Lipid-loss in blubber biopsies is universal in cetaceans highlighting a need for new health assessment measures

For cetaceans to be sentinels of environmental change, reliable methods to assess overall health and physiological state are required. Blubber lipid content of remotely darted biopsies has been used to approximate energy stores and overall health. However, studies on beluga (Delphinapterus leucas), fin (Balaenoptera physalus) and killer whales (Orcinus orca) found a sampling effect (lipid-loss) biasing blubber biopsy lipid content. To determine if this applies to all cetaceans, we conducted a literature review, comparing the lipid content of outer blubber from biopsy (darted) and stranding (excised) samples for 27 species. For 16 species of five taxa (Balaenidae, Balaenopteridae, Delphinidae, Physeteridae and Ziphiidae), independent observations (n = 1346) of both biopsies and strandings were available. With taxon as a factor, a beta regression model (pseudo-R² = 0.638) determined that the mean lipid content of biopsies is 11.1 ± 1.9% lower than that of strandings. Post hoc Šidák tests confirmed that the difference among sampling methods was statistically significant (α = 0.05) for all taxa (p < 0.001). This is a universal problem, likely due to tissue disruption associated with the force of the biopsy dart resulting in lipid loss and confirms that biopsy lipid content estimates are unreliable indicators of health or body condition. Our results have unexplored implications for the quantification of blubber biopsy lipid fractions for fatty acid or contaminant analyses, for example. There is a welfare and conservation imperative to develop alternative markers of overall health and physiological state from biopsies. In this regard, emerging technologies such as ‘omics analyses look particularly promising.