Why Did The Southern Chum Salmon Cross The Road? Importance of Long Term Data Sets to Understand Changes in Species Distributions

The northward contraction of southern populations of Pacific salmon has been long predicted.  However, little documentation of these contractions has been observed, partly because of confusing historical evidence of abundance and identification.  In 1905-06 chum salmon juveniles were reported to be the most abundant salmon species in streams surveyed between the Sacramento and Columbia rivers.  During this time, the species was also observed spawning as far south as the San Lorenzo River and as far as 322 km upstream in the Sacramento River in California.  Today, all these populations have greatly declined or are extinct, with even the Columbia River populations in OR and WA are listed under the ESA as a threatened species.

As little information was available on these southern populations, we surveyed historical documents and collected present day life history, abundance, and genetic data to more carefully define these populations to determine if present populations are native wild fish, hatchery strays, or fish from the previously larger such as the Columbia Rive. We discuss both our recent findings and the difficulties we encountered in determining what has been lost, without clear historical information on abundance of past populations.