HAL (Le Centre pour la Communication Scientifique Directe), 2017
De nouvelles données sur le Dauphin à bosse de l'Atlantique (Sousa teuszii) en Guinée, au Nigéria... more De nouvelles données sur le Dauphin à bosse de l'Atlantique (Sousa teuszii) en Guinée, au Nigéria, au Cameroun et au Togo soulignent la pression des pêcheries et de la demande en viande d'origine marine.-Le Dauphin à bosse de l' Atlantique (Sousa teuszii) est une espèce encore mal connue: sa biologie, sa distribution détaillée et l'existence de populations restent encore à préciser. Des suivis de terrain, des enquêtes et des observations opportunistes ont permis d'identifier plusieurs nouveaux spécimens, observés en mer ou retrouvés après leur capture, dans quatre pays, dont le Nigéria et le Togo où la présence de S. teuszii, bien que fortement suspectée, n'avait jamais été prouvée. De nouvelles données, provenant des îles Tristao et de l'estuaire du Río Nuñez en Guinée du nord, indiquent que les populations du Rio do Jêba-Bijagos (Guinée-Bissau) et Guinée du sud devraient être combinées dans une seule population Guinéenne. La population du golfe de Guinée, qui correspond à la population historique de S. teuszii, anciennement appelée « dauphins du Cameroun », s'étend au minimum du Togo au sud du Cameroun. Plusieurs spécimens prouvent que la mortalité de S. teuszii causée par des captures accidentelles ou ciblées est significative, répandue et difficilement quantifiable en raison des contrôles sporadiques qui sont réalisés. Ces captures sont préoccupantes en Guinée, au Nigéria et au Cameroun. Les dauphins sont capturés accidentellement dans des filets maillants de pêcheries artisanales littorales, puis consommés comme « viande de brousse marine ». La commercialisation de ce type de viande étant croissante, les captures intentionnelles risquent aussi d'être encouragées. La rareté des observations et la petite taille des groupes dans le golfe de Guinée du nord indiquent des communautés de dauphins qui semblent plutôt en déclin. Des variations de répartition de l'espèce peuvent apparaître de novo le long des côtes fortement peuplées par l'Homme, après des décennies de prises accessoires, de compétition pour les ressources alimentaires, et de perte d'habitat suite à un développement côtier irréversible. Nous suggérons que le manque d'effort de suivi n'explique pas entièrement l'absence d'observations de S. teuszii sur les 1900 km de littoral allant du Ghana à la Sierra Leone, et particulièrement au Ghana où le suivi des petits cétacés est mieux documenté. La mise en oeuvre d'une politique de conservation rigoureuse devient dès lors de plus en plus urgente. De nouvelles Aires Marines Protégées binationales et transfrontalières pourraient avoir des effets positifs et mesurables en termes de conservation en limitant la compétition pour les proies avec les pêcheries, en limitant les captures accidentelles dans les filets et en limitant la destruction des habitats. L'installation d'un groupe de travail ad hoc, à l'échelle de la région considérée, est recommandée afin d'identifier des mesures pratiques visant à éviter que le Dauphin à bosse de l'Atlantique, maintenant menacé, ne se dirige vers l'extinction. SUMMARY.-The Atlantic humpback dolphin's biology, small-scale distribution and population structure are poorly known. Dedicated surveys and incidental observations resulted in new specimens and sighting records in four nations, of which Nigeria and Togo comprise long-suspected but newly documented range states. Multiple records at the Tristao Islands and Río Nuñez Estuary in northern Guinea indicate that the management stocks of Rio do Jêba-Bijagos (Guinea-Bissau) and South Guinea should be combined into a single Guineas stock. A Gulf of Guinea stock, the historical 'Cameroon dolphins', extends from Togo to (at least) southern Cameroon. Specimen evidence shows fisheries-caused mortality of S. teuszii is significant, widespread, and non-quantifiable at present due to only sporadic monitoring of landings. Of special concern are catches in Guinea, Nigeria and Cameroon. All dolphins were killed in small-scale nearshore fisheries, mostly from incidental gill-net entanglement, and were
HAL (Le Centre pour la Communication Scientifique Directe), Apr 17, 2018
ICAWA : International Conference AWA, Lanzarote, ESP, 17-/04/2018 - 20/04/2018In Atlantic Africa ... more ICAWA : International Conference AWA, Lanzarote, ESP, 17-/04/2018 - 20/04/2018In Atlantic Africa there is a crucial need to better assess the effect of climate change on marine ecosystems, particularly over the continental shelf and inside the national exclusive economic zones. Nevertheless there is a lack of observation carried out in the African ecosystems and the times series are often short or disrupted. Space-based observations allow precise synoptic observation of marine ecosystem and is often use to monitor, e.g., Eastern boundary upwelling ecosystems, from 36 years of constant monitoring from some major parameters as Sea Surface Temperature and more than twenty years for Ocean-Colour related parameters as surface primary productivity. The spatially heterogeneous trends observed show that these systems are highly variable, at temporal scales decades) that potentially impact some of their marine resources at rates that compete with the decline of human activities, beyond over-fishing. In this work we will present the effect of global warming at regional level for the three large marine ecosystems of Atlantic Africa on the sea surface temperature, wind stress and chlorophyll concentration as a proxy of primary production. The Canary and the Benguela systems are particularly impacted by the global warming, especially in their tropical parts, while Pacific systems show a more stable trend, due to their constantly high activity that partly counteracts some effects of the global warming
Small pelagic fish (SPF) species are heavily exploited in the four main eastern boundary upwellin... more Small pelagic fish (SPF) species are heavily exploited in the four main eastern boundary upwelling systems (EBUS), including both Atlantic African ones, as their transformation are increasingly used in the world food chain. Management rely on regular monitoring, but there is a lack of model for population traits emergence and evolution according to the variability of the environment. We attempt to extract some general rules based on the analysis of a life cycle biophysical individual based model applied to the round sardinella (Sardinella aurita, Clupeidae) population off North West Africa. Our analysis focused on the processes responsible for seasonal migrations, spatio-temporal body-length distribution, and inter-annual biomass fluctuations. These patterns were found at individual level in the dynamic change of preferred habitat, and variability in exploration capacities. The former resulted from complex interactions between natal homing behavior and environmental variability, while the last was determined by individual swimming capacities, the mesoscale structure of the habitat and the horizontal currents. Observed spatio-temporal abundance variability emerged from a superposition of numerous distinct individual life histories. This work also suggested an alongshore pattern in size distributions confirmed by in situ surveys. New insights about population structure are provided, with a focal area in Mauritania and mainly two migrating sub-populations centered at 18°N and 21°N, respectively. Inter-annual biomass fluctuations were linked to variability in Sahara Bank's fish recruitment, itself depending on southward current intensity. The identified processes constitute an analytical frame that can be transposed to study Small pelagic fish in all eastern boundary upwelling systems and used to study potential effect of regional climate change
Small-boat and shore-based surveys in 2017 confirm that Atlantic humpback (Sousa teuszii) and com... more Small-boat and shore-based surveys in 2017 confirm that Atlantic humpback (Sousa teuszii) and common bottlenose dolphins (Tursiops truncatus) are resident in shallow neritic waters surrounding the protected MPA Tristao Islands in northern Guinea. Inshore-type T. truncatus were encountered also between Conakry and Kayar. First documented in 2012, dolphin bycatches in local fisheries continue to occur. The frequency of beach-cast remains suggests a significant conservation issue. Both multi- and monofilament gillnets are widely deployed, but it remains unclear which gear is the main cause of mortality. Forensic evidence shows that captured dolphins are often utilized for local consumption. Marine bushmeat of cetaceans is documented in many coastal nations in West and Central Africa. In Tristao Islands their use is synchronous with and thought related to declining fish stocks. Significant anthropogenic mortality relative to their low abundance, besides suspected pressures such as prey ...
De nouvelles données sur le Dauphin à bosse de l’Atlantique (Sousa teuszii) en Guinée, au Nigéria... more De nouvelles données sur le Dauphin à bosse de l’Atlantique (Sousa teuszii) en Guinée, au Nigéria , au Cameroun et au Togo soulignent la pression des pêcheries et de la demande en viande d’origine marine. Le Dauphin à bosse de l’Atlantique (Sousa teuszii) est une espèce encore mal connue : sa biologie , sa distribution détaillée et l’existence de populations restent encore à préciser. Des suivis de terrain, des enquêtes et des observations opportunistes ont permis d’identifier plusieurs nouveaux spécimens, observés en mer ou retrouvés après leur capture, dans quatre pays, dont le Nigéria et le Togo où la présence de S. teuszii, bien que fortement suspectée, n’avait jamais été prouvée. De nouvelles données, provenant des îles Tristao et de l’estuaire du Río Nuñez en Guinée du nord, indiquent que les populations du Rio do Jéba-Bijagos (Guinée-Bissau) et Guinée du sud devraient être combinées dans une seule population Guinéenne. La population du golfe de Guinée, qui correspond à la pop...
ABSTRACT We summarize diversity, group size and habitat of cetaceans documented through ship-base... more ABSTRACT We summarize diversity, group size and habitat of cetaceans documented through ship-based visual survey effort (13,694 km; 1163.5 h) off NW Africa (Conakry to Tangier) in spring and fall of 2011-2013. Study area covered mainly continental shelf with some slope waters. Platform-of-opportunity surveying yielded 270 primary sightings of 14 species. Due to passing mode, 35.7% were identifiable only to family/category: unidentified Delphinidae (25.0%), unidentified rorquals (5.88%) and unidentified whales (4.78%). Delphinus delphis predominated with 28.7% of total sightings (32.7%, including probable) and a massive 71.3% (76.5%) of total number of cetaceans observed (n=15,595). Encounter rate was 81.2 common dolphins 100 km-1; mean group size 124.92. Tursiops truncatus, primarily inshore ecotype (median depth, 44.5 m), accounted for 9.56% (11.4%) of sightings and 1.35% (1.83%) of total cetaceans. Megaptera novaeangliae (6.25%) was regularly seen south of Dakar with a Southern Hemisphere seasonality. Other species showed a relatively low % occurrence: Globicephala spp. (2.57), Orcinus orca (1.10), Grampus griseus (0.73), Stenella frontalis (1.84), S. attenuata (0.37), S. clymene (0.37), S. coeruleoalba (0.37), Balaenoptera brydei (1.10), B. musculus (0.37), beaked whale (0.37), probable-B. borealis (0.37). Baleen plates recovered from a bottom-trawl also evidenced B. borealis presence. Seven new range state records included: G. griseus, S. coeruleoalba (Atlantic Morocco); O. orca, B. musculus (The Gambia), G. macrorhynchus, S. frontalis (Guinea-Bissau) and S. attenuata (Guinea).
Total visual survey effort was 468 h, 01 min, covering 5335 km. Depending on the exclusion or inc... more Total visual survey effort was 468 h, 01 min, covering 5335 km. Depending on the exclusion or inclusion of probable records, the sum of group sizes totalled 33 or 43 individuals, respectively. Humpback whale encounter rates between Conakry and Dakar then amounted to 1.74 or 2.27 whales/ 100 km, respectively. Group sizes ranged from 1-6 individuals (mean = 1.94, S.D. = 1.20, n = 17; median = 2). Minimally five of 17 groups (29.4%) consisted of adult-calf pairs, with a minimum crude birth rate ranging from 0.060-0.152. All sightings occurred in shallow water, 22-60 m (mean = 35.0 m, S.D. = 10.13, n = 17) but survey effort in deeper, offshore water was negligible. Sea-surface temperature at sighting locations ranged from 25.5-29.0°C (mean = 27.34, S.D. = 0.96, n = 17). No humpback whales were sighted during a second survey covering Conakry-Tangier-Las Palmas, from 9 May to 22 July 2012 (519 h, 13 min; 6278 km). The Cape Verde Islands comprised, to date, the only known wintering ground located in the NorthEast Atlantic. This study showed that Senegal, The Gambia, Guinea-Bissau and Guinea are normal range states for M. novaeangliae. A temporal signature, six to seven months out-of-phase with mid-season in the Cape Verde Islands, and neonate presence strongly suggest that the wide Conakry-Dakar continental shelf serves as both wintering and nursery grounds for a South Atlantic stock, in agreement with Bamy et al. (2010). This stock may comprise the northwesternmost component of the large humpback whale assemblage migrating in and out of the northern Gulf of Guinea in austral winter/spring. Further research is required to consolidate insights linking temporal and spatial distribution off western Africa with hemispheric stock identity and migration paths.
The distribution, status, and biology of the Atlantic humpback dolphin (Sousa teuszii) is critica... more The distribution, status, and biology of the Atlantic humpback dolphin (Sousa teuszii) is critically reviewed, and results of recent research are discussed. The species' known distribution limits are, in the north, Dahkla Bay (23º50'N), Western Sahara, and in the south, Tombua (15º47'S), southern Angola. Its habitat is predominantly inshore coastal and estuarine, over soft-sediment bottoms. There is no evidence that it might occur beyond the brackish waters of estuaries into a riverine, fresh-water habitat. There are no records for the Senegal, Casamance, and Niger Rivers. A total of eight stocks are provisionally discerned for management purposes. Six of these are confirmed-contemporary (based on recent records), including Dahkla Bay, Banc d'Arguin, Saloum-Niumi, Canal do Gêba-Bijagos, South Guinea, and Angola. Two stocks, the Cameroon Estuary and Gabon, are historical, and new fieldwork needs to confirm their current presence. No inference is made on degree of reproductive isolation and biological population status of any named stock. The potential existence of a western Togo stock is currently under study. Nine coastal states, including Morocco (Western Sahara),
An initial inventory of the dolphins and whales occurring in Guinea's coastal waters is documente... more An initial inventory of the dolphins and whales occurring in Guinea's coastal waters is documented primarily from specimens and photographic evidence obtained from strandings and by-catches. Seven species are fully validated, four odontocetes, Tursiops truncatus, Sousa teuszii, Stenella frontalis, Kogia breviceps and three balaenopterid whales: Balaenoptera brydei, Balaenoptera acutorostrata and Megaptera novaeangliae. Another three reported species (Globicephala macrorhynchus, Steno bredanensis and Delphinus delphis) are insufficiently supported but thought to be valid. Small cetaceans landed as by-catch and a stranded whale were used for human consumption, but no evidence of substantial takes, directed or by-catch, was found. However, concern is raised about even minimal takes of the vulnerable Atlantic humpback dolphin. The seasonal presence of three confirmed humpback whales, two strandings (July and September) and a sighting (October), is synchronous with the species' southern hemisphere wintering/breeding season in low latitudes. We hypothesize that these whales may comprise the north-westernmost range of the population that breeds/overwinters in coastal waters of the Bight of Benin, northern Gulf of Guinea.
The limited information available on the status of inshore common bottlenose dolphins Tursiops tr... more The limited information available on the status of inshore common bottlenose dolphins Tursiops truncatus along the coasts of West Africa is reviewed. Although reported from at least ten countries, it is unclear whether their distribution is continuous. Population structure and genetics have not been studied, however cranial morphology suggests that the West African dolphins differ from North Sea bottlenose dolphins. Mean group sizes are small (3.19 – 12.91 individuals/group) and are smallest in Guinea-Bissau. There are no estimates of abundance but by analogy with a well-studied population in Sarasota, Gulf of Mexico, the Guinea-Bissau population may number only in the hundreds. It is essential that scientific estimates be obtained through dedicated surveys. In some areas of Guinea-Bissau with a high density of fishing activities, bottlenose dolphins are now less frequently encountered than they were in the recent past. Key parameters besides abundance, including population identity...
In northern Guinea, we sighted two groups of Sousa teuszii (n=25; n=40 dolphins) off the Tristao ... more In northern Guinea, we sighted two groups of Sousa teuszii (n=25; n=40 dolphins) off the Tristao Islands during exploratory small-boat surveys in 2011-12. Based on these and recent (2013) observations in the contiguous Río Nuñez estuary, we propose a single 'Guineas stock', combining the former 'Rio do Jêba-Bijagos' and South Guinea stocks. Significant mortality of S. teuszii from fisheries interactions is widely recognised however not quantifiable as monitoring effort is sporadic. In Guinea, catches were documented in 2002 (n=1) and in 2011-12 (n=5). Landed specimens were recorded in Cameroon (n=2) and Nigeria (n=2). All individuals were killed in small-scale coastal fisheries, presumably as accidental net entanglements, though directed takes cannot be excluded. All landed dolphins were butchered for human consumption (marine bushmeat). Nigerian fishers indicated also an alternative use as shark bait. If local markets in cetacean bushmeat and bait develop, as in Ghana, that will exacerbate pressures by encouraging directed takes. Catch records in Nigeria and sightings in Togo authenticate both nations as (long-suspected) range states for S. teuszii, a belated documenting of the primary, historical distribution. The Gulf of Guinea stock ('Cameroon dolphins') extends at least from Togo to southern Cameroon, and probably into Equatorial Guinea. However, rare sightings of small groups point to remnant, not thriving, dolphin communities. We anticipate de novo distribution gaps emerging and consolidating, following decades of fisheries interactions and creeping encroachment on once pristine coastal habitat. Developed coastlines in Ghana and Côte d'Ivoire devoid of records may already constitute such gaps. As the lack or scarcity of records warn about formidable challenges to the long-term survival of S. teuszii, innovative, workable protection measures are needed, soonest. We recommend the implementation of several new border-straddling marine protected areas (cf. Saloum Delta-Niumi National Park Complex) which could bring forth a major conservation effect. Binational involvement bears obvious advantages, from sharing responsibilities and allowing for larger protected areas. Suggested dolphin sanctuary examples could include MPAs straddling borders between Cameroon/Equatorial Guinea and Guinea-Bissau/Guinea-Conakry.
We summarize diversity, group size and habitat of cetaceans documented through ship-based visual ... more We summarize diversity, group size and habitat of cetaceans documented through ship-based visual survey effort (13,694 km; 1163.5 h) off NW Africa (Conakry to Tangier) in spring and fall of 2011-2013. Study area covered mainly continental shelf with some slope waters. Platform-of-opportunity surveying yielded 270 primary sightings of 14 species. Due to passing mode, 35.7% were identifiable only to family/category: unidentified Delphinidae (25.0%), unidentified rorquals (5.88%) and unidentified whales (4.78%). Delphinus delphis predominated with 28.7% of total sightings (32.7%, including probable) and a massive 71.3% (76.5%) of total number of cetaceans observed (n=15,595). Encounter rate was 81.2 common dolphins 100 km-1; mean group size 124.92. Tursiops truncatus, primarily inshore ecotype (median depth, 44.5 m), accounted for 9.56% (11.4%) of sightings and 1.35% (1.83%) of total cetaceans. Megaptera novaeangliae (6.25%) was regularly seen south of Dakar with a Southern Hemisphere ...
An initial inventory of the dolphins and whales occurring in Guinea's coastal waters is documente... more An initial inventory of the dolphins and whales occurring in Guinea's coastal waters is documented primarily from specimens and photographic evidence obtained from strandings and by-catches. Seven species are fully validated, four odontocetes, Tursiops truncatus, Sousa teuszii, Stenella frontalis, Kogia breviceps and three balaenopterid whales: Balaenoptera brydei, Balaenoptera acutorostrata and Megaptera novaeangliae. Another three reported species (Globicephala macrorhynchus, Steno bredanensis and Delphinus delphis) are insufficiently supported but thought to be valid. Small cetaceans landed as by-catch and a stranded whale were used for human consumption, but no evidence of substantial takes, directed or by-catch, was found. However, concern is raised about even minimal takes of the vulnerable Atlantic humpback dolphin. The seasonal presence of three confirmed humpback whales, two strandings (July and September) and a sighting (October), is synchronous with the species' southern hemisphere wintering/breeding season in low latitudes. We hypothesize that these whales may comprise the north-westernmost range of the population that breeds/overwinters in coastal waters of the Bight of Benin, northern Gulf of Guinea.
The limited information available on the status of inshore common bottlenose dolphins Tursiops tr... more The limited information available on the status of inshore common bottlenose dolphins Tursiops truncatus along the coasts of West Africa is reviewed. Although reported from at least ten countries, it is unclear whether their distribution is continuous. Population structure and genetics have not been studied, however cranial morphology suggests that the West African dolphins differ from North Sea bottlenose dolphins. Mean group sizes are small (3.19 -12.91 individuals/group) and are smallest in Guinea-Bissau. There are no estimates of abundance but by analogy with a well-studied population in Sarasota, Gulf of Mexico, the Guinea-Bissau population may number only in the hundreds. It is essential that scientific estimates be obtained through dedicated surveys. In some areas of Guinea-Bissau with a high density of fishing activities, bottlenose dolphins are now less frequently encountered than they were in the recent past. Key parameters besides abundance, including population identity, bycatch levels and other anthropogenic threats need to be documented and quantified before any deliberate exploitation is considered. A small-scale, botched live-capture operation in Senegal in 2003, in which all dolphins died, serves as warning against such opportunistic schemes. In management terms, live-capture operations are equivalent to hunting and multi-year, large-scale removals of bottlenose dolphins in Guinea-Bissau would have the potential to effectively extirpate the wild population from its waters.
Seventeen confirmed and four probable sightings of humpback whales, Megaptera novaeangliae, were ... more Seventeen confirmed and four probable sightings of humpback whales, Megaptera novaeangliae, were documented from platform-of-opportunity Research Vessel (R/V) Dr. Fridtjof Nansen in a passing-mode visual survey of continental shelf waters between Conakry and Cap Vert Peninsula (Dakar), 21 October -5 November 2011. None were encountered in the northern stratum Dakar-Agadir, 6 November -15 December 2011. Total visual survey effort was 468 h, 01 min, covering 5335 km. Depending on the exclusion or inclusion of probable records, the sum of group sizes totalled 33 or 43 individuals, respectively. Humpback whale encounter rates between Conakry and Dakar then amounted to 1.74 or 2.27 whales/ 100 km, respectively. Group sizes ranged from 1-6 individuals (mean = 1.94, S.D. = 1.20, n = 17; median = 2). Minimally five of 17 groups (29.4%) consisted of adult-calf pairs, with a minimum crude birth rate ranging from 0.060-0.152. All sightings occurred in shallow water, 22-60 m (mean = 35.0 m, S.D. = 10.13, n = 17) but survey effort in deeper, offshore water was negligible. Sea-surface temperature at sighting locations ranged from 25.5-29.0°C (mean = 27.34, S.D. = 0.96, n = 17). No humpback whales were sighted during a second survey covering Conakry-Tangier-Las Palmas, from 9 May to 22 July 2012 (519 h, 13 min; 6278 km). The Cape Verde Islands comprised, to date, the only known wintering ground located in the North-East Atlantic. This study showed that Senegal, The Gambia, Guinea-Bissau and Guinea are normal range states for M. novaeangliae. A temporal signature, six to seven months out-of-phase with mid-season in the Cape Verde Islands, and neonate presence strongly suggest that the wide Conakry-Dakar continental shelf serves as both wintering and nursery grounds for a South Atlantic stock, in agreement with Bamy et al. (2010). This stock may comprise the northwesternmost component of the large humpback whale assemblage migrating in and out of the northern Gulf of Guinea in austral winter/spring. Further research is required to consolidate insights linking temporal and spatial distribution off western Africa with hemispheric stock identity and migration paths.
The distribution, status, and biology of the Atlantic humpback dolphin (Sousa teuszii) is critica... more The distribution, status, and biology of the Atlantic humpback dolphin (Sousa teuszii) is critically reviewed, and results of recent research are discussed. The species' known distribution limits are, in the north, Dahkla
HAL (Le Centre pour la Communication Scientifique Directe), 2017
De nouvelles données sur le Dauphin à bosse de l'Atlantique (Sousa teuszii) en Guinée, au Nigéria... more De nouvelles données sur le Dauphin à bosse de l'Atlantique (Sousa teuszii) en Guinée, au Nigéria, au Cameroun et au Togo soulignent la pression des pêcheries et de la demande en viande d'origine marine.-Le Dauphin à bosse de l' Atlantique (Sousa teuszii) est une espèce encore mal connue: sa biologie, sa distribution détaillée et l'existence de populations restent encore à préciser. Des suivis de terrain, des enquêtes et des observations opportunistes ont permis d'identifier plusieurs nouveaux spécimens, observés en mer ou retrouvés après leur capture, dans quatre pays, dont le Nigéria et le Togo où la présence de S. teuszii, bien que fortement suspectée, n'avait jamais été prouvée. De nouvelles données, provenant des îles Tristao et de l'estuaire du Río Nuñez en Guinée du nord, indiquent que les populations du Rio do Jêba-Bijagos (Guinée-Bissau) et Guinée du sud devraient être combinées dans une seule population Guinéenne. La population du golfe de Guinée, qui correspond à la population historique de S. teuszii, anciennement appelée « dauphins du Cameroun », s'étend au minimum du Togo au sud du Cameroun. Plusieurs spécimens prouvent que la mortalité de S. teuszii causée par des captures accidentelles ou ciblées est significative, répandue et difficilement quantifiable en raison des contrôles sporadiques qui sont réalisés. Ces captures sont préoccupantes en Guinée, au Nigéria et au Cameroun. Les dauphins sont capturés accidentellement dans des filets maillants de pêcheries artisanales littorales, puis consommés comme « viande de brousse marine ». La commercialisation de ce type de viande étant croissante, les captures intentionnelles risquent aussi d'être encouragées. La rareté des observations et la petite taille des groupes dans le golfe de Guinée du nord indiquent des communautés de dauphins qui semblent plutôt en déclin. Des variations de répartition de l'espèce peuvent apparaître de novo le long des côtes fortement peuplées par l'Homme, après des décennies de prises accessoires, de compétition pour les ressources alimentaires, et de perte d'habitat suite à un développement côtier irréversible. Nous suggérons que le manque d'effort de suivi n'explique pas entièrement l'absence d'observations de S. teuszii sur les 1900 km de littoral allant du Ghana à la Sierra Leone, et particulièrement au Ghana où le suivi des petits cétacés est mieux documenté. La mise en oeuvre d'une politique de conservation rigoureuse devient dès lors de plus en plus urgente. De nouvelles Aires Marines Protégées binationales et transfrontalières pourraient avoir des effets positifs et mesurables en termes de conservation en limitant la compétition pour les proies avec les pêcheries, en limitant les captures accidentelles dans les filets et en limitant la destruction des habitats. L'installation d'un groupe de travail ad hoc, à l'échelle de la région considérée, est recommandée afin d'identifier des mesures pratiques visant à éviter que le Dauphin à bosse de l'Atlantique, maintenant menacé, ne se dirige vers l'extinction. SUMMARY.-The Atlantic humpback dolphin's biology, small-scale distribution and population structure are poorly known. Dedicated surveys and incidental observations resulted in new specimens and sighting records in four nations, of which Nigeria and Togo comprise long-suspected but newly documented range states. Multiple records at the Tristao Islands and Río Nuñez Estuary in northern Guinea indicate that the management stocks of Rio do Jêba-Bijagos (Guinea-Bissau) and South Guinea should be combined into a single Guineas stock. A Gulf of Guinea stock, the historical 'Cameroon dolphins', extends from Togo to (at least) southern Cameroon. Specimen evidence shows fisheries-caused mortality of S. teuszii is significant, widespread, and non-quantifiable at present due to only sporadic monitoring of landings. Of special concern are catches in Guinea, Nigeria and Cameroon. All dolphins were killed in small-scale nearshore fisheries, mostly from incidental gill-net entanglement, and were
HAL (Le Centre pour la Communication Scientifique Directe), Apr 17, 2018
ICAWA : International Conference AWA, Lanzarote, ESP, 17-/04/2018 - 20/04/2018In Atlantic Africa ... more ICAWA : International Conference AWA, Lanzarote, ESP, 17-/04/2018 - 20/04/2018In Atlantic Africa there is a crucial need to better assess the effect of climate change on marine ecosystems, particularly over the continental shelf and inside the national exclusive economic zones. Nevertheless there is a lack of observation carried out in the African ecosystems and the times series are often short or disrupted. Space-based observations allow precise synoptic observation of marine ecosystem and is often use to monitor, e.g., Eastern boundary upwelling ecosystems, from 36 years of constant monitoring from some major parameters as Sea Surface Temperature and more than twenty years for Ocean-Colour related parameters as surface primary productivity. The spatially heterogeneous trends observed show that these systems are highly variable, at temporal scales decades) that potentially impact some of their marine resources at rates that compete with the decline of human activities, beyond over-fishing. In this work we will present the effect of global warming at regional level for the three large marine ecosystems of Atlantic Africa on the sea surface temperature, wind stress and chlorophyll concentration as a proxy of primary production. The Canary and the Benguela systems are particularly impacted by the global warming, especially in their tropical parts, while Pacific systems show a more stable trend, due to their constantly high activity that partly counteracts some effects of the global warming
Small pelagic fish (SPF) species are heavily exploited in the four main eastern boundary upwellin... more Small pelagic fish (SPF) species are heavily exploited in the four main eastern boundary upwelling systems (EBUS), including both Atlantic African ones, as their transformation are increasingly used in the world food chain. Management rely on regular monitoring, but there is a lack of model for population traits emergence and evolution according to the variability of the environment. We attempt to extract some general rules based on the analysis of a life cycle biophysical individual based model applied to the round sardinella (Sardinella aurita, Clupeidae) population off North West Africa. Our analysis focused on the processes responsible for seasonal migrations, spatio-temporal body-length distribution, and inter-annual biomass fluctuations. These patterns were found at individual level in the dynamic change of preferred habitat, and variability in exploration capacities. The former resulted from complex interactions between natal homing behavior and environmental variability, while the last was determined by individual swimming capacities, the mesoscale structure of the habitat and the horizontal currents. Observed spatio-temporal abundance variability emerged from a superposition of numerous distinct individual life histories. This work also suggested an alongshore pattern in size distributions confirmed by in situ surveys. New insights about population structure are provided, with a focal area in Mauritania and mainly two migrating sub-populations centered at 18°N and 21°N, respectively. Inter-annual biomass fluctuations were linked to variability in Sahara Bank's fish recruitment, itself depending on southward current intensity. The identified processes constitute an analytical frame that can be transposed to study Small pelagic fish in all eastern boundary upwelling systems and used to study potential effect of regional climate change
Small-boat and shore-based surveys in 2017 confirm that Atlantic humpback (Sousa teuszii) and com... more Small-boat and shore-based surveys in 2017 confirm that Atlantic humpback (Sousa teuszii) and common bottlenose dolphins (Tursiops truncatus) are resident in shallow neritic waters surrounding the protected MPA Tristao Islands in northern Guinea. Inshore-type T. truncatus were encountered also between Conakry and Kayar. First documented in 2012, dolphin bycatches in local fisheries continue to occur. The frequency of beach-cast remains suggests a significant conservation issue. Both multi- and monofilament gillnets are widely deployed, but it remains unclear which gear is the main cause of mortality. Forensic evidence shows that captured dolphins are often utilized for local consumption. Marine bushmeat of cetaceans is documented in many coastal nations in West and Central Africa. In Tristao Islands their use is synchronous with and thought related to declining fish stocks. Significant anthropogenic mortality relative to their low abundance, besides suspected pressures such as prey ...
De nouvelles données sur le Dauphin à bosse de l’Atlantique (Sousa teuszii) en Guinée, au Nigéria... more De nouvelles données sur le Dauphin à bosse de l’Atlantique (Sousa teuszii) en Guinée, au Nigéria , au Cameroun et au Togo soulignent la pression des pêcheries et de la demande en viande d’origine marine. Le Dauphin à bosse de l’Atlantique (Sousa teuszii) est une espèce encore mal connue : sa biologie , sa distribution détaillée et l’existence de populations restent encore à préciser. Des suivis de terrain, des enquêtes et des observations opportunistes ont permis d’identifier plusieurs nouveaux spécimens, observés en mer ou retrouvés après leur capture, dans quatre pays, dont le Nigéria et le Togo où la présence de S. teuszii, bien que fortement suspectée, n’avait jamais été prouvée. De nouvelles données, provenant des îles Tristao et de l’estuaire du Río Nuñez en Guinée du nord, indiquent que les populations du Rio do Jéba-Bijagos (Guinée-Bissau) et Guinée du sud devraient être combinées dans une seule population Guinéenne. La population du golfe de Guinée, qui correspond à la pop...
ABSTRACT We summarize diversity, group size and habitat of cetaceans documented through ship-base... more ABSTRACT We summarize diversity, group size and habitat of cetaceans documented through ship-based visual survey effort (13,694 km; 1163.5 h) off NW Africa (Conakry to Tangier) in spring and fall of 2011-2013. Study area covered mainly continental shelf with some slope waters. Platform-of-opportunity surveying yielded 270 primary sightings of 14 species. Due to passing mode, 35.7% were identifiable only to family/category: unidentified Delphinidae (25.0%), unidentified rorquals (5.88%) and unidentified whales (4.78%). Delphinus delphis predominated with 28.7% of total sightings (32.7%, including probable) and a massive 71.3% (76.5%) of total number of cetaceans observed (n=15,595). Encounter rate was 81.2 common dolphins 100 km-1; mean group size 124.92. Tursiops truncatus, primarily inshore ecotype (median depth, 44.5 m), accounted for 9.56% (11.4%) of sightings and 1.35% (1.83%) of total cetaceans. Megaptera novaeangliae (6.25%) was regularly seen south of Dakar with a Southern Hemisphere seasonality. Other species showed a relatively low % occurrence: Globicephala spp. (2.57), Orcinus orca (1.10), Grampus griseus (0.73), Stenella frontalis (1.84), S. attenuata (0.37), S. clymene (0.37), S. coeruleoalba (0.37), Balaenoptera brydei (1.10), B. musculus (0.37), beaked whale (0.37), probable-B. borealis (0.37). Baleen plates recovered from a bottom-trawl also evidenced B. borealis presence. Seven new range state records included: G. griseus, S. coeruleoalba (Atlantic Morocco); O. orca, B. musculus (The Gambia), G. macrorhynchus, S. frontalis (Guinea-Bissau) and S. attenuata (Guinea).
Total visual survey effort was 468 h, 01 min, covering 5335 km. Depending on the exclusion or inc... more Total visual survey effort was 468 h, 01 min, covering 5335 km. Depending on the exclusion or inclusion of probable records, the sum of group sizes totalled 33 or 43 individuals, respectively. Humpback whale encounter rates between Conakry and Dakar then amounted to 1.74 or 2.27 whales/ 100 km, respectively. Group sizes ranged from 1-6 individuals (mean = 1.94, S.D. = 1.20, n = 17; median = 2). Minimally five of 17 groups (29.4%) consisted of adult-calf pairs, with a minimum crude birth rate ranging from 0.060-0.152. All sightings occurred in shallow water, 22-60 m (mean = 35.0 m, S.D. = 10.13, n = 17) but survey effort in deeper, offshore water was negligible. Sea-surface temperature at sighting locations ranged from 25.5-29.0°C (mean = 27.34, S.D. = 0.96, n = 17). No humpback whales were sighted during a second survey covering Conakry-Tangier-Las Palmas, from 9 May to 22 July 2012 (519 h, 13 min; 6278 km). The Cape Verde Islands comprised, to date, the only known wintering ground located in the NorthEast Atlantic. This study showed that Senegal, The Gambia, Guinea-Bissau and Guinea are normal range states for M. novaeangliae. A temporal signature, six to seven months out-of-phase with mid-season in the Cape Verde Islands, and neonate presence strongly suggest that the wide Conakry-Dakar continental shelf serves as both wintering and nursery grounds for a South Atlantic stock, in agreement with Bamy et al. (2010). This stock may comprise the northwesternmost component of the large humpback whale assemblage migrating in and out of the northern Gulf of Guinea in austral winter/spring. Further research is required to consolidate insights linking temporal and spatial distribution off western Africa with hemispheric stock identity and migration paths.
The distribution, status, and biology of the Atlantic humpback dolphin (Sousa teuszii) is critica... more The distribution, status, and biology of the Atlantic humpback dolphin (Sousa teuszii) is critically reviewed, and results of recent research are discussed. The species' known distribution limits are, in the north, Dahkla Bay (23º50'N), Western Sahara, and in the south, Tombua (15º47'S), southern Angola. Its habitat is predominantly inshore coastal and estuarine, over soft-sediment bottoms. There is no evidence that it might occur beyond the brackish waters of estuaries into a riverine, fresh-water habitat. There are no records for the Senegal, Casamance, and Niger Rivers. A total of eight stocks are provisionally discerned for management purposes. Six of these are confirmed-contemporary (based on recent records), including Dahkla Bay, Banc d'Arguin, Saloum-Niumi, Canal do Gêba-Bijagos, South Guinea, and Angola. Two stocks, the Cameroon Estuary and Gabon, are historical, and new fieldwork needs to confirm their current presence. No inference is made on degree of reproductive isolation and biological population status of any named stock. The potential existence of a western Togo stock is currently under study. Nine coastal states, including Morocco (Western Sahara),
An initial inventory of the dolphins and whales occurring in Guinea's coastal waters is documente... more An initial inventory of the dolphins and whales occurring in Guinea's coastal waters is documented primarily from specimens and photographic evidence obtained from strandings and by-catches. Seven species are fully validated, four odontocetes, Tursiops truncatus, Sousa teuszii, Stenella frontalis, Kogia breviceps and three balaenopterid whales: Balaenoptera brydei, Balaenoptera acutorostrata and Megaptera novaeangliae. Another three reported species (Globicephala macrorhynchus, Steno bredanensis and Delphinus delphis) are insufficiently supported but thought to be valid. Small cetaceans landed as by-catch and a stranded whale were used for human consumption, but no evidence of substantial takes, directed or by-catch, was found. However, concern is raised about even minimal takes of the vulnerable Atlantic humpback dolphin. The seasonal presence of three confirmed humpback whales, two strandings (July and September) and a sighting (October), is synchronous with the species' southern hemisphere wintering/breeding season in low latitudes. We hypothesize that these whales may comprise the north-westernmost range of the population that breeds/overwinters in coastal waters of the Bight of Benin, northern Gulf of Guinea.
The limited information available on the status of inshore common bottlenose dolphins Tursiops tr... more The limited information available on the status of inshore common bottlenose dolphins Tursiops truncatus along the coasts of West Africa is reviewed. Although reported from at least ten countries, it is unclear whether their distribution is continuous. Population structure and genetics have not been studied, however cranial morphology suggests that the West African dolphins differ from North Sea bottlenose dolphins. Mean group sizes are small (3.19 – 12.91 individuals/group) and are smallest in Guinea-Bissau. There are no estimates of abundance but by analogy with a well-studied population in Sarasota, Gulf of Mexico, the Guinea-Bissau population may number only in the hundreds. It is essential that scientific estimates be obtained through dedicated surveys. In some areas of Guinea-Bissau with a high density of fishing activities, bottlenose dolphins are now less frequently encountered than they were in the recent past. Key parameters besides abundance, including population identity...
In northern Guinea, we sighted two groups of Sousa teuszii (n=25; n=40 dolphins) off the Tristao ... more In northern Guinea, we sighted two groups of Sousa teuszii (n=25; n=40 dolphins) off the Tristao Islands during exploratory small-boat surveys in 2011-12. Based on these and recent (2013) observations in the contiguous Río Nuñez estuary, we propose a single 'Guineas stock', combining the former 'Rio do Jêba-Bijagos' and South Guinea stocks. Significant mortality of S. teuszii from fisheries interactions is widely recognised however not quantifiable as monitoring effort is sporadic. In Guinea, catches were documented in 2002 (n=1) and in 2011-12 (n=5). Landed specimens were recorded in Cameroon (n=2) and Nigeria (n=2). All individuals were killed in small-scale coastal fisheries, presumably as accidental net entanglements, though directed takes cannot be excluded. All landed dolphins were butchered for human consumption (marine bushmeat). Nigerian fishers indicated also an alternative use as shark bait. If local markets in cetacean bushmeat and bait develop, as in Ghana, that will exacerbate pressures by encouraging directed takes. Catch records in Nigeria and sightings in Togo authenticate both nations as (long-suspected) range states for S. teuszii, a belated documenting of the primary, historical distribution. The Gulf of Guinea stock ('Cameroon dolphins') extends at least from Togo to southern Cameroon, and probably into Equatorial Guinea. However, rare sightings of small groups point to remnant, not thriving, dolphin communities. We anticipate de novo distribution gaps emerging and consolidating, following decades of fisheries interactions and creeping encroachment on once pristine coastal habitat. Developed coastlines in Ghana and Côte d'Ivoire devoid of records may already constitute such gaps. As the lack or scarcity of records warn about formidable challenges to the long-term survival of S. teuszii, innovative, workable protection measures are needed, soonest. We recommend the implementation of several new border-straddling marine protected areas (cf. Saloum Delta-Niumi National Park Complex) which could bring forth a major conservation effect. Binational involvement bears obvious advantages, from sharing responsibilities and allowing for larger protected areas. Suggested dolphin sanctuary examples could include MPAs straddling borders between Cameroon/Equatorial Guinea and Guinea-Bissau/Guinea-Conakry.
We summarize diversity, group size and habitat of cetaceans documented through ship-based visual ... more We summarize diversity, group size and habitat of cetaceans documented through ship-based visual survey effort (13,694 km; 1163.5 h) off NW Africa (Conakry to Tangier) in spring and fall of 2011-2013. Study area covered mainly continental shelf with some slope waters. Platform-of-opportunity surveying yielded 270 primary sightings of 14 species. Due to passing mode, 35.7% were identifiable only to family/category: unidentified Delphinidae (25.0%), unidentified rorquals (5.88%) and unidentified whales (4.78%). Delphinus delphis predominated with 28.7% of total sightings (32.7%, including probable) and a massive 71.3% (76.5%) of total number of cetaceans observed (n=15,595). Encounter rate was 81.2 common dolphins 100 km-1; mean group size 124.92. Tursiops truncatus, primarily inshore ecotype (median depth, 44.5 m), accounted for 9.56% (11.4%) of sightings and 1.35% (1.83%) of total cetaceans. Megaptera novaeangliae (6.25%) was regularly seen south of Dakar with a Southern Hemisphere ...
An initial inventory of the dolphins and whales occurring in Guinea's coastal waters is documente... more An initial inventory of the dolphins and whales occurring in Guinea's coastal waters is documented primarily from specimens and photographic evidence obtained from strandings and by-catches. Seven species are fully validated, four odontocetes, Tursiops truncatus, Sousa teuszii, Stenella frontalis, Kogia breviceps and three balaenopterid whales: Balaenoptera brydei, Balaenoptera acutorostrata and Megaptera novaeangliae. Another three reported species (Globicephala macrorhynchus, Steno bredanensis and Delphinus delphis) are insufficiently supported but thought to be valid. Small cetaceans landed as by-catch and a stranded whale were used for human consumption, but no evidence of substantial takes, directed or by-catch, was found. However, concern is raised about even minimal takes of the vulnerable Atlantic humpback dolphin. The seasonal presence of three confirmed humpback whales, two strandings (July and September) and a sighting (October), is synchronous with the species' southern hemisphere wintering/breeding season in low latitudes. We hypothesize that these whales may comprise the north-westernmost range of the population that breeds/overwinters in coastal waters of the Bight of Benin, northern Gulf of Guinea.
The limited information available on the status of inshore common bottlenose dolphins Tursiops tr... more The limited information available on the status of inshore common bottlenose dolphins Tursiops truncatus along the coasts of West Africa is reviewed. Although reported from at least ten countries, it is unclear whether their distribution is continuous. Population structure and genetics have not been studied, however cranial morphology suggests that the West African dolphins differ from North Sea bottlenose dolphins. Mean group sizes are small (3.19 -12.91 individuals/group) and are smallest in Guinea-Bissau. There are no estimates of abundance but by analogy with a well-studied population in Sarasota, Gulf of Mexico, the Guinea-Bissau population may number only in the hundreds. It is essential that scientific estimates be obtained through dedicated surveys. In some areas of Guinea-Bissau with a high density of fishing activities, bottlenose dolphins are now less frequently encountered than they were in the recent past. Key parameters besides abundance, including population identity, bycatch levels and other anthropogenic threats need to be documented and quantified before any deliberate exploitation is considered. A small-scale, botched live-capture operation in Senegal in 2003, in which all dolphins died, serves as warning against such opportunistic schemes. In management terms, live-capture operations are equivalent to hunting and multi-year, large-scale removals of bottlenose dolphins in Guinea-Bissau would have the potential to effectively extirpate the wild population from its waters.
Seventeen confirmed and four probable sightings of humpback whales, Megaptera novaeangliae, were ... more Seventeen confirmed and four probable sightings of humpback whales, Megaptera novaeangliae, were documented from platform-of-opportunity Research Vessel (R/V) Dr. Fridtjof Nansen in a passing-mode visual survey of continental shelf waters between Conakry and Cap Vert Peninsula (Dakar), 21 October -5 November 2011. None were encountered in the northern stratum Dakar-Agadir, 6 November -15 December 2011. Total visual survey effort was 468 h, 01 min, covering 5335 km. Depending on the exclusion or inclusion of probable records, the sum of group sizes totalled 33 or 43 individuals, respectively. Humpback whale encounter rates between Conakry and Dakar then amounted to 1.74 or 2.27 whales/ 100 km, respectively. Group sizes ranged from 1-6 individuals (mean = 1.94, S.D. = 1.20, n = 17; median = 2). Minimally five of 17 groups (29.4%) consisted of adult-calf pairs, with a minimum crude birth rate ranging from 0.060-0.152. All sightings occurred in shallow water, 22-60 m (mean = 35.0 m, S.D. = 10.13, n = 17) but survey effort in deeper, offshore water was negligible. Sea-surface temperature at sighting locations ranged from 25.5-29.0°C (mean = 27.34, S.D. = 0.96, n = 17). No humpback whales were sighted during a second survey covering Conakry-Tangier-Las Palmas, from 9 May to 22 July 2012 (519 h, 13 min; 6278 km). The Cape Verde Islands comprised, to date, the only known wintering ground located in the North-East Atlantic. This study showed that Senegal, The Gambia, Guinea-Bissau and Guinea are normal range states for M. novaeangliae. A temporal signature, six to seven months out-of-phase with mid-season in the Cape Verde Islands, and neonate presence strongly suggest that the wide Conakry-Dakar continental shelf serves as both wintering and nursery grounds for a South Atlantic stock, in agreement with Bamy et al. (2010). This stock may comprise the northwesternmost component of the large humpback whale assemblage migrating in and out of the northern Gulf of Guinea in austral winter/spring. Further research is required to consolidate insights linking temporal and spatial distribution off western Africa with hemispheric stock identity and migration paths.
The distribution, status, and biology of the Atlantic humpback dolphin (Sousa teuszii) is critica... more The distribution, status, and biology of the Atlantic humpback dolphin (Sousa teuszii) is critically reviewed, and results of recent research are discussed. The species' known distribution limits are, in the north, Dahkla
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