Neutral lipid fatty acid composition in the epidermis and blubber of long-finned pilot whales (Globicephala melas) in the Northeast Atlantic confirms tissue-specific stratification

Fatty acid profiling is a widely used tool in cetacean dietary and health assessments, yet most studies focus exclusively on blubber, overlooking the epidermis – the largest organ and primary barrier against environmental stressors – which remains largely uncharacterised, despite its accessibility for sampling of live and deceased animals. Here, we present a comparative analysis of fatty acid composition across the epidermis and the outer and inner blubber layer of long-finned pilot whales (Globicephala melas). Gas chromatography-mass spectrometry on total lipid extracts identified several major lipid classes in the cetacean epidermis: free fatty acids (~ 25%), wax and steryl esters (~ 40%), and triacylglycerols (~ 30%). Monounsaturated fatty acids (MUFAs) dominated (> 59%) across the layers. Polyunsaturated fatty acids (PUFAs), generally linked to dietary intake, were more abundant in the inner blubber layer, while saturated fatty acids (SFAs) were highest in the epidermis. Inter-layer differences in abundance of 29 out of 34 (~ 85%) identified fatty acids were statistically significant, confirming tissue-specific stratification and that epidermal and blubber fatty acid profiles are not equivalent for current fatty acid dietary analyses. The distinct fatty acid composition of the epidermis suggests roles in antimicrobial defence and thermal regulation, indicating its potential as a biomarker for monitoring the health of cryptic cetacean species under changing environmental conditions. These findings establish a baseline knowledge of the neutral lipid fatty acid profile in cetacean epidermis and reaffirm the continued importance of blubber rather than skin biopsies for dietary assessments.