4. Tuna Fisheries in the Eastern Tropical Atlantic (Contd.)

4.5.10. Japan

4.5.10.1. Generalities

The Japanese tuna fleets have been among the most oldest to have exploited the zone. Three Japanese fleets - longliners, pole and line boats and purse seiners - have exploited the Gulf of Guinea. The excellent fishing statistics submitted to ICCAT by Japan permit close monitoring of these fisheries from their first years of activity to the present.

4.5.10.2. Boats and fishing methods

a) longliners

The Japanese longline fleet has applied a large fishing effort in the Gulf of Guinea zone from 1957 – 1967, when deep adult tuna stocks were mostly virgin. These Japanese longliners are of the classical type described in paragraph 4.2.3. Recently, deep longlines, intended to catch more bigeye, have developed.

The change in the number of longliners in operation in the Atlantic is given in table 4.34. This same table gives the proportion of fishing effort (percentage of the number of hooks) that has been applied in the study zone. This table shows that the fishing effort of Japanese longliners was especially important in the sector during the years 1957 – 1967 (54%), but kept is at a low level recently (22% from 1970 – 1982).

b) Pole and line boats

This fleet was introduced in the Gulf of Guinea in 1962 (5 tuna boats) then developed during 1970 – 1974 where it grew from 6 to 24 boats (table 4.4). Based during their peak period in the ports of Freetown and Tema, these pole and line boats were little by little moved exclusively to Tema where their numbers followed a decreasing curve, leading to their disappearance in 1984 (by transfer of boats to Korean then Ghanean flag).

c) purse seiners

Japanese purse seiners were among the first to exploit the sector as they were present in the Gulf of Guinea from November 1964 with two tuna boats. Maximum fishing effort reached 8 to 11 purse seiners from 1968 – 1973 and become non-existent in 1975 (table 4.5). The fishing method of certain Japanese purse seiners is very specific, operating in pairs, each pair being accompanied by one or two accompanying vessels. A maximum of 3 pairs was in activity in the zone. This type of fishing disappeared in the Atlantic from February 1975, for apparently economic reasons (excessive operation costs for catch rates obtained). The Japanese purse seiners in activity since 1982 are of classical American type.

4.5.10.3. Fishing zones and seasons

a) longliners

Fishing zones and seasons of Japanese longliners changed considerably during 1957 – 1982 in relation to the change in target species. During the initial phase of the fishery (1957–68), longliner fishing took place mostly in the first quarter in the zone situated around the equator (figure 4.32). Recently, the fishing effort has been concentrated in the northern and southern sub-sectors of the study zone at the first and fourth quarters, principally targeting on bigeye concentrations (figure 4.33).

b) purse seiners

Fishing grounds and seasons for Japanese purse seiners from 1964 – 1968 are described by Marcille (1969). Those from 1969 – 1975 are known from statistics submitted to ICCAT (figure 4.34). From 1964 – 1974, fishing grounds of Japanese purse seiners were coastal zones in the the Gulf of Guinea between Angola and Guinea Bissau with a most of the catch taken in the area of Cape Three Points and Cape Lopez.

c) Pole and line boats

Fishing grounds and seasons of Japanese pole and line boats are well known since 1969. The fishing zones are primarily situated off the Côte d'Ivoire and Ghana and secondly off Sierra Leone and Cape Lopez (figure 4.35). These fishing grounds have changed little in spite of changes in fishing effort for both pole and line boats and purse seiners. A detailed analysis of Japanese pole and line fishing effort is presented by Wise (1986).

4.5.10.4. Species

a) longliners

As a rule, longlines catch a large number of species. However, they aim preferentially at a group of species, by setting them in the stratum of maximal abundance of target species. This is the case for Japanese longliners that targeted yellowfin until 1968 (around) and that have preferentially targeted bigeye since around 1970 (tables 4.7 and 4.12). Catch by species for Japanese longliners in the study area in numbers of individuals is given for all tuna species and xiphiids in table 4.35 (data based on log books).

b) purse seiners

Tables 4.8, 4.11 and 4.13 give the annual catches by species for Japanese purse seiners in the zone. The proportions of three principal species are variable, yellowfin being generally the dominant species, skipjack being very abundant in the catch, however, when in certain years (1964 for example), this species was caught very rarely by other fleets.

c) Pole and line boats

Tables 4.9, 4.10 and 4.14 give annual catches by species for Japanese pole and line boats in the zone. These tables show that skipjack is clearly the target species in this fishery and is always dominant in the catches. It should be noted, however, that the exact specific composition of catches has been subject to numerous discussions within ICCAT. It is very probable that the proportions of yellowfin and bigeye in the catch are not always exact as a result of true difficulties in identifying these two species at the time of landing, and as a result of measures taken by ICCAT to limit the catches of these species less than 3.2 kg in weight. These regulations could have lead to false declarations (in particular, the presence of undersized yellowfin declared as bigeye before enforcing the size limit on bigeye in 1978). In spite of these very serious doubts, the accepted catch numbers are consist of official declarations of fishing countries, sampling data not permitting, as is the case for purse seiners, the estimation of the specific catch composition in an exact manner. It is noteworthy however that the size sampling carried out in Puerto Rico each year and submitted to ICCAT frequently confirm the problems of the official species composition of the Tema landings.

Figure 4.32 Quarterly catches of yellowfin (a) and bigeye (b) in the region by the Japanese longline fleet by 5° square; average for the period 1957 to 1967, in number of individuals. (The catches observed each year are superimposed on the 5° sectors).

Figure 4.33 Quarterly catches of yellowfin (a) and bigeye (b) in the region by the Japanese longline fleet by 5° square; average for the period 1976 to 1982, in number of individuals. (The catches observed each year are superimposed on the 5° sectors).

Figure 4.34 Quarterly catches of yellowfin (a) and skipjack (b) by Japanese purse seiners by 1° square, in tonnes (The catches observed each year are superimposed on the 1° sectors).

Figure 4.35 Quarterly catches of skipjack by Japanese pole and line boats by 1° square; period 1969 to 1982 (The catches observed each year are superimposed on the 1° sectors).

4.5.10.5. Sizes caught

a) longliners

This fleet has had a good sampling coverage since the beginning of the fishery. Yellowfin and bigeye annual catch frequencies during the historical period and recently are given in figure 4.20 (Korean longliners). These figures confirm that longliner catches always consist of large fish.

b) purse seiners

The size frequency histograms of yellowfin catches, the dominant species, during 1970–1974 (figure 4.36) present very variable sizes, in a range of sizes comparable to, but slightly larger than, those of large FIS and Spanish purse seiners during the recent period.

c) Pole and line boats

The three species caught by the pole and line boats of Tema are always small (figure 4.31). These accepted size frequencies are from the FRU sampling of Tema landings; size frequencies furnished by Japan appear very biased for certain years (for undetermined causes).

4.5.10.6. Catch Rates

Japanese statistics are in general of excellent quality and make possible the analysis of catch rates of various fleets.

• Longliners: longline catch rates have been calculated by dividing the annual catch in weight in the study sector by the number of hooks set. Yellowfin catch rates manifest an extraordinary drop between the initial period 1957 – 1963 where the catch rates reach an average of 3.9 tonnes per 1000 hooks and recently with only 44 kg/1000 hooks from 1976 – 1982 (this low is due largely to changes in target species and does not correspond to low stock abundance). Bigeye catch rates, on the other hand, have regularly increased: from around 150 kg/1000 hooks until 1960; they oscillate between 300 and 600 kg/1000 hooks between 1961 and 1978. The average catch rate from 1979–82 is slightly less than 510 kg/1000 hooks.

• purse seiners: Japanese purse seine yellowfin and skipjack catch rates were very varuakbe from one year to the next between 1964 and 1975 (figures 4.22 and 4.29). Yellowfin catch rates show decreasing trend between the initial period 1964 – 1969 where the average catch rate reached 6.6. tonnes/day and the 1970 – 1975 period when it is only 3.1 tonnes/day. Skipjack catch rates are also very variable, but without marked trend, at an average level of 3.5 tonnes/day. The average bigeye catch rates, none until 1966, are 0.24 tonnes/day from 1968 – 1974.

• Japanese pole and line fleet catch rates are combined in the Tema fleet, which is considered to be relatively uniform. The catch rates are estimated according to the method described in paragraph 4.5.9.6. The pole and line boats of Tema have variable yellowfin catch rates (between 0.5 and 1.7 tonnes/day) at an average level of 1.1 tonnes/day (1969 – 1983). Skipjack catch rates, the target species of this fleet, are on the other hand high (between 3.4 tonnes/day and 7.6 tonnes/day), the average catch rate in skipjack during 1969–82 being 4.5 tonnes/day at sea. Bigeye catch rates on the other hand are always low with an average level equal to 0.26 tonnes/day. These figures give the order of magnitude of catch rates. In detail, biases in the species composition of the catch and in the estimation of fishing effort, limit the value of these figures.

Table 4.34 Numbers of Japanese longliners active in the Atlantic and percentage of effort exerted in the study area.

Table 4.35 Catch by species by Japanese longliners in the study zone (in thousands of individuals).

Figure 4.36 Examples of annual size-frequency distributions of yellowfin, skipjack, and bigeye caught by Japanese purse seiners.

4.5.11. Korea - Panama

4.5.11.1. Generalities

These two fleets are fleets of Korean commercial interests, in which one part operates for fiscal reasons under Panamanian flag. The boats seem to change flags frequently, maintaining the same crews and fishing zones which makes impossible and pointless to distinguish between Korea and Panama. There are two fleets, one longliners, operational since 1963 exploiting only the zone from 1968, the other, freezer pole and line boats, based in Tema since 1971. The relative fishing statistics of these two fleets are fragmented and apply only to the recent period, from 1974 for longliners and from 1980 for pole and line boats. The total annual catch by species is known since the beginning of the fishery, but the longline fishing zone, and thus the catch in the study area, is only known from 1974.

4.5.11.2. Boats and fishing methods

a) Pole and line boats

The size of Korean and Panamanian pole and line fleets is given in table 4.4. The pole and line fleet was introduced in Tema with two boats in 1971 and developed regularly reaching 23 pole and line boats in 1978. This increase in Korean fishing effort in fact operated largely by flag transfer and purchase by Korea of Japanese pole and line boats. A very rapid decrease in size of this fleet then occurred so that there were only 4 active pole and line boats in 1983.

b) longliners

The fishing method of these longliners, described in detail by Woo Il Choo (1975), is outlined in paragraph 4.2. The Korean longline fleet seems to have been active in the sector since 1968 after not exploiting southern albacore during its initial phase of activity. The total strength of the Korean longline fleet in operation in the Atlantic is known from 1969, but the fraction of activity exerted in the study zone is unknown until 1974 (table 4.36).

4.5.11.3. Fishing zones and seasons

a) Pole and line boats

The pole and line fishery catches principally skipjack in the coastal zone situated off Ghana. These fishing grounds are identical to those of Japanese pole and line boats (figure 4.35). Fishing takes place all year in the same sector.

b) longliners

Korean longliner fishing zones appear in figure 4.37. On examination of this figure one notices a cyclic seasonal balance of fishing zones previously recognized by various authors such as Yanez (1971) and Fonteneau (1981) and characteristic of longline fishing with yellowfin as the target species.

4.5.11.4. Species

a) Pole and line boats

The specific composition of Korean pole and line catches is characteristic of the Tema fleet, i.e. a very large dominance in skipjack (table 4.9), with a variable proportion of yellowfin and bigeye of similar size (tables 4.9 and 4.14). The exact species composition of catches is the subject of diverse controversies within ICCAT. It seems that, at least during certain years, the yellowfin and bigeye catches are poorly estimated, in particular, as a result of ICCAT 3.2 kg size limitations.

b) longliners

The Korean longline fleet has, for a considerable period of time, preferentially sought albacore in the north and south Atlantic. From the beginning of the 1970's its activity is oriented more and more toward tropical tuna in the study area, in particular toward yellowfin which make up 30% of the catch until 1978. Finally, from the beginning of the 1980's, there is a progressive reorientation of fishing effort toward bigeye (a fishing strategy comparable to that adopted more than a decade ago by Japanese longliners in the sector). These changes appear clear on examination of annual catches by species (table 4.7 and 4.12).

4.5.11.5. Sizes caught

Fish landed by Korean pole and line boats are as a general rule small for the three species (figure 4.31). This is due to the fishing method and the activity zone of vessels; the boats preferentially target schools of small tunas frequently of mixed species, skipjack being dominant. The size frequencies of yellowfin and bigeye caught by longliners in the Gulf of Guinea are given in figure 4.20. These fish are always large.

4.5.11.6. Catch rates by Korean fleets

• Longliners: catch rates of Korean longliners in the sector have been known since 1974. Yellowfin catch rates show weak fluctuations at an average level of 263 kg/1000 hooks (1974–82), without a marked trend. The catch rates are close to those of Cuban longliners (slightly lower) and much higher to those of Japanese longliners. Theses differences in catch rates are very probably due to fishing strategies and to different target species. Bigeye catch rates have shown a marked increase during the recent period: the catch rate equals 100kg/1000 hooks from 1974 – 1978 and reaches an average level of 312 kg/1000 hooks from 1979 – 1982. This improvement in bigeye catch rates is described by Lee (1986). It is clearly tied to a change in target species of Korean longliners, analogous but to a lesser degree, to the change of target species of Japanese longliners.

• Pole and line boats: catch rates from Korean pole and line boats based at Tema are comparable to those of Japanese pole and line boats for which good statistical data are available. Refer to section 4.5.10.6. for a discussion of this fleet combined with Tema fleet pole and line boats which is considered homogeneous.

4.5.12. Morocco

Morocco traditionally catches variable quantities of tropical tuna, principally skipjack, along its coasts during summer. Morocco being situated outside of the study zone, this fishery is not covered in the analysis. Morocco however has had a small fleet of purse seiners (1 purse seiner from 1972–1976, 4 purse seiners from 1977) since 1972. These purse seiners operate in the zone with French (3 purse seiners) and Spanish (1 purse seiner) fleets. We will not present the assessment of the activities of this fleet for lack of statistical data and will refer to French and Spanish fleets for which the activities are comparable to those of Moroccan purse seiners.

Figure 4.37 Quarterly catches of yellowfin (a) and bigeye (b) in the region by Korean and Panamanian longline fleets by 5^o square in tonnes (The catches observed each year are superimposed on the 5^o sectors).

4.5.13. Norway

We will cite Norway as a matter of interest only in that this country has run exploratory tropical tuna fishing by purse seine in the Gulf of Guinea in 1959 and 1960. The results of these campaigns were deceptive, and not followed commercial fishing. Nevertheless, Norway had a purse seiner in activity in the zone in 1972 and 1973 with an annual average catch of only 400 tonnes.

4.5.14. Portugal

As well as its tuna fisheries off Madeira and off the Azores, situated outside of the study zone, Portugal has fished tropical tuna in the zone from 1978. The number of active Portuguese purse seiners has varied from 1 to 3 units. All fishing statistics pertaining to this small fleet are of mediocre quality, consisting of the number of boats and total catches. One can however consider that the fishing zones and species caught are comparable to those of the FIS fleet; see paragraph 4.5.8.

4.5.15. Senegal

The Senegalese artisanal fishery of canoes has probably captured tuna for several centuries, especially small tuna and sailfish. It is currently very active and well covered by fishing statistics.

The Senegalese industrial tuna fishery started with a fleet of freezer pole and line boats in 1965 (table 4.4), then of small purse seiners in 1969 (table 4.5). After having rapid expansion until 1976, (reaching 20 freezer tuna boats in 1974), the Senegalese fleet recently has no more than a limited number of tuna boats (5 purse seiners and 1 ice pole and line boat in 1983). The Senegalese tuna fleet constitutes with the French and Ivory Coast fleets, a fishery in which the operations, fishing zones and target species are uniform. Taking into account this uniformity for reasons mentioned in paragraph 4.5.8, all relevant detailed information on the Senegalese tuna fleet has been combined with that of the French fleet within the FIS statistical entity.

4.5.16 Sao Tomé and Principe

Sao Tomé declared tuna catches of 100 to 300 tonnes per year for 1980 to 1983 to ICCAT with an average of 62% yellowfin and 38% skipjack. The exact fishing method which produced these catches is not known but was very probably artisanal fisheries (lines) catching tuna for local consumption.

4.5.17. Spain

4.5.17.1. Generalities

The Spanish tuna fleet has been present in the zone from the beginning of the industrialization of this fishery. Although historical fishing statistics are incomplete, it is known from reliable sources, in particular the numerous articles appearing in the magazine La Pêche Maritime, that the Spanish pole and line boats have been active in the zone extending from Mauritania to Cape Three Points from 1954 to 1965. Attempts at purse seine fishing by the Spanish were also among the first carried out in the Atlantic starting 1962 (purse seiner Marinero), the first commercial purse seiner being active since 1963. The relevant fishing statistics of the Spanish fleet are unfortunately mediocre until recently. Up to 1978, only very general indications on the size of fleets, fishing zones and catches are available. Only after 1979, are there excellent Spanish statistics and intensive size sampling.

4.5.17.2. Boats and fishing methods

a) Pole and line boats

The activities of these tuna boats are not well known. Catches by this fleet are published by ICCAT from 1962. Various sources, in particular Vincent Cuaz (1959), positively indicate Spanish tuna boat activity in the sector since 1954. The fishing methods of these boats seem different depending on their geographical origin: the Canary Island tuna boats practice dead bait fishing, while the Basque boats, much more numerous, practice live bait fishing.

b) purse seiners

The Spanish fleet sizes by tonnage are well known since the origin of the fleet (table 4.5) from figures submitted to ICCAT. After a relatively slow increase of the fleet until 1969 (7 purse seiners), the strength of Spanish purse seiners developed strongly, reaching 50 units, most of them large purse seiners in 1984. Table 4.37 gives the number of Spanish purse seiners in activity in the region by carrying capacity. The Spanish fleet is thus since 1978 the largest tuna fleet in the region (also in the Atlantic).

The fishing method of Spanish purse seiners was characterized until 1975 by the association of purse seiners with auxiliary baitboats. The baitboats stop schools of tuna which are then caught by the purse seiner (Pereiro et al., 1975). This association disappeared around 1975 (Fernandez and Garcia Mamolar, 1980) probably as a result of the extension of fishing grounds to offshore areas. However, in the Dakar sector, catches by purse seine of schools stopped by French baitboats based at Dakar remain frequent.

4.5.17.3. Fishing Zones and Seasons

a) Baitboats

There is no documentation published on this subject. It is known from multiple sources, however, that from 1954 and until 1965, a variable number of spanish tuna boats made trips for tropical tuna from November to January off Senegal and Sierra Leone (Freetown).

b) purse seiners

The changes of fishing zones and seasons of Spanish purse seiners during the history of this fishery is made difficult because of the small number of log books available until 1978. However, the observations of Fernandez and Garcia Mamolar (1980) broadly describe this change:

“up to 1969 the fleet exploits, as a group, all year round, the zone from Dakar to Freetown. From 1970 to 1974, the fishing zone extended (seasonally) in the Gulf of Guinea: in the first and fourth quarter in the Abidjan sector, the rest of the year in the northern sector (Senegal). From 1975, the fleet exploited all of the Gulf of Guinea, including the offshore areas, of Pointe Noir and Angola.”

These fishing zones have stayed relatively stable during the period 1975 – 1983; they are represented in figure 4.38.

4.5.17.4. Species

a) Pole and line boats

Catches by species of Spanish pole and line boats have only been submitted to ICCAT for 1962–65, even though the fishery existed since 1954; it is however possible to estimate catches for 1954 – 1961 from various sources (La Pêche Maritime, imports of Spanish tuna to the USA, personal communications of Spanish captains). These figures are given in tables 4.9 and 4.10. (These estimates could be very significantly low.) Nevertheless, the proportion of skipjack of this fleet is significantly larger (56% skipjack on average from 1962 to 1965) than that of the FIS pole and line boats operating simultaneously in the same sector (14%). This difference, is probably due to commercial reasons as the Spanish pole and line fleet were exporting tuna to the USA, the FIS fleet to France.

b) purse seiners

Catches by species of Spanish purse seiners are known from the start of the fishery in 1962. As with FIS fishery, specific catches registered in the log books are in general seriously biased and lead, among other biases, to an under estimation of bigeye catches. Procedures have therefor been implemented, as for the FIS fleet, to try and get non biased estimations of specific captures (Cayre, 1984). These estimates are given in tables 4.8, 4.11 and 4.13. The Spanish fleet has traditionally had skipjack as the target species, much more than other purse seiner fleets, in particular FIS purse seiners. This leads to a high percentage of skipjack in the 1963–1980 catches: 61% skipjack from 1964–69, while FIS purse seiners landed only 17% skipjack during the same period.

Figure 4.38.a Quarterly catches of yellowfin by Spanish purse seiners by 1° square; period 1975 to 1983, in tonnes (The catches observed each year are superimposed on the 1° sectors).

Figure 4.38.b Quarterly catches of skipjack by Spanish purse seiners by 1° square; period 1975 to 1983, in tonnes (The catches observed each year are superimposed on the 1° sectors).

4.5.17.5. Sizes caught

The Spanish fleet was not subject to an intensive size sampling until 1979. Up to that date, the sizes caught are similar to those of FIS purse seiner catches operating simultaneously in the same geographic and temporal stratum. The sizes caught remain unknown during the periods where the Spanish purse seiners operate in isolation, a frequent case until recently where only Spanish purse seiners exploited the northern zone.

4.5.17.6. Catch Rates

catch rates of the Spanish fleet are only known for purse seiners and from 1978, the date when log books became general in this fleet. Various estimates of Spanish purse seine catch rates before this date have been published by various authors, in particular Fernandez (1977) and Fernandez and Mamolar (1980), but these catch rates are not comparable to those of the recent period and will not be discussed.

Spanish purse seine catch rates have been estimated by dividing catches by species declared by Spain to ICCAT by standardized Spanish effort calculated at the CRODT from Spanish log books (in accordance with an identical procedure to that for FIS purse seiners). Spanish yellowfin catch rates are relatively stable from 1979–83, at an average level equal of 4.2 tonnes/day. Yellowfin catch rates are less than those of FIS purse seiners up to 1980 and higher starting in 1981. This difference in FIS and Spanish catch rates has been analyzed by Fonteneau (1986) and seems due to a change in fishing strategy and target species of the FIS fleet. Skipjack catch rates fluctuate without trends from 1978–83 at an average level of 2.6 tonnes/day. Those of bigeye are relatively low (compared to the two other species) and oscillate between 0.29 and 0.79 tonnes/day (average 1978 – 1983 = 0.49 tonnes/day). They are however much higher to those of FIS purse seiners that exceed only rarely 0.2 tonnes/day. This difference has not been analyzed by any author; it is probably not due to a sampling problem as the FIS and Spanish systems are the same.

4.5.18. U.S.A.

It is noted for the record that the first purse seiner in to operate commercially in the sector was an American purse seiner, the May Queen. The USA fleet is a fleet of large purse seiners, originating in the East Pacific, that fished seasonally in the Gulf of Guinea between 1967 and 1980. Most of these tuna boats fished yellowfin during the first quarter in the East Pacific until the catch quota set by the IATTC was attained; some of the boats exploited the Gulf of Guinea until the end of the year. This fleet obtained excellent catch rates during the initial period, but these dropped rapidly. This reduction in catch rate was most likely the cause of reduction in fishing effort in 1976 and subsequent complete departure of the fleet in 1982 (numerous vessels operating instead in the West Pacific). Good fishing statistics allow the examination of activities of this fleet during all phases of its operation.

4.5.18.2. Boats and methods

The American fishing fleet is almost exclusively large purse seiners (keeping in mind that 6 American freezer pole and line boats operated from the port of Tema during 1973). These large purse seiners are the classical type described in paragraph 4.2.2.

The first fishing carried out by an American purse seiner is probably the first for a purse seiner in the Eastern Atlantic. The May Queen, a small Californian purse seiner of 140 tonnes capacity first fished by purse seine from the end of 1960 to June 1962 in the Gulf of Guinea. It was not until 1967 that the first American commercial fishing was seen again in the zone (3 purse seiners). The size of the American fleet grew rapidly as 24 boats participated from 1969 in the Gulf of Guinea (table 4.5). The fleet decreased from 1979 to become totally absent from the zone in 1983.

4.5.18.3. Fishing zones and seasons

Fishing zones and seasons of American purse seiners are well known thanks to fishing statistics submitted to ICCAT. American purse seiners rapidly exploited all of the coastal zone from Guinea to Angola (figure 4.39). The principal fishing seasons were at Cape Three Points in the third quarter and off Angola in the fourth quarter. American purse seiners have practically never exploited the concentrations of large yellowfin in the first quarter, nor of skipjack situated off Senegal.

4.5.18.4. Species

Tables 4.8, 4.11 and 4.13 give the annual catch by species declared by the USA. The specific composition is based on log books and has not been corrected to eliminate potential biases leading to under estimation of bigeye catches. The examination of these tables reveals the strong interannual variability of the specific composition of American catches:

• in some years the two principal species, yellowfin and skipjack, for certain years, are in equal proportion (1970, 1972, 1976 – 1979).

• for other years, yellowfin is largely dominant (1968, 1969, 1975) while for others skipjack is by far the principal species (1971, 1973, 1974, 1975). This conveys the strong interannual variability of fishing strategies of the USA fleet that completely changes its target species from year to year, probably for economic motives.

4.5.18.5. Sizes caught

Sampling of USA tuna boat catches was done in Puerto Rico at the time of canning tuna and allows the examination of changes in sizes caught (keeping in mind that the rates of sampling are at times very weak, therefor not very significant). There is a strong interannual variability in yellowfin sizes landed (table 4.24); this variability is probably in relation to changes in target species and fishing strategies from one year to another.

4.5.18.6. Catch Rates

Catch rates of American purse seiners are known precisely for the whole duration of the fishery. Yellowfin catch rates are very variable according to years. The general average from 1969 to 1981 is 3.1 tonnes/day. Catch rates are very high during the first 3 years (14.0 tonnes/day from 1967–69) but are less than those of the FIS purse seiners during 1970–81, 3.5 tonnes/day for the large American purse seiners and 4.8 tonnes/day for the large FIS purse seiners. (American purse seine fishing was significant only during the second half of the year.) Skipjack catch rates fluctuate greatly from 2 to 17 tonnes/day and without apparent trend, the average catch rate for 1967 – 1981 being 5.8 tonnes/day. This catch rate is much higher than that of the FIS fleet which is only 2.0 tonnes/day from 1969 – 1981. Bigeye catch rates are very variable from 0 to 0.5 tonnes/day, without apparent trend and low on average (0.18 tonnes/day), at a level near those of other purse seine fleets.

4.5.19. U.S.S.R.

4.5.19.1. Generalities

USSR tuna fleets are comprised of longliners, purse seiners and non-identified surface fishing vessels. Qualitative information and relevant statistics of these diverse fleets are unfortunately very mediocre and incomplete: in particular methods, fishing zones, the number and characteristics of the boats are not known. The specific composition of catches often appears doubtful, as do the available measurements. One can only make a summary of the few official figures submitted to ICCAT.

Figure 4.39 Quarterly catches of yellowfin (a) and skipjack (b) by United States purse seiners by 1° square, period 1969 to 1980, in tonnes (The catches observed each year are superimposed on the 1° sectors).

4.5.19.2. Boats and fishing methods

No assessment of fleets in activity nor analysis of fishing methods have been presented to ICCAT. It seems however that the first longliners and purse seiners of the USSR were of a Japanese type and and classical American type respectively. The change in size of the fleets is unknown. The declared high catches by “surface” means were obtained by non-identified methods; perhaps by troll lines, deployed by fleets other than tuna boats, probably trawlers. During certain years (1970, 1971, 1973, 1974, 1975) large yellowfin catches were declared for “unknown” gear, which were probably made by longliners.

4.5.19.3. Fishing zones and seasons

Declared fishing zones are not represented as diverse criteria indicate that the fishing zones and seasons declared to ICCAT are very improbable.

4.5.19.4. Species

The specific composition of declared catches by the USSR seem very improbable if compared to that of other countries. Catches by species declared to ICCAT by the USSR are however incorporated in the catch by species tables.

4.5.19.5. Sizes caught

Very little size sampling has been submitted to ICCAT. These often seem to be not representative of landings.

4.5.20. Yugoslavia

It is noted for the record that Yugoslavia had a purse seiner in activity in the Gulf of Guinea in 1967. The catches have not been declared to ICCAT but it is known that more than 500 tonnes were landed in Abidjan by this purse seiner (Caveriviere, 1974).

4.5.21. Other countries

A certain number of countries not previously mentioned have fished tuna in the region. These are usually countries that do not submit statistics to ICCAT. Among these countries are: Grand Cayman Islands, Dutch Antilles, Mexico. Scientists of ICCAT attempt to estimate the catches by species of these various fleets from various sources of information (log books, commercial data). These estimates are then incorporated in the statistical tables in spite of their notable imprecision.

4.6. CONCLUSION

The history of tuna fisheries operating in the Eastern tropical Atlantic turns out to be relatively complete and simple to reconstitute. Statistical information is, for the most part from large fleets, complete and entirely available at ICCAT, a commission that includes all of the large fishing countries of the region. It is a extremely favorable situation, and very few geographical regions of the world can be as closely monitored from the point of view of tuna fishing statistics, and this since the beginning of the industrial fisheries. The principal difficulty to resolve in this type of assessment is a result of the excessive volume and heterogeneity of statistical information published as well as by the multiplicity of information sources. At the end of this review a certain number of “shadow areas” remain for which information is absent, incomplete or erroneous. This is the case for numerous artisanal fisheries and for some industrial fleets (beginning of the Spanish fishery, USSR, flags of convenience). In spite of these problems, it is possible to consider that changes in tuna fishing in the region have been correctly followed since its origin, as much for the volume of catch by species and by size, as for the importance of fishing gear used and fishing zones exploited.