Mass dolphin strandings may be because their pod leaders have Alzheimer’s, study says

Several species of dolphins may suffer from Alzheimer’s disease, according to a new study.

The research could help explain the widespread yet puzzling phenomenon of mass dolphin strandings, which occur when multiple dolphins become beached, often resulting in their deaths.

The brains of 22 stranded toothed whales, known as odontocetes and which includes dolphins, were studied by researchers at multiple universities in the United Kingdom, according to a study published on Dec. 13 in the European Journal of Neuroscience. Five separate species were examined, including the the bottlenose dolphin, Risso’s dolphin and the harbor porpoise.

Through a series of diagnostic tests, researchers looked for telltale signs of Alzheimer’s disease (AD), a brain disorder that gradually destroys memory and other cognitive functions, according to the study.

All of the toothed whale brains exhibited amyloid plaque, which are lesions made up of protein deposits. The plaque is one of the defining characteristics of Alzheimer’s. Three of the species, in addition to plaque build-ups, had phosphorylated tau in their neurons, another sign of Alzheimer’s, meaning these species develop an illness like Alzheimer’s “spontaneously,” researchers said.

The degenerative disease might contribute to the mass strandings of some dolphins and other toothed whales, researchers said.

Their findings reinforce the “sick leader” theory, which says that if a dominant individual, often an mature female, becomes sick and disoriented, “the pod will not realize and continue to follow her lead,” Ailsa Hall, a professor at the University of St. Andrews and member of the research team, told McClatchy News in an email. “This may cause the pod to come into shallow waters or encounter spits of land (such as happens in New Zealand) which they are then unable to swim out of.”

Alzheimer’s appears ‘spontaneously’ in dolphins and humans

Going forward, toothed whales could prove more useful than non-human primates for studying Alzheimer’s because the illness appears to “spontaneously “ appear in both humans and the marine mammals, researchers said.

“What is also very interesting is what this might tell us about AD in humans as cetacean brains are quite different,” Hall said. “For example these animals undergo prolonged periods of oxygen deprivation (hypoxia) when they dive and can manage their oxygen stores so that their brains are not starved of oxygen during diving. So thinking more about such adaptive differences between humans and cetaceans might just help us think a bit more ‘out of the box’ about the causes of and treatments for this devastating disease.”

Further research would need to examine living animals, Hall said, adding that a group of dolphins trained by the U.S. Navy could prove useful.

Whales, dolphins and porpoises have been stranding in greater numbers worldwide, according to 2020 study published in the journal Scientific Reports, though the cause of the phenomenon is not known. Oceanographic events, pollution and disease have previously been put forward as a potential causes.

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