Change in Elasmobranchs and Other Incidental Species in the Spanish Deepwater Black Hake Trawl Fishery off Mauritania (1992–2001)

From 1992 to 2001, by-catch that was landed from the Spanish deepwater trawl fishery for black hake off Mauritania was closely monitored. This is a highly specialised fishery, with two species of black hake (Merluccius senegalensis and Merluccius polli) constituting between 77–99% of total landings, which have annually averaged 9 300 tons over the past two decades. Landings of Sparidae were highest among by-catch species of commercial value, with the large-eye dentex, Dentex macrophthalmus being the most important until 1996, after which the family Lophiidae and others predominated. Next were the Elasmobranchii, including large demersal squalids and several species of rays, although their annual landings fell from 182 tons in 1992 to only 4 tons in 1999, rising to 37 tons in 2001. The present paper analyses these changes using by-catches retained in the black hake fishery. We believe that the decline could be due to a set of different factors: a change in depths fished, economic reasons and probable over-exploitation of both targeted species and by-catch. Elasmobranchs constituted only 0.1% of total landings in 1999, compared to 1.9% in 1992, although their contribution to total commercial by-catch was constant. Seasonality was clearly evident, with an absolute and proportional rise in elasmobranch by-catch during warm periods, reaching 75% of by-catch landings in some months, coinciding with a drop in total by-catch. These seasonal variations could be related to the migratory habits of the fishery's target species, black hake

Composition of Demersal Fish Assemblages in Deep-waters of the Western Guinean Gulf

Data from deep water hauls carried out during the Spanish Research trawling Survey 'GUINEA -90', conducted in Sierra Leone, Liberia, Ivory Coast and Ghana, between 100 and 700 m depth, were analysed. The taxonomic list of the survey showed a total of 91 fish species caught between 100 and 700 m depth. The maximum species richness and the highest abundances were found between 2000 and 300 m (60 species), depth range corresponding to the breaking of the continental shelf and to the upper part of the slope. Despite the local differences, the 'GUINEA -90' Survey showed the existence of fish assemblages

Faunistic Composition of Catches from the Spanish Bottom-longline Fishery in Deep-waters of Mauritania

The Spanish bottom-longline fleet started fishing in Mauritania in the 1990s targeting the hakes. In November 2000, an experimental longliner survey was carried out. The data showed 85% of the catches were used commercially and 15% were discarded, 84% of the commercial catches belonged to two hakes, Merluccius senegalensis and Merluccius polli. The areas of greatest abundance and species richness seem to correspond to upwelling zones, located by satellite imagery, where the highest values of both chlorophyll concentrations and pelagic resources were detected

Time-space reproductive differences of black hakes, M. polli and M. senegalensis off the NW African Coast

PosterThe named black hake in the Northwest Africa, M. polli and M. senegalensis, are distributed in Saharan, Mauritanian and Senegalese waters, where they are target species of Spanish trawling fleet and by some longliners. The separation of both species is quite difficult in practice, hence they are usually considered as black hake (mixed) in commercial catch statistics. This fact and the considerable deep distribution range of M. polli, results in a marked scarcity of comparative detailed studies about these species. The aim of this work was to analyze detailed biological data, collected during research trawl surveys and scientific observations onboard of commercial trawlers and longilenrs in Mauritanian and Senegalese waters during 2003-2006. By macroscopic analysis of the gonadic stages and the seasonal evolution of gonadosomatic indices (GSI), it has been determined the spawning season of both species. In order to determine the size at first sexual maturity, a logistic model was fitted to the mature fraction by length separated by species, considering different time periods. In other hand, the monthly time series of commercial gonad yields between 1986 and 2006 were split up in the trend and the seasonal components using a X-12 ARIMA routine. The spawning took place during the cold season, from November to February with the strongest signal during December-January for both species, but it occurs quite early in M. senegalensis. Males consistently maturing earlier than females, but there was a little length difference of sexual maturity for the two species. M. senegalensis reached the first maturity (35,4 cm) at slightly lower length than M. polli (37,0 cm) for combined sexes model. The sex ratio was skewed to females in both species. Because these species inhabits into a highly dynamic oceanographic area, and taking in account that recently it has been suggested a strong dependence between the climate-environment proxy NAO and the black hakes adult abundance dynamics, we explored possible deterministic relationships between reproduction features and sexual maturity of both species in phase with NAO index. It was not possible to determine if the difference in length-maturity values with some previous analyses were related with changes in abundance, the environmental forcing, or due to calculus procedures. However there was synchrony between the pronounced negative NAO phase and decreasing amplitude of seasonal peak of gonad yields for both species. Finally, despite of there was a slightly asynchrony in spawning timing among both species, we believe that in general terms it is justified to consider one set of maturity parameter values to perform the assessment procedures.Instituto Español de Oceanografía (IEO

Life history baseline of unexploited populations: The case of Beryx splendens from the Sierra Leone Rise

This study examines for the first time the biology of alfonsino (Beryx splendens) from three small seamounts of the Sierra Leone Rise (SLR), an unexploited and fragile ecosystem in the Atlantic, using data from an experimental survey carried out in 2001 by Spanish longliners. In general, the lack of rigorous baseline data limits the implementation of efficient management and conservation plans in fisheries strategies. Therefore, the main aim of present study was to provide baseline information on basic biological parameters of the alfonsino population associated with an unexploited ecosystem. A total of 17296 individuals of alfonsino were sampled from SLR. Alfonsino is gonochoric and presented an unbalanced sex ratio, there were significantly more females than males. Taking into account the results in stage of maturity of alfonsino and the gonadosomatic index values during studied period, we can conclude that at least one reproductive period in these seamounts was in the late spring and early summer. The spawning stage was attained at a minimum fork length of 23 and 25 cm for males and females, respectively. The size at which 50% of the population attains sexual maturity was approximately 28 and 27 cm for males and females, respectively. The stock structure of alfonsino showed a segregation of the size with the depth, as they increase in size they move into the deeper water.Versión del edito

Demersal Fauna on Deep Seamounts of Sierra Leone Rise (Gulf of Guinea, Africa)

From January to March 2001 an experimental fishing survey was carried out on the Sierra Leone Rise by four Spanish commercial boats, with the aim of prospecting the fishing potential for longliners of the demersal resources inhabiting the seamounts located between 9ºN-5ºN and 19ºW-27ºW, at depths between 200 m and 1 000 m. A preliminary analysis of the data recorded shows that the demersal fish fauna composition was similar in three of the ten seamounts, with an absolute dominance of the alfonsino, Beryx splendens Lowe, 1838, which accounted for more than 90% of the total catch between 200 and 800 m depth. Other commercial species in catches were Beryx decadacthylus and some Scorpenidae. The size structure and the distribution of alfonsino oscillated between 27 and 52 cm showing an increase of the mean size with depth which is similar to the pattern found in other seamounts worldwide Major abundances were located at the northern surveyed seamount where the highest yields, up to 750 kg per 1 000 hooks, were obtained. The southernmost surveyed seamount exhibited the lowest abundances and was characterized by the absence of the alfonsino in the catches. The species richness of these deep communities was very low, the accompanying fauna comprising less than 30 species. Discarded fishes were, in order of abundance: Promethicthys prometeus, Coloconger cadenati, Polymixia nobilis, Ruvettus pretiosus, Etmopterus princeps, Serranus accraensis and Gephyroberyx darwini

MANUEL À L’USAGE DES OBSERVATEURS SCIENTIFIQUES À BORD DES BATEAUX MERLUTIÈRS DANS LES EAUX D’AFRIQUE OCCIDENTALE

Ce manuel a été développé dans le cadre du projet « Study on improvement for the analysis and exploitation of observer reports in EU fisheries from NW African waters », Specific Contract No 12 dans le Framework Contract EASME/EMFF/2016/008, et consolidé par toutes les institutions impliquées lors de l’« Atelier sur la normalisation des méthodes d’observateurs au bord » qui s’est tenu à Santa Cruz de Tenerife du 27 au31 janvier 2020.Centro Oceanográfico de Málag

Informe de resultados de la campaña `Maurit-0911'. Estudio de los ecosistemas de la plataforma y margen contiental de Mauritania

Versión del edito

Some biological parameters of black hakes Merluccius senegalensis and Merluccius polli in Mauritanian waters

The black hakes Merluccius senegalensis Cadenat 1950 and Merluccius polli Cadenat 1950 are demersal species whose geographical distribution overlaps off Mauritanian waters. Spanish trawling and longliner fleets catch both species. During 2003 and 2004, 8101 and 2691 specimens of M. polli and M . senegalensis respectively were sampled biologically in several scientific watching campaigns onboard of commercial trawling ships and two longline experimental campaigns. From the information stored, it has been calculated the total length (cm) vs. total weight (g) and total length vs. total gutted weight relationships by sexes and species, as well as the conversion factor from gutted to total weight. By means of macrocospic analysis of the gonadic stages and the evolution of the gonadosomatic indexes (GSI) of both species it has been located the spawning season and zones. The spawning season extends mainly from November to February with a peak in December-January for both species, but with quite early in M. senegalensis . The males reaches the sexual maturity at lower lengths than females in both hake species ( 34, 3 - 39,2 cm in M. polli and 33,0 -39,2cm ;in M. senegalensis ) and females of both species reaches at the same length the first maturity. For the combined sexes, M. senegalensis reach the firsts maturity at slightly lower length (35,4 cm) than M. polli (37,0 cm). Females dominate the sex ratio in the populations of both species. The largest specimen caught (79,6 cm) corresponded to a female of M. senegalensis ,aswellastwomalesof great size for the same specie of (65,7 and 67,5 cm total length)