how many species of pacific salmon are there?

Last night at a dinner party that was loaded with great tasting seafood, we had a discussion about salmon, recipes, spawning runs and number of species. However, we could not agree on everything. How many species of Pacific salmon are there?

Pacific species belong to the genus Oncorhynchus, some examples include;

Cherry salmon (Oncorhynchus masu or O. masou) is found only in the western Pacific Ocean in Japan, Korea and Russia and also landlocked in central Taiwan's Chi Chia Wan Stream. [8]
Chinook salmon (Oncorhynchus tshawytscha) is also known locally as King, Tyee, Spring salmon, Quinnat, Tule, or Blackmouth salmon. Chinook are the largest of all Pacific salmon, frequently exceeding 30 lbs. (14 kg).[9]
Chum salmon (Oncorhynchus keta) is known locally as Dog or Calico salmon. This species has the widest geographic range of the Pacific species[10] : south to the Sacramento River in California in the eastern Pacific and the island of Kyūshū in the Sea of Japan in the western Pacific; north to the Mackenzie River in Canada in the east and to the Lena River in Siberia in the west.
Coho salmon (Oncorhynchus kisutch) is also known locally as Silver salmon. This species is found throughout the coastal waters of Alaska and British Columbia and up most clear-running streams and rivers.
Pink salmon (Oncorhynchus gorbuscha), known as humpies in south east Alaska, are found from northern California and Korea, throughout the northern Pacific, and from the Mackenzie River in Canada to the Lena River in Siberia, usually in shorter coastal streams. It is the smallest of the Pacific species, with an average weight of 3.5 to 4 lbs. (1.6 - 1.8 kg).[11]
Sockeye salmon (Oncorhynchus nerka) is known in the USA as Red salmon.[12] This lake-rearing species is found south as far as the Klamath River in California in the eastern Pacific and northern Hokkaidō Island in Japan in the western Pacific and as far north as Bathurst Inlet in the Canadian Arctic in the east and the Anadyr River in Siberia in the west. Although most adult Pacific salmon feed on small fish, shrimp and squid; sockeye feed on plankton that they filter through gill rakers.[3]
Steelhead or Steelhead trout or Rainbow trout (Oncorhychus mykiss) are river spawners, usually found in the same rivers that produce chinook, especially the Columbia, Snake, Skeena, and other large rivers on the Pacific Coast. Steelhead have also been introduced into some rivers surrounding the Laurentian Great Lakes.