Domoic acid is an algal toxin that has caused neurologic disease and reproductive failure in California sea lions (Zalophus californianus). In affected sea lions, necrotic neurons have been observed in the olfactory bulb and pyriform lobe of the brain, indicating potential for disrupted olfactory capability in addition to other documented neurological effects. Sea lions use olfaction in social interactions, and deficits could lead to maladaptive interactions, including between mothers and pups. Here, to assess olfactory capability in wild California sea lions, we developed a behavioral assay for use in a clinical context. We tested 24 stranded sea lions with no apparent neurological symptoms and 22 sea lions with a clinical diagnosis of chronic domoic acid toxicosis, probing differential responses to a scented and unscented object. The neurologically healthy animals spent significantly more time with the scented object than with the unscented object, establishing this method as effective in demonstrating olfactory discrimination in California sea lions. The domoic acid toxicosis group showed a nonsignificant reduction in response to the scented stimulus. However, variability in responses suggests that olfactory sensitivity is impaired in at least some sea lions with domoic acid toxicosis. 

De Maio, L.M., Cook, P.F., Reichmuth, C., Gulland, F.M.D. 2018. The evaluation of olfaction in stranded California sea lions (Zalophus californianus) and its relevance to domoic acid toxicosis. Aquatic Mammals. 44(3): 231-238.