User:Clayoquot/Orca

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[edit] Dorsal fin collapse

This male (Tilikum), at SeaWorld Orlando, has a collapsed dorsal fin.
This male (Tilikum), at SeaWorld Orlando, has a collapsed dorsal fin.

Most male captive Orcas, and some females, have collapsed (droopy) dorsal fins. Several theories exist as to why this happens. A dorsal fin is held erect by collagen, or compressed lipid cells. The collagen normally hardens in late adolescence.

One theory is that in deep ocean waters, the pressure the water exerts on the fin allows it to remain supported while the collagen hardens. In captivity, however, shallow tanks lack sufficient water pressure to produce this effect, and the fin collapses before the collagen solidifies.[1] According to another theory, the Orca is almost always in a state of turning in a tank, since it is not large enough to allow swimming in one direction for any normal duration. The constant turning exerts pressure on the dorsal fin, which in turn causes it to collapse.[2]

Other possible explanations include alterations in water balance caused by the stresses of captivity or dietary changes, lowered blood pressure due to reduced activity patterns, or overheating of the collagen brought on by greater exposure of the fin to the ambient air.[3]

In the wild, dorsal fin collapse is rare, and the deformity is believed to have a different set of causes than in captivity. In wild Orcas, it usually results from a serious injury to the fin. After the 1989 Exxon Valdez oil spill, the dorsal fins of two male resident Orcas who had been exposed to the oil collapsed, and the animals subsequently died. In 2002, the dorsal fin of a stranded Orca showed signs of collapse after three days, but regained its natural upright appearance as soon as it resumed strong normal swimming upon release.[3]

Amongst the well-studied wild Orcas off the coast of British Columbia, the rate of dorsal fin collapse is around 1%.[4] According to one study, 23.3% of wild Orca males off the coast of New Zealand have collapsed dorsal fins, compared with 4.7% in British Columbia and 0.57% in Norway. [5]



[edit] from source

The collapsed dorsal fins commonly seen in captive killer whales do not result a pathogenic condition, but are instead thought to most likely originate from an irreversible structural change in the fin’s collagen over time. Possible explanations for this include (1) alterations in water balance caused by the stresses of captivity dietary changes, (2) lowered blood pressure due to reduced activity patterns, or (3) overheating of the collagen brought on by greater exposure of the fin to the ambient air. Collapsed or collapsing dorsal fins are rare in most wild populations and usually result from a serious injury to the fin, such as from being shot or colliding with a vessel.

The dorsal fins of two male resident whales in Alaska began to fold soon after their pod’s exposure to oil during the Exxon Valdez spill in 1989 and were completely flattened within two years. Both animals were suspected to be in poor health and subsequently died. The dorsal fin of a male transient stranded at Dungeness Bay, Washington, in 2002 showed signs of collapse after three days, but regained its natural upright appearance as soon as the whale resumed strong normal swimming upon release.

  1. ^ Todd Nivens. Why Killer Whale Fins Flop Over. Retrieved on 2006-12-27.
  2. ^ Jonathan Wright. Why does the Orca (Killer Whales) fin start to bend when it is in captivity?. Retrieved on 2006-12-27.
  3. ^ a b National Marine Fisheries Service Northwest Regional Office (August 2005). Proposed Conservation Plan for Southern Resident Killer Whales (Orcinus orca). Retrieved on 2007-05-07.
  4. ^ Cite error: Invalid <ref> tag; no text was provided for refs named Hoyt
  5. ^ Ingrid N. Visser. Prolific body scars and collapsing dorsal fins on killer whales (Orcinus orca) in New Zealand waters. Retrieved on 2008-03-28.