Cap Vert Peninsula Research Articles

Physical and Mechanical Features of the Quaternary Basanites of the Cap-Vert Peninsula of Dakar (Senegal, West Africa)

Physical and Mechanical Features of the Quaternary Basanites of the Cap-Vert Peninsula of Dakar (Senegal, West Africa)

Green Turtles Highlight Connectivity Across a Regional Marine Protected Area Network in West Africa

Networks of marine protected areas (MPAs) are invaluable for the protection of species with high dispersal capacity, yet connectivity within networks is poorly understood. We demonstrate the connectivity within the regional MPA network in West Africa (RAMPAO), mediated by the largest green turtle population in the eastern Atlantic Ocean. We equipped with satellite tags 45 female green turtles nesting in the Bijagós Archipelago, Guinea-Bissau, and tracked them during internesting, migration, and foraging to quantify the degree of coverage the RAMPAO network provides during each of these critical periods. During the internesting period, turtles were largely concentrated around the nesting islands, with a mean of 94.8% (SD 0.1%, range: 46% - 100%, n = 40 turtles) of tracking positions falling within MPA limits. Among the 35 turtles successfully tracked into the foraging period, we identified variable migratory strategies, with 12 turtles remaining near-resident at distances of 40-90 km from breeding sites, 10 turtles migrating 300-400 km to The Gambia and Senegal, and 13 turtles traveling >1000 km to northern Mauritania. Of the 35 foraging turtles, 26 used MPAs, with a mean of 78.0% (SD 34.8%, range: 3.7% - 100%) of their tracking positions falling within the limits of RAMPAO MPAs, across Guinea-Bissau, Senegal and Mauritania. Migration corridors with high concentrations of passing turtles were mostly located nearshore, and 21% of these high passage areas fell within the MPA network. Overall, we found that this population connects five RAMPAO MPAs, yet some foraging sites (e.g., in the Bijagós) and important migration areas (e.g., Cap-Vert peninsula) described here are currently unprotected. These results are relevant to any considerations of MPA extension or establishment within the regional network, which would contribute towards meeting the Convention on Biological Diversity targets for national marine protected area estate coverage. By documenting biological connectivity across RAMPAO, this study represents an important example of the relevance of international protected area networks for green turtle conservation and for wider conservation action at a regional scale.

Embodying the Mahdi: Islamic Messianism and the Body in Colonial Senegal

Abstract This study explores modern Islamic messianism as a mode of tajdid, or religious renewal, during the colonial era. It analyzes the case of a nineteenth-century religious movement among the Lebou people of the Cap-Vert peninsula in French West Africa, now Senegal, known as the Layene Brotherhood (La Confrérie Layenne). The sect began when Libasse Thiaw (d. 1909), known as Mouhammadou Limamou Laye, proclaimed himself the awaited Mahdi, and his eldest son, Issa Thiaw (d. 1949), the second coming of Jesus. Most distinctively, Thiaw taught that he was the reincarnation of the Prophet Muhammad—the Black African embodiment of his soul. Through embodiment, Thiaw elided existing epistemological conflicts in modern Islam and asserted prophetic authority. In the process, he accelerated the process of tajdid for his community and nullified his lack of scholarly or ancestral credentials to join the revered ranks of the marabouts of Senegal.

Trends in Sea Level around the Cap Vert Peninsula, Senegal

ABSTRACT Thoreux, T.; Sakho, I.; Sall, M.; Testut, L., and Woppelmann, G., 2018. Trends in sea level around the Cap Vert peninsula, Senegal. In: Almar, R.; Almeida, L.P.; Trung Viet, N., and Sall, ...

New fossil scombrid (Pelagia: Scombridae) fishes preserved as predator and prey from the Eocene of Senegal

ABSTRACT. Lower Eocene fossil fish material from the Thies Formation in the region of Bargny near the Cap-Vert peninsula, Senegal, reveals predator-prey interaction between two scombrid fishes, the first ever described in the fossil record for the clade. The material is a part and counterpart concretion preserving nearly complete skulls of both predator and prey in 3-dimensions. The larger, predator-fish is here proposed as the second specimen of †Auxides huberti, the only non-Tethyan representative of †Auxides. The smaller, prey-fish is a new genus and species, †Eoscomber senegalicus, closely resembling Scomber. Evidence that †E. senegalicus gen. et sp. nov. was swallowed includes the presence of several of its caudal vertebrae obscured near the area of the opercle of †A. huberti and continuing into its pharynx. Additionally, the skull of †E. senegalicus. is partially enclosed within the abdominal ribs of †A. huberti. †Auxides huberti is the only species of †Auxides recovered with serrated pelvic fin spi...

The Geodynamic Context of the Cenozoic Volcanism of the Cap-Vert Peninsula (Senegal)

The Cenozoic alkaline volcanism of the Senegalo-Mauritania sedimentary basin presents an episodic long-lasting volcanic activity from the Eocene-Oligocene boundary up to the Quaternary. Two volcanic episodes are usually distinguished on stratigraphical grounds: a Miocene one and a Quaternary one separated by a period of quiescence of several million years corresponding to the main phase of lateritic weathering. The Tertiary lavas are highly silica-undersaturated alkaline rocks ranging from nephelinites to basanites. They contain nepheline and fassaite-type clinopyroxene in their mineralogy. The Quaternary lavas are more evolved with Hy-normative in comparison to the Tertiary ones; they are composed of basanites and medium to coarser-grained dolerites. The distribution of the REE and other incompatible elements are typical of alkaline lavas with generally strong LREE enrichment without significant Eu anomaly. The Cenozoic Cap-Vert lavas have OIB (oceanic islands basalts)-affinities as shown by their relatively radiogenic Nd and unradiogenic Sr characters closed to the HIMU-OIB. This suggests a HIMU-type end member in the magma sources which is fairly comparable to those erupted in the Canaries and Cape Verde archipelagoes during the same period.

The Prophet Muhammad reincarnated and his son, Jesus: re-centering Islam among the Layenne of Senegal

This article explores how the Layenne of Senegal have employed the historical geography of the Cap Vert peninsula as an archive to effectively re-center the Islamic world away from Arabia to the coast of West Africa. Annual pilgrimages to Layenne religious sites and shrines that serve as lieux de mémoire provide ‘foyers’ on which contemporary collective and individual identities are contemplated with regard to Layenne perceptions of the past. The Layenne historical imagination is tied to the geographic space that constitutes Cap Vert in a symbiotic relationship by which history gives meaning to place and vice versa. While the rituals practiced at the Layenne places of memory revolve around the hagiography of their founder, Seydina Limamou Laye, who claimed to be the Mahdi and the reincarnation of the Prophet Muhammad, the Layenne have also appropriated sites and symbols associated with French colonization and a post-colonial Senegal into a vibrant and fluid conception of modernity that is simultaneously indigenous and global.

New evidence for a South Atlantic stock of humpback whales wintering on the Northwest African continental shelf

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, off-shore 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.

New Evidence for a South Atlantic Stock of Humpback Whales Wintering on the Northwest African Continental Shelf

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.

English

The quaternary sandy sediments which cover most part of the Cap Vert peninsula bear considerable groundwater resources. The aquifer lying beneath a densely populated suburb zone is encountered with major issues such as induced recharge from anthropogenic surface derived pollution and rising water table to ground surface. The present study was aimed at investigating the recharge in the unconfined aquifer of Thiaroye zone using both water table fluctuation (WTF), chloride mass balance (CMB) methods and environmental isotopes. Seasonal fluctuations of groundwater in response to precipitation are monitored during time period (2010 to 2011) using “Thalimede Orpheus mini” recorders in two piezometers (P3-1 and PSQ1) as well as long term record. Chemical and isotopic characterization of groundwater, rainfall and the unsaturated zone were also carried out using a network of 48 points consisting of 8 rainfall stations, 10 unsaturated zone profiles and 30 dug wells, boreholes and piezometers. The concentrations of chloride in rainwater are between 3.2 and 53.4 mg/L. These unsaturated zone profiles range from 65 and 572 mg/L. The recharge obtained by WTF method ranged between 18 and 144 mm during the rainy season (June to October), whereas the recharge given by CMB method ranged ​​between 8.7 and 73 mm/year. The Thiaroye aquifer recharge obtained from these different methods also showed relatively similar range values. In this study, the WTF method applied computes both infiltration from rainwater and domestic waste water, while the CMB method estimates potential recharge from rainwater. Therefore, in the urban area, the CMB method cannot be applied due to the chloride input from waste water infiltration.    Key words: Thiaroye basin, recharge, isotopes, chloride mass balance (CMB), quaternary sandy aquifer (Dakar)

Impacts of climate change on the Senegalese coastal zones: Examples of the Cap Vert peninsula and Saloum estuary

Following a first study made to assess the impacts of sea level rise on the Senegalese coastline ( Dennis et al., 1995), this vulnerability and adaptation (V&A) study tried to determine the impacts of climate change on two representative coastal zones, the Cap Vert peninsula and the Saloum estuary as well as potential adaptation options. The Intergovernmental Panel on Climate Change (IPCC) Methodology ( Carter et al., 1994), completed by the United Nations Environment Programme (UNEP) Handbook ( Feenstra et al., 1998), were used together with different models (like the Bruun rule, the FEFLOW model), geographical information system and economic data to determine the physical and socio-economic impacts of different climate change scenarios on these coastal zones. Land losses are expected due to sea level rise that will enhance coastal erosion and increase inundation levels, the second phenomenon being responsible for most of these losses, especially in low lying areas like the Saloum estuary (27% of the total area lost with a 1 m inundation level). The combination of sea level rise and decreased precipitation will increase the salt water intrusion in a number of coastal aquifers, especially around Dakar and in the Saloum estuary. Population at risk of inundation in the Cap Vert peninsula could represent between 1 and 12% of the total population of this area. Economic values at risk were estimated by considering socio-economic scenarios and discount rates. For a 1 m inundation level by 2050, this could represent (for the two areas) 14.1% of the actual Gross Domestic Product. While housings represent more than 90% of this value in the Cap Vert peninsula, in the Saloum estuary, it is the agricultural production which represents the dominant form of value at risk (55%). Only two adaptation options, protection works (sea walls and groins) and afforestation of littoral dunes, were evaluated and costed. For a 1 m inundation level by 2050, this will represent 7.3% of the actual Gross Domestic Product. The main result of this study is the demonstration that protection costs will be lower than economic value at risk contrary to the results of the previous study. This is mainly attributed to the consideration of socio-economic scenarios and a better economic evaluation of the goods and services at risk of inundation.

The EU Migration Regime and West African Clandestine Migrants

This article examines the relationship between the EU migration regime and clandestine migration from West Africa to Europe. A review of the development of EU border and immigration policy reveals significant and sustained moves towards securitisation of migrants and the externalisation of border controls to countries of origin and transit. This emphasis on repression limits the scope of cooperation with ‘third countries’ (those outside Europe) in co-development, labour mobility, sea patrols and repatriation, which are examined separately as deterrents to uncontrolled emigration. This paper then analyses the motivations and intentions of Senegalese youth around the Cap Vert peninsula. This analysis includes the role of emigration in development and more recently, the impact of human losses and repatriations resulting from the clandestine journey by pirogue (open fishing boat) to the Canary Islands. This article argues that in this case, youth are excluded both from labour and asylum policies and instead are managed as a security threat, contradicting the factors driving this journey.

Shark Attacks in Dakar and the Cap Vert Peninsula, Senegal: Low Incidence despite High Occurrence of Potentially Dangerous Species

BackgroundThe International Shark Attack File mentions only four unprovoked shark attacks on the coast of West Africa during the period 1828–2004, an area where high concentrations of sharks and 17 species potentially dangerous to man have been observed. To investigate if the frequency of shark attacks could be really low and not just under-reported and whether there are potentially sharks that might attack in the area, a study was carried out in Dakar and the Cap Vert peninsula, Senegal.Methodology/Principal FindingsPersonnel of health facilities, administrative services, traditional authorities and groups of fishermen from the region of Dakar were interviewed about the occurrence of shark attacks, and visual censuses were conducted along the coastline to investigate shark communities associated with the coasts of Dakar and the Cap Vert peninsula. Six attacks were documented for the period 1947–2005, including two fatal ones attributed to the tiger shark Galeocerdo cuvieri. All attacks concerned fishermen and only one occurred after 1970. Sharks were observed year round along the coastline in waters 3–15 m depth. Two species potentially dangerous for man, the nurse shark Ginglymostoma cirratum and the blacktip shark Carcharhinus limbatus, represented together 94% of 1,071 sharks enumerated during 1,459 hours of observations. Threatening behaviour from sharks was noted in 12 encounters (1.1%), including 8 encounters with C. limbatus, one with Galeocerdo cuvieri and 3 with unidentified sharks.Conclusions/SignificanceThese findings suggest that the frequency of shark attacks on the coast of West Africa is underestimated. However, they also indicate that the risk is very low despite the abundance of sharks. In Dakar area, most encounters along the coastline with potentially dangerous species do not result in an attack. Compared to other causes of water related deaths, the incidence of shark attack appears negligible, at least one thousand fold lower.

Datation par les foraminiferes planctoniques d'une activite volcanique d'age lutetien a Toubab Dialow (Senegal occidental)

Abstract A level of silicified limestones with nummulites and daucines has been discovered in Toubab Dialaw, located in the horst of Ndiass. Interbedded between the diatreme and the ferruginous lateritic crust, this level is characterized by sheath folds. The biostratigraphic analysis revealed the presence of nummulites, daucina and a planktonic association with Globigerinatheka kugleri (Bolli, Loeblich et Tappan, 1957) which characterizes P11-P13 zones of late Lutetian to early Bartonian age. This indicates that the Tertiary volcanic activity in the Cap Vert peninsula, here represented by the Toubab Dialaw diatreme, till now considered late Eocene to late Pliocene, began earlier, during the Middle Eocene and more precisely between 48 and 45 Ma. Moreover, the presence of sheath folds indicates that the sedimentary material has been subject to a submarine slide along a low slope. Finally, all the petrographical, palaeontological and structural data allow to precise the set up history of the volcanic and sedimentary formations constituting the littoral cliffs of Toubab Dialaw.

La bioérosion des substrats magmatiquesen milieu littoral: L'exemple de la presqu'ile du Cap Vert (Sénégal Occidental)

Magmatic rocks (mainly dolerites and basanites) and thick ferruginous crusts (ironpans) outcroping on the shore of the Cap Vert peninsula (Western Senegal) are not uniformely abraded by borers and scrapers. Bioabrasion and bioattack are faint in basanites and thick ferrunginous crust. Conversely, dolerites are penetrated by microorganisms, essentially fungi, in particular related to the genus Ostracoblabe and actively bored by the sea-urchin Echinometra lucunter: Fungi are rather numerous throughout the intertidal zone, particularly in its upper half-part, and persist in the lower part of the supralittoral zone actively moistened by sprays. E. lucunter inhabits the lower part of the intertidal zone and the upper part of the subtidal zone. The study of thin sections showed that fungi first behave like chasmoendoliths before to act as euendoliths. Pyroxenes and peridots can be intensively permeated, whereas plagioclases are generally poorly affected by fungal attacks. Although very scarce, the cyanobacteria Hyella sp. can invade plagioclases situated at the sample surface, at least up to the half level of low tide. Frequencies of borers and scrapers were determined in the different biological horizons recognized by Sourie (1954). Boring activity of E. lucunter was surveyed veyed during 21 months. The deepening of their dwelling holes is about 1 mm/year in the lower half of the intertidal zone whereas it is only about 0,4 mm/year in the associated thick ferruginous crusts. The calculated rate of bioerosion can reach annually about 2 050 g/m 2 in the lower horizon of low tide where the population of E. lucunter is particularly important. The rate of biological erosion decreases rapidly in the overlying horizons. The bioerosion of the dolerites of the Cap Vert peninsula is an active process, contribution of which to the destruction of the rocky shore and to the coastal morphogenesis during the Quaternary is certainly significant.

Cenozoic volcanism in Western Senegal and its relationship to the opening of the Central Atlantic Ocean

Abstract The westernmost part of the Senegalese basin in West Africa is characterized by an extensive magmatic event, exposed in the form of sills and dykes, mainly during the Quaternary but beginning in the Tertiary (35 + 0.1 Ma (Miocene) to 0.8 + 0.1 Ma (Pleistocene)). The main exposures are located in the Cap-Vert Peninsula and Thies Plateau to the East of Dakar. This magmatic event postdated the opening of the Central Atlantic and displays chemical similarities to the Tertiary-Quaternary magmatic centres within the African plate. Two main facies are distinguished among the flows: microporphyric and doleritic textured olivine-rich alkaline basalts, the former often containing spinel-lherzolite mantle inclusions. The alkaline sodic affinity of the volcanic series and the Ti, K + Na, Nb, P2O5 and Zr content of the lavas are typical of magmas generated in a within-continent plate tectonic setting. This volcanism appears to have resulted from an active mantle hotspot, over which the African plate migrated as the central Atlantic Ocean opened, using reactivated faults (contemporaneous with Central Atlantic opening) as magmatic pathways.

Cenozoic volcanism in Western Senegal and its relationship to the opening of the Central Atlantic Ocean

The westernmost part of the Senegalese basin in West Africa is characterized by an extensive magmatic event, exposed in the form of sills and dykes, mainly during the Quaternary but beginning in the Tertiary (35 + 0.1 Ma (Miocene) to 0.8 + 0.1 Ma (Pleistocene)). The main exposures are located in the Cap-Vert Peninsula and Thiès Plateau to the East of Dakar. This magmatic event postdated the opening of the Central Atlantic and displays chemical similarities to the Tertiary-Quaternary magmatic centres within the African plate. Two main facies are distinguished among the flows: microporphyric and doleritic textured olivine-rich alkaline basalts, the former often containing spinel-lherzolite mantle inclusions. The alkaline sodic affinity of the volcanic series and the Ti, K + Na, Nb, P 2O 5 and Zr content of the lavas are typical of magmas generated in a within-continent plate tectonic setting. This volcanism appears to have resulted from an active mantle hotspot, over which the African plate migrated as the central Atlantic Ocean opened, using reactivated faults (contemporaneous with Central Atlantic opening) as magmatic pathways.