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200 bottlenose dolphins have been found dead along the East Coast from Virginia to New York so far this year. That includes 70 that have washed up in the lower Chesapeake Bay just this month.

This “unusual mortality event” has been killing off dolphins at a rate not seen since the 1980s, and the worst part is that we don’t yet know what’s behind it.

Baltimore’s National Aquarium has been performing necropsies on the dolphins to get answers. While the necropsises haven’t taught us anything yet, some speculate that — given how widespread the phenomenon is — the deaths could be the result of disease.