How did mercury contamination affect seabirds and cats in Minamata?

In Minamata, Japan, the industrial discharge of methyl mercury into the sea led to the contamination of local fish and shellfish. Because seabirds and household cats in the area subsisted primarily on these contaminated marine animals, they suffered from the same mercury poisoning as the local human population.123

These animals exhibited symptoms characteristic of Minamata disease, a condition caused by organic mercury compounds that damage the central nervous system. The observation of these symptoms in animals was a critical factor that helped researchers trace the source of the poisoning to industrial effluent, leading to the discovery of high concentrations of methyl mercurials in the bay's aquatic life.3