#killer whale

This is Bentip, a male killer whale who got his name for a lateral curl at the tip of his dorsal fin. Over the years, his fin has continued to bend - this observation shows him in December 2025, showing a fin that is moderately, but not yet completely, collapsed. Other views of Bentip show that tip of his fin curls inward toward his body. 

The reasons for dorsal fin collapse in cetaceans are not entirely understood, and require further study. Physical injury to the fin is responsible in many cases, but in many it is not; illness and/or loss of body condition may be an instigator of collapse, but isn't required for its persistence, as most cetaceans with bent fins are clearly in fine fettle. Simple wear and tear with advancing age could be responsible. There does not appear to any notable impact of bent fins on the ability of these animals to survive or thrive, nor does a bent fin necessarily indicate poor health. Killer whales exhibit the highest incidence of dorsal fin bending and collapse - with their very large fins, especially in males where they may be 1.5-1.9m (5-6.2 feet) tall, this should be no surprise. 

Cetacean dorsal fins are fairly stiff structures, but lack any kind of internal skeletal or muscular support; instead, they are supported by stiff collagen fibers. Watching videos of killer whales moving with purpose - especially doing something high-energy like breaching - will show a gentle wobble of the dorsal fin as they move. An explanation for fin collapse that is widely circulated - and that I find convincing in light of the data, but would be excellent to see studied in more depth - is that individual cetaceans that spend an increased amount of time at the surface, for whatever reason (in wild cetaceans, this could be resting at the surface during illness; in captive cetaceans, this would be because they interact with their trainers at the surface and spend much more time there than their wild counterparts usually do; in both, a general weakening of connective tissues with age could also be a contributing factor), have lessened support on their fins and in the warmer, thinner air the collagen fibers slacken and the fin begins to collapse under its own weight.

Though it is not common in wild killer whales, dorsal fin collapse is not vanishingly rare, either - incidence varies between populations with reported frequency ranging from about 0.7-5.6% of individuals; around 2-3% seems fairly typical. In captive killer whales, almost all adult males (and some females) have bent fins. Increased time spent at the surface interacting with trainers/care staff and enrichment handily accounts for this in general, but there is certainly more to learn: the degree of bending/collapse varies between individuals, from fins that are only bent over at the upper portion to others with fins that are slumped completely at the base; in some cases, there may be a genetic component at play (Katina of SeaWorld Orlando had a fin with an unusually prominent bend for a female, which two of her daughters also have had from an early age); and perhaps most intriguingly, the adult bulls at Shanghai Haichang Ocean Park have fins that are perfectly upright. While continued study on this topic is warranted as practices for management of cetaceans in aquaria continue to evolve, it is worth reiterating that dorsal fin collapse is not an indicator of poor health, and there is certainly no reason to think it is connected to poor mental health as is occasionally claimed.

This paper, cited below, gives a good summary of fin bending/collapse in wild cetaceans. 

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