For some time, there's been a heated debate about why killer whales in captivity have dorsal fins that are flopped over or collapsed. Animal-rights activists say that these fins collapse because the conditions under which killer whales - or orcas - are held in captivity are not healthy. Others, such as water parks that keep killer whales in captivity and use them in theme-park shows, argue that there are no health threats to killer whales held in captivity and that dorsal fin collapse is natural.
The Lowdown on Dorsal Fins
All killer whales have a dorsal fin on their back, but the male's dorsal fin is much taller than a female's and can grow up to 6 feet tall. Despite the fact that the dorsal fin is very straight, it is supported not by bone but a fibrous connective tissue called collagen. All males in captivity have collapsed dorsal fins, but the condition, also known as dorsal fin collapse, flaccid fin, or folded fin syndrome, does occur in many captive females.
Scientists are not certain why orcas have dorsal fins or what purpose the appendages serve. But, there is some speculation. Whales Online says that the large dorsal fin enhances the hydrodynamics of killer whales:
"(The dorsal fin) helps them slip through the water more efficiently. Similar to the ears of elephants or the tongues of dogs, dorsal, caudal and pectoral fins also help eliminate excess heat during intense activities such as hunting."
Orca Live agrees that the fins help regulate a killer whale's body temperature:
"Excess heat, generated as they swim along, is released into the surrounding water and air via the dorsal fin - much like a radiator!"
Though there are different theories about their specific purpose, it's a fact that dorsal fin collapse is far more prevalent in whales that are held in captivity.
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. 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.
SeaWorld of Hurt, a website operated by animal rights organization PETA, takes this stance, noting that dorsal fins of captive whales likely collapse
"Because they have no space in which to swim freely and are fed an unnatural diet of thawed dead fish. SeaWorld claims that this condition is common - however, in the wild, it rarely ever happens and is a sign of an injured or unhealthy orca."
SeaWorld announced in 2016 that it would stop breeding whales in captivity immediately and phase out killer whale shows at all its parks by 2019. (In San Diego, the shows ended in 2017.) The company has said, however, that the shape of a killer whale's dorsal fin is not an indicator of its health. "The dorsal fin is a structure like our ear," said Dr. Christopher Dold, SeaWorld's head veterinarian:
"It doesn't have any bones in it whatsoever. So our whales spend a lot of time at the surface, and accordingly, tall, heavy dorsal fins (of adult male killer whales) without any bone in it, will slowly bend over and assume a different shape."
While 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 of killer whales in New Zealand showed a relatively high rate - 23 percent - of collapsing, collapsed, or even bent or wavy dorsal fins. This was higher than that observed in populations in British Columbia or Norway, where only one male from the 30 studied had a fully collapsed dorsal fin, the study said.
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 thought to be a sign of poor health, as both whales died soon after the collapsed fins were documented.
Researchers have theorized that dorsal fin collapse in wild whales may be due to age, stress, injury, or altercations with other killer whales.
- 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, )." orcaOrcinus
- 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.