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 COI 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 On 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 O N T H E OCCURRENCE OF SPAWNING CONCENTRATIONS OF SOME OVER THE NW AFRICAN SHELF IN THE SUMMER OF 1967 By

J . R a z n i e w s k i Sea Institute, Aleja Zjednoczenia I, Gdynia, Poland

Observations on spawning areas and spawning pe­ fishing grounds of the NW African Shelf, mainly in riods of some important food in this region, made the region between Cap Blanco and the Gambia between 12th June and 5th August, 1967, are pre­ River, have shown that many fish species gather into sented in this paper. fairly large concentrations during summer in con­ Caranx rhonchus occurs in the catches throughout nection with their pre-spawning activities. The present the year, but only in summer does it congregate in report deals in the first instance with those species, for dense, pre-spawning concentrations. Spawning takes which an increase in the catches during the spawning place from the end of July, and the peak is probably period was noted when compared with other periods reached in August. The main spawning area seems to of the year. be between 19° N and 20°30' N at depths between Our observations were made together with other 25 and 35 m. ichthyological researches in the period from 12th June Lichia vadigo also occurs somewhat sporadically in to 5 th August, 1967. the catches throughout the year, but gathers in pre­ Of the greatest importance to fisheries at this period spawning shoals during summer. Spawning starts were spawning concentrations of Caranx rhonchus, towards the end of July and most of the spawning which is one of the most valuable commercial species takes place in August. The main concentrations were of the family . In the summer period, this found between 19° N and 21° N at depths between species also occurs in the catches throughout the year, 25 and 90 m. The shoals were intensively feeding on but only as a relatively small admixture among other Engraulis encrasicholus, and included some immature carangoid fishes. Its participation in the catches in­ specimens. creases considerably in the summer period, when it is Pre-spawning concentrations of Vomer setapinnis gathering into numerous concentrations of great densi­ and Hynnis goreensis were observed in June and July, ty. Analysis of the gonads showed that these were the latter chiefly in the southern part of the area spawning concentrations. In mid-June the gonads of investigated. most of the individuals of Caranx rhonchus were in Other species of commercial importance observed the Stage IV of maturity (according to M a i e r ’s scale) were Mycropteryx chrysurus, Dent ex filosus, Pagrus and some were in Stage V. At the end of July most of ehrenbergii, Diagramma mediterraneum, Sphyraena the gonads reached maturity Stage V and some even sphyraena and Trichiurus lepturus. Stage VI (running gonads). With the onset of sexual maturity the concentrations of Caranx rhonchus be­ came more dense, and at the same time they migrated from deeper into shallower waters. Our observations Very little is known as yet about the biology and did not include the spawning period, which seems to the spawning periods of most fish species occurring be mainly in August, when the yield of this species is over the NW African Shelf. still very good. A knowledge of the times and places of spawning is In the period covered by our observations the con­ of great significance for the fisheries, since fish in pre­ centrations of Caranx rhonchus occurred over a very spawning periods usually gather into more or less extensive area situated between 21° N and 16° N at a dense concentrations, thereby making efficient oper­ depth range of 25 to 100 m. The largest and most ations possible. Particularly important is the know­ abundant concentrations occurred in July between ledge about times and places of spawning concen­ 19° N and 20°30'N at depths between 25 and 35 m. trations of those species, which are of high commerical This is probably the spawning region for this species. value, but whose participation in the catches at other The concentrations consisted solely of individuals pre­ times of the year is insignificant. Observations made paring for spawning. Their lengths ranged from 25 to in 1967 during the voyage of M .T. “Wieczno” to the 43 cm. The average participation of Caranx rhonchus 200 J. Razniewski

in the catches in the above mentioned region amount­ fluctuated between 24 and 41 cm, with a peak at ed to about 20 % in June and more than 40 % at the 28-30 cm. end of July. Considerably less frequent and less abundant were The most valuable commercial carangoid species is pre-spawning shoals of Hynnis goreensis. As a more Lichia vadigo, a fish of medium size. During most of thermophil fish it occurred mainly in the central and the year, L. vadigo was rather scarce in the catches, southern parts of the region, where the water temper­ but usually with several specimens in a haul. During ature was a few degrees higher (24-25° C). Some the summer period, however, when L. vadigo is pre­ small concentrations of this fish were noted, mainly paring for spawning, it gathers into large concentra­ between the parallels 17°24'N and 18°01'N at depths tions. According to our observations in the middle of of 35 to 60 m. Its participation in the catches fluctu­ June, 50 % of the specimens investigated were already ated within 15 to 40 %, but with a very low general in maturity Stage V, and the rest in Stage IV. yield. The only haul of a more substantial yield (over Towards the end of July spawning started. Over 50 % 2 tons per 1 hour ) was obtained in the region reached the maturity Stage VI, the rest was in Stage V. of the Bissagos islands at a depth of 60 m, in which Similarly to what had been observed for Caranx sexually mature (maturity Stage V) Hynnis goreensis rhonchus, the concentrations of L. vadigo became amounted to more than 20 % of the catch. Here it more dense when approching the period of spawning, occurred along with Micropteryx chrysurus. The latter which seems also to take place mainly in August. The made over 60 % of the catch and was also ready for average participation of L. vadigo in the catches at spawning (maturity Stage V). the places where it occurred in these concentrations, Noteworthy among the family Sparidae are Dentex did not exceed 25 %. The concentrations of L. vadigo filosus and Pagrus ehrenbergii, two species spawning were in the period mentioned found at a depth range in summer time. Both are of high commercial value of 25 to 90 m in a rather limited area between 19° N and of large size, but particularly the first named. and 21° N. With the maturation of the gonads, the With the exception of the summer period, when our concentrations tended to shift towards shallower observations show them to gather into considerable waters. The best fishing results for this species were concentrations in connection with spawning, their obtained in July between the parallels 19°58'N and participation in the catches is small, and rarely more 20°06' N at depths below 35 m. The concentrations of than a few specimens are found in a haul. L. vadigo consisted mainly of individuals above 43 cm, On 5th July, 1967, in the region of 20°04'N and although sometimes juvenile individuals (from 32 to 17°14'W M.T. “Wieczno” encountered for the first 42 cm), the gonads of which did not exceed the time concentrations of sexually mature Dentex filosus maturity Stage III, were included. All specimens of and obtained an exceptional result of 5 tons in 1 L. vadigo, both adults and juveniles, were feeding hour’s haul. Dentex filosus made up 68 % of the catch, intensively in the period under consideration. It may, and the rest contained Diagramma mediterraneum, therefore, be assumed that the concentrations of also sexually mature. Most probably the spawning L. vadigo are not only associated with the approach of ground of these species is situated in the region the spawning period, but that they are also feeding mentioned, since the gonads of both were in a very concentrations. This is so with the concentrations advanced stage of maturity, a part of them running occurring at greater depths, where the gonads were (maturity Stage VI). Both specimens were represented in a less advanced stage of maturity. The food of in the concentrations solely by adults. The length of L. vadigo consisted of the abundant shoals of Engrau- Dentex filosus ranged from 52 to 98 cm, and the lis encrasicholus occurring at this period. length of Diagramma mediterreneum from 40 to Among other noteworthy fish of the family Caran- 60 cm. Since it was the first time we observed such gidae, gathering in the period of our observations into concentrations, we are unable to establish whether the pre-spawning concentrations, were Vomer setapinnis species always gathers in common spawning con­ and Hynnis goreensis. Pre-spawning concentrations of centrations or whether their spawning grounds partly Vomer setapinnis (maturity Stage V) were noted, as overlap each other. In the same extensive shallow a matter of fact, only in two regions; in June within region between the parallels 19°50'N and 20°08'N the parallels 15°16' N and 15°52'N at different we have several times noted fairly large concentrations depths (35 to 105 m), and in July between the parallels of Pagrus ehrenbergii in the second half of July. 19°58' N and 20°06'N at depths of 25 to 35 m. The These occurred at depths not greater than 32 to 35 m, participation of V. setapinnis in the catches in the and the participation of this species in the catches areas where it occurred did not exceed an average of increased on shallow grounds (about 22 m) up to 50 %, 20 %, and only in a single case it reached over 50 %. with a relatively high fishing yield (2 to 4 tons per The length of the individuals in the concentrations 1 hour trawling). Spawning concentrations over the NW African shelf 201

The analysis of the gonads of Pagrus ehrenbergii The spawning period of Thrichiurus lepturus had showed that the spawning had already commenced, already begun, according to our observations, in June, and that some of the individuals were even spent. It and lasted until about the end of July. Concentrations was noted that the males of this species showed nuptial of individuals of T. lepturus with running gonads oc­ colours. Their coloration was more bright and in­ curred in most cases at greater depths (90-140 m), tensive than the coloration of the females, which re­ most often between the parallels 17°30r and 19°03'N. mained unchanged. The length of the individuals in The participation of this species in the catches on the the concentrations ranged from 35 to 65 cm, and all above mentioned fishing grounds sometimes reached specimens were mature. No concentrations of Pagrus 90 %, but the total yield was very low and did not, ehrenbergii were found in other regions. as a rule, exceed 1 ton per hour trawling. Besides the species mentioned above, a number of The spawning periods were also recorded for some others gathered into spawning concentrations in the other species of no great commercial value to the period under observation. Among these of greatest fisheries. Towards the end of June, in the region of importance for the fisheries were Sphyraena sphyraena the Gambia River mouth, spawning of two typically and Trichiurus lepturus. I he participation of S. pelagic species, viz. Hemiramphus brasiliensis and sphyraena in the catches often reached 20 %. The Strongylura crocodila, were noticed, and at the end fishing yield of this species in the region where such of June and beginning of July rather large pre-- concentrations occurred, did not exceed, however, ing concentrations of Cubiceps sp. (family Stromate- 1 ton per hour trawling. Most often the spawning idae) were found, particularly in the region of Cap concentrations of S. sphyraena occurred throughout Timiris. In the middle of July the spawning in Tra- the month of July between the parallels 15°42' and chinus radiatus commenced, the males of which were 17°55'N at depths from 45 to 75 m. The concen­ observed with bright nuptial colorations. In the last trations consisted of mature individuals (most of them ten days of July spawning concentrations of Dactylop- with gonads in maturity Stage V) of lengths from 34 terus volitans were encountered in the region of 11N at a depth of 55 m. The species made up 100 % of to 51 cm. the catch there, amounting to nearly 1 ton.