Quantifying Pacific Salmon Extinctions and Loss of Diversity
In 1991 Nehlsen et al. completed an analysis of Pacific salmon and steelhead losses in the western United States and its publication started a firestorm of controversy because for the first time the failure of fish management was made evident to the citizens in the states of California, Idaho, Oregon and Washington.
A recent assessment by the National Marine Fisheries Service Northwest Science Center (Gustafson et al. 2007) builds on the Nehlsen et al. work by providing an estimate of extinction and loss of diversity in Pacific salmon. They point out that salmonids that have a stream maturing life history are “much more vulnerable to anthropogenic (human caused) threats” and compiled a separate extinction data for the two types of salmonids (stream maturing and ocean maturing species). The salmonids that exhibit the stream type life history are spring chinook, coho and summer steelhead.
According to the authors before Euro-American contact there were nearly 1,400 Pacific salmon populations historically occurring in the study area from southern California to the Canadian border including the upper Columbia River in British Columbia. Based on their study, they listed the number of species that remain and those that have gone extinct. Below I present the total numbers, leaving out the ecological regions that define this list of extinct and extant populations, but show the extant populations and (extinct) populations.
Steelhead 436 (131), extinct 23%
Chinook 237 (159), extinct 40%
Sockeye 38 (34), extinct 47%
Coho 135 (50), extinct 27%
Chum 89 (23), extinct 21 %
Pink 42 ( 9), extinct 18 %
Total 977 (406), extinct 29%
“Nearly 1,400 Pacific salmon populations historically occurred in the study area, and an estimated 29% have gone extinct since substantial Euro-American contact.” The authors say that overall, the six species no longer occur in about one-third of the 6 ecological regions they once occupied in this study.
“The estimated proportion of extinct historical populations was relatively low in coastal drainages from Vancouver Island to northern California (20%), but increased dramatically in southern California (31%), the California Central Valley (57%), and the interior Columbia River Basin (35-62% in areas still accessible to Pacific salmon). All historical anadromous populations were extirpated from the Upper Snake River and Columbia River headwaters regions following installation of impassable dams.”
“Extinctions were also non-random with respect to species and major maturation types. Coho salmon once occupied a range almost as large as that of chinook salmon and steelhead, which historically occupied all ecological regions, but native coho salmon populations have disappeared from large portions of California and the Columbia River Basin. Coho salmon may be particularly at risk due to their lengthy (greater than one year) juvenile freshwater residence where they are exposed to freshwater habitat alterations) and a nearly fixed three-year life cycle (providing less of a buffer against year-class failure than most other salmon species).”
“Stream-maturing steelhead (summer steelhead) had significantly more proportional population losses than ocean-maturing steelhead (winter steelhead), and stream-maturing chinook salmon (spring and summer chinook) had a significantly higher proportion of population losses than ocean-maturing chinook (fall and winter chinook). High losses of stream-maturing populations are likely due to widespread loss of crucial high elevation (generally 500 m) holding habitats and to their vulnerability during prespawning holding period.”
“The loss of major genetic groups (27%) was nearly as high as extirpation from ecological regions (33%), but the loss of major life history types was less extensive (an estimated 15%) and perhaps confined to two species (chum and coho salmon).”
“Estimated number of stream and ocean maturing steelhead and chinook salmon populations that are extinct in the study area.
Steelhead (stream maturing) Total Extinctions in Study Area: 54 populations, 31% of populations.
Steelhead (ocean maturing) Total Extinctions in Study Area: 77 populations, 19% of populations
Chinook (stream maturing) Total Extinctions in Study Area: 124 populations, 19% of populations
Chinook (ocean maturing) Total Extinctions in Study Area: 35 populations, 21% of populations.
Extinction of Ecological (33 populations), life history (15 populations), and genetic diversity (27 populations) of Pacific salmonids was also estimated.”
The authors say, “Our analysis indicated that Pacific salmon in this region retain substantial evolvability as demonstrated by the persistence of over two-thirds of historical populations…it is apparent that to preserve biodiversity at multiple scales in wild Pacific salmon, both the local population and its habitat (freshwater and marine) must become the basic unit of conservation.”
“Because over one-third of the remaining populations belong to threatened or endangered species listed under the U.S. Endangered Species Act, it is apparent that a critical juncture has been reached in efforts to preserve what remains of Pacific salmon diversity.”
The historical decline in wild salmonids, with 29% of these populations now extinct and losses in the diversity of existing populations over the last 135 years of salmon management constitutes a failure of management by any measure.
Gustafuson, Robin Waples, Rick, Jim Myers, Laurie Weitkamp, G.J. Bryant, Orlay Johnson, and Jeff Hard. 2007. Pacific salmon extinctions: quantifying lost and remaining diversity. Conservation Biology (4): 1009-1020.