An adult female harbor seal (Phoca vitulina richardsi) stranded in northern California on 25 June 2004, exhibited progressive weakness, disorientation, and seizures, and despite therapy, died within 4 days. On pathologic examination, a lead fishing sinker was in the stomach, and changes in the brain, heart, kidney, liver, lymph nodes, and spleen were supportive of acute lead toxicosis. The diagnosis was made on the basis of concentrations of lead in the sinker (90–98% lead), antemortem whole blood (0.66 ppm), and postmortem tissues (84 ppm, wet weight liver). This first documented case of lead toxicosis in a wild marine mammal demonstrates an additional way in which human fishing activities can harm marine mammals.

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