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MEPS 658:237-252 (2021)  -  DOI: https://doi.org/10.3354/meps13585

Poor body condition associated with an unusual mortality event in gray whales

Fredrik Christiansen1,2,3,*, Fabian Rodríguez-González4, Sergio Martínez-Aguilar4,5, Jorge Urbán4,5, Steven Swartz5, Hunter Warick3, Fabien Vivier6, Lars Bejder2,3,6

1Aarhus Institute of Advanced Studies, Høegh-Guldbergs Gade 6B, 8000 Aarhus C, Denmark
2Zoophysiology, Department of Biology, Aarhus University, C.F. Møllers Allé 3, 8000 Aarhus C, Denmark
3Centre for Sustainable Aquatic Ecosystems, Harry Butler Institute, Murdoch University, Murdoch, 6150 Western Australia, Australia
4Departamento de Ciencias Marinas y Costeras, Universidad Autónoma de Baja California Sur, La Paz, BCS 23081, Mexico
5Laguna San Ignacio Ecosystem Science Program (LSIESP), Darnestown, MD 20874, USA
6Marine Mammal Research Program, Hawaii Institute of Marine Biology, University of Hawaii at Manoa, Kaneohe, HI 96744, USA
*Corresponding author:

ABSTRACT: The eastern North Pacific gray whale Eschrichtius robustus experienced an unusual mortality event (UME) in 2019-2020, with 384 whales found dead along the Pacific coasts of Mexico, USA and Canada. A similar UME in 1999-2000 was speculated to have been caused by starvation, but body condition data were not available to test this hypothesis. Between 2017 and 2019, we used unmanned aerial vehicles (drones) and photogrammetry methods to measure the body condition of gray whales in San Ignacio Lagoon, Baja California Sur, Mexico. Body condition was calculated from the residual of the relationship between body volume and length. The body condition of gray whales was significantly lower in 2018 (-11.1%, SE = 1.74, n = 531) and 2019 (-9.7%, SE = 1.76, n = 628) compared to 2017 (n = 59) for all reproductive classes (calves, juveniles, adults and lactating females). Overall, lactating females were in good body condition. The reduction in body condition of whales in 2018-2019 is unlikely to have affected their survival, but could have reduced their reproductive rate by prolonging the post-weaning recovery time. This could explain the low number of mother-calf pairs observed in the San Ignacio Lagoon in 2018 and 2019. For juveniles and adults that arrived in the lagoons with less energy reserves, their reduced body condition may have been close to their survival threshold. This could explain the high proportion of juveniles and adults among the stranded dead whales in 2019-2020. Although the underlying cause of the reduction in gray whale body condition is unknown, starvation likely contributed to the 2019-2020 UME.


KEY WORDS: Baleen whales · Bioenergetics · Reproduction · Starvation · Survival · Unmanned aerial vehicles


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Cite this article as: Christiansen F, Rodríguez-González F, Martínez-Aguilar S, Urbán J and others (2021) Poor body condition associated with an unusual mortality event in gray whales. Mar Ecol Prog Ser 658:237-252. https://doi.org/10.3354/meps13585

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