The pale referred to in the idiom is usually taken to mean the English Pale, the part of Ireland under English rule, and therefore, as perceived by its rulers, within the bounds of civilization. pale see: beyond the pale
For the food, see Salmon as food. The chum salmon (Oncorhynchus keta) is a species of anadromous fish in the salmon family. It is a Pacific salmon, and may also be known as dog salmon or keta salmon, and is often marketed under the name silverbrite salmon.
Chum are the most widely dispersed of the Pacific species. They are found both further south in California and further north in Canada than the other species. They are also found in parts of Siberia. Silvery green in color, the salmon appear yellow when spawning. They are also known as dog's or Keta salmon.