An estimated 29 percent of the nearly 1,400 historical salmon and steelhead "populations" that once that once ranged the West Coast have been lost since Euro-American appearance in California and the Pacific Northwest, according to a research paper published in the August edition of Conservation Biology.
The mid- and upper Columbia River stocks, and those from California's Central Valley, have been the hardest hit, according to the paper, titled "Pacific Salmon Extinctions: Quantifying Lost and Remaining Diversity."
An estimated 76 populations (100 percent) were lost in the upper Snake River (51) and Columbia River headwaters (26) regions when passage was blocked with the construction of hydro projects -- the Hells Canyon Complex on the Idaho-Oregon border and Grand Coulee in north-central Washington. In total it is estimated that 40 percent of the West's salmon and steelhead habitat is no longer accessible to the fish.
Six of the eight highest percentage losses charted in the study were in Columbia/Snake "ecological regions" --35 percent of the historic populations in the Willamette and lower Columbia have gone extinct, 52 percent in the Mid-Columbia, 62 percent in the upper Columbia (below Coulee) and 36 percent in lower Snake, in addition to the total losses in the upper Snake and Columbia headwaters regions. California's Central Valley has lost 57 percent of its estimated historic populations and the Southern California region has lost 35 percent.
The researchers identified 13 different ecological regions for the purposes of the study, ranging from Southern California up into British Columbia.
Lead author for the report is Richard G. Gustafson of the National Marine Fisheries Service's Northwest Fisheries Science Center. Also contributing were the NWFSC's Robin S. Waples, James M. Myers and Laurie A. Weitkamp, Gregory J. Bryant of NMFS' Southwest Region and Orlay W. Johnson and Jeffrey J. Hard, also of the NWFSC in Seattle.
The article can be viewed at the Conservation Biology web site, http://www.blackwell-synergy.com/doi/abs/10.1111/j.1523-1739.2007.00693.x
or copies can be obtained by contacting Gustafson at Rick.Gustafson@noaa.gov
The goal of the research was to estimate as well as possible the number of individual populations that have gone extinct within six species – chinook, chum, coho, pink and sockeye and ocean-going rainbow trout, called steelhead. The scientists then calculated the consequent loss of ecological, genetic, and life-history diversity.
Such losses can lead to extinction of evolutionarily significant units or ESUs and ultimately entire species, something that NMFS is trying to ward off in the Columbia River basin and elsewhere. ESUs are collections of related populations within species. Many have dwindled to the point of requiring listing under the Endangered Species Act.
"Any attempt to assemble a comprehensive list of historical populations and ESUs of Pacific salmon is somewhat conjectural because many extirpations likely went unnoticed before initiation of biological surveys and extensive out-of-basin stocking practices may have either replaced native populations or resulted in extensive hybridization with nonindigenous fish," according to the report.
"Nonetheless, we have attempted to establish an appropriate historical baseline (Pauly 1995) of Pacific salmon diversity because this will help identify realistic and achievable targets for ongoing conservation efforts."
The research showed "a highly significant difference in the proportion of population extinctions between coastal (0.14 extinct) and interior (0.55 extinct) regions. Sockeye salmon (which typically rely on lacustrine habitats for rearing) and stream-maturing Chinook salmon (which stay in freshwater for many months prior to spawning) had significantly higher proportional population losses than other species and maturation types."
The study showed higher proportional losses in southern versus northern coastal regions as well.
"These patterns can be attributed to a myriad of causes including differences in regional distribution of species or maturation types, regional differences in human activities (e.g., dam-building and land-use practices), and perhaps differing regional impacts of climate change," the report says.
All interior Columbia River basin coho stocks east of the Cascade Mountains were extirpated, as an example, while chinook and steelhead populations remain.
"Coho salmon may be particularly at risk due to their lengthy (>1 year) juvenile residence in freshwater (making them vulnerable to perturbations of freshwater habitat) and a nearly fixed 3-year life cycle (providing less of a buffer against year-class failure than most other salmon species)," according to the research paper. "Sockeye salmon are also particularly vulnerable, no doubt a result of that species' almost exclusive dependence for juvenile rearing on lake habitats, which have often been blocked by impassable dams."
Stream-maturing steelhead and chinook salmon had more population losses than ocean-maturing counterparts, which spawn soon after entering freshwater.
"Higher losses of stream-maturing populations are likely due to widespread loss of crucial high-elevation (generally >500 m) holding habitats and to their lengthy exposure to a host of risk factors during the prespawning holding period," the report says.
The study identified 10 extinct groups of Pacific salmon that represented either certain or likely historical ESUs that were all located in either the San Joaquin or interior Columbia river basins. Half were Columbia River sockeye salmon that occupied tributary lake habitats.
Overall losses of major ecological, life-history, and genetic biodiversity components across all species because of population extinctions are estimated at 33 percent, 15 percent, and 27 percent, respectively. That offers rays of hope for Columbia basin recovery efforts.
"Collectively, we believe these population extirpations represent a loss of between 16 percent and 30 percent of all historical ESUs in the study area," the paper says.
"On the other hand, over two-thirds of historical Pacific salmon populations in this area persist, and considerable diversity remains at all scales.
"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 paper's abstract says. "It is also evident that persistence of existing, and evolution of future, diversity will depend on the ability of Pacific salmon to adapt to anthropogenically altered habitats."
"Fortunately, our analyses indicate that Pacific salmon in this region retain substantial evolvability as demonstrated by the persistence of over two-thirds of historical populations and substantial levels of biodiversity -- testimony to the past resilience of these species despite extensive anthropogenic changes," the report concludes.