Sea lions from Santa Barbara to Ventura are stranding themselves, apparently poisoned by a neurotoxin from toxic algal blooms. Photo: Vandenburg Space Force Base
Sea lions along the California coastline are stranding themselves on beaches, and experts believe it may be because they’ve been poisoned.
According to the Channel Islands Marine & Wildlife Institute (CIMWI), there have been daily reports from concerned citizens of sick sea lions along a 155-mile stretch of coast in Santa Barbara and Ventura counties. What’s making them sick is a bit of a mystery as of this writing, but it’s likely that it’s due to a bloom of toxic algae.
“Domoic acid (DA) is a neurotoxin produced by the microscopic marine algae, Pseudo-nitzschia,” CIMWI explained. “This phytoplankton grows when our coastal ecosystem provides favorable conditions, such as when upwelling of water causes the nutrients from deeper water to rise to the surface where sunlight is present which proliferates algal growth. This typically occurs during transitional periods in the spring and fall.”
The sea lions are likely not getting sick from the algae itself, but instead from the sea lion’s prey. Female adult California sea lions are most affected by it, especially when they’re pregnant since they eat more. The algae carries domoic acid, a neurotoxin that affects the brain and heart.
“When filter-feeders (e.g., small fish, shellfish, and bivalves) consume the toxic algae, they are not affected,” CIMWI continued. “But when predators like sea lions and sea birds eat these filter-feeders, they are negatively impacted by the toxin accumulated in their prey. This phenomenon of increased pollutant concentration from the bottom of the food chain to the top is called biomagnification. Because the predators at higher levels in the food chain, such as sea lions, eat larger amounts of prey, they ingest a higher level of domoic acid.”
Harmful algal blooms, as they’re known, are relatively common along the Southern California coastline, but now and then they bloom a little more than normal. Such events have taken place in 2002, 2006, 2007, 2017, 2022, 2023, and now 2024. Researchers in the area constantly monitor these blooms hoping for a way to protect the wildlife and the ecosystems they live in.
So far, 23 animals have been rescued by CIMWI due to the current algal bloom. Symptoms of domoic acid poisoning inclulde lethargy, disorientation, unresponsiveness, head bobbing/weaving, foaming at the mouth, vomiting, bulging eyes, involuntary muscle spasms, inability to move, seizures, and in severe cases, death.
“If you encounter a California sea lion, or any marine mammal, exhibiting strange behaviors such as head swaying back and forth, foaming at the mouth, or seizure activity, please keep your distance!” CIMWI wrote. “The animal is most likely suffering from domoic acid toxicity.”
