As It Happens

Cronutt the sea lion's experimental brain surgery offers hope for dying sea mammals

When Cronutt the sea lion wandered ashore in California three years ago, he was so disoriented and confused and that he tried to break into people's houses. Since then, his condition has only gotten worse.

Thousands of marine mammals suffer brain damage from climate change-induced toxic algae blooms

Cronutt the sea lion has undergone an experimental surgery to treat epilepsy caused by algae bloom toxins. (Dianne Cameron/University of California San Francisco)

When Cronutt the sea lion wandered ashore in California three years ago, he was so disoriented and confused that he tried to break into people's houses. Since then, his condition has only gotten worse.

The seven-year-old marine mammal suffers from epilepsy, the result of brain damage caused by domoic acid released by toxic algae blooms. It's a condition that affects hundreds of marine mammals every year, and it's only getting worse as climate change raises ocean temperatures and increases the frequency of the blooms.

"He started to have seizures more frequently. And then the changes in his brain seemed to just make him uninterested in food, and so there were times over two months where he went for almost two weeks at a time without eating," Dr. Claire Simeone, Cronutt's primary veterinarian, told As It Happens host Carol Off.

"We were running out of options on how to manage him."

But the scientific stars aligned and, last week, Cronutt underwent an experimental brain surgery — the first of its kind performed on a large mammal. If it works, marine scientists will have a new tool in their kit for helping sea creatures whose health is negatively impacted by climate change. 

Cronutt, a sea lion with toxin-induced epilepsy, gets prepped for surgery at the SAGE Veterinary Centers in Redwood City, Calif. (D. Robles/University of California San Francisco)

Cronutt first started coming ashore in 2017.

Once he wandered into a parking lot. Another time he tried to enter people's residences. And then finally, he planted himself in front of a public bathroom at the beach, blocking people from getting in and out. 

This behaviour is not typical of sea lions, according to Simeone.

"A wild sea lion should be wary of humans and not want to approach them," she said. 

The third time Cronutt appeared, the Marine Mammal Center in Sausalito, Calif., took him in. They decided his condition meant he was very unlikely to survive on his own in the wild.

They bestowed upon him his name — a pastry that is half croissant, half doughnut. "They're really delicious and something that we've been eating a lot of as we've been treating him," Simeone said.

In 2018, he was transferred to the Six Flags Discovery Kingdom in Vallejo, Calif., which has specialized veterinary facilities for animals in need of extra care. Simeone, founder of Sea Change Health, became his primary veterinarian. 

Dr. Claire Simeone, a marine mammal veterinarian, monitoring Cronutt during his procedure. (Submitted by Claire Simeone)

As the sea lion's condition worsened, Simeone says she and her colleagues considered putting him down. After all, this type of epilepsy in marine mammals only gets worse, not better. 

But instead, they tried one last Hail Mary and called Dr. Scott C. Baraban, an epilepsy researcher at the University of California San Francisco (UCSF).

"We got to the point where where we thought, you know, we have to give him one last shot," Simeone said. "And this was the type of research that everything came together in exactly the right way at the right time, amazingly, during a pandemic to be able to give him the shot."

How the surgery works 

Baraban's team had been pioneering a new cell-based therapy that had proven highly effective in treating lab mice with epilepsy. And it just so happened, they were in the market for a larger test subject. 

"Over the years, I've come to learn how many marine mammals can't be released into the wild due to domoic acid poisoning, and it's our hope is that if this procedure is successful it will open the door to helping many more animals," Baraban said in a university press release.

Doctors look at brain scans from Cronutt, a sea lion who developed epilisepy from toxins produced by algae blooms in a warming ocean. (Shawn Johnson/University of California San Francisco)

On Tuesday, Oct. 6, Cronutt went under the knife — or more precisely, the drill — at SAGE Veterinary Centers in Redwood City, Calif.

A team of specialists from Six Flags and UCSF drilled a hole in Cronutt's skull and used an ultrathin needle to inject embryonic brain cells from a baby pig into his hippocampus, the brain region responsible for his seizures.

If all goes according to plan, those cells will integrate into Cronutt's brain and repair the damaged circuitry. It'll be a few months before they know whether it was successful.

"I'm really happy to report the Cronutt is stable and doing well in his recovery," Simeone said. "For right now, we're just providing all of the post-operative supportive care until we can get to that point where we where we start to see those expected changes."

Cronutt, who can cannot survive in the wild due to his epilepsy, is being cared for at the Six Flags Discovery Kingdom in Vallejo, Calif., which has facilities for wildlife with special veterinary needs. (Dr. Claire Simeone/University of California San Francisco)

If the surgery is successful, Babaran says it will have immediate implications for marine mammals suffering from domoic acid poisoning. 

But he warned it won't be able to help human epilepsy patients any time soon.

"For a number of reasons, including regulatory hurdles, cellular therapies for people with epilepsy are probably still a long way off. However, marine mammals with brain damage from domoic acid poisoning are in a very similar boat — with no effective treatments that would let them ever be returned to the wild," he said. 

Thousands of sea lions have been affected by increasing algae blooms. They often wash up en masse on beaches, disoriented and prone to seizures. While many have been taken into care and treated, most eventually die.

"As a marine mammal veterinarian, I saw close up the effects of all of the different impacts that we as humans are having on our planet," Simeone said.

"So for me, Cronutt represents a possibility for hope that we could use these innovative tools that we have developed to be able to give back, because the impacts that we have are so widespread on this planet."


Written by Sheena Goodyear. Interview with Claire Simeone produced by Kate Cornick. 

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