Assessment of the ecophysiological conditions and trophic ecology of two cetacean species (Tursiops truncatus and Globicephala macrorhynchus) in Madeira Archipelago, using RNA/DNA ratios and Carbon/Nitrogen stable isotopes

• Autor(a) principal: Dromby, Morgane
• Data de Publicação: 2018
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.1/12550
• topic: Índices derivados de ácidos nucleicos; Dinâmica de teias alimentares; Mamíferos marinhos; Isótopos estáveis; Amostragem por biópsia; Domínio/Área Científica::Ciências Naturais::Ciências Biológicas

Madeira is home of up to 22 cetacean species, which makes this place an important spot for conservation measures. There is a need to assess the nutritional state of marine mammals in the region, to prevent or monitor detrimental effects from natural and anthropogenic stressors. This study investigates the nutritional state of bottlenose dolphins and short-finned pilot whales in Madeira, via the usage of RNA/DNA ratios and provides an insight into their trophic ecology and habitat residency thanks to carbon and nitrogen stable isotopes analysis. In 2017-2018, RNA/DNA ratios and stable isotopes were determined from skin samples, and stable isotopes were compared with those in samples of their potential preys. SIMMs (Stable Isotope Mixing Models) determined the contribution of each prey species in the diet of the two cetacean species. RNA/DNA ratios of both species indicated that cetaceans were in good nutritional states and that ratios were different across taxa. Ratios were not significantly different across seasons and residency patterns. The δ13C values supported preferences for offshore waters for short-finned pilot whales and inshore waters for bottlenose dolphins and underlined spatial segregation between the two species. The δ15N values informed that pilot whales (mean=12.7‰, SD=0.5) and bottlenose dolphins (mean=10.9‰; SD=0.7) occupied high trophic levels. SIMMs did not support that pilot whales adopted a theuthophagus preferential diet, but rather consumed large amounts of mackerels and tuna species. Moreover, there were no significant differences in their diets across seasons but there were differences between residency patterns. SIMMs predicted that bottlenose dolphins fed on demersal and pelagic fishes and it existed intra-season variabilities in isotopic values. The study provides a better understanding of the two species ecology and highlights their organisation in space in Madeira. It suggests that RNA/DNA ratios, could be good proxies for the determination of nutritional states in cetaceans and help for successful conservation.