Wildlife veterinarians working on Chile’s remote Guafo Island discovered fatal heart damage, known as cardiomyopathy, in five South American fur seal pups that they had captured and placed in bags for up to 30 minutes, a standard practice to examine small seals. As part of an ongoing biological survey of the island, the researchers had caught and released fur seals for 4 years with no captivity-related deaths, but the sudden cluster triggered 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 accelerate the heart, so the team believes that captivity and trauma from bagging pushed the seal pups over the edge. The exams, reported in Marine Mammal Science, revealed the unmistakable lesions of cardiomyopathy in the pups' heart muscles. Fur seals become only the second marine mammals, after dolphins, shown to develop heart disease after handling or captivity. The biologists suggest that fieldworkers should look for signs of chronic infections in seals—such as malaise or unusually rapid breathing—before handling the animals and risking further harm.