Harbor seals (Phoca vitulina) are one of the most common species admitted to rehabilitation facilities on both the eastern and western coasts of the United States, and in Europe. Study of animals at rehabilitation centers offers an opportunity to identify and describe marine mammal diseases1, but no national centralized database for comparison across regions currently exists. Moreover, published literature typically reflects individual or small group case studies or outbreaks of disease and rarely describes annual trends.2 Marine mammals are often considered "sentinels" of ocean health and monitoring trends in populations is critical to understanding ocean health. This project has two main objectives: 1) to describe and characterize causes of stranding within this species and to evaluate temporal and spatial trends between each region and 2) to place each individual in one of the following health categories in an effort to standardize reporting of harbor seal health: biotoxin, infectious disease (known pathogen), infectious disease (non-specific), malnutrition, maternal separation, neoplasia, anthropogenic trauma, non-anthropogenic trauma, and other causes of disease. A total of 952 harbor seals stranded live along the central California coast and 143 harbor seals along the coast of New England between January 2001 and December 2015. Each animal's medical record was examined to determine the primary cause of stranding, and the secondary factors which contributed to stranding, using criteria consistent with a prior study on causes of harbor seal stranding in California.3 The majority of stranded harbor seals on both coasts were pre-weaned and recently weaned pups, with maternal separation and malnutrition as leading causes of stranding. At least 5 documented cases of domoic acid toxicosis were confirmed on the West Coast while no cases of biotoxin exposure were confirmed on the East Coast. Verminous obstructive bronchitis/pneumonia due to Otostrongylus circumlitis was primarily observed on the West Coast. Understanding changes in harbor seal health across regions provides critical information to better understand wild marine mammal populations, and helps to prioritize future research and management activities.
The authors wish to thank the many volunteers and staff of the Marine Mammal Center and the Mystic Aquarium Animal Rescue Program for their time and effort in caring for the animals.
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1. Gulland FMD, Hall AJ. Is marine mammal health deteriorating? Trends in the global reporting of marine mammal disease. EcoHealth. 2007;4:135–150.
2. Simeone CA, Gulland FMD, Norris T, Rowles TK. A systematic review of changes in marine mammal health in North America, 1972–2012: the need for a novel integrated approach. PLoS One. 2015;10(11):e0142105.
3. Colegrove KM, Greigh DJ, Gulland FMD. Causes of live strandings of Northern Elephant Seals (Mirounga angustirostris) and Pacific Harbor Seals (Phoca vitulina) along the central California coast, 1992–2001. Aquatic Mammals. 2005;31(1):1–10.