Dorsal Fin Collapse
A killer whale’s dorsal fin can grow several feet long, with an adult male’s fin growing up to six feet – the tallest dorsal fin of all cetaceans. Despite its size, the dorsal fin is not supported by bone but a fibrous connective tissue called collagen. Wild orcas often travel far, and quickly, in deep water. The water provides pressure to the fin, keeping the tissues inside healthy and encouraging the dorsal fin to remain straight.
However, in captivity, the ability to travel is vastly limited. As a result, captive killer whales spend more time at the surface (gravity takes over) and are forced to swim endless circles, often in the same direction, in a relatively small tank. Consequentially, the dorsal fin gets less of a workout and less support in the water causing it to partially or completely collapse. Other factors thought to cause dorsal fin collapse in captivity are stress, fitness, medication, chemicals used in the water, warmer water temperatures, a reduced ability to thermoregulate due to excessive exposure above water, and a lower water content diet leading to dehydration. 100% of adult male orcas in captivity have the condition, as well as some females (Katina, Nalani, Kayla, Shouka, Narnia, Stella, and Kiska), although there is no record of a able-bodied female orca with a collapsed dorsal fin in the wild.
In fact, according to h Dr. Astrid van Ginneken, less than one percent of all wild orcas have the condition. However, it varies from population to population. For example, according to Dr. Ingrid Visser’s 1998 study on fin abnormalities, the percentage rate of wild whales with collapsed, collapsing or bent dorsal fins sits at 4.7% in British Columbia, 0.57% in Norway and 23% in New Zealand (although only one male was found to have a fully folded fin). Researchers have theorised that dorsal fin collapse in wild whales may be due to emaciation and/or human causes such as entanglement, bullet wounds, boat strikes or exposure to oil spills - factors which are completely different to the causes of the condition in captivity.
Photo: Kylie Milliken (photobucket)