Populations of Pacific Salmon have been declining across a major swathe of the range that it occupied across the North West of the American continent. There are many and varied reasons for this and you should inform yourself of the complexity involved.
An Executive Summary of the problem with the
Pacific Salmon (from the National Academy of Sciences, Washington - in a
publication called 'Upstream')
The full publication is available on-line from the National Academy of Sciences
Website: Upstream:
Salmon and Society in the
Pacific Northwest (1996)
The Full Book : http://books.nap.edu/books/0309053250/html/index.html
Many of the populations have already become extinct or are so rare that they fall under the provisions of the Endangered species act passed by the National Congress.
The Endangered Species Act and the Pacific Salmons 
(on NOAA website)
(this excellent site includes a detailed leaflet
that explains the problem and the administrative
attempts to reverse the situation
It also includes maps of the ESU's - the Evolutionarily Significant Units for
various species
Follow the arrow and click on the ESU Maps links
)
Page Author: Dr Rick T Leah, Univ of L'pool - Contents last reviewed 15/12/2005