Have you ever wondered why killer whales in captivity have a dorsal fin that is flopped over, or 'collapsed?' Read on to learn the theories.
About Killer Whales
All killer whales have a dorsal fin on their back. The male's dorsal fin is much taller than a female's.
A male killer whale's dorsal fin can grow to as much as 6 feet tall. Despite the fact that the dorsal fin is very straight, it is not supported by bone, but a fibrous connective tissue called collagen. Since a male's dorsal fin is taller, more captive males (100%, actually) than females have collapsed fins, but the condition can occur in females. This condition is known as dorsal fin collapse or flaccid fin or folded fin syndrome.
The same thing can happen to the whale's tail flukes, which often flop over at the ends.
Why Does the Dorsal Fin Collapse?
A wild orca often travels far, and quickly, in deep water. The water provides pressure to the fin, keeping the tissues inside healthy and straight, and encouraging the dorsal fin to remain straight.
continue reading below our video
What are the Seven Wonders of the World
One theory as to why dorsal fins collapse in captivity is because the orca spends much of its time at the water surface and doesn't swim very far. This means that the fin tissue gets less support than it would if the orca were in the wild, and it starts to fall over. The whales also often swim in a repetitive circular pattern.
Other potential causes for fin collapse may be dehydration and overheating of fin tissue due to warmer water and air temperatures, stress due to captivity or changes in diet, reduced activity that causes low blood pressure, or age.
Do the Fins of Wild Orcas Collapse?
While it is less likely, it is not impossible for a wild orca's dorsal fin to collapse or become bent, and it may be a trait that varies among whale populations.
A study in 1998 of killer whales in New Zealand showed a relatively high rate (23%) of collapsing, collapsed, or even bent or wavy dorsal fins, and noted that this was higher than that observed in populations in British Columbia or Norway. Only one male from the 30 studied had a fully collapsed dorsal fin. Reports from British Columbia also show killer whales with bent dorsal fins.
Researchers have theorized that dorsal fin collapse in wild whales may be due to age, stress, injury or altercations with other killer whales.
In 1989, the dorsal fins of two male killer whales collapsed after exposure to oil during the Exxon Valdez oil spill - the whales' collapsed fins were though to be a sign of poor health, as both whales died soon after the collapsed fins were documented.
Further Information:
- Composition of Whale Dorsal Fins (WhaleNet)
- Dorsal Fin Collapse in Killer Whales Explained (Video)
- Evans, W.A. 1996. 'Flaccid' Fin Syndrome: Natural or Captive Phenomenon. A Capstone Review Paper in Partial Fulfillment of the Requirements for the Degree of Master of Science in Marine Biology. Nova Southeastern University.
- Orca Dorsal Fin Controversy: Experts vs. SeaWorld. (Ocean Advocate Blog)
- Matkin, C. O. and E. Saulitis. 1997. Restoration notebook: killer whale (Orcinus orca). Exxon Valdez Oil Spill Trustee Council, Anchorage, Alaska.
- National Marine Fisheries Service Northwest Regional Office. 2005. Proposed Conservation Plan for Southern Resident Killer Whales (Orcinus orca). Accessed March 23, 2016.
- Visser, I.N. 1998. Prolific body scars and collapsing dorsal fins on killer whales (Orcinus orca) in New Zealand Waters. Aquatic Mammals 24.2,71-81