Sample extraction
For each of the whales, we processed ten replicates, approximately 0.4 g of blubber each: five endogenous (un-spiked) and five spiked with 400 µL of a calibrant mixture of the 11 target analytes (masses in Supplementary Table 2). In addition to three blanks, we ran three un-spiked replicates from a standard reference material (NIST SRM 1945), taken from a pregnant female short-finned pilot whale. For quantification, we diluted neat standards in methanol to create ten calibration standards covering a physiologically relevant range of concentrations (Supplementary Table 2). We created an IS mix with ten isotopically labeled matched ISs (Supplementary Table 2), which we added to all samples (blanks, SRMs, calibrants, and blubber) before extraction. We prepared all stocks and samples gravimetrically and extracted all samples, including blanks and calibrants, using a bead homogenization and QuEChERS extraction protocol previously detailed (6).