Abstract
The eastern North Pacific gray whale (Eschrichtius robustus) population is considered “recovered” since the days of commercial whaling, with a population of over 25,000 animals. However, gray whale habitat is changing rapidly due to urbanization of the migratory coastal corridor, increases in shipping, and climate change altering water conditions and prey distribution. Increased single strandings and intermittent large-scale mortality events have occurred over the past twenty years, raising questions about how gray whale health is affected by whale population size (density dependence), climate change and coastal development. To understand the impacts of these factors on health and the role of health changes in whale population dynamics, increased understanding of the pathogenesis and epidemiology of diseases in gray whales is needed. To date, most information on gray whale health and disease are in single case reports, in sections of larger papers on whale ecology, or in technical memoranda and conference proceedings. Here we review existing data on gray whale health and disease to provide a synthesis of available information and a baseline for future studies, and suggest priorities for future study of gray whale health. The latter include nutritional studies to distinguish annual physiological fasting from starvation leading to mortality, identification of endemic and novel viruses through increased use of molecular techniques, quantifying parasitic infections to explore interactions amongst prey shifts and parasite infection and body condition, as well as enhancing necropsy efforts to identify stochastic causes of mortality such as ship strikes, entanglements and predation. Integration of health and disease studies on individual animals with population monitoring and models of whale/prey dynamics will require interdisciplinary approaches to understand the role of health changes in population dynamics of this coastal whale.
Highlights
The recovery of the eastern North Pacific gray whale population since its decimation by commercial whaling has been heralded as a conservation success
Despite regular population surveys and post-mortem examination of individual whale carcasses, our understanding of gray whale health and how it is affected by whale population size, climate change, and coastal development remains poor
Information on gray whale health and disease is available from four sources: whaling records, especially those from 1964 to 1969 for whales taken off the Richmond whaling station in central California (Rice and Wolman, 1971); the aboriginal whaling scheme (AWS) in Chukotka, Russia, and their ongoing harvest monitoring program1; examination of stranded animals; and health assessment of live whales using both remote sampling and hands on sampling of two temporarily captive whales
Summary
The recovery of the eastern North Pacific gray whale population since its decimation by commercial whaling has been heralded as a conservation success. The detection and characterization of infectious agents, especially viruses, in marine mammals have increased considerably; establishment of a causal association between pathogens and clinical presentation or pathology for many agents has been difficult “due to inconsistencies in marine mammal morbidity/mortality investigative effort and the logistical and economic limitations for adequate pathologic investigations” (Bossart and Duignan, 2018). This is true for gray whales, with limited studies available. We review existing data on gray whale health and disease to provide a baseline, synthesize existing information, and suggest priorities for future study of gray whale health
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