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An alarming number of Mediterranean monk seals, an endangered species, have recently died. Postmortem analysis showed the presence of an as yet unidentified virus, as well as evidence of a known bacterial toxin. Seawater samples from the area where the seals died did contain unusually high concentrations of the toxic bacterium. Therefore, although both viruses and bacterial toxins can kill seals, it is more likely that these deaths were the result of the bacterial toxin.