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- Fine-scale foraging segregation in a green turtle (Chelonia mydas) feeding ground in the Bijagós archipelago, Guinea BissauPublication . Madeira, Fernando Miguel; Rebelo, Rui; Catry, Paulo; Neiva, João Guilherme; Barbosa, Castro; Regalla De Barros, Aissa; Patrício, Ana RitaGreen turtles (Chelonia mydas) are highly dependent on neritic foraging areas throughout much of their life. Still, knowledge of recruitment dynamics, foraging habits, and habitat use in these areas is limited. Here, we evaluated how the distribution and food preferences of green sea turtles from different life stages varied within a foraging aggregation. We focused on two islands in Guinea-Bissau, Unhocomo and Unhocomozinho, using water captures and survey dives to record habitat use and characteristics, and stable isotopes to infer diet. Additionally, we used stable isotopes to infer their diet. Two habitat types were sampled: deeper (2.26 ± 0.4 m) rocky sites fringed by mangrove with macroalgae, and sandy shallows (1.37 ± 0.12 m) surrounded by rocky reefs with macroalgae and seagrass. The two benthic communities were similar isotopically and in terms of species composition, except for the presence or absence of seagrass, which had unique signatures. We captured 89 turtles ranging from 35 cm to 97 cm in curved carapace length (i.e., juvenile to adult stages). Size distribution was habitat-dependent, with most smaller turtles present in sandy shallows and larger turtles favoring slightly deeper rocky sites. Turtle isotopic signatures differed between the habitat of capture, regardless of size, revealing a marked dichotomy in foraging preference. All turtles fed primarily on macroalgae, mostly rhodophytes. However, individuals captured in sandy habitats had evident seagrass skewed isotopic signatures. Larger turtles may be unable to use the more diverse shallower foraging sites due to increased vulnerability to predation. Despite the proximity of the sampled foraging sites (2.7 km apart), the two foraging subgroups seem to maintain consistently different feeding habits. Our study highlights how heterogeneous green turtle foraging habits can be within populations, even at small geographic scales.
- Inter-island nesting dynamics and clutch survival of green turtles Chelonia mydas within a marine protected area in the Bijagós Archipelago, West AfricaPublication . Raposo, Cheila; R., Rebelo; Catry, Paulo; Ferreira-Airaud, Betania; Barbosa, Castro; Garcia, Tumbulo Bamba; Regalla De Barros, Aissa; Sá Sampaio, Manuel; Patrício, Ana RitaUnderstanding spatial heterogeneity in reproductive success among at-risk populations facing localised threats is key for conservation. Sea turtle populations often concentrate at one nesting site, diverting conservation efforts from adjacent smaller rookeries. Poilão Island, Bijagós Archipelago, Guinea-Bissau, is a notable rookery for green turtles Chelonia mydas within the João Vieira-Poilão Marine National Park, surrounded by three islands (Cavalos, Meio and João Vieira), with lower nesting activity. Poilão’s nesting suitability may decrease due to turtle population growth and sea level rise, exacerbating already high nest density. As the potential usage of secondary sites may arise, we assessed green turtle clutch survival and related threats in Poilão and its neighbouring islands. High nest density on Poilão leads to high clutch destruction by later turtles, resulting in surplus eggs on the beach surface and consequently low clutch predation (4.0%, n = 69, 2000). Here, the overall mean hatching success estimated was 67.9 ± 36.7% (n = 631, 2015–2022), contrasting with a significantly lower value on Meio in 2019 (11.9 ± 23.6%, n = 21), where clutch predation was high (83.7%, n = 98). Moderate to high clutch predation was also observed on Cavalos (36.0%, n = 64) and João Vieira (76.0%, n = 175). Cavalos and Meio likely face higher clutch flooding compared to Poilão. These findings, alongside observations of turtle exchanges between islands, may suggest a source-sink dynamic, where low reproductive output sink habitats (neighbouring islands) are utilized by migrants from Poilão (source), which currently offers the best conditions for clutch survival.
- track2KBA: An R package for identifying important sites for biodiversity from tracking dataPublication . Beal, Martin; Oppel, Steffen; Handley, Jonathan; Pearmain, Elizabeth J.; Pujol, Virginia Morera; Carneiro, Ana P. B.; Davies, Tammy; Phillips, Richard A.; Taylor, Philip R.; Miller, Mark G. R.; Franco, Aldina; Catry, Inês; Patrício, Ana Rita; Regalla De Barros, Aissa; Staniland, Iain; Boyd, Charlotte; Catry, Paulo; Dias, Maria P.Abstract 1. Identifying important sites for biodiversity is vital for conservation and management. However, there is a lack of accessible, easily applied tools that enable practitioners to delineate important sites for highly mobile species using established criteria. 2. We introduce the R package ‘track2KBA’, a tool to identify important sites at the population level using tracking data from individual animals based on three key steps: (a) identifying individual core areas, (b) assessing population-level representativeness of the sample and (c) quantifying spatial overlap among individuals and scaling up to the population. 3. We describe package functionality and exemplify its application using tracking data from three taxa in contrasting environments: a seal, a marine turtle and a migratory land bird. 4. This tool facilitates the delineation of sites of ecological relevance for diverse taxa and provides output useful for assessing their importance to a population or species, as in the Key Biodiversity Area (KBA) Standard. As such, ‘track2KBA’ can contribute directly to conservation planning at global and regional levels.
- Coastal waters of a marine protected area of the Bijagós Archipelago, West Africa, shelter juvenile fishes of economic and ecological importancePublication . Correia, Edna; Granadeiro, J. P.; Regalla De Barros, Aissa; Catry, PauloIn many marine ecosystems small pelagic fish exert a crucial role in controlling the dynamics of the community, mainly due to their high biomass at intermediate levels of the food web. These fish use coastal marine ecosystems as nursery areas, but also to forage and to avoid predation or competition. We studied spatial, seasonal, lunar and diel variations in a coastal fish community from a marine protected area of the Bijagós Archipelago, Guinea-Bissau. Fish were sampled with 46 beach seine net sessions in 2015 and 2016. A total of 35 fish species of 25 families were captured. Fish abundance varied between years and seasons, with a higher abundance in the dry season, but not by lunar tide. Nonetheless, the community composition was broadly similar over the seasons, among islands and between lunar tides. Clupeidae, Haemulidae and Gerreidae were the most abundant fish families. Sardinella maderensis highly dominated the captures throughout the year, with catches much higher than any other species. The differences in abundance between seasons and years may be related with movements to or from the shore due to feeding activity or to avoid predation, or else to differences in recruitment between years. There were no significant diel differences in species richness and diversity, although higher numbers of fish were captured during daytime. For most species the majority of individuals captured were immature, highlighting the importance of the archipelago as nursery area for several species. These small pelagics, and particularly Sardinella maderensis, represent the main prey for several marine predators. Thus, the conservation of such fish species may be key for the management of the Bijagós Archipelago.
- Movement patterns of green turtles at a key foraging site: the Banc d’Arguin, MauritaniaPublication . Mestre, Julie; Patrício, Ana Rita; Sidina, Ebaye; Senhoury, Cheibani; El’bar, Nahi; Beal, Martin; Regalla De Barros, Aissa; Catry, PauloABSTRACT: Interactions with fisheries is a major threat to sea turtles. However, space-use at foraging locations remains overlooked in many populations, preventing effective protection. We assess the space-use of 14 juvenile and 24 adult green turtles (Chelonia mydas) satellite-tracked in 2018–2022 within a foraging site of global importance for this species, the Banc d’Arguin in Mauritania, West Africa. Turtles exhibited a patchy distribution and used overlapping habitats irrespective of sexes and life stages. Mean individual home range was larger (151.5 ± 160.5 km²) than values reported in most green turtle populations. Individuals concentrated in two main areas used year-round. Inshore/offshore movements seem to occur within the central part of the Banc d’Arguin, with turtles moving to deeper areas during colder months. More than half of the turtles performed within-season range shifts and switched between up to four distinct areas, with some individuals returning to previously visited sites. Turtles mostly exploited shallow areas (4.30 ± 3.42 m) and seemed to use disproportionally more of the areas inside the Parc National du Banc d’Arguin, than areas of similar bathymetry outside this marine protected area. This suggests that foraging green turtles have been benefiting from the management of the Park since it was established in 1976. However, turtles’ home range overlapped greatly with artisanal fisheries, which operate in the central shallow waters of the Park. The present study provides valuable ecological information that can be used to inform the planning of fisheries management zones, aiming to reduce the interactions between turtles and artisanal fisheries. © The Author(s) 2024.
- Atlantic connectivity of a major green sea turtle Chelonia mydas foraging aggregation at the Banc d’Arguin, MauritaniaPublication . Patrício, Ana Rita; Coveney, Sophia A.; Barbanti, Anna; Barbosa, Castro; Broderick, Annette; El’Bar, Nahi; Godley, Brendan; Hancock, Joana M.; Regalla De Barros, Aissa; Senhoury, Cheibani; Sidina, Ebaye; de Thoisy, Benoît de; Tilley, Dominic; Weber, Sam; Catry, PauloABSTRACT: Understanding population connectivity is paramount for effective conservation. While genetic tools have elucidated sea turtle migration patterns, notable data gaps limit our understanding of ocean-wide connectivity, especially regarding east Atlantic green turtles. We characterized the genetic composition of a globally important green turtle foraging aggregation at the Banc d’Arguin, Mauritania, incorporating data from 323 individuals captured between 2018 and 2021. Using extended mitochondrial DNA D-loop (738 base pairs [bp]) and mitochondrial short tandem repeat (mtSTR; ~200 bp) markers, we assessed the genetic structure of Atlantic green turtle foraging aggregations and estimated the most likely origin of immature green turtles from the Banc d’Arguin using mixed stock analyses (MSAs). We identified 6 D-loop haplotypes, with a clear dominance of CM-A8.1 (91.8%) followed by CM-A5.1 (6.3%) and 4 rare haplotypes: CM-A1.4, CMA6.1, CM24.1 and CM36.1. We found 13 mtSTR haplotypes, with ‘7-12-4-4’ being dominant (89.0%). The genetic composition at the Banc d’Arguin differed significantly from the only foraging aggregation studied in West Africa to date — in the archipelago of Cabo Verde (located ca. 750 km from the Banc d’Arguin) — dominated by haplotype CM-A5. The MSA combining both genetic markers indicated that 87.6% of immature green turtles at the Banc d’Arguin originate from the major East Atlantic rookery at Poilão (Guinea-Bissau), but 11.6% come from more distant rookeries in South America (8.1%) and potentially Ascension Island (3.4%). We suggest that green turtle transatlantic movements may be more common than previously thought and highlight the importance of the Banc d’Arguin as a regional foraging hub for this species.
- Spatial distribution of inter-nesting green turtles from the largest Eastern Atlantic rookery and overlap with a marine protected areaPublication . Raposo, Cheila; Mestre, Julie; Rebelo, Rui; Regalla De Barros, Aissa; Davies, Alasdair; Barbosa, Castro; Patrício, Ana RitaUnderstanding the spatial distribution of wildlife is fundamental to establish effective conservation measures. Tracking has been key to assess movement patterns and connectivity of sea turtles, yet some regions of great significance are largely understudied. We tracked 44 green turtles from the largest rookery in the Eastern Atlantic, on Poilão Island, Guinea-Bissau, during 2018 through 2020, to assess their inter-nesting movements, connectivity with nearby islands and fidelity to inter-nesting sites. Additionally, we investigated individual and environmental factors that may guide inter-nesting distribution and assessed the adequacy of a marine protected area to support this population during the breeding period. Green turtles had an overall home range of 124.45 km2 , mostly occupying a restricted area around Poilão Island, with 52% of this home range falling within the no-take zone of the João Vieira-Poilão Marine National Park. Turtles exhibited strong fidelity to inter-nesting sites, likely as a strategy to save energy. Only 2 turtles performed significant excursions out of the park, and connectivity between Poilão and nearby islands within the park was limited. Larger turtles and turtles tagged later in the nesting season tended to have smaller core areas and home ranges; thus, experienced breeders may be moving less and potentially benefit from energy saving. This study highlights the importance of a marine protected area for the conservation of one of the largest green turtle breeding populations globally, and provides suggestions for further increasing its effectiveness.
- eDNA metabarcoding for diet analyses of green sea turtles (Chelonia mydas)Publication . Díaz-Abad, Lucía; Bacco-Mannina, Natassia; Madeira, Fernando Miguel; Neiva, João; Aires, Tânia; Serrao, Ester A.; Regalla De Barros, Aissa; Patrício, Ana Rita; Frade, P. R.Understanding sea turtle diets can help conservation planning, but their trophic ecology is complex due to life history characteristics such as ontogenetic shifts and large foraging ranges. Studying sea turtle diet is challenging, particularly where ecological foraging observations are not possible. Here, we test a new minimally invasive method for the identifcation of diet items in sea turtles. We fngerprinted diet content using DNA from esophageal and cloacal swab samples by metabarcoding the 18S rRNA gene. This approach was tested on samples collected from green turtles (Chelonia mydas) from a juvenile foraging aggregation in the Bijagós archipelago in Guinea-Bissau. Esophagus samples (n=6) exhibited a higher dietary richness (11±5 amplicon sequence variants (ASVs) per sample; average±SD) than cloacal ones (n=5; 8±2 ASVs). Overall, the diet was dominated by red macroalgae (Rhodophyta; 48.2±16.3% of all ASVs), with the main food item in the esophagus and cloaca being a red alga belonging to the Rhodymeniophycidae subclass (35.1±27.2%), followed by diatoms (Bacillariophyceae; 7.5±7.3%), which were presumably consumed incidentally. Seagrass and some invertebrates were also present. Feeding on red algae was corroborated by feld observations and barcoding of food items available in the benthic habitat, validating the approach for identifying diet content. We conclude that identifcation of food items using metabarcoding of esophageal swabs is useful for a better understanding of the relationships between the feeding behavior of sea turtles and their environment.