Domoic acid (DA) is a biotoxin that causes strandings of California sea lions (Zalophus californianus) due to a suite of effects including seizures, abnormal mentation, abnormal migration, decreased recognition of auditory stimuli, impaired memory, and death.^1,2,3,4 Since 1990, 1,647 California sea lions (CSL) rescued by The Marine Mammal Center (Sausalito, California) have been diagnosed with DA toxicosis. A CSL with chronic damage to the brain may appear clinically normal between seizures or other neurological signs, it is difficult to predict the extent of brain damage and thus releasability (NOAA release criteria include likelihood of survival post release) without performing MRI or EEG studies that involve sedation, as well as logistical and financial challenges.¹ In order to develop a practical, reproducible test to predict whether a sea lion will be releasable after treatment for DA toxicosis without performing advanced imaging or EEGs, we developed a scoring system based on observations of mentation, reactions to auditory and tactile stimuli, presence of abnormal involuntary movements, and locomotion.⁵ Scoring was performed every other day following a week-long stabilization period for each patient, for up to 5 scoring sessions. We hypothesized that our current scoring system was accurately predicting the releasability of CSL affected by DA toxicosis. To test the predictive accuracy of the scoring system, scores from 250 stranded CSLs were used to predict outcome (release or death in rehabilitation). A logistic regression model was used to assess the relationship amongst outcome (released vs. euthanized or died) and multiple variables including behavioral scores, trends of consecutive scores, co-morbidities, seizures, strand location, and admit state of nutrition. Behavioral score correlated significantly with outcome (P<0.0001, AUC=0.88), where the most recent score resulted in the best prediction. The best model correctly predicted the outcome of 77% of cases (model without behavioral score: 72%; AUC=0.80). Interestingly, the change in consecutive scores was not a good outcome predictor (P=0.11, AUC=0.81).

These results suggest that a behavioral scoring system such as the one described here may be used to assess the releasability of CSL affected by DA toxicosis. Although the current version of this scoring system performs well, we look to further improve it by changing the relative importance of different categories within the current behavioral score. If these changes result in better model predictions, a new behavioral scoring system will be tested and refined in a future prospective study. It is important to note that although this scoring system can be used to predict releasability, it has not been used to date to investigate prediction of survival post release.

Acknowledgements

The authors thank the staff at AnimalScan in Redwood City, California, especially Dr. Kris Kruse-Elliott for the use of the MRI and anesthesia expertise. We also thank the dedicated volunteers and staff at The Marine Mammal Center for their excellent care and compassion for all of the animals.

* Presenting author
+ Student presenter

Literature Cited

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