Baby Seals, Stress, and Fragile Hearts – The Extended Edition

21 December 2013 by Nsikan Akpan, posted in TBS Journal Club

Back in November, I wrote this ScienceShot about a stress-related heart condition discovered in seals for the first time. Given baby seals are always topical (I mean look at them !!) and given some misunderstood the point, you can find the reporting/images that didn’t fit into the 150-word bulletin pasted below. 


"Relax or you’ll have a heart attack" applies not only to stressed people, but to baby fur seals as well. Wildlife veterinarians working on Chile’s remote Guafo Island uncovered a fatal heart condition, known as cardiomyopathy, in five South American fur seal pups. Though stress-related conditions are well-known in humans, fur seals become only the third marine mammals, after dolphins and whales, shown to develop heart disease after handling or captivity.

Marine specialists had long believed that fur seals could withstand captivity-related stress. Adult fur seals require a tranquilizer injection before handling, and it’s standard for biologists to use capture bags for baby fur seals rather than risking a shot.

A capture bag has a large front opening and a drape that slides over the sides of the pup to keep it on the ground for typically up to 30 minutes. The team working in Chile had caught and released hundreds of fur seals on Guafo island in this manner for four years with no captivity-related deaths.

South American fur seals sitting in the sun on Guafo Island.

Credit: Mauricio Seguel. South American fur seals sitting in the sun on Guafo Island.

However, a cluster of five pups suddenly died in the austral summer of 2012, warranting an investigation. Necropsies revealed that the pups had chronic hookworm infections, which aggravated their immune systems and sent their adrenal glands into hyperdrive. Adrenal glands produce stress hormones that set off the fight-or-flight response. Two varieties, adrenaline and norepinephrine, accelerate the heart—useful if one is escaping a lion, but harmful if hormone levels remain high.

The necropsy reports, published online recently in Marine Mammal Science, revealed the unmistakable hallmarks of cardiomyopathy: muscular lesions and depleted myoglobin, a vital oxygen-carrying protein, in the pups' heart muscles. The damage arose from the chronic infections causing lengthy exposure to elevated stress hormones, the team believes. Captivity and trauma from bagging pushed the seal pups over the edge, they conclude.

Wildlife veternarian Mauricio Seguel of the University of Georgia in Athens, who led the study, believes the condition has always existed among fur seals, but was overlooked by researchers. “These procedures are performed on a daily basis, and this [study] shows animals can have very different reactions to the same procedure,” says Seguel. His lab caught the damage through its routine deep-tissue analysis during necropsy, but this post-mortem practice is not standard among vets, he notes.

Chronic infections are widespread in fur seals, affecting up to 40% of the animals in some populations. This fatal combination of infection and sudden stress could arise elsewhere, the team maintains. Seguel suggests that field workers should minimize their capture time and look for signs of chronic infections in seals—such as malaise or severely rapid respiration—before handling animals and risking further harm. Moreover, catching pups in pairs or more appears to relax them, a simple step to take since they naturally hangout in groups of 20 to 30.

“If this incident had happened in the U.S., there would be some discussion on how to mitigate any future mortalities,” says veterinarian Shawn Johnson of the Marine Mammal Center in Sausalito, California, which rescues sick and injured ocean animals nearly every day. However, Johnson noted, it is always difficult to predict how wild animals will react when captured.

South American fur seals taking a nap on Guafo Island, Chile.

Credit: Mauricio Seguel. South American fur seals taking a nap on Guafo Island, Chile.

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