Browsing by Author "Dromby, Morgane"
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- 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 isotopesPublication . Dromby, Morgane; Teodósio, Maria A.; Alves, Filipe M. A.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.
- Ecophysiological traits of highly mobile large marine predators inferred from nucleic acid derived indicesPublication . Alves, Filipe; Dromby, Morgane; Baptista, Vânia; Ferreira, R.; Correia, A. M.; Weyn, M.; Valente, R.; Froufe, E.; Rosso, M.; Sousa-Pinto, I.; Dinis, A.; Dias, E.; Teodosio, M ANucleic acid-derived indices such as RNA/DNA ratios have been successfully applied as ecophysiological indicators to assess growth, nutritional condition and health status in marine organisms given that they provide a measure of tissue protein reserves, which is known to vary depending on changes in the environment. Yet, the use of these biochemical indices on highly mobile large predators is scarce. In this study, we tested the applicability of using nucleic acids to provide insights on the ecophysiological traits of two marine mammal species (common bottlenose dolphins and short-finned pilot whales) and explored potential related factors (species, sex, season, and residency pattern), using skin tissue (obtained from biopsy darts) of apparently healthy and adult free-ranging animals. Significantly higher RNA/DNA ratios were obtained for bottlenose dolphins (p < 0.001), and for visitor pilot whales when compared with resident pilot whales (p = 0.001). No significant changes were found between the sexes. Based on the percentile approach, the samples contain individuals in a general good condition (as the 10th percentile is not closer to the mean than the 75th percentile), suggesting that the studied region of Macaronesia may be considered an adequate habitat. The combination of this effective tool with genetic sexing and photographic-identification provided an overall picture of ecosystem health, and although with some limitations and still being a first approach, it has the applicability to be used in other top predators and ecosystems.
- Isotope-based inferences of the trophic niche of short-finned pilot whales in the WebbnesiaPublication . Escánez, Alejandro; Marrero-Pérez, Jacobo; Dromby, Morgane; Pimentel-González, Atenary; Dias, Ester; García-Pastor, Ester M.; Weyn, Mieke; Ferreira, Rita; Montañés-Pérez, Alexandra; Fernandez, Marc; Dinis, Ana; Alves, FilipeKnowledge of predator-prey interactions is key in ecological studies and understanding ecosystem function, yet this is still poorly explored in the deep-sea environment. Carbon (delta C-13: C-13/C-12) and nitrogen (delta N-15: N-15/N-14) stable isotope ratios of a deep-diving species, the short-finned pilot whale (Globicephala macrorhynchus), were used to explore knowledge gaps on its ecological niche and foraging habitats in the Webbnesia marine ecoregion (Tenerife Island, n = 27 animals vs. Madeira, n = 31; 500 km apart) where animals display distinct levels of site fidelity. Specifically, we tested whether intraspecific isotopic variation results from differences between geographic areas (due to possible foraging plasticity between regions), sexes, and/or years (2015-2020) using Generalized Linear Models. In general, significant differences (p < 0.05) were found in the stable isotope profiles of pilot whales between the two archipelagos, which were also reflected in their isotopic niche. The higher mean and wider range of delta N-15 values in Tenerife suggest that pilot whales consume prey of higher trophic levels and more diverse than Madeira. The higher mean and wider range of delta C-13 values in Madeira suggest that in that island, pilot whales rely on prey from more diverse habitats. There was significant variation between some years, but not between sexes. Finally, we discuss pilot whales' foraging strategies worldwide and infer the reliance on benthic or benthopelagic food sources in the Webbnesia.
- Trophic ecology of common bottlenose dolphins in a pelagic insular environment inferred by stable isotopesPublication . Dias, Ester; Dromby, Morgane; Ferreira, Rita; Gil, Ágatha; Tejerina, Raquel; Castro, L. Filipe C.; Rosso, Massimiliano; Sousa-Pinto, Isabel; Hoffman, Joel C.; Teodosio, Maria; Dinis, Ana; Alves, FilipeThe common bottlenose dolphin (Tursiops truncatus) is a top marine predator widely dispersed in coastal and pelagic habitats and with a generalist feeding behavior. Yet, information on the trophic ecology of animals inhabiting pelagic environments is still scarce. Using carbon (& delta;C-13: C-13/C-12) and nitrogen (& delta;N-15: N-15/N-14) stable isotope ratios, we identified and quantified the main groups of prey assimilated by bottlenose dolphins inhabiting an oceanic habitat (Madeira Island, East Atlantic). Bottlenose dolphins assimilated pelagic, schooling fish (such as blue jack mackerel, Trachurus picturatus) and mesopelagic and demersal squids, which reinforces the pelagic dietary composition of insular/oceanic dolphins. Also, intra-seasonal differences were found in their stable isotope ratios, which suggest intraspecific variability in the feeding behavior among individuals living in the same area. Sex was not the main factor contributing to these differences, suggesting the lack of trophic niche segregation between adult males and females in this offshore environment. Nonetheless, further studies including different life stages and information on the ecophysiological requirements are necessary to disclose the factors responsible for the observed variability. This study showed that insular dolphins fed primarily on economically important pelagic prey, highlighting the need of developing management strategies that integrate conservation in fisheries plans.