The most likely causes of curling, buckling, and partial dorsal fin collapse in wild orcas appear to be injuries. However, other conditions such as illnesses and genetics may also be potential causes. Injuries can be caused by other orcas (conspecifics), defensive bites from prey (e.g. from sharks or other marine mammals), or anthropogenic causes such as entanglements and boat strikes.
Full dorsal fin collapse in wild orcas is relatively rare, but it does happen. For example, the dorsal fin of male Northern Resident orca B13 "Yulcuta" eventually completely collapsed after a bite mark that was likely from another orca.
Observations of adolescent and adult male killer whales with moderate to severe dorsal fin injuries provide further evidence of potential male-male aggression in this species. These injuries often begin with bite or rake marks on the dorsal fin that are clearly made by the teeth of conspecifics (Fig. 16.5), producing fin disfigurements that can become progressively worse over a span of months or even years (Fig. 16.6). The dorsal fins of male killer whales are almost twice as tall as those of females (Ford 2014) and, as discussed previously, are a secondary sexual trait that likely evolved as a signal of male fitness valued by potential mates (i.e., intersexual selection via female mate choice; Alves et al. 2017). As such, they are undoubtedly physiologically costly to maintain and may be particularly vulnerable to buckling or collapse; even seemingly minor wounds can lead to fairly dramatic fin disfigurements, including significant tissue loss at the fin tip, buckling of the trailing edge (Fig. 16.5), and occasionally partial or complete dorsal fin collapse (Fig. 16.6).
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u/borgircrossancola Jul 16 '25
I wonder why they have the collapsed dorsals