PRÉFACE

Bien que depuis sa création l’essentiel de ses activi­ publié en 1969 par la FAO et qui contient, outre tés se soit développé dans l’Atlantique nord-est, le un résumé des contributions, les rapports établis par Conseil International pour l’Exploration de la mer chacun des présidents des sections. a toujours été ouvert aux problèmes soulevés par la Mais l’abondance et la qualité des documents pré­ connaissance des ressources exploitées dans les regions sentés rendaient nécessaire la publication intégrale de plus méridionales, bordant le nord-ouest africain, et la plupart d’entre eux. On verra en effet qu’ils con­ il a toujours fait une large place aux travaux qui leur stituent à la fois une synthèse précieuse et un apport étaient consacrés. C’est pourquoi, lorsqu’en 1964 les d’éléments nouveaux pour la connaissance d’une ré­ Présidentes du Comité Atlantique, du Comité des gion, trop seuvent méconnue jusqu’alors, mais pour­ Poissons scombriformes et du Comité de la Sardine tant remarquable par l’ampleur des phénomènes dy­ le proposèrent, le Conseil décida de tenir un Sympo­ namiques que l’on y observe, la haute productivité sium sur l’Océanographie et la pêche dans F Atlantique qui la caractérise et l’importance des pêcheries qui africain, au nord de l’Equateur (Résolution 1964/7). s’y sont développées. A la réunion statutaire de 1965, les objectifs du Ils montrent que le stade des études de base semble Symposium furent précisées et limités à l’étude des sinon dépassé, du moins assez avancé dans la plupart ressources du plateau continental africain, leurs stocks des domaines et que l’on possède suffisamment de et leur pêche, entre le détroit de Gibraltar et le Cap données pour organiser des travaux plus approfondis Vert, la région plus au sud devant faire l’objet de destinés à mieux comprendre les phénomènes qui se deux réunions particulières: un colloque sur l’océano­ déroulent dans cette région, les processus qui les graphie et les ressources halieutiques de l’Atlantique unissent et l’influence qu’ils peuvent avoir sur la distri­ tropical organisé par l’UNESCO, la FAO et l’OAU bution et l’abondance des ressources vivantes. à Abidjan en 1966 et une conférence technique de Si ce volume permet de faire le point de nos con­ la FAO sur les pêcheries de l’ouest-africain, à Dakar naissance au moment où fut tenu le Symposium, il en 1967. constitute également une contribution au projet de L’initiative du CIEM se situait donc a un moment recherchez en commun dans le nord-est de l’Atlan- et dans un contexte particulièrement favorables. Le tique central, adopté par la C O I en 1969, et dont la concours que lui apporta la FAO et la large partici­ réalisation a été confiée au Conseil. pation que connût le Symposium, du 25 au 29 mars 11 s’inscrit donc dans le cadre de la mise en oeuvre 1968 à l’Université de la Laguna, à Santa Cruz de d’un vaste programme scientifique et il faut souhaiter Ténérife, témoignent de l’intérêt qu’il suscita. qu’il soit le début d’une collaboration bénéfique entre O n en trouvera le reflet dans le compte rendu chercheurs et organisations d’Europe et d’Afrique.

R. L e t a c o n n o u x , A. E. J. W e n t T H E CHARACTERISTICS OF THE FISHING GROUND AT CAP TIMIRIS ON THE COAST OF WEST AFRICA

By

Z . K a r n i c k i The Sea Fisheries Institute, 1, Aleja Zjednoczenia, Gdynia, Poland

Figure 96. Echo-sounder record of the rocky^threshold at a depth of about 32 m.

The fishing ground at Cap Timiris extends from 40* 2 0 ’ 16° W 18°50'N to about 19°20'N, with depths from 25 to 40" 60 m. The bottom is slightly undulated and rather hard, with dense vegetation covering some spots. In CAP the depth range mentioned, the bottom is as a rule TIMIRIS

smooth, although single obstacles are found at some 20 ' places. The northern boundary of this fishing ground 2 O ' is formed by a rocky threshold, running from Cap Timiris (Fig. 96), over which trawling is impossible. Attempts to do so always occasioned the loss of gear.

HYDRO-METEOROLOGICAL CONDITIONS Detailed observations were carried out in the period from November 8, 1965 to January 15, 1966. In this period NE winds prevailed ; their occurrence is shown in Figure 98. Their force did not exceed 3° to 4° B. with a frequency of about 15 % in the period of observation. In November about 80 % of wind ob­ servations were in the range of forces 1° to 2° B. mainly in the NNE direction. In December and Jan­ 20- uary winds were NE. The state of the sea did not exceed 3° B, and 90 % of the observations were for winds of forces 1° to 2° B. 32 * The cloudiness of the sky was variable as shown in

Figure 99. 40' 20' Air-temperature varied from 20°C to 27°C with the Figure 97. Map of the fishing ground. The fishing ground at Cap Timiris 219

NE ploitation of these fishing grounds is dependant on the efficiency of capture of these species. L. vadigo provided up to 45 % of the total catches. The ex­ ploited stock consisted of well-grown individuals 40 to 60 cm long, weighing from 0-5 to 2 kg. Specimens below 35 cm were, as a rule, not found in the catches. The stomachs of L. vadigo were well filled with an­ chovy. The meat of L. vadigo is of dark colour and rather dry, being of average edible value, although it is one of the species with a good storage life in this NNE region. In this species during storage until freezing there is a tendency towards loosening of the texture of the meat tissue, which is very firm at first, and with simultaneous slow autolytic changes of the belly flaps. The deterioration of the meat quality is much slower than in blue fish or mackerel (Scomber colias). L. vadigo, caught in the afternoon before 5 p.m. in a haul of 10 to 12 tons and iced with flake ice on deck, remained in fairly good condition until the next morn­ ENE calm ing. This made it possible to store the bulk of fish for freezing during the night, when because of disper­ sion of fish shoals and their migration to the surface bottom trawling was ineffective. It should be mentioned that the bulk of fish for 4.4 6.6 40.1 22.1 20.2 6.6 % freezing aboard the B-23 type trawler, on which the observations were made, is kept in the fish pond on Figure 98. Wind direction frequencies. deck. The fish are iced in layers 75 to 90 cm thick, with flake ice produced aboard the vessel. Owing to following mean monthly temperatures: November high temperature of fish and of the air the ice melts 25°C, December 23°C and beginning of January quickly, and replacement of this loss is possible only 21-8°C. The water-temperature (measurements made over the surface of the fish layer. The storage life of in Kingston valve, 2 m depth) showed a clear tendency fish iced in this way is, therefore, not very long. The to drop during the period of observations (Fig. 99), problems are different aboard vessels of the B-18 type, with mean temperatures: 22°C in November, 19'4°C where fish for freezing are stored in tanks with re­ in December and 17-9°C at the beginning of January. frigerated seawater. In fishing operations in tropical On the fishing ground currents running along the regions the application of refrigerated seawater for shore towards the open sea with a speed of about prechilling has hitherto shown an advantage over the 1 knot were frequently noted. traditional method of icing, and permits the storage

TW°C t/h SPECIES COMPOSITION OF THE CATCHES The most abundant species on this fishing ground was the anchovy (Engraulis encrasicholus). This small fish, of a length of about 10 cm, concentrated during day-time into very large shoals reaching sometimes a 2.0 hundred meters in length. In view of its small size and the lack of resistance to damage, this fish is only suitable as a raw material for fish-meal, although its mass occurrence most probably caused the gathering

of a large number of Lichia vadigo and blue fish 0.5 (Pomatomus saltatrix), for which the anchovy is an important food. 10 12 14 16 18 20 2 4 6 8 1012 14 16 18 20 22 6 8 10 12 14 16 L. vadigo and blue fish are both of commercial Nov«mb«r Decembsr January importance being suitable for freezing and in great demand on the African market. The commercial ex­ Figure 99. Catch efficiency, water temperature and cloudiness. 220 Z. Karnicki

Figure 100. A good catch of L . vadigo aboard the B-23 trawler taken in the region of Cap Timiris.

of fish prechilled down to 50°G for a period of 10 to one night’s storage the smell of the fish became objec­ 15 hours without any considerable deterioration. tionable. Parasitic infestation, manifested by the pre­ Less abundant in the catches on these fishing sence of white cysts in the muscle tissue, is also grounds, though not less valuable than L. vadigo, is against its acceptance. These parasites, although harm­ the blue fish. It made up over 10 % of the total catch. less to man, nevertheless do spoil its appearance. The size variation was rather considerable (30 to Although no data on the development of the gonads 100 cm, and even more), though most of the specimens is available the concentrations of these fish on the were of a total length of 50 to 70 cm. The stomachs fishing grounds of Cap Timiris seem to be post-spawn­ of the blue fish were tightly packed with anchovy, in ing feeding concentrations. This is suggested by the the same way as had been noted for L. vadigo, thus fact that some running individuals of L. vadigo, blue giving an indication of intensive feeding. As a rule fish and large red snapper (Dentex filosus) were found feeding took place at night, when the shoals of an­ in July 1966 at 19°51'N and at a depth of 28 m. chovy dispersed, although some individuals were found 1 he stomachs of these fish were heavily filled in spite with well packed stomachs in daytime (in the after­ of their running gonads. noon) as well. About 17 % of the total catch consisted of other The meat of blue fish is of dark-grey colour and of species, among which should in the first place be a more loose consistency than the meat of L. vadigo. mentioned S argus sp. and yellow horse-mackerel The storage life of this species is rather short. Deteri­ (Decapterus rhonchus). O ther species, occurring spora­ oration of the meat texture and autolysis of the belly dically, were barracuda (Sphyraena barraccuda), Dia- flaps are obvious signs of quality changes. After only gramma mediterraneum and Dentex sp. The fishing ground at Cap Timiris 221

B. ------* Figure 101. Echo-sounder record of daily vertical migrations of anchovy. A. - at daybreak, B. - at nightfall.

The by-catch, utilized for fish-meal, was composed Maximum yields of catches of L. vadigo were ob­ of anchovies, small specimens of horse-mackerel and tained at the end of November, giving on an average yellow horse-mackerel and of other species, occurring 916 kg per 1 hour’s trawling. The maximum total in small numbers but unsuitable for human consump­ yield was also high in this period and amounted to tion. A small by-catch of sharks and rays was thrown 1750 kg per 1 hour’s trawling. In December a general overboard. drop in the catches was noted, though the yield was still maintained at a level suitable for the B-23 type trawler (freezing capacity 18 tons per day). The THE CATCHES average catch of L. vadigo was 725 kg per 1 hour’s Catches were made with a 110 feet nylon trawl, trawling, and the maximum total took place in the with a trawling speed of 4-3 to 4-5 knots. In view of first ten days of January. The vessel then left this the small area of the fishing ground and the con­ region for more prolific grounds. figuration of the bottom the following trawling pro­ As the catches of L. vadigo decreased, those of gramme was adapted: After the net was shot, e.g. at Sparidae increased, mainly Sargus sp., which occurred an approximate position of 18°50'N, trawling was sporadically in November and were rather abundant carried out at the suitable depth in the general direc­ in the catches in January making up 12 % of the total tion of NW. Having approached the rocky threshold catch, with an average yield of 1’5 tons per day. (see Fig. 97) the otter boards were brought up by Trawling was carried out during day-time, from the stern, the ship made a slow turn and the trawling day-break till nightfall, with an average trawling time was performed again in the opposite direction. of 10 hours per day in November, 12 hours in Decem­ At first catches obtained were at depths from 58 to ber and 13 hours in January. In the late afternoon 60 m. Later on the fish shoals moved towards shall­ a gradual migration of anchovy shoals towards the ower waters and at the end of December and beginning surface was noted, followed by L. vadigo and blue fish. of January they reached a depth of about 24 to 30 m, After sunset the shoals dispersed completely, and at and about mid-January they finally disappeared. Echo- that time bottom trawling gave no results. Pelagic sounding and trial hauls did not show any large con­ fishing gear was not used in that area. centrations of fish, except anchovy shoals. At night, blue fish and L. vadigo were feeding 222 Z. Karnicki

Figure 102. Characteristic echo-sounder record of anchovy shoal.

intensively as shown by the full digestive tracts of of the dispersion of the concentrations of L. vadigo, specimens captured sporadically at night and in mass remained on the fishing ground. It appears from quantities before dawn, as well as of individuals Figure 99 that the fishing yield dropped with the captured in great numbers on hooks at night. Most diminishing cloudiness (0 - cloudless, 4 - overcast). of the night catches were of Sparidae, which were Further investigations are, however, needed, in view caught in equal quantities also at day-time. of the fact that the water-temperature data are of a The echo-sounder records of the fish shoals were too general character. quite characteristic. Shoals of anchovy were very dist­ It is possible that intensive fishing on this restricted inctly recorded in the form of dense stripes of different fishing ground may have had some influence upon height and length (Fig. 101 and 102). No graphic the disappearance of the shoals of L. vadigo. In the echosounder records were observed for L. vadigo and period under consideration 3 to 4 vessels regularly blue fish, but the presence of these fish could sometimes carried out fishing operations on this fishing ground, be discovered by indications on the echo-sounder landing over 1500 tons of L. vadigo, apart from some screen. It appears, therefore, that L. vadigo and blue other species. The influence of intensive fishing is not, fish do not gather into dense concentrations, but re­ however, supported by observations from previous pe­ main in a somewhat dispersed state. riods, when only 2 or 3 trawlers were operating on the Some relationship between fishing yield and the same fishing ground, and still L. vadigo disappeared hydro-meteorological conditions could be seen. It seems for some time, to reappear later. Unfortunately, ac­ that water-temperature has the greatest influence, curate data are lacking for those periods. Neither has while sun irridiation and the state of the sea are of it been established if and when L. vadigo reappeared less importance. The effect of water-temperature upon on this fishing ground after it vanished in January the fishing yield is clearly shown in Figure 99. The 1966. Echo-sounding carried out until 24th January fishing yield dropped with a decrease in water-tem­ gave no positive results. The water-temperature at perature in the case of L. vadigo and blue fish. (Table that time was about 19°C. 32). The drop in water-temperature did not affect to It is assumed that the shoals of L. vadigo, owing to any great degree the shoals of anchovy, which in spite unfavourable conditions, moved southwards and dis­ persed there. The fact that in April 1965 some small Table 32. Species composition of catches (in %) concentrations of L. vadigo were found at a depth of 30-40 m at the position 15°40'N may serve as an Fish species November December January indication of this. The pattern of currents in this region would also point to the possibility of shoals of Lichia vadigo...... 51 47 38 Blue fish ...... 13 12 5 L. vadigo migrating southwards rather than elsewhere, Yellow horse-mackerel . . . 5 3 _ thus moving towards warmer waters. These are, how­ Other species...... 7 11 25 ever, assumptions, for the support of which it was not B y-catch...... 24 27 32 possible to collect sufficient data.