Mexico’s fur seals are suffering from alopecia

Sea lions in Mexico are suffering from alopecia, or severe hair loss. A group of scientists has been studying these creatures for a decade, specifically a subspecies called fur seals. These relatives of sea lions live on the island of Guadalupe and the San Benito archipelago in Mexico’s Baja California Peninsula, which separates the Gulf of California from the Pacific Ocean. The researchers noticed that these animals — which normally have two layers of hair — were suffering from hair loss. The shocking images they saw prompted them to capture 13 specimens to carry out medical studies and discover the reason for their sudden baldness. Initially, they posed the theory that rising sea temperatures were linked to the disease hurting the fur seals. But now, they’ve altered this theory and are currently analyzing if the warming in that area of the ocean has affected the food chain, thus impacting the seals’ diet and resulting in hair loss due to a lack of critical nutrients.

The Guadalupe fur seal is named after the island where these animals principally live. They also live across the San Benito archipelago. Both areas are along the coast of the Mexican state of Baja California. As these seals were on the brink of extinction a century ago, the Mexican government classified them as a “priority species for conservation.” Among the threats that the species still faces, according to the government, is human activity, “such as the contamination of the marine environment by fuels” or “the introduction of exotic species and associated pathogens to the islands.” All of this, in addition to the increase in sea surface temperatures during the phenomenon known as El Niño and “its effect on the availability of prey.”

According to Fernando Elorriaga from the Marines Sciences Interdisciplinary Center of the National Polytechnic Institute, this species went almost extinct 100 years ago, but in the late-1990s, they began to be seen again in western Mexico. Since then, scientists have been studying how this population recovery occurred. To understand the return of the fur seals, they’ve monitored the health and feeding habits of these animals. Then, they discovered the problem of alopecia. “One of the things that we began to find, especially since 2013 and 2014, is that some of these animals had spots. We could see spots or abnormalities in their fur from a distance.”

With the difficulties involved in capturing the seals, the team managed to catch only 13 specimens in 2018, in order to study them. They swabbed them, taking blood and hair samples. The team was looking for the cause of alopecia. For that, they reviewed the factors that normally cause it in animals, such as fungi, mites, or bacteria. But they found no trace of any of this. A couple of studies of similar alopecia in other pinnipeds (marine mammals that have front and rear flippers) from other parts of the world pointed to causes such as heat stress or nutritional problems. This served as a basis to continue the study, based on the possibility of the effects of climate change taking a toll on the fur seals.

While reviewing the variations in temperatures across the Baja California Peninsula, a mass of warm water stood out. It had crossed the Pacific in 2013, flowing from Alaska to Mexico, destroying the marine ecosystems in its path. Water temperatures were about 2.5 degrees above normal. “This type of environmental alteration can impact [seals’] thermoregulation, but can also lead to tremendous cellular stress,” says scientist Karina Acevedo, from the Microbiology Unit of the Autonomous University of Querétaro. “It’s not an immediate factor — there are factors that are delayed, [but they] also impact the entire food chain,” the researcher adds. “It wouldn’t cause direct damage to the fur. Rather, it’s an alteration at the level of the trophic (food) chain.”

Between 2015 and 2021 — as a result of the increases in sea surface temperature caused by the blob of warm water, which was also mixed with the climate of El Niño — an unusual mortality event for the Guadalupe fur seals was triggered, explains Elorriaga, who participated in an earlier study into the effects of this heat wave on the birth rate of fur seals. “It involved animals in a very deteriorated state, where there weren’t enough resources for them to consume… [And the population] eventually fell.”

The fur seals primarily feed on one type of squid, which researchers believe migrated to a deeper or more distant site due to the heat. This has forced the fur seals to change their diet to a type of squid that has fewer nutritional properties. “If they’re feeding on prey with less [nutritional] value, of course there’s an impact on the generation of the entire biochemical pathway of keratin,” says Acevedo. Keratin is the main component of hair.

These types of pinnipeds have two coats, one on top of the other. The one below looks like it’s made of fluff. The top one is a layer of hard hair, which protects the animals from external factors, such as pollution or radiation from the sun, explains Ariadna Guzmán Solís, one of the students who have collaborated on this study, which is pending publication in an international science journal. The main function of the double coat of hair is to keep animals warm. This system works like a kind of neoprene: it keeps air between the two layers, which helps the fur seals maintain their body temperature when they’re submerged in the water. Due to their damaged fur, these specimens cannot maintain their temperature as easily and are forced to use more energy to stay warm. The end result is more energy wastage to be able to get food.

The researchers are not entrenched in the idea that the increase in temperature is the sole cause of this disease. They admit that there could be factors that have contributed to the alopecia affecting these animals, such as pollution in the marine environment. However, the team cautions that this may just be the tip of the iceberg. The visible impact on the seals’ fur is actually “a sign of something much broader at the environmental level that can affect the entire marine ecosystem,” Acevedo concludes.

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