Dramatic fluctuations of west coast (USA) California sea lion (CSL) population sizes are well-known historical events. More recently, the episodes have involved extensive losses from pup starvation. However, beyond dams' lactation failure that results from loss of preferred prey, proximate causes of malnutrition-related death among youngest CSL remain somewhat speculative. We hypothesized that age-related differences in presentation status and postmortem pathology would clarify elements of death trajectories. Records of 494 California sea lions included young pups to late adolescents, all present in the same environment and ecology. We identified differential starvation-related im-pacts among young CSL populations. Rapid and extreme loss of muscle and fat body mass, and resulting emaciation, were the primary overall features of morbidity. More specifically, the death trajectory among young pups was associated more proximately with contributing fluid deficit, hypovolemia, hypoglycemia, and loss of respiratory capacity. The death trajectory among non-pups was associated more proximately with negative effects of forced diet change that resulted in severe-to-overwhelming chronic parasitism. The vast majority of death trajectories appeared to be non-reversible, either in short term or over longer term. The sentinel status of marine mammals such as CSL forewarns of potential threats to local or regional ecology. It is especially concerning if recurring similar events appear to differ causally from historical patterns. We suggest that starvation events occurring in seemingly new patterns can signal new influences on a marine ecology.