Abstract
Domoic acid (DA) intoxication in marine mammals is becoming an increasing problem along the west coast of the United States.2 The California sea lion (Zalophus californianus) appears particularly sensitive to the neurotoxic effects of DA. Stranding events in relation to DA have occurred annually since 1998 (with the exception of 1999).1 The prevalence of domoic acid producing blooms of Pseudonitzschia australis appear to be increasing.The direct cause is unknown. However, possible causes have been proposed including global climate change and overfishing.2 Z. californianus become intoxicated with DA after consumption of contaminated finfish such as anchovies.3 The neuroanatomical effects of domoic acid intoxication include hippocampal atrophy and ischemic neuronal necrosis of the granular cells in the dentate gyrus.4 Clinical signs can include disorientation and ataxia along with a suite of physiological changes (primarily spastic or uncoordinated muscle movements) and abnormal behaviors.2 Current laboratory diagnostic methods for DA intoxication are challenging as the toxin is water soluble and excreted from the affected animal's system within 2–48 hours. Clinical signs such as seizures and lethargy are similar to signs associated with other diseases, further complicating diagnosis.
The goal of our research is to identify behavioral signs that are significantly correlated to DA intoxication in Z. californianus, which can then be used as a diagnostic tool in both rehabilitation and field settings. From March 2011 through December 2012, we observed 152 animals, undergoing rehabilitation at the Marine Mammal Center in Sausalito California, by using focal animal continuous scanning. Individuals were observed for up to 15 minutes during a single observation session where continuous data was obtained. An ethogram containing abnormal behaviors seen during the study was used. We ran the Wilcoxon test for all abnormal behaviors observed at the Marine Mammal Center. We ran the Fisher's exact test for all abnormal behaviors observed at either the Marine Mammal Center or while the animal was on the beach during rescue.
Animals with DA intoxication performed more head weaving (Wilcoxon's Z = 6.38050 p < 0.0001) were hypervigilant (Wilcoxon's Z = 3.35475 p > 0.001), and dragged their hind flippers during locomotion more often (Wilcoxon's Z = 2.39282 p < 0.01) than animals with other diagnoses. Animals with DA toxicosis experienced more muscle fasciculations in both rehabilitation and field settings than animals with other diseases (Fisher's Exact Test, p < 0.0001).
We also observed a novel behavior in two animals. In both cases the animals repeatedly touched the rostrum or head to the back flippers in either a vertical or horizontal position, resulting in a "doughnut" profile however results from the Wilcoxon were not significant (p > 0.05). Results from the 2011 field season were consistent with those from the 2012 field season indicating possible use as diagnostic criteria. We conclude that applications of our research may provide a behavioral method of diagnosing DA toxicosis in Z. californianus in situ and therefore the ability to assess what percentage of a rookery is affected by DA at any given point in time.
Acknowledgments
The authors wish to thank Dr. Francis Gulland for her expertise in pinniped biology and Deb Wickham for technical support around the Marine Mammal Center. We would also like to thank the volunteers who assisted with the project to date, including Roger Conant, Mike Minton, Jake Trusheim, Misuzu Toyama, David Ellis, and Tracey Sonneborn.
* Presenting author
+ Student presenter
Literature Cited
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