This dataset provides the values of stable carbon and nitrogen stable isotopes in bulk muscle samples of 11 species of cetacea from the Macaronesian regions (Canary, Madeira, and Azores Islands) collected between 1996 and 2018. The values of nitrogen stable isotopes in amino acids of muscle samples of the common dolphin (Delphinus delphis) were also provided. The samples were collected from stranded animals by trained personnel. Cetacean samples were obtained from necropsies of stranded cetaceans following a standard protocol defined by the European Cetacean Society (after Kuiken and García Hartmann 1991). Additional data included body length, age (adult, juvenile) and sex for each animal, along with carbon, nitrogen, and lipid content of muscle samples. Isotope data for bulk samples included values for samples with and without lipids. Exact latitude and longitude coordinates for each sample are not available, geographical position of the center of a circle including each island is given instead. Samples were freeze dried or dried (60°C, 48h) before analysis. Stable isotopes in bulk muscle samples were analysed in an isotope-ratio mass spectrometer coupled to an elemental analyser. Aliquots of each sample were analysed whole or after lipid extraction with trichloromethane:methanol (Bligh and Dyer, 1959). Stable nitrogen isotopes in amino acids were analysed after hydrolisis and derivatization of samples in an isotope-ratio mass spectrometer coupled to a gas chromatograph. Details on the analytical procedures can be found in Bode et al. (2021).

This research was supported by the Madeira Cetacean Stranding Network (RACAM) of the Machico Municipality, Madeira, Portugal.