Surfers in Rye, NH reported the washed-up carcasses of six young harbor seals on a beach late last fall. Since then, reports have been streaming in from the coast of Massachusetts, New Hampshire, and Maine. The death count has exceeded one hundred to date. In a typical year, only twenty-four harbor seal deaths are reported. Not only are harbor seals affected, but whales, tuna, and birds are washing up dead on shores. The most unique aspect of this event is that the majority of harbor seals found are this year’s young.
Scientists are presently unsure as to the cause of this outbreak. The first steps are testing for bio-toxin and for disease. Due to necropsies, human foul play and lack of food are ruled out; stomach dissections revealed a healthy, normal diet. Authorities from the federal government, NOAA, Woods Hole Oceanographic Institution, the University of New Hampshire, and the New England Aquarium are working together to identify the cause of this die-off.
Upon first glance, the washed-up seals appeared physically healthy. However seals are quite susceptible to internal parasites. They may be succumbing to a parasite that targets their young immune systems. Scientists are also entertaining the possibility that natural toxin-emitting algal blooms in the New England coastal area are causing the deaths. Other theories include toxins from jellyfish strings, radiation from an unreported release of nuclear power plant cooling water, and last year’s oil spill in the Gulf of Mexico.
Seal die-offs like this one are certainly not unprecedented. If history repeats itself, the most likely cause of this year’s outbreak is a virus. In 1979 and 1980, a similar die-off occurred due to an outbreak of avian influenza that the seals probably contracted by lying on rocks covered with bird feces. Recently, Northern European harbor seals were decimated by a virus resembling canine distemper. Morbillivirus is a likely cause, too. It is accountable for at least five aquatic mammal die-offs in the past ten years. All of the seals found had pneumonia and lesions on their fins and bellies, prime symptoms of mobillivirus.
Stomach content and toxin analyses are currently being performed, which could take weeks. Once these results are back, more specific testing for viruses or bacteria may be ordered. When performing necropsies on seals, testing for disease is complicated and sometimes inaccurate. The animals carry many different diseases, most of which do not affect them.
Fortunately the New England coastline has a healthy population of harbor seals, so the deaths don’t signify major trouble yet. If the results of the tests indicate human activity or contaminants, then this behavior can be altered to ensure a safer living environment for young seals. Sobering cases like this one encourage reflection upon what we as humans do in our coastal waters.
Sarah Hutchinson is a junior in the College of Agriculture and Life Sciences. She may be reached at email@example.com. The Missing Link: Ecology, Natural Resources and Sustainability appears on Mondays.