longline and surface bluefin catches in each size classe, in the east and west Atlantic, average for 1985-93.

A) E. Atlantic (& Med.) bluefin tuna.

B) W. Atlantic bluefin tana.

Figure 14. Average size frequencies of yellowfin tuna catches for the east and west Atlantic stocks, by surface and longline gears, 1985-93.

A) E. Atlantic yellowfin tuna. Longline and surface plotted on a same scale.

B) E. Atlantic yellowfin tuna. Longline and surface plotted on different scales.

C) W. Atlantic yellowfin tuna. Longline and surface plotted on a same scale.

Figure 15. Percentage of longline and surface yellowfin tuna catches in each size classe, in the east and west Atlantic, average for 1985-93.

A) E. Atlantic yellowfin tuna.

B) W. Atlantic yelowfin tuna.

Figure 16. Average size frequencies of albacore catches in the north and south Atlantic, by surface and longline gears, 1985-93.

A) N. Atlantic albacore.

B) S. Atlantic albacore.

Figure 17. Percentage of longline and surface albacore catches in each size classe, in the north and south Atlantic, average for 1985-93.

A) N. Atlantic albacore.

B) S. Atlantic albacore