Antarctic
Around 25，000 orcas are estimated around the Antarctic， and four types have been documented. Two dwarf species， named Orcinus nanus and Orcinus glacialis， were described during the 1980s by Soviet researchers， but most cetacean researchers are skeptical about their status， and linking these directly to the types described below is difficult.
Some examples of variations in orcas
Type A or Antarctic orcas look like a “typical“ orca， a large， black-and-white form with a medium-sized white eye patch， living in open water and feeding mostly on minke whales.
Type B1 or pack ice orcas are smaller than type A. It has a large white eye patch. Most of the dark parts of its body are medium grey instead of black， although it has a dark grey patch called a “dorsal cape“ stretching back from its forehead to just behind its dorsal fin. The white areas are stained slightly yellow. It feeds mostly on seals. Type B1 orca are abundant between Adelaide Island and the mainland Antarctic peninsula.
Type B2 or Gerlache orcas are morphologically similar to Type B1， but smaller. This ecotype has been recorded feeding on penguins and seals， and is often found in the Gerlache Strait.
Type C or Ross Sea orcas are the smallest ecotype and live in larger groups than the others. Its eye patch is distinctively slanted forwards， rather than parallel to the body axis. Like type B， it is primarily white and medium grey， with a dark grey dorsal cape and yellow-tinged patches. Its only observed prey is the Antarctic cod.
Type D or Sub-Antarctic orcas were first identified based on photographs of a 1955 mass stranding in New Zealand and six at-sea sightings since 2004. The first video record of this type was made in 2014 between the Kerguelen and Crozet Islands， and again in 2017 off the coast of Cape Horn， Chile. It is recognizable by its small white eye patch， narrower and shorter than usual dorsal fin， bulbous head (similar to a pilot whale)， and smaller teeth. Its geographic range appears to be circumglobal in sub-Antarctic waters between latitudes 40°S and 60°S. Although its diet is not determined， it likely includes fish， as determined by photographs around longline vessels， where Type D orcas appeared to be preying on Patagonian toothfish (Dissostichus eleginoides).
这章没有结束，请点击下一页继续阅读！
请大家记得我们的网站：乡村书屋(m.xcshuwu.com)海洋霸主崛起史更新速度全网最快。