Scaled mass index as a metric of body condition in free-ranging St. Lawrence Estuary belugas and comparison with the lipidomic profile

Meredith Sherrill, Alexandre Bernier-Graveline, Robert Michaud, Jonathan Verreault

Long-term monitoring of the St. Lawrence Estuary (SLE) beluga (Delphinapterus leucas) population has revealed a number of potential stressors that may be limiting this endangered population’s recovery. Recent evidence has suggested that a period of unstable population dynamics between 1999-2012, coincided with decreasing fatty acid concentrations in the blubber layer of stranded animals. While this finding suggests that a loss of energy reserves may have contributed to this period of decline, there is currently no reliable non-invasive method of estimating the body condition of free-ranging SLE belugas. The purpose of this study is therefore to develop a technique for calculating the Scaled Mass Index (SMI) of free-ranging animals, and to compare this condition index to the actual lipidome of the blubber layer. Between 2019 and 2021, 44 animals (17 females and 27 males) were both biopsied and identified in aerial video footage recorded via unmanned aerial vehicle (UAV). Morphometric measurements of these animals were extracted from video frames and used to calculated the SMI for each individual. The SMI of females ranged from 281-800 kgs, while males ranged in SMI from 380-2531 kgs. In parallel, an untargeted lipidomic analysis performed in the blubber portion of the biopsies (using an LC-MS based method), detected approximately 10,000 lipid features. Preliminary analysis of the nearly 2,000 features identified at the level of class or category, has suggested that individual glycerolipids, glycerophospholipids, sphingolipids and prenol lipids, are correlated with SMI in both males and females.