Year-round algal toxin exposure in free-ranging sea lions

Harmful algal bloom toxins cause illness and mortality in marine mammals worldwide, yet the potential for year-round exposure to these toxins has not previously been studied. We measured concentrations of domoic acid and saxitoxin in scats from Steller sea lions Eumetopias jubatus (n = 383 scats) and California sea lions Zalophus californianus (n = 125 scats) over a 2 yr period. Toxin concentrations in the scats were compared to the prey remains in the scats and to concentrations in nearshore bivalves. Saxitoxin was detected in 45% and domoic acid was detected in 17% of all scats tested, and both toxins were detected in all seasons and months of the year. A variety of benthic and pelagic fish were significantly associated with toxins in sea lion scats, including prey with low occurrence in the sea lions' diet. Toxins detected in winter scats confirm that US West Coast marine mammals are exposed to domoic acid and saxitoxin through their prey outside of the expected algal bloom seasons.