Gray whale (Eschrichtius robustus) stranding records in Mexico during the winter breeding season in 2019
S. MartÃnez-Aguilar, E. Mariano-MelÃ©ndez, N. LÃ³pez-Paz, F. Castillo-Romero, G.A. Zaragoza-Aguilar, F. Castillo-Romero, J. Rivera-Rodriguez, S. Swartz, L. Viloria-GÃ³mora and J. UrbÃ¡n R.
While the occasional death and stranding of gray whales occurs as part of their life cycle, sometimes unusual mortality events occur (UME). The specific cause of the 1999 â€“ 2000 UME for gray whale was undetermined, but some evidence suggests that a decline in body condition resulting from nutritional stress (lack of sufficient food) may have contributed to the increase in gray whale mortality by starvation. Since that event, the incidence of gray whale strandings decreased throughout the species range in the North Pacific. Information collected between December 2018 and April 2019 from four sources in Mexico reported 73 gray whales stranded along the Pacific coast of Baja California and the Gulf of California, Mexico. 83.5% of the dead whales were encountered in Laguna Ojo de Liebre (ScammonÂ´s lagoon) and the surrounding areas. Forty-four of these were female gray whales, 16 were males and 13 were of undetermined sex. The age classes of the dead whales were: 28 adults, 39 subadults, 2 calves and 4 of unknown age/sex. Compared to mortalities reported in previous years from 2012-2018, the number of stranded calves decreased, but the number of dead gray whales sub-adults and adults increased. In relation to sex, the number of females stranded also increased during this year. A similar increase in gray whale mortalities was observed in 1999-2001. This high number of gray whale stranding in 2019 appears to be related to the decline in body condition evident in numerous gray whales observed in the gray whale's winter aggregation areas and breeding lagoons. The examination of environmental data from the whales' summer feeding grounds is needed to establish any significant correlation with this increase in mortality.