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.]

WordNet (r) 3.0 (2006):

red salmon
    n 1: fatty red flesh of salmon of Pacific coast and rivers [syn:
         red salmon, sockeye, sockeye salmon]
    2: small salmon with red flesh; found in rivers and tributaries
       of the northern Pacific and valued as food; adults die after
       spawning [syn: sockeye, sockeye salmon, red salmon,
       blueback salmon, Oncorhynchus nerka]