Browsing by Author "Regalla, Aissa Said"
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- Dispersal of green turtles from Africas' largest rookery assessed through genetic markersPublication . Patrício, Ana Rita; Formia, Angela; Barbosa, Castro; Broderick, Annette C.; Bruford, Michael; Carreras, Carlos; Catry, Paulo; Ciofi, Claudio; Regalla, Aissa Said; Godley, Brendan JohnMarine turtles are highly migratory species that establish multiple connections among distant areas, through oceanic migration corridors. To improve the knowledge on the connectivity of Atlantic green turtles Chelonia mydas, we analysed the genetic composition and contribution to juvenile aggregations of one of the world's largest rookeries at Poilao Island, Guinea-Bissau. We amplified 856 bp mitochondrial DNA (mtDNA) control region sequences of this population (n = 171) containing the similar to 490 bp haplotypes used in previous studies. Haplotype CM-A8 was dominant (99.4%), but it divided in 2 variants when the whole 856 bp was considered: CM-A8.1 (98.8%) and CM-A8.3 (0.6%). We further identified the haplotype CM-A42.1 (0.6%), found previously only in juvenile foraging grounds at Argentina, Brazil and Equatorial Guinea. The Poilao breeding population was genetically different from all others in the Atlantic (FST range: 0.016-0.961, p < 0.001). An extensive 'many-to-many' mixed-stock analysis (MSA) including 14 nesting populations (1815 samples) and 17 foraging grounds (1686 samples) supported a strong contribution of Poilao to West Africa (51%) but also to the Southwest Atlantic (36%). These findings, in particular the strong connectivity within West Africa, where illegal harvesting is still common, should motivate conservation partnerships, so that population protection can be effectively extended through all life stages. Our study expands the knowledge on migration patterns and connectivity of green turtles in the Atlantic, evidences the importance of larger sample sizes and emphasizes the need to include more finely resolved markers in MSAs and more genetic sampling from West African foraging grounds to further resolve the connectivity puzzle for this species.
- Ecology and behaviour of Palm-nut Vultures Gypohierax angolensis in the Bijagós Archipelago, Guinea-BissauPublication . Carneiro, Camilo André Ferreira Carneiro; Henriques, Mohamed; Barbosa, Castro; Tchantchalam, Quintino; Regalla, Aissa Said; Patrício, Ana Rita; Catry, PauloPopulations of many vulture species have undergone substantial declines. In Africa, 82% are threatened and although research on vultures has increased, the biology and ecology of several species is still poorly known. The Palm-nut Vulture Gypohierax angolensis has peculiar ecological characteristics, feeding on palm fruits, associated with the aquatic environment and taking a wide variety of prey. It has been over 40 years since the last thorough study on the ecology of the species was undertaken. This study investigated several ecological and behavioural aspects of Palm-nut Vultures, using a combination of direct observations, stable isotope analysis and Bayesian mixing models. The population of this species within the João Vieira and Poilão Marine National Park is estimated to be 21–30 birds km−2. Egg laying started in November (early dry season) and some chicks were still growing in early May. A minimum of 54% of nests produced a fledgling. Observations suggest that Palm-nut Vultures moult all flight feathers annually, between January and November. Their foraging behaviour is described and cafeteria trials showed their preference for fish over oil palm fruits. However, it is estimated that oil palm fruits account for almost 50% of the assimilated diet, followed by fish, crabs and Green Turtle hatchlings or eggs, as revealed by stable isotopes and Bayesian mixing models.
- Estimation of mercury background values in sediment and biota of the Bijagós archipelago, Guinea-BissauPublication . Coelho, J. P.; Monteiro, R. J. R.; Catry, Teresa; Lourenço, Pedro Miguel; Catry, Paulo; Regalla, Aissa Said; Catry, Inês; Figueira, Paula; Pereira, Eduarda; Vale, Carlos; Granadeiro, José PedroThis work evaluates the mercury (Hg) contamination status (sediments and biota) of the Bijagós archipelago, off the coast of Guinea-Bissau. Sediments exhibited very low concentrations (<1-12ngg(-1)), pointing to negligible sources of anthropogenic Hg in the region. Nevertheless, Hg is well correlated to the fine fraction, aluminium, and loss on ignition, indicating the effect of grain size and organic matter content on the presence of Hg in sediments. Mercury in the bivalves Tagelus adansoni and Senilia senilis did not vary considerably among sites, ranging within narrow intervals (0.09-0.12 and 0.12-0.14μgg(-1) (dry weight), respectively). Divergent substrate preferences/feeding tactics may justify slight differences between species. The value 11ngg(-1) is proposed as the sediment background concentration for this West-African coastal region, and concentrations within the interval 8-10ngg(-1) (wet weight) may be considered as reference range for S. senilis and T. adansoni in future monitoring studies.
- Length-weight relationship of fish species from the Bijagós Archipelago, Guinea-BissauPublication . Correia, Edna; Granadeiro, José Pedro; Regalla, Aissa Said; Catry, PauloLength–weight relationships were estimated for six teleost fish species occurring in Bijagós Archipelago, Guinea-Bissau. Samples were collected seasonally during three dry seasons (2013/2014, 2014/2015, 2015/2016) and two rainy seasons (2015 and 2016). Fishes were captured by three methods: angled from the beach or a boat; using beach seine with a mesh size ranging 0.5–1 cm; drift netting from a boat (mesh size 2 cm). This work provides the length-weight relationship for three fish species that are not reported in FishBase (Citharichthys stampflii, Gerres nigri and Psettodes belcheri) as well as for three species from which we present a wider size range (Eucinostomus melanopterus, Scomberomorus tritor and Sphyraena afra).
- Nest site selection repeatability of green turtles, Chelonia mydas , and consequences for offspringPublication . Patrício, Ana Rita; Varela, Miguel R.; Barbosa, Castro; Broderick, Annette C.; Airaud, Maria B.Ferreira; Godley, Brendan John; Regalla, Aissa Said; Tilley, Dominic; Catry, PauloNest site selection is a critical behaviour, particularly in species with no parental care, as it can greatly impact offspring survival. Marine turtles depend on sandy beaches to nest, where they select from a range of microhabitats that may differently affect hatchling survival and phenotype. Here we describe the degree of nest site selection at one of the largest green turtle rookeries globally, in Guinea-Bissau, West Africa, and how this impacts offspring. In 2013 and 2014 we recorded the spatial distribution of 1559 nests, and monitored 657 females during oviposition, to assess population and individual preferences on nesting site. Overall, females tended to nest close to the vegetation, at a preferred elevation of 4.8e5.0 m, which was above the highest spring tide (4.7 m), enhancing clutch survival. Individuals displayed high repeatability in nesting microhabitat type (open sand, forest border and forest), distance along the beach, distance to the vegetation and elevation, which may result from this behaviour having a genetic basis or from fine-scale nest site philopatry. Hatchlings from cooler nests were larger, potentially dispersing faster and more able to evade predators, while smaller hatchlings, from warmer nests, retained more energetic reserves (residual yolk), which may also be advantageous for initial dispersal, particularly if food is scarce. Thus, individual preferences in nest site selection led to trade-offs in offspring phenotype, but overall, most nesting females selected sites that increased offspring survival, suggesting that nest site selection is an adaptive trait that has been under selection. As under future climate change scenarios females nesting in upper shaded areas should have higher fitness, individual consistency in nesting microhabitat provides opportunity for natural selection to occur.
- Nest-site characteristics and aspects of the breeding biology of the endangered Timneh Parrot Psittacus timneh in Guinea-BissauPublication . Lopes, Daniel C; Martin, Rowan O; Henriques, Mohamed; Monteiro, Hamilton; Regalla, Aissa Said; Tchantchalam, Quintino; Indjai, Bucar; Cardoso, Seco; Manuel, Celestino; Cunha, Manjaco; Cunha, Domingos; Catry, PauloTimneh Parrots Psittacus timneh are endemic to the moist forests of West Africa. Concerns over rapid declines in populations due to overharvesting for the pet trade and forest loss prompted the species’ categorisation as Endangered on the IUCN Red List of Threatened Species in 2016. Despite these threats, few data exist on their biology in the wild, impeding the development of effective conservation initiatives to protect populations. One of the few recorded breeding sites for this species occurs in the Bijagós Archipelago in Guinea-Bissau, where chicks have been historically harvested from nests and forest clearance for agriculture is common. We investigated the breeding ecology of Timneh Parrots in the Bijagós Archipelago focusing on two islands that harbour the densest populations. Specifically, we describe nest-site characteristics, breeding phenology and reproductive productivity. Timneh Parrots were found to use secondary nest cavities in 17 species of trees, predominantly nesting in trees between 20 m and 50 m in height. Nest cavities were generally aggregated, with a density of up to 14 nests ha−1 in some areas, although nests also occurred in isolated large trees. The distribution of nests likely reflected a heterogeneous distribution of large trees containing suitable nest cavities, emphasising the importance of protecting mature trees. Nesting efforts were initiated between early January until late March, suggesting that nest surveillance efforts to deter poaching can be efficiently focused at a small number of key sites during February to May each year, when fledgling chicks are most likely to be present. These data further suggest that the population may be limited by the availability of suitable nest cavities and that the installation of artificial nest cavities could help increase the breeding population.
- Not in wilderness: African vulture strongholds remain in areas with high human densityPublication . Henriques, Mohamed; Granadeiro, José Pedro; Monteiro, Hamilton; Nuno, Ana; Lecoq, Miguel; Cardoso, Paulo Eduardo; Regalla, Aissa Said; Catry, PauloVultures constitute an important functional group in many ecosystems, providing crucial ecosystem services both in natural and humanized environments. These scavengers are facing massive declines worldwide, but in several African countries virtually nothing is known on populations' status and threats, hampering the development of adequate conservation strategies. In Guinea-Bissau, globally important populations of Hooded Necrosyrtes monachus and African white-backed vultures Gyps africanus were recently reported. Using the country as a study area, we aim to characterize human-vulture interactions in West Africa applying a multidisciplinary approach. We assessed the status and distribution of vulture populations using data from 1711 km of roadside transects, examined predictors of their distribution, and produced a nationwide population estimate for the Hooded Vulture, using an innovative method based on the relationship between the size of human population in settlements and vulture numbers. We conducted 47 stakeholder interviews to assess perceived roles played by vultures, and to investigate potential anthropogenic threats. Hooded vultures were strongly associated with high human population densities, whereas no relation was found between African white-backed and Rüppell's vultures and any of the tested predictors, which included cattle density, precipitation and Normalized Difference Vegetation Index, among others. We estimate a national population of 43347 Hooded vultures, the largest population reported in the species range. Respondents were generally aware of the services provided by vultures, especially waste and carcass removal, including in urban areas. Hunting for witchcraft and traditional medicine was the most frequently recognised threat, while poisoning was ranked as having the highest impact. We hypothesise that poisoning-related mortality may be affecting African white-backed and Rüppell's vultures' distribution and explain their scarcity in apparently highly suitable habitats. Our results suggest a mutualistic rather than a commensalistic relationship between vultures and humans, with important implications for designing and implementing conservation strategies.
- Predatory pelagic fishes of the Bijagós Archipelago (Guinea-Bissau) show high overlap in diets dominated by sardinellaPublication . Correia, Edna; Granadeiro, José Pedro; Regalla, Aissa Said; Dias, Emanuel; Almeida, Ana Pereira; Catry, PauloKnowledge of trophic interactions between the key components of marine communities is required to understand food-web dynamics and develop ecosystem-based management approaches. In West Africa, where fisheries sustain the livelihoods of a significant part of the human population, this understanding is even more urgent, especially in the face of rapidly expanding fisheries and some stock collapses in the region. We studied the feeding ecology of the Crevalle jack Caranx hippos, West African Spanish mackerel Scomberomorus tritor and Guinean barracuda Sphyraena afra in the Bijagós Archipelago, Guinea-Bissau. These are the most abundant pelagic predatory teleost fishes in the area, but little is known about their ecology despite being species with commercial and recreational value, and they likely also play an important role in various African coastal ecosystems. Our findings show a high degree of dietary overlap among these three predator species, despite some degree of segregation by prey size and type. All three predators depend on Sardinella maderensis as the most important prey, which together with other members of the Clupeidae represented 47–96% of the ingested prey items. There was little difference in the diets of the predators between the dry and rainy seasons. These novel findings suggest a ‘wasp-waist’-structured ecosystem in the Bijagós Archipelago in which S. maderensis is the central small-sized pelagic fish species, and stress the need for an ecosystem-based approach to fisheries management in the region, with precautionary measures taken to avoid the overexploitation of clupeids.
- Status of birds of prey in Guinea-Bissau: First assessment based on road surveysPublication . Henriques, Mohamed; Lecoq, Miguel; Monteiro, Hamilton; Regalla, Aissa Said; Granadeiro, José Pedro; Catry, PauloSeveral studies have reported marked declines in populations of birds of prey across the African continent, including West Africa. However, there are still regions of which virtually nothing is known, as is the case for Guinea-Bissau. Because birds of prey play important roles in ecosystems and several species are threatened, it is important to establish baseline knowledge on their status. This is the first study in the country focusing exclusively on birds of prey. We conducted 1 711 km of roadside transects from mid-February to the end of May 2016, covering most of Guinea-Bissau. In total 4 989 birds of 33 species were counted, of which Hooded Vultures Necrosyrtes monachus were the most common (252 birds per 100 km, the second highest abundance in all the species’ range). Observations outside transects, including during regular field trips throughout the country, particularly between 2012 and 2016, were used as complementary information adding 13 species to the list, and contributing three new species for Guinea-Bissau: Ayres’s Hawk-eagle Hieraaetus ayresii, Booted Eagle Hieraaetus pennatus and Lesser Kestrel Falco naumanni. Most species showed differences in abundance in relation to vegetation cover (based on the normalised difference vegetation index). Apart from Hooded Vultures and White-backed Vultures Gyps africanus, all other raptors in the IUCN Red List were found to be scarce, including other vultures and several medium-to-large eagles.
- The diet of two opportunistic seabirds (Caspian and Royal Terns) confirms the importance of Sardinella spp. in West African coastal food websPublication . Correia, Edna; Granadeiro, J. P.; Regalla, Aissa Said; Monteiro, Hamilton; Catry, PauloDespite their importance for fisheries, livelihoods and biodiversity conservation, shelf ecosystems in West Africa are poorly known. Caspian Tern (Hydroprogne caspia) and Royal Tern (Thalasseus maximus) are two of the most numerous and widespread nesting seabirds in the region, and an understanding of the diet of these opportunistic predators may throw light on important elements of the local food webs. This study describes and compares the prey consumed by these two species in Guinea and Guinea-Bissau collected from 2013 to 2015. Our results show that both tern species feed mostly on pelagic fish from which Clupeidae (mostly Sardinella maderensis) dominated the diet at all locations and seasons. Pristigasteridae and Polynemidae were the next most frequent prey in the diet of these two tern species. Our findings strengthen the recent suggestion of a wasp-waist ecosystem for our study area, with sardinella as the key prey for several predators, including seabirds and pelagic fishes, and potentially influencing their distribution and abundance. Moreover, our results show a higher diversity in the diet of the Caspian Tern, with this species preying on a greater range of benthopelagic fishes (e.g. Gerreidae; Mugilidae) which fits with observations of inshore foraging that seems rarer in Royal Terns. We further show that prey identification based only on otoliths from pellets, as opposed to the use of all hard structures (e.g. otoliths, vertebrae, scales), seriously underestimates the occurrence of species with fragile and small otoliths, including clupeids and other small pelagics.