Browsing by Author "Raposo, Cheila"
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- Evidence for trophic differences between live and bycatch oceanic juvenile loggerhead sea turtlesPublication . Raposo, Cheila; Patrício, Ana Rita; Catry, Paulo; Dellinger, Thomas; Granadeiro, J. P.The loggerhead sea turtle Caretta caretta is a vulnerable migratory species that spends its first years of life in the open sea. During this developmental phase, loggerheads can be found foraging in the epipelagic zone of the waters surrounding the Madeira Archipelago, providing a rare opportunity to gather information on the ecology of its oceanic developmental stage. In this study, we characterized the isotopic niche of these juveniles, using stable isotope analysis. We assessed two groups of turtles, turtles captured alive (n = 24) and turtles captured as bycatch on local longlines (n = 12), and explored whether animals caught in the local fishing gear represented a random sample of the population, or whether there is some evidence for a specialized foraging behaviour. We found that turtle bycatch had a significantly higher mean stable nitrogen isotope value in whole blood (δ15N = 8.5 ± 0.6‰ SD) compared to the group of turtles captured alive in the same period (δ15N = 7.6 ± 0.5‰ SD), indicating that they had a different diet. While there was a tendency for turtle bycatch to be slightly larger, we found no effect of body size on δ15N values. We propose a distinct foraging behaviour strategy hypothesis, with a group of turtles being more susceptible to interactions with fisheries and thus having a higher mortality risk, which should motivate the implementation of existing guidelines to reduce sea turtle bycatch.
- 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.
- Key issues in assessing threats to sea turtles: Knowledge gaps and future directionsPublication . Fuentes, Mariana M. P. B.; McMichael, Erin; Kot, Connie Y.; Silver-Gorges, Ian; Wallace, Bryan P.; Godley, Brendan; Brooks, Annabelle M. L; Ceriani, Simona A; Cortés-Gómez, Adriana A.; Dawson, Tiffany M.; Dodge, Kara L.; Flint, Mark; Jensen, Michael P; Komoroske, Lisa M.; Kophamel, Sara; Lettrich, Matthew; Long, Christopher A.; Nelms, Sarah E.; Patrício, Ana Rita; Robinson, Nathan J.; Seminoff, Jeffrey; Ware, Matthew; Whitman, Elizabeth R.; Chevallier, Damien; Clyde-Brockway, Chelsea E.; Korgaonkar, Sumedha A.; Mancini, Agnese; Mello-Fonseca, J; Monsinjon, Jonathan; Neves-Ferreira, Isabella; Ortega, Anna A.; Patel, Samir H.; Pfaller, Joseph B.; Ramirez, Matthew D.; Raposo, Cheila; Smith, Caitlin E.; Abreu-Grobois, F. Alberto; Hays, Graeme C.Sea turtles are an iconic group of marine megafauna that have been exposed to multiple anthropogenic threats across their different life stages, especially in the past decades. This has resulted in population declines, and consequently many sea turtle populations are now classified as threatened or endangered globally. Although some populations of sea turtles worldwide are showing early signs of recovery, many still face fundamental threats. This is problematic since sea turtles have important ecological roles. To encourage informed conservation planning and direct future research, we surveyed experts to identify the key contemporary threats (climate change, direct take, fisheries, pollution, disease, predation, and coastal and marine development) faced by sea turtles. Using the survey results and current literature, we also outline knowledge gaps in our understanding of the impact of these threats and how targeted future research, often involving emerging technologies, could close those gaps.
- 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.