Clinical signs and mortality of non-released stranded California sea lions housed in display facilities: the suspected role of prior exposure to algal toxins

What is it about?

Context: Stranded California sea lions considered unable to survive in the wild are often placed in public display facilities, yet studies of long-term health and survival are lacking. Exposure to the biotoxin domoic acid (DA) is the most common cause of neurologic abnormalities in stranded California sea lions, and chronic effects are observed long after initial exposure. This study investigates development, clinical signs and survival of these individuals.

Main conclusion: Neurologic disease is relatively common in non-releasable California sea lions, and an increase in neurologic signs was detected in animals that stranded as neonates compared to other age classes. These data coupled with stranding records and epidemiological data on DA-producing algal blooms suggest further research into effects of neonatal exposure to DA on risk of neurological disease in later life is warranted.
 
Approach: Medical records for 171 sea lions placed in U.S. institutions between 2000 and 2016 were reviewed, including results from clinical examinations, histopathology, behavioural testing and advanced imaging.

Results: Neurologic disease occurred in 14% of all cases and in 24% of all neonates. 60% of all neurologic cases died during the study period. In the 11 neurologic neonate cases, six died (55%) and five are still alive with three of five developing epilepsy during placement. Of the six neurologic neonate cases that died, one was attributed to DA toxicosis, one to seizures, and four to acute unexplained neurologic disease.

Interpretation: This survey suggests delayed neurological disease can develop in sea lions after stranding as neonates.

Significance of findings: The increase in neurologic signs detected in neonates compared to other age classes after placement, including the development of epileptic seizures and the increased mortality in neonates due to neurologic disease indicates that future placement of neonates may not be in the best welfare interest for this age class due to increasing environmental exposure to DA in utero or during nursing. Rehabilitation facilities, permitting agencies, and managed care institutions must recognize the risk of neurologic disease for each animal that is deemed non-releasable and placed in permanent care, and continue to investigate behavioural, clinical and morphological changes in these animals to improve our understanding of the impacts of DA exposure on mammals.


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