In this study, we developed and cross-validated a novel, non-invasive method to quantify total body lipid-stores of free-ranging cetaceans based upon their tissue body density. Fieldwork was conducted with a beaked whale (northern bottlenose whale) and a mysticete (humpback whale), using suction cup attached tags , measurement of body shape, and remote biopsy sample collection. Tissue densities for bottlenose whales over 21 tag deployments in the Gully and Jan Mayen (1028.4 to 1033.9 kg m-3) covered a narrow range compared to humpback whales (1027.8 to 1050.8 kg m-3) over 59 tag deployments in Canada and Norway, con finning the role of Lipid store cycling in capital breeding baleen whales . Tissue body density of humpback whales decreased by 0.03 kg m-3 per day (2.7 kg m-3 over 90 days)over the feeding season. A similar seasonal trend was found for the body shape width to length ratios , which correlated as predicted with tissue body density across adult humpback whales (r2=29.9%, N=l8), though neither of those measures correlated with cortisol concentrations in blubber samples. Humpback whales with higher body density (lower Lipid store) fed more intensely, as predicted, whereas the opposite effect was found for bottlenose whales . By advancing methods to measure body condition of free -ranging cetaceans, this study enables fuller evaluation of the possible biologically-significant effects of anthropogenic disturbance on cetaceans.