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

An Ecological and Neural Argument for Developing Pursuit-Based Cognitive Enrichment for Sea Lions in Human Care

While general enrichment strategies for captive animals attempt to elicit variable and species-typical behaviors, approaches to cognitive enrichment have been disappointingly one-size-fits-all. In this commentary, we address the potential benefit of tailoring cognitive enrichment to the "cognitive niche" of the species, with a particular focus on a reasonably well-studied marine carnivore, the sea lion. Sea lions likely share some cognitive evolutionary pressures with primates, including complex social behavior. Their foraging ecology, however, like that of many terrestrial carnivores, is based on the rapid and behaviorally flexible pursuit of avoidant prey. Unlike terrestrial carnivores, sea lions carry out this pursuit in a truly fluid three-dimensional field, computing and executing sensorimotor transformations from any solid angle to any other. The cognitive demands of flexible prey pursuit are unlikely to be fully elicited by typical stationary puzzle box style foraging enrichment devices or screen-based interactive games. With this species, we recommend exploring more water-based movement activities generally, and complex pursuit challenges specifically.

The symptomatology and diagnosis of domoic acid toxicosis in stranded California sea lions (Zalophus californianus): a review and evaluation of 20 years of cases to guide prognosis

Introduction

Domoic acid (DA) is a glutaminergic excitatory neurotoxin that causes the morbidity and mortality of California sea lions (Zalophus californianus; CSL) and other marine mammals due to a suite of effects mostly on the nervous and cardiac systems. Between 1998 and 2019, 11,737 live-stranded CSL were admitted to The Marine Mammal Center (TMMC; Sausalito, CA, USA), over 2,000 of which were intoxicated by DA. A plethora of clinical research has been performed over the past 20 years to characterize the range of toxic effects of DA exposure on CSLs, generating the largest dataset on the effects of natural exposure to this toxin in wildlife.

Materials and methods

In this study, we review published methods for diagnosing DA intoxication, clinical presentation, and treatment of DA-intoxicated CSL and present a practical, reproducible scoring system called the neuroscore (NS) to help assess whether a DA-affected CSL is fit for release to the wild following rehabilitation. Logistic regression models were used to assess the relationships between outcome (released vs. euthanized or died) and multiple variables to predict the outcome for a subset of 92 stranded CSLs.

Results

The largest proportion of DA-intoxicated CSLs was adult females (58.6%). The proportions of acute and chronic cases were 63.5 and 36.5% respectively, with 44% of affected CSL released and 56% either dying naturally or euthanized. The average time in rehabilitation was 15.9 days (range 0-169) for all outcomes. The best-performing model (85% accuracy; area under the curve = 0.90) assessing the relationship between outcome and predictor variables consisted of four variables: final NS, change in NS over time, whether the animal began eating in rehabilitation, and the state of nutrition on admission.

Discussion

Our results provide longitudinal information on the symptomatology of CSL intoxicated by domoic acid and suggest that a behavioral scoring system is a useful tool to assess the fitness for the release of DA-intoxicated CSL.

Pinniped electroencephalography: Methodology and findings in California sea lions (Zalophus californianus)

This study was designed to identify abnormalities in the electroencephalograms (EEGs) recorded from stranded California sea lions (Zalophus californianus) with suspected domoic acid (DA) toxicosis. Recordings from animals presenting for non-neurological issues were also obtained to better understand the normal EEG (background activity and transient events) in this species, as, to date, studies have focused on examining natural sleep in pinnipeds. Most animals were sedated for electrode placement and EEG acquisition with some receiving antiepileptic medications or isoflurane during the procedure. A total of 103 recordings were read and scored from 0 (normal) to 3 (severely abnormal). Epileptiform discharges, consisting of spikes, sharp waves, slow waves, and/or spike waves, were present in all EEGs with scores of 1, 2, or 3. The distribution of these events over the scalp varied. While often generalized, others were lateralized over one hemisphere, bifrontal, bioccipital, and/or bitemporal, while some discharges were multifocal. Findings were different between sea lions and occasionally changed within the EEG on a given sea lion. No clinical seizures were observed during the recording but a few sea lions had findings consistent with electroencephalographic seizures. When available, supporting diagnostic results obtained from magnetic resonance imaging (MRI) and/or necropsy/histopathology were described, as well as the status of those sea lions that recovered and were released with satellite tags.

Adult-onset epilepsy and hippocampal pathology in a California sea lion (Zalophus californianus): A case study of suspected in utero exposure to domoic acid

Domoic acid (DA) is a naturally occurring marine neurotoxin produced by Pseudo-nitzschia diatoms. Adult California sea lions (Zalophus californianus) can experience multiple post-exposure syndromes, including acute toxicosis and chronic epilepsy. Additionally, a delayed-onset epileptic syndrome is proposed for California sea lions (CSL) exposed in utero. This brief report explores a case of a CSL developing adult-onset epilepsy with progressive hippocampal neuropathology. Initial brain magnetic resonance imaging (MRI) and hippocampal volumetric analyses relative to brain size were normal. Approximately 7 years later, MRI studies to evaluate a newly developed epileptic syndrome demonstrated unilateral hippocampal atrophy. While other causes of unilateral hippocampal atrophy cannot be completely excluded, this case may represent in vivo evidence of adult-onset epileptiform DA toxicosis in a CSL. By estimating in utero DA exposure time period, and extrapolating from studies conducted on laboratory species, this case provides circumstantial evidence for a neurodevelopmental explanation correlating in utero exposure to adult-onset disease. Evidence of delayed disease development secondary to gestational exposure to naturally occurring DA has broad implications for marine mammal medicine and public health.

RETROSPECTIVE REVIEW OF NEUROLOGIC DISEASE IN STRANDED ATLANTIC HARBOR SEALS (PHOCA VITULINA CONCOLOR) ALONG THE NEW ENGLAND COAST

Harbor seals (Phoca vitulina) are a common species admitted to marine mammal rehabilitation facilities. As important indicators of marine ecosystem health, monitoring trends of disease in harbor seal populations is critical. However, few studies have evaluated neurologic disease in this species. The general objective of this study was to retrospectively review and delineate neurologic disease in free-ranging Atlantic harbor seals (P. vitulina concolor) that stranded along the New England (United States) coast and entered a rehabilitation facility between 2006 and 2019. Any Atlantic harbor seal that stranded live along the New England coast during the study period and was diagnosed with neurologic disease on either antemortem or postmortem evaluation was included; medical records and pathologic reports were reviewed. From 211 records, 24 animals met the inclusion criteria. Prevalence of neurologic disease was 11% in the study population and six major categories of neurologic disease were identified including: inflammatory (54%), idiopathic (33%), trauma (4%), congenital (4%), and degenerative (4%). Of the seals diagnosed with neurologic disease, 13 (54%) seals died during rehabilitation, 10 (42%) seals were euthanized, and 1 (4%) seal survived to release. Unique cases seen included a seal with Dandy-Walker-like malformation and another seal with histopathologic findings compatible with neuroaxonal dystrophy, a degenerative process that has not been previously reported in marine mammals. This study contributes to the overall knowledge of the health of free-ranging Atlantic harbor seals and may aid clinicians in characterizing neurologic conditions that may be present in seals undergoing rehabilitation.

Xenotransplantation of porcine progenitor cells in an epileptic California sea lion (Zalophus californianus): illustrative case

BACKGROUND

Domoic acid (DA) is a naturally occurring neurotoxin harmful to marine animals and humans. California sea lions exposed to DA in prey during algal blooms along the Pacific coast exhibit significant neurological symptoms, including epilepsy with hippocampal atrophy.

OBSERVATIONS

Here the authors describe a xenotransplantation procedure to deliver interneuron progenitor cells into the damaged hippocampus of an epileptic sea lion with suspected DA toxicosis. The sea lion has had no evidence of seizures after the procedure, and clinical measures of well-being, including weight and feeding habits, have stabilized.

LESSONS

These preliminary results suggest xenotransplantation has improved the quality of life for this animal and holds tremendous therapeutic promise.

Maternal-fetal disposition of domoic acid following repeated oral dosing during pregnancy in nonhuman primate

Domoic acid (DA) is a marine algal toxin that causes acute and chronic neurotoxicity in animals and humans. Prenatal exposure to DA has been associated with neuronal damage and cognitive and behavioral deficits in juvenile California sea lions, cynomolgus monkeys and rodents. Yet, the toxicokinetics (TK) of DA during pregnancy and the maternal-fetal disposition of DA have not been fully elucidated. In this study, we investigated the TK before, during, and after pregnancy and the maternal-fetal disposition of DA in 22 cynomolgus monkeys following daily oral doses of 0.075 or 0.15 mg/kg/day of DA. The AUC0-τ of DA was not changed while the renal clearance of DA was increased by 30-90% during and after pregnancy when compared to the pre-pregnancy values. DA was detected in the infant plasma and in the amniotic fluid at delivery. The infant plasma concentrations correlated positively with both the maternal plasma and the amniotic fluid concentrations. The paired infant-to-maternal plasma DA concentration ratios ranged from 0.3 to 0.6 and increased as a function of time which suggests placental efflux and longer apparent fetal half-life than the maternal half-life. The paired amniotic fluid-to-infant plasma DA concentration ratios ranged from 4.5 to 7.5 which indicates significant accumulation of DA in the amniotic fluid. A maternal-fetal TK model was developed to explore the processes that give the observed maternal-fetal disposition of DA. The final model suggests that placental transport and recirculation of DA between the fetus and amniotic fluid are major determining factors of the maternal-fetal TK of DA.