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Possible Role of Viral Disease in Gray Whale (Eschrichtius robustus) Unusual Mortality Events (UMEs)
Steven L. Swartz, Daniel Douek, P?draig Duignan, Tracey Goldstein, Frances M.D. Gulland, Sue E. Moore, Stephen Raverty, Mario Roederer, Teri Rowles, Raphaela Stimmelmayr, Jorge Urb?n R., David W. Weller
The ENP gray whale population has undergone two official Unusual Mortality Events (UME) in the past 25 years. While the location and density of gray whale benthic prey has seen changes as the result of oceanographic features and conditions, there is no clear indication of prey limitation. Furthermore, although gray whales are well adapted for benthic feeding, they can also feed on pelagic prey. Thus food availability during periods of high gray whale abundance may not be a limiting factor. Common characteristics in both the 1999-2000 and 2019-2021 UMEs included: 1) increased stranding numbers throughout the species North American range (Mexico to Alaska), 2) apparent emaciation in a proportion of stranded whales, 3) low lipid content of blubber and body tissues in some whales, 4) apparent reduced reproduction (low calf counts) occurred during and following each event, and 5) average to good condition of post-parturient females and their calves observed in the breeding lagoons of Baja California during 2019 to 2021. Emaciation, low lipid content of blubber and body tissues, poor body condition, and reduced fecundity can be associated with a number of infectious diseases of wildlife, in addition to being features of purely nutritionally driven mortalities. This paper explores the possible role of chronic viral infections in gray whale unusual mortality events and highlights the utility of viral discovery work using unbiased metagenomic sequencing for prospective and retrospective investigations of gray whale mortalities.