The ESA (section 3) defines the term "endangered species" as "any species which is in danger of extinction throughout all or a significant portion of its range." The term "threatened species" is defined as "any species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range." According to the ESA, the determination of whether a species is threatened or endangered should be made on the basis of the best scientific information available regarding its current status, after taking into consideration conservation measures that are proposed or are in place. In this review, we did not evaluate likely or possible effects of conservation measures. Therefore, we do not make recommendations as to whether identified ESUs should be listed as threatened or endangered species, because that determination requires evaluation of factors not considered by us. Rather, we have drawn scientific conclusions about the risk of extinction faced by identified ESUs under the assumption that present conditions will continue.
The BRT considered a variety of information in evaluating the level of risk faced by each ESU. Important considerations include 1) absolute numbers of fish and their spatial and temporal distribution; 2) current abundance in relation to historical abundance and carrying capacity of the habitat; 3) trends in abundance, based on indices such as dam or redd counts or on estimates of spawner-recruit ratios; 4) natural and human-influenced factors that cause variability in survival and abundance; 5) possible threats to genetic integrity (e.g., selective fisheries and interactions between hatchery and natural fish); and 6) recent events (e.g., a drought or a change in management) that have predictable short-term consequences for abundance of the ESU. Additional risk factors, such as disease prevalence or changes in life-history traits, may also be considered in evaluating risk to populations. The BRT conclusions for each chinook salmon ESU follow.
Presently listed as Endangered under the California and federal Endangered Species Acts; not reviewed further here.
The majority of the BRT concluded that chinook salmon in this ESU are in danger of extinction; a minority felt that this ESU is not presently in danger of extinction, but is likely to become so in the foreseeable future. The BRT identified several concerns regarding the status of this ESU. Native spring-run chinook salmon have been extirpated from all tributaries in the San Joaquin River Basin, which represents a large portion of the historic range and abundance. The only streams considered to have wild spring-run chinook salmon are Mill and Deer Creeks, and possibly Butte Creek (tributaries to the Sacramento River), and these are relatively small populations with sharply declining trends. Demographic and genetic risks due to small population sizes are thus considered to be high.
Habitat problems were considered by the BRT to be the most important source of ongoing risk to this ESU. Spring-run fish cannot access most of their historical spawning and rearing habitat in the Sacramento and San Joaquin River Basins (which is now above impassable dams), and current spawning is restricted to the mainstem and a few river tributaries in the Sacramento River. The remaining spawning habitat accessible to fish is severely degraded. Collectively, these habitat problems greatly reduce the resiliency of this ESU to respond to additional stresses in the future. The general degradation of conditions in the Sacramento River Basin (including elevated water temperatures, agricultural and municipal diversions and returns, restricted and regulated flows, entrainment of migrating fish into unscreened or poorly screened diversions, and the poor quality and quantity of remaining habitat) has severely impacted important juvenile rearing habitat and migration corridors.
The BRT also expressed concern for threats to genetic integrity posed by hatchery programs in the Central Valley. Most of the spring-run chinook salmon production in the Central Valley is of hatchery origin, and naturally spawning populations may be interbreeding with both fall- and spring-run hatchery fish. This problem is exacerbated by the increasing production of spring-run chinook salmon from the Feather River and Butte Creek Hatcheries, especially in light of reports suggesting a high degree of mixing between spring- and fall-run broodstock in the hatcheries. In addition, hatchery strays are considered to be an increasing problem due to the management practice of releasing a larger proportion of fish off-station (primarily into the Sacramento River delta and San Francisco Bay).
A majority of the BRT concluded that chinook salmon in this ESU are not in danger of extinction but are likely to become so in the foreseeable future. A minority of the BRT felt that chinook salmon in this ESU are not presently at significant risk or were undecided on its status. Although total population abundance in this ESU is relatively high, perhaps near historical levels, the BRT identified several concerns regarding its status. The abundance of natural fall-run chinook salmon in the San Joaquin River Basin is low, leading a number of BRT members to conclude that a large proportion of the historic range of this ESU has been lost or is in danger of extinction. Most of the historical spawning habitat for this ESU is downstream from impassable dams, so habitat blockage is not as severe as for winter- and spring-run chinook salmon in this region. However, there has been a severe degradation of the remaining habitat, especially due to agricultural and municipal water use activities in the Central Valley (which result in point and non-point pollution, elevated water temperatures, diminished flows, and smolt and adult entrainment into poorly screened or unscreened diversions).
Natural runs throughout the ESU are very depressed. Returns to hatcheries account for only about 20% of fall-run chinook salmon spawners in the Central Valley; however, due to high rates of straying by hatchery fish released off-station, production from hatcheries may be responsible for a much larger proportion of natural spawning escapement. A mitigating factor for the overall risk to the ESU is that a few of the Sacramento and San Joaquin River Basin tributaries are showing recent, short-term increases in abundance. However, those streams supporting natural runs considered to be the least influenced by hatchery fish have the lowest abundance and the most consistently negative trends of all populations in the ESU. In general, high hatchery production combined with infrequent monitoring of natural production make assessing the sustainability of natural production problematic, resulting in substantial uncertainty in assessing the status of this ESU.
Other concerns identified by the BRT are the high ocean and freshwater harvest rates in recent years, which may be higher than is sustainable by natural populations given the productivity of the ESU under present habitat conditions.
The BRT was unanimous in its conclusion that chinook salmon in this ESU are likely to become at risk of extinction in the foreseeable future. Overall abundance of spawners is highly variable among populations, with populations in California and spring-run chinook salmon throughout the ESU being of particular concern. There is a general pattern of downward trends in abundance in most populations for which data are available, with declines being especially pronounced in spring-run populations. The BRT felt that the extremely depressed status of almost all coastal populations south of the Klamath River is an important source of risk to the ESU. There was a general concern expressed by the BRT that no current information was available for many river systems in the southern portion of this ESU, which historically maintained numerous large populations. These populations form a genetically distinct subgroup within the ESU. Although (as discussed above) the majority of the BRT concluded that these California coastal populations do not form a separate ESU, they represent a considerable portion of genetic and ecological diversity within this ESU.
Current hatchery contribution to overall abundance is relatively low except for the Rogue River spring run, which also contains almost all of the documented spring-run abundance in this ESU. Fall-run chinook salmon in the Rogue River represent the only relatively healthy population we could identify in this ESU. The BRT questioned whether there are sustainable populations outside the Rogue River Basin. All river basins have degraded habitats resulting from agricultural and forestry practices, water diversions, urbanization, mining, and severe recent flooding. The BRT was very concerned about the risks to spring-run chinook in this ESU; their stocks are in low abundance and they have continued to decline dramatically in recent years. In addition, the lack of population monitoring, particularly in the California portion of the range, led to a high degree of uncertainty regarding the status of these populations.
A majority of the BRT concluded that chinook salmon in this ESU are not at significant risk of extinction nor likely to become so in the forseeable future. One minority concluded that the ESU is not presently in danger of extinction but is likely to become so in the foreseeable future, while another minority was undecided about the status of this ESU. The question of overall risk was difficult to evaluate because of the large disparity in the status of spring- and fall-run populations within the ESU.
Spring-run chinook salmon were once the dominant run type in the Klamath-Trinity River Basin. Most spring-run spawning and rearing habitat was blocked by the construction of dams in the late 1800s and early 1900s in the Klamath River Basin and in the 1960s in the Trinity River Basin. As a result of these and other factors, spring-run populations are at less than 10% of their historic levels, and at least 7 spring-run populations that once existed in the basin are now considered extinct. The remaining spring runs have relatively small populations sizes and are isolated in just a few areas of the basin, resulting in genetic and demographic risks.
On a more positive note, trends in abundance for some populations in this ESU are stable or increasing slightly. Substantial numbers of fall-run chinook salmon spawn naturally in many areas of the ESU. However, natural populations have frequently failed to meet modest spawning escapement goals despite active harvest management. In addition to habitat blockages, there continues to be severe degradation of remaining habitat due to mining, agricultural and forestry activities, and water storage and transfer. Furthermore, hatchery production in the basin is substantial, with considerable potential for interbreeding between natural and hatchery fish. The BRT expressed concern that hatchery fish spawning naturally may mask declines in natural populations.
In summary, all BRT members were concerned about the depressed status of spring-run chinook salmon in this ESU, and the loss of access to a large proportion of historical habitat. However, the majority concluded that, because of the relative health of the fall-run populations, the ESU as a whole is not currently at significant risk of extinction.
The BRT unanimously concluded that chinook salmon in this ESU are neither presently in danger of extinction nor are they likely to become so in the foreseeable future. Abundance of this ESU is relatively high, and fish are well distributed among numerous, relatively small river basins. Some suitable spawning habitat remains blocked, but access of chinook salmon to spawning areas is better than it was at the turn of the century.
Production in this ESU is mostly dependent on naturally-spawning fish, and spring-run chinook salmon in this ESU are in relatively better condition than those in adjacent ESUs. Long-term trends in abundance of chinook salmon within most populations in this ESU are upward.
In spite of a generally positive outlook for this ESU, the BRT identified several concerns regarding its status. First, several populations are exhibiting recent and severe (> 9% per year) short-term declines in abundance. In addition, while hatchery production is not as pervasive as in other ESUs, there are several hatchery programs and Salmon and Trout Enhancement Programs (STEP) releasing chinook salmon throughout the ESU, and many of the fish released are derived from a single stock (Trask River). Most importantly, although hatchery production is thought to be low relative to natural production, there is a lack of clear information on the degree of straying of these hatchery fish into naturally-spawning populations. There are also many populations within the ESU for which there are no abundance data; the BRT expressed concern about the uncertain risk assessment given these data gaps. Third, exploitation rates on chinook salmon from this ESU have been high in the past, and the BRT felt that the level of harvest could be a significant source of risk if it continues at historically high rates. Finally, freshwater habitats are generally in poor condition, with numerous problems such as low summer flows, high temperatures, loss of riparian cover, and streambed changes.
The BRT unanimously concluded that chinook salmon in this ESU are not in danger of extinction nor are they likely to become so in the foreseeable future. Recent abundance has been relatively high, although it is less than estimated peak historical abundance in this region. Chinook salmon in this ESU are distributed among a relatively large number of populations, most of which are large enough to avoid serious genetic and demographic risks associated with small populations.
Long-term trends in population abundance have been predominantly upward for the medium and larger populations but are sharply downward for several of the smaller populations. In addition, the BRT was concerned about significant short-term declines in abundance that have been observed in several populations. In general, abundance and trend indicators are more favorable for stocks in the northern portion of the ESU, and more favorable for fall-run populations than for spring- or summer-run fish. This disparity was a source of concern to the BRT regarding the overall health of the ESU.
Hatchery production is substantial in several basins within the range of the ESU, and several populations are identified as being of composite production. There is considerable potential for hatchery fish to stray into natural populations, especially since some hatcheries are apparently unable to attract returning adults effectively. Hatchery influence is greatest in the southern part of the ESU region, especially in Willapa Bay, where there have been numerous introductions of stocks from outside of the ESU. Furthermore, the use of an exotic spring-run stock at the Sol Duc Hatchery was cited as a concern.
All basins are affected by habitat degradation, largely related to forestry practices. Tributaries inside Olympic National Park are generally in the best condition regarding habitat quality. Special concern was expressed regarding the status of spring-run populations throughout the ESU and fall-run populations in Willapa Bay and parts of the Grays Harbor drainage.
A majority of the BRT concluded that chinook salmon in this ESU are not presently in danger of extinction, but they are likely to become so in the foreseeable future. A minority concluded that this ESU is not presently at significant risk or were uncertain about its status. Overall abundance of chinook salmon in this ESU has declined substantially from historical levels, and many populations are small enough that genetic and demographic risks are likely to be relatively high. Contributing to these reduced abundances are widespread stream blockages, which reduce access to spawning habitat, especially in upper reaches. Both long- and short-term trends in abundance are predominantly downward, and several populations are exhibiting severe short-term declines. Spring-run chinook salmon populations throughout this ESU are all depressed.
Tens of millions of hatchery fish have been released annually throughout the ESU. More than half of the recent total Puget Sound escapement returned to hatcheries. The BRT was concerned that the preponderance of hatchery production throughout the ESU may mask trends in natural populations and makes it difficult to determine whether they are self-sustaining. This difficulty is compounded by the dearth of data pertaining to proportion of naturally spawning fish that are of hatchery origin. There has also been widespread use of a limited number of hatchery stocks, resulting in increased risk of loss of fitness and diversity among populations.
Freshwater habitat throughout the range of the ESU has been blocked or degraded, with upper tributaries widely affected by poor forestry practices and lower tributaries and mainstem rivers affected by agriculture and urbanization. There also is concern that harvest rates of natural stocks in mixed-stock fisheries may be excessive, as evidenced by recent declines in most stocks managed for natural escapement despite curtailed terminal fisheries. Finally, special concern was expressed regarding the status of spring- and summer-run populations.
A majority of the BRT concluded that chinook salmon in this ESU are not presently in danger of extinction but are likely to become so in the foreseeable future. A minority felt that this ESU is not presently at significant risk or were uncertain as to its status. Estimated overall abundance of chinook salmon in this ESU is not cause for immediate concern. However, apart from the relatively large and apparently healthy fall-run population in the Lewis River, production in this ESU appears to be predominantly hatchery-driven with few identifiable native, naturally reproducing populations. Long- and short-term trends in abundance of individual populations are mostly negative, some severely so. About half of the populations comprising this ESU are very small, increasing the likelihood that risks due to genetic and demographic processes in small populations will be important. Numbers of naturally spawning spring-run chinook salmon are very low, and native populations in the Sandy and Clackamas Rivers have been supplanted by spring-run fish from the Upper Willamette River. There have been at least six documented extinctions of populations in this ESU, and it is possible that extirpation of other native populations has occurred but has been masked by the presence of naturally spawning hatchery fish. The BRT was particularly concerned about the inability to identify any healthy native spring-run populations.
The large numbers of hatchery fish in this ESU make it difficult to determine the proportion of naturally produced fish. In spite of the heavy impact of hatcheries, genetic and life-history characteristics of populations in this ESU still differ from those in other ESUs. The BRT, however, identified the loss of fitness and diversity within the ESU as an important concern. There was a special concern regarding recent releases of Rogue River fall-run fish at Youngs Bay and their documented straying into many tributaries in the Lower Columbia River.
Freshwater habitat is in poor condition in many basins, with problems related to forestry practices, urbanization, and agriculture. Dam construction on the Cowlitz, Lewis, White Salmon, and Sandy Rivers eliminated access to a substantial portion of the spring-run spawning habitat, with a lesser impact on fall-run habitat.
A majority of the BRT concluded that chinook salmon in this ESU are not presently in danger of extinction but are likely to become so in the foreseeable future. A minority felt that this ESU is not presently at significant risk or were uncertain as to its status, and one member considered this ESU to be at risk of extinction. Total abundance has been relatively stable at approximately 20,000 to 30,000 fish; however, recent natural escapement is less than 5,000 fish and has been declining sharply. Furthermore, it is estimated that about two-thirds of the natural spawners are first-generation hatchery fish, suggesting that the natural population is falling far short of replacing itself. The BRT noted a similarity between these population dynamic parameters and those for the upper Columbia River steelhead ESU, which was recently listed as endangered by NMFS.
The introduction of fall-run chinook salmon into the basin and laddering of Willamette Falls have increased the potential for genetic introgression between wild spring- and hatchery fall-run chinook salmon, but there is no direct evidence of hybridization (other than an overlap in spawning times and spawning location) between these two runs.
The proximate sources of risk to chinook salmon in this ESU are habitat blockage of large areas of important spawning and rearing habitat by dam construction. Remaining habitat has been degraded by thermal effects of dams, forestry practices, agriculture, and urbanization. Another concern for this ESU is that commercial and recreational harvest are high relative to the apparent productivity of natural populations.
The BRT agreed that chinook salmon in this ESU are not presently in danger of extinction nor likely to become so in the foreseeable future. The majority of the BRT concluded that the ESU is not at significant risk at the present time, although a minority of BRT members felt that the ESU is likely to become at risk of extinction in the foreseeable future. Total abundance of this ESU is low relative to the total basin area, and 1994-96 escapements have been very low. Several historical populations have been extirpated, and the few extant populations in this ESU are not widely distributed geographically. In addition, there are only two populations (John Day and Yakima Rivers) with substantial run-sizes.
Despite of low abundances relative to estimated historical levels, long-term trends in abundance have been relatively stable, with an approximately even mix of upward and downward trends in populations. Two major river basins (John Day and Yakima Rivers) are comprised predominantly of naturally produced fish, and both of these exhibit long-term increasing trends in abundance. Recent analyses done as part of the PATH process indicates that productivity of natural populations in the Deschutes and John Day Rivers has been more robust that most other stream-type chinook salmon in the Columbia River (Schaller et al. 1996).
Hatchery production accounts for a substantial proportion of total escapement to the region. However, screening procedures at the Warm Springs River weir apparently minimize the potential for hatchery-wild introgression in the Deschutes River basin. Although straying is less of a problem with returning spring-run adults, the use of the composite, out-of-ESU Carson Hatchery stock to reestablish the Umatilla River spring run would be a cause for concern if fish from that program stray out of the basin.
Spawning and rearing habitat has been affected by agriculture (water withdrawals, livestock grazing, and agricultural effluents) throughout the range of the ESU, and migration corridors have been affected substantially by hydroelectric development. In addition, lack of agreement between run-size estimates based on dam counts and spawner surveys contribute to the uncertainty in evaluating this ESU.
In an earlier review, this ESU was determined to be neither at risk of extinction nor likely to become so. Its status is not reviewed in detail here. However, the BRT did express concern regarding new data that show the proportion of naturally spawning summer-run chinook salmon of hatchery origin has been increasingly rapidly in areas above Wells Dam. This raises a question about the sustainability of natural populations in that area and is also a concern because of possible genetic/life-history consequences of the shift in hatchery releases from subyearlings to yearlings.
The majority of the BRT concluded that chinook salmon in this ESU are in danger of extinction. A minority concluded that this ESU is not presently in danger of extinction, but it is likely to become so in the foreseeable future. Recent total abundance of this ESU is quite low, and escapements in 1994-96 were the lowest in at least 60 years. At least 6 populations of spring-run chinook salmon in this ESU have become extinct, and almost all remaining naturally-spawning populations have fewer than 100 spawners. The BRT expressed concern about the genetic and demographic risks associated with such small populations. In addition to extremely small population sizes, both recent and long-term trends in abundance are downward, some extremely so.
Hydrosystem development has substantially affected this ESU. Grande Coulee Dam blocked access to important spawning and rearing habitat, and downstream dams are an impediment to migration (both juvenile and adult fish from this ESU must navigate past as many as nine mainstem dams). The BRT also had substantial concerns over degradation of the remaining spawning and rearing habitat.
Risks associated with interactions between wild and hatchery chinook salmon are also a concern, as there continues to be substantial production of the composite, non-native Carson stock for fishery enhancement and hydropower mitigation. For example, estimates of hatchery contribution to natural spawning escapements are 39% in the Methow River Basin.
Snake River fall-run chinook salmon are currently listed as a threatened species under the ESA. As discussed above, the BRT concluded that the Snake River fall-run ESU also includes fall-run chinook salmon in the Deschutes River and, historically, populations from the John Day, Umatilla, Walla Walla Rivers that have been extirpated in the 20th century.
Assessing extinction risk to the newly configured ESU is difficult because of the geographic discontinuity and the disparity in the status of the two remaining populations. Historically, the Snake River populations dominated production in this ESU; total abundance is estimated to have been about 72,000 in the 1930s and 1940s, and it was probably substantially higher before that. Production from the Deschutes River was presumably only a small fraction of historic production in the ESU. In contrast, recent (1990-96) returns of naturally spawning fish to the Deschutes River (about 6,000 adults per year) have been much higher than in the Snake River (5-year mean about 500 adults per year, including hatchery strays). Long term trends in abundance are mixed--slightly upward in the Deschutes River and downward in the Snake River. On a more positive note, short-term trends in both remaining populations are upward.
In spite of the relative health of the Deschutes River population, a majority of the BRT concluded that the ESU as a whole is likely to be in danger of extinction in the foreseeable future, with the remainder being undecided on its status. The BRT was concerned that almost all historical spawning habitat in the Snake River Basin was blocked by the Hells Canyon Dam complex, and other habitat blockages have occurred in Columbia River tributaries. Hydroelectric development on the mainstem Columbia and Snake Rivers continues to affect juvenile and adult migration. Remaining habitat has been reduced by inundation in the mainstem Snake and Columbia Rivers, and the ESU's range has also been affected by agricultural water withdrawals, grazing, and vegetation management.
An additional source of risk to the Snake River chinook salmon is the continued straying by non-native hatchery fish into natural production areas. The BRT also noted that considerable uncertainty regarding the origins of fall-run chinook salmon in the lower Deschutes River and their relationship to fish in the upper Deschutes River.
This ESU is presently listed as a threatened species under the U.S. ESA and is not reviewed further here.