The Collaborative International Dictionary of English v.0.48:

Nerka \Ner"ka\, n. [Russ. niarka, prob. fr. native name.]
   (Zool.)
   The most important salmon of Alaska (Oncorhinchus nerka),
   ascending in spring most rivers and lakes from Alaska to
   Oregon, Washington, and Idaho; -- called also red salmon,
   redfish, blueback, and sawqui.
   [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Blueback \Blue"back`\, n. (Zool.)
   (a) A trout (Salmo oquassa) inhabiting some of the lakes of
       Maine.
   (b) A salmon (Oncorhynchus nerka) of the Columbia River and
       northward.
   (c) An American river herring (Clupea [ae]stivalis),
       closely allied to the alewife.
       [1913 Webster]