Modelling shiftsnin cetacean distribution under future scenarios of climate change in the Eastern North Atlantic provisório

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Trophic ecology of common bottlenose dolphins in a pelagic insular environment inferred by stable isotopes

Publication . 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, Filipe

The 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.

2023Journal article

Open Access

Assessing data bias in visual surveys from a cetacean monitoring programme

Publication . Oliveira-Rodrigues, Cláudia; Correia, Ana M.; Valente, Raul; Gil, Ágatha; Gandra, Miguel; Liberal, Marcos; Rosso, Massimiliano; Pierce, Graham; Sousa-Pinto, Isabel

Long-term monitoring datasets are fundamental to understand physical and ecological responses to environmental changes, supporting management and conservation. The data should be reliable, with the sources of bias identified and quantified. CETUS Project is a cetacean monitoring programme in the Eastern North Atlantic, based on visual methods of data collection. This study aims to assess data quality and bias in the CETUS dataset, by 1) applying validation methods, through photographic confirmation of species identification; 2) creating data quality criteria to evaluate the observer's experience; and 3) assessing bias to the number of sightings collected and to the success in species identification. Through photographic validation, the species identification of 10 sightings was corrected and a new species was added to the CETUS dataset. The number of sightings collected was biased by external factors, mostly by sampling effort but also by weather conditions. Ultimately, results highlight the importance of identifying and quantifying data bias, while also yielding guidelines for data collection and processing, relevant for species monitoring programmes based on visual methods.

2022Journal article

Open Access