"Another topic she (Naomi Rose, HSUS) thought about including in her case against captivity was the collapsed dorsal fin seen in 100 percent of the captive adult males. Based on her knowledge of biology and what she had learned about the species in the wild, Naomi considered a number of potential causes of the deformity. They included the stress of captivity, dietary changes, restricted physical activity, and simple gravity acting on the collagen-like tissue in the fin that had been heated and softened by the abnormal time spent at the surface in captivity, especially in sunny, subtropical locales such as Florida, Texas, and California.
In the wild, collapsed fins are extremely rare, usually the result of an identifiable cause such as gunshot wounds or collisions with boats. In 1989, following the Exxon Valdez oil spill, two male killer whales exposed to the toxic slick quickly experienced a folding in their fins, which, within two years, had flattened to their backs entirely. Marine mammal scientists on the scene assumed the animals were ailing. Both animals died shortly after, suggesting fin collapse could also be a sign of chronic health problems.” -Death at Seaworld, David Kirby
Front view of manatee, head and back layered with barnacle-like crust by James A. Sugar