Exploring the body condition of gray whales (Eschrichtius robustus) through adipocyte analysis during unusual mortality events

Abstract

The blubber is the characteristic fatty tissue of most marine mammals; it comprises adipocytes, blood vessels, lymphatics, and abundant collagen and elastic fibers. Containing the reserve of excess and accumulated energy from feeding. Previous studies found that the adipocyte area may change according to the amount of accumulated and expended energy during migration, reproduction, lactation and breeding. This cellular characteristic reflects the energetic status of an individual (i.e., the balance between intake and total energy investment), which can be interpreted as reproductive success and general health. In the present study, we measured the adipocyte area of the gray whales wintering in Laguna San Ignacio, Baja California Sur, Mexico, to evaluate body condition. Adipose tissue was sampled from 116 individuals (31 calves, 22 mothers, and 63 solitary individuals) over a study period of 62 days. Each whale was assigned a priori body condition (good, fair, poor). Histological preparations stained with hematoxylin-eosin were microphotographs used to measure the adipocyte area with the software Adiposoft as a plugin to ImageJ. The adipocyte area of the calves was significantly lower than that of the adults and showed an increase during the study period. The three body condition categories found no differences in the adipocyte area. The adipocyte area analysis applied in the present study appears to be a useful tool in assessing body condition in calves, although it appears to be limited to adults. According to the OneHealth paradigm, environmental health is closely related to the health of the gray whale, which in turn is related to public health and the socioeconomic well-being of local communities that use this species as a resource.