What Causes Dorsal Fin Collapse?


When I view pictures or video of wild orcas, I can’t help but be impressed by the majestic dorsal fins positioned atop the backs of the male members of the pod. They can stand more than 6 feet tall. In captivity, every adult male orca, and even some females, experience dorsal fin collapse.  This is also seen in smaller cetaceans such as bottlenose dolphins.  Many patrons of marine parks question the cause of this phenomenon, no doubt, which is hotly debated among captivity supporters and opponents. SeaWorld and other marine parks tend to divert or avoid the topic of dorsal fin collapse.

In the past, it was theorized by captivity opponents that dorsal fin collapse may be a sign of depression. This theory is now largely rejected by both sides. Here are a few of the most common explanations of dorsal fin collapse:

1.Gravity

Wild whales spend their lives in constant motion, travelling vast distances underwater in a weightless environment. The water current against the fin helps to shape it into an erect position. On the other hand, captive whales spend most of their time floating at the surface of their small pools. Because they do not spend their time submerged or in motion, the majestic fin, the pride of the male orca, slowly begins to droop and fall over.

While this theory implies that captive orcas are experiencing unnatural lives at the surface of their small pools, it is the only theory out there that does not tie fin collapse to the whale’s physical well-being. This may be why the majority of captivity supporters cling to this explanation and reject all others. By adopting this position, supporters are choosing the lesser of two evils. They may be required to admit that the orcas experience chronic surface resting, but at least they don’t have to admit that the dorsal fin may collapse due to captivity-related health issues. From the paper Killer Controversy“In the Killer Whales Animal InfoBook, SeaWorld states that no one knows why dorsal fins “bend,” but that some possible causes are “genetics, injuries, or because the fins can be taller than many humans without any hard bones or muscles for support.” If, as this statement suggests, gravity alone might cause a fin to collapse in nature, logic dictates that this would be a common rather than a rare phenomenon in wild whales.” 

In other words, while gravity may be a factor in fin collapse, it is unscientific to completely reject the influence of other factors, such as:

2. Dehydration

Dorsal fins are composed of a fibrous tissue called collagen; the same substance that composes our ligaments and tendons. Collagen is also responsible for the elasticity of our skin, and is mostly made of water. The question of how dehydration affects a whale’s dorsal fin is a question of how dehydration affects collagen. There have been multiple studies demonstrating that dehydration causes collagen to become weak and brittle. Wild whales receive hydration through their live prey. In captivity, the whales eat fish which have gone through a process of freezing, depleting much of the freshwater content. Because of this, hydration is a major topic of interest in captive cetaceans. All captive cetaceans require supplemental hydration through a hydration hose, ice, freshwater injection in their food, or jell-o.

If dehydration causes fin collapse, why do some emaciated animals have straight fins? Not all dehydration symptoms may manifest. This is true for humans as well as other non-human animals. Fin collapse may also be less prominent in young, or female orcas with shorter fins, such as Morgan or Springer. Scientists who work with stranded orcas, such as Ingrid Visser, have come across dehydrated whales with collapsed fins which erect after their condition improves. The idea that dehydration affects collagen and thus causes fin collapse is largely rejected by pro-captivity activists. This comes as no surprise given that the notion implies that some captive orcas may be dehydrated, and thus lacking in care.

3. Illness and Injury

This one is pretty self explanatory. There is no doubt that some wild whales have collapsed fins. However, this number is very small. According to cetacean scientists, less than 1% of wild whales have dorsal fin collapse, and most of these cases are attributed to illness or injury, with a small genetic factor. Dr. Ingrid Visser published a paper which demonstrates that 23% of New Zealand orcas have abnormal dorsal fins. SeaWorld and their fans, have often distorted and misused this statistic by applying it to all wild orcas.

If you want to learn more about fin collapse, watch this interview with Dr. Astrid van Ginneken and Dave Ellifrit of Orca Survey by Dr. Jeff Ventre and David Kirby. I hope you all had a wonderful holiday and a happy new year! I know that things have been slow-going lately, but be sure to stick around for all of the happenings that are sure to take place in 2013!

EDIT:

Hey guys! So today I came across this great scientific paper regarding fin collapse in killer whales. It actually describes about 13 possible causes for dorsal fin collapse, and provides evidence that ‘flacid fin syndrome,’ may be a result of the whale’s fitness and feeding habits. Be sure to check it out if you want to learn more about this topic!

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11 thoughts on “What Causes Dorsal Fin Collapse?

  1. The only thing I thought of when I saw that picture of the sea world orca was ‘That’s Tilikum.’

    If you don’t know the name, look it up.

  2. Pingback: A Note on Blackfish | Sciency Things

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