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Defining Dwarfism

Orca dwarfism is a medical disorder that affects killer whales (Orcinus orca), altering the length of an adult to a size under 3 feet 10 inches. The majority of dwarfism cases in Orcas are caused by achondroplasia and growth hormone deficiency. The most common of the two is achondroplasia, which accounts for 70 percent of dwarfism cases and produces short fins, increased spinal curvature, and distortion of skull growth. This is an autosomal dominant disorder caused by a faulty allele in the whale’s genome, specifically a mutation in the fibroblast growth factor receptor gene 3 (FGFR3) which regulates whale growth.

Growth hormones, also called somatotropins, are polypeptide hormones that stimulate growth and cell reproduction. A lack of this hormone stunts, and sometimes even halts, growth and may become apparent as desired. Dwarf Orcas with this deficiency grow slowly and puberty may be delayed several years or permanently.

The four ecotypes of killer whales that have been identified and separated as species in regards to their unique physical features.

Background of Discovery

In 1981, Soviet researchers proposed a new species of the killer whale, Orcinus nanus, based on 321 samples of whales that were captured in the Southern Ocean during 1961-1978. Only body lengths were measured and used, and as a result, Orcinus nanus is considered a nomen nudem.

In 1982, another team of Soviet researchers independently described another new species, Orcinus glacialis, based on 906 whale catches that took place between 1979-1980. Due to the lack of holotype specimens and poor descriptions, the possibility of additional species of Orcinus has received little attention and a lack of support from the scientific community. Based off of this research, four ecotypes of killer whales have currently been established in regards to size and physical characteristics: A, B, C, and D.

Ecotype A

Type A is the most common known killer whale with a large black and white body with a medium-sized white eye patch. This killer whale is located in Antarctic open waters while preying upon Antarctic minke whales (Balaenoptera honaerensis). They follow the migration patterns of the minke whales in and out of Antarctic waters. Type A comprise the largest orcas, reaching up to about 9.5 meters long in body length.

Ecotype B

Type B killer whales, also known as Park Ice Orcas, are gray, black, and white colored with a dorsal cape and a very large eye patch. They are located in loose-packed ice waters and prey upon pinnipeds. They may seem to appear brown or yellowish due to the presence of diatoms in the water and have a cape of pale color. Park Ice Orcas prey mainly on seals by using a famous technique called wave-washing. Wave-washing is when the orcas use their tails and bodies to create waves which wash the seals off of ice blocks into the waters.

Ecotype C

Type C killer whales are also gray, black, and white but have a narrow, slanted eye patch. They reside in dense-packed ice waters and feed mainly on fish. This ecotype is the smallest in size, with males only reaching 6 meters long.

Ecotype D

Ecotype D represents a group of killer whales that have been discovered in the 1950's in New Zealand, but only have rarely been seen since. They have black and white coloring along with a saddle patch, but they have shorter dorsal fins, a rounder head, and the smallest eye patch of any of the other ecotypes known.

The Dwarf Killer Whale

Due to the lack of color observations made by Soviet researchers in 1981, Ornicus nanus cannot be labeled as either ecotype B or C. However, the body length descriptions of the new species suggested that they were smaller than normal killer whales, with Ornicus nanus being 1-1.5 meters shorter. A more recent study proposed by Pitman et al. (2007) provided evidence that ecotype C killer whales represent even a smaller size than what the Soviet researchers indicated. Therefore, scientific evidence is starting to make the connection between ecotype C and the Dwarf Killer Whale.

Migration Patterns

Killer whales travel in groups of varying size depending on the ecotype. Type A have an average group size of 13, type B with 11.8, and type C with 46.1 individuals. There is little information on Orcas seasonal movements, but all three ecotypes of killer whales occur in Antarctica during the Austral summer. Most types of killer whales leave Antarctica during austral winter and migrate to lower latitudes.

Future Implications for Research

There may be other ecotypes that have evolved over time. However, there is currently not enough scientific information and/or evidence in order to determine separate species. These small populations of killer whales do not appear to interact and/or interbreed with other ecotypes and are therefore at a high risk of becoming extinct due to emerging concerns such as climate change. Low numbers and lack of knowledge have important conservation implications for the survival of these communities.