Quantifying the Association Between Inbreeding and Mortality in Endangered St. Lawrence Estuary Beluga Whales

Understanding factors that limit the growth of endangered populations is crucial for conservation. Depleted populations are vulnerable to losses of genetic variation and inbreeding depression. Genetic factors have been cited as one of the potential contributors to the lack of recovery of the isolated St. Lawrence Estuary (SLE) beluga ( Delphinapterus leucas ) population, which remains endangered despite decades of protection from hunting. This population is known to exhibit markedly low levels of genetic variability. Whether the high rates of neonate mortality and increased prevalence of peripartum complications observed since 2010 are linked to genetic factors or environmental conditions remains unclear. We examined the possible role of genetic factors in the lack of recovery of this population by quantifying the association between genomic estimates of inbreeding, derived from ddRAD sequencing of 154 individuals, and susceptibility to various causes of mortality. Our results indicated that genome‐wide inbreeding alone is unlikely to explain mortality trends; however, we found that individual inbreeding interacted in association with other factors, including beluga age and year of death, suggesting that the expression of inbreeding depression may be modulated by exposure to environmental stressors. Conservation actions should remain focused on mitigating anthropogenic stressors to prevent further population declines.