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Publication
Mergulho e seleção de habitat de tartarugas-verdes chelonia mydas da África Ocidental
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Abstract(s)
A ilha de Poilão, na Guiné-Bissau, alberga uma das seis maiores populações
nidificantes de tartarugas-verdes Chelonia mydas do mundo. Face à ausência de conhecimento
sobre o comportamento de mergulho das tartarugas desta população, foram colocados
transmissores Fast GPS equipados com sensores de profundidade em treze fêmeas nidificantes
em 2021. Os movimentos horizontais e as profundidades ocupadas pelos indivíduos foram
analisados para três períodos do ciclo de vida – reprodução, migração e alimentação. Durante
o período de reprodução, as tartarugas permaneceram próximas a Poilão, onde a média das
profundidades máximas de mergulho foi 13,9 m (± 5,0 m). Durante a migração, as tartarugas
estabeleceram duas rotas distintas. Nove indivíduos migraram para a Mauritânia e um indivíduo
migrou para o Gana. A maioria das rotas foram costeiras, observando-se uma única rota
oceânica. A média das profundidades máximas de mergulho durante a migração para a
Mauritânia e para o Gana foi 21,8 m (± 13,9 m) e 29,4 m (± 9,5 m), respetivamente. Nas áreas
de alimentação, a média das profundidades máximas de mergulho foi 9,9 m (± 5,7 m) na
Mauritânia e de 26,1 m (± 9,3 m) no Gana. A ocupação de águas pouco profundas durante o
período de reprodução sugere que as tartarugas repousam durante parte do tempo sob estruturas
rochosas para contrabalançar a flutuabilidade positiva. As profundidades usadas pelas
tartarugas durante as migrações costeiras foram idênticas às usadas por conspecíficos no
Mediterrâneo. Na Mauritânia, a ocupação frequente de profundidades para além do limite de
crescimento de ervas marinhas e algas marinhas sugere que durante o inverno as tartarugas
apresentam atividade alimentar reduzida. Por sua vez, as profundidades usadas no Gana podem
sugerir que a tartaruga que frequentou esta zona terá tido uma dieta omnívora. Este estudo, para
além de aumentar o conhecimento sobre a ecologia e o comportamento de mergulho das
tartarugas-verdes de Poilão, contém dados que podem informar os regulamentos zonais da
atividade pesqueira e os regulamentos sobre o uso de artes de pesca, de forma a reduzir as
capturas acessórias de tartarugas desta população ao longo da costa oeste africana.
Poilão Island, in Guinea-Bissau, hosts a green turtle Chelonia mydas nesting population among the top six worldwide. Due to the lack of knowledge about the diving behaviour of the turtles of this population, Argos linked FastGPS tags equipped with depth sensors were placed in thirteen nesting females in 2021. The horizontal movements and the depths occupied by the turtles were analysed for three periods of the life cycle – breeding, migration and foraging. During the breeding period turtles remained close to Poilão, where the average maximum dive depths was 13.9 m (± 5.0 m). During migration, turtles established two distinct routes. Nine turtles travelled to Mauritania and one travelled to Ghana. Turtles followed coastal routes and a single oceanic route was observed. The average maximum dive depths during the migration to Mauritania and Ghana were 21.8 m (± 13.9 m) and 29.4 m (± 9.5 m), respectively. On foraging grounds, the average maximum dive depths were 9.9 m (± 5.7 m) in Mauritania and 26.1 m (± 9.3 m) in Ghana. The occupation of shallow waters during the breeding season suggests that turtles may rest part of the time under rocky structures to counterbalance positive buoyancy. The depths used by turtles during coastal migrations were identical to those used by conspecifics in the Mediterranean. In Mauritania, the frequent occupation of depths beyond the limits of seagrass and algal growth suggests that during the winter turtles have reduced feeding activity. In turn, the depths used in Ghana may suggest that this particular turtle had an omnivorous diet. This study, in addition to increasing knowledge about the ecology and diving behavior of the green turtles of Poilão, contains data that can inform zonal fishing regulations and regulations on gear-use to reduce bycatch of turtles from this population along the West African coast.
Poilão Island, in Guinea-Bissau, hosts a green turtle Chelonia mydas nesting population among the top six worldwide. Due to the lack of knowledge about the diving behaviour of the turtles of this population, Argos linked FastGPS tags equipped with depth sensors were placed in thirteen nesting females in 2021. The horizontal movements and the depths occupied by the turtles were analysed for three periods of the life cycle – breeding, migration and foraging. During the breeding period turtles remained close to Poilão, where the average maximum dive depths was 13.9 m (± 5.0 m). During migration, turtles established two distinct routes. Nine turtles travelled to Mauritania and one travelled to Ghana. Turtles followed coastal routes and a single oceanic route was observed. The average maximum dive depths during the migration to Mauritania and Ghana were 21.8 m (± 13.9 m) and 29.4 m (± 9.5 m), respectively. On foraging grounds, the average maximum dive depths were 9.9 m (± 5.7 m) in Mauritania and 26.1 m (± 9.3 m) in Ghana. The occupation of shallow waters during the breeding season suggests that turtles may rest part of the time under rocky structures to counterbalance positive buoyancy. The depths used by turtles during coastal migrations were identical to those used by conspecifics in the Mediterranean. In Mauritania, the frequent occupation of depths beyond the limits of seagrass and algal growth suggests that during the winter turtles have reduced feeding activity. In turn, the depths used in Ghana may suggest that this particular turtle had an omnivorous diet. This study, in addition to increasing knowledge about the ecology and diving behavior of the green turtles of Poilão, contains data that can inform zonal fishing regulations and regulations on gear-use to reduce bycatch of turtles from this population along the West African coast.
Description
Dissertação de Mestrado apresentada no ISPA
– Instituto Universitário para a
obtenção de grau de Mestre na
especialidade de Biologia Marinha
e Conservação
Keywords
África ocidental Chelonia mydas Mergulho Telemetria Uso de habitat West Africa Diving Telemetry Habitat Use