<P> Most captive male killer whales, and some females, have a dorsal fin that is partially or completely collapsed to one side . Several hypotheses exist as to why this happens . A dorsal fin is held erect by collagen, which normally hardens in late adolescence . </P> <P> Scientists from the National Marine Fisheries Service (NMFS) have reported that "the collapsed dorsal fins commonly seen in captive killer whales do not result from a pathogenic condition, but are instead thought to most likely originate from an irreversible structural change in the fin's collagen over time . Possible explanations for this include: (1) alterations in water balance caused by the stresses of captivity dietary changes, (2) lowered blood pressure due to reduced activity patterns, or (3) overheating of the collagen brought on by greater exposure of the fin to the ambient air ." According to SeaWorld's website, another reason for the fin to bend may be the greater amount of time that captive whales spend at the surface, where the fin is not supported by water pressure . The Whale and Dolphin Conservation Society says that dorsal fin collapse is largely explained by captive killer whales swimming in small circles due to the inadequate space in which they have to swim . SeaWorld, however, claims that "Neither the shape nor the droop of a whale's dorsal fin are indicators of a killer whale's health or well - being ." </P> <P> Collapsed or collapsing dorsal fins are rare in most wild populations and usually result from a serious injury to the fin, such as from being shot or colliding with a vessel . After the 1989 Exxon Valdez oil spill, the dorsal fins of two male resident killer whales who had been exposed to the oil collapsed, and the animals subsequently died . In 2002, the dorsal fin of a stranded killer whale showed signs of collapse after three days but regained its natural upright appearance as soon as the orca resumed strong normal swimming upon release . </P> <P> It has been reported that seven out of the 30 (23%) wild adult male killer whales from New Zealand waters have bent dorsal fins, though this figure includes a variety of dorsal fin abnormalities, including rippled or twisted fins, in addition to simple one - sided collapse . The New Zealand study noted that, in addition to the high prevalence of dorsal fin deformities, two of the 30 adult males in this population also had prolific body scarring that was consistent with bite marks from other killer whales . The prevalence of dorsal fin deformities is 4.7% among adult male orcas in British Columbia and 0.57% in Norway . Amongst the well - studied wild killer whales off the coast of British Columbia, the total rate of dorsal fin collapse is around 1% . </P>

Why do orcas have collapsed dorsal fins in the wild