14Elucidating predator-prey relationships is an important part of understanding and assessing the 15 structure and function of ecosystems. Sharks are believed to play a significant role in marine 16 ecosystems, although their specific trophic ecology is largely unexplored. Stable isotopes of 17 nitrogen (δ 15 N) and carbon (δ 13 C) are a widely applied tool in food web studies but there is a 18 need to quantify stable isotope dynamics in animals, particularly sharks. In this study, diet-tissue 19 discrimination factors (DTDF = stable isotope in consumer tissue -stable isotope in diet) and 20 turnover rates (time for the isotope to be assimilated into the consumer's tissue) of stable 21 isotopes were estimated in blood, fin, and muscle tissue for the shark species Scyliorhinus 22 stellaris fed two diets with different isotope values. Subsequently, these diet-and tissue-specific 23DTDFs were used in isotopic mixing models to quantify the diet of Scyliorhinus canicula caught 24 in the North Sea and compared with stomach content data. DTDFs for δ 15 N (∆ 15 N) and δ 13 C 25 (∆ 13 C) ranged from -1.95‰ to 3.49‰ and from 0.52‰ to 5.14‰, respectively, and varied with 26 tissue and diet type. Isotope turnover rates in plasma and red blood cells, expressed as half-lives, 27 range from 39 to 135 days. A majority of the variability of DTDFs reported in this and other 28 studies with sharks can be explained by linear relationships between DTDF and dietary isotopic 29 values. From these relationships, we propose a method for isotope mixing models that uses diet-30 specific DTDFs, which improves diet reconstruction estimates of animals, particularly 31 mesopredator sharks that consume a large range of prey types. 32 33