My co-authors and I are pleased to share our new publication “Seals and sea lions are what they eat, plus what? Determination of trophic discrimination factors for seven pinniped species” in the journal Rapid Communications in Mass Spectrometry: http://onlinelibrary.wiley.com/doi/10.1002/rcm.7539/abstract *Abstract: * *Rationale:* Mixing models are a common method for quantifying the contribution of prey sources to the diet of an individual using stable isotope analysis; however, these models rely upon a known trophic discrimination factor (hereafter, TDF) that results from fractionation between prey and animal tissues. Quantifying TDFs in captive animals is ideal, because diet is controlled and the proportional contributions and isotopic values of all prey items are known. *Methods: *To calculate TDFs for the Hawaiian monk seal, northern elephant seal, bearded seal, ringed seal, spotted seal, harbor seal, and California sea lion, we obtained whiskers, serum, plasma, red blood cells, and prey items from nine captive individuals. We obtained δ13C and δ15N values using continuous-flow isotope-ratio mass spectrometry. The average δ13C and δ15N values from bulk and lipid-corrected prey from the diet were subtracted from theδ13C and δ15N values of each blood and whisker sample to calculate tissue-specific TDFs for each individual (∆13C or ∆15N). *Results: *The ∆13C values ranged from +1.7 to +3.2‰ (bulk prey) and from +0.8 to +1.9‰ (lipid-corrected prey) for the various blood components, and from +3.9 to +4.6‰ (bulk prey) or +2.6 to +3.9‰ (lipid-corrected prey) for whiskers. The ∆15N values ranged from +2.2 to +4.3‰ for blood components and from +2.6 to +4.0‰ for whiskers. The TDFs tended to group by tissue, with whiskers having greater ∆13C values than blood components. In contrast, the ∆15N values were greater in serum and plasma than in red blood cells and whiskers. *Conclusions: *By providing the first TDF values for five seal species (family Phocidae) and one otariid species (family Otariidae), our study facilitates more accurate mixing models for these species. These values are particularly important for critically endangered Hawaiian monk seals and the three Arctic seal species (bearded, ringed, and spotted) that are faced with a rapidly changing environment. Please contact me if you have any questions or do not have access to the article. Take care, Roxanne -- Roxanne Santina Beltran NSF Predoctoral Fellow Ph.D. Student, Burns and Breed Labs University of Alaska Anchorage/Fairbanks www.roxannebeltran.com