U.S. Dept Commerce/NOAA/NMFS/NWFSC/Publications NOAA-NWFSC Tech Memo-19: Status Review for Klamath Mountains Province Steelhead NOAA Technical Memorandum NMFS-NWFSC-19Status Review for Klamath Mountains Province SteelheadPeggy J. Busby, Thomas C. Wainwright, and Robin S.       WaplesNational Marine Fisheries ServiceNorthwest       Fisheries Science CenterCoast Zone and Estuarine Studies       Division2725 Montlake Blvd. E.Seattle WA 98112-2097       
December 1994
U.S. DEPARTMENT OF COMMERCERonald H. Brown,       Secretary       
National Oceanic and Atmospheric AdministrationD.       James Baker, Administrator

National Marine Fisheries ServiceRolland A.       Schmitten, Assistant Administrator for Fisheries 
CONTENTS- Summary   
- Acknowledgments   
- Introduction    
- Scope   of Present Status Review   
- Key   Questions in ESA Evaluations  
- The   "Species" Question 
- Hatchery   Fish and Natural Fish 
- Thresholds   for Threatened or Endangered Status   
- Summary   of Information Relating to the Species Question    - Environmental     Features 
  - Ecoregions     and Zoogeography 
  - Klamath     Mountains Geological Province 
  - California     Current System 
  - In-Stream     Water Temperature 
  - Life     History 
  - Anadromy-Nonanadromy      
  - Steelhead     Run-Types 
  - Age     Structure 
  - Half-Pounders 
  - Oceanic     Migration Patterns  
  - Straying      
  - History     of Hatchery Stocks and Outplantings  
  - Steelhead     Hatcheries  
  - Oregon     Hatchery Stocks  
  - California     Hatchery Stocks  
  - Population     Genetic Structure 
  - Previous     Studies  
  - New     Data  
  - Discussion     and Conclusions on the Species Question 
  - Reproductive     Isolation  
  - Ecological/Genetic     Diversity  
  - Conclusions 
- Abundance   and Threshold Determination    - Population     Trends 
  - Coastwide     Overview of Steelhead Abundance 
  - Historical     Abundance in Southern Oregon and Northern California  
  - The     Threshold Question  
  - Reductions     in Available Steelhead Habitat  
  - Dams      
  - Other     Activities  
  - Discussion and Conclusions on the Status of the ESU  
  - Threshold     Assessment  
  - Conclusion    - Citations   
  - Appendix     A - Glossary   
  - Appendix     B - Stock Abundance and Trends     SUMMARY   The Endangered Species Act (ESA) allows listing of "distinct population   segments" of vertebrates as well as named species and subspecies. The policy   of the National Marine Fisheries Service (NMFS) on this issue for Pacific   salmon and steelhead is that a population will be considered "distinct" for   purposes of the ESA if it represents an Evolutionarily Significant Unit (ESU)   of the species as a whole. To be considered an ESU, a population or group of   populations must 1) be substantially reproductively isolated from other   populations, and 2) contribute substantially to ecological/genetic diversity   of the biological species. Once an ESU is identified, a variety of factors   related to population abundance are considered in determining whether a   listing is warranted. NMFS received a petition in May 1992 asking that winter   steelhead of Oregon's Illinois River be listed as a threatened or endangered   species under the ESA. In May 1993, NMFS published a Federal Register notice   concluding that Illinois River winter steelhead did not by themselves   constitute a species as defined by the Endangered Species Act (ESA). At the   same time, NMFS indicated that it would undertake a broader status review to   determine the boundaries of the Evolutionarily Significant Unit (ESU) that   contains Illinois River winter steelhead and determine whether this broader   group was threatened or endangered. This report summarizes biological and   environmental information gathered in that status review  Based on genetic, life history, zoogeographic, geologic, and environmental   information, we conclude that the ESU that contains Illinois River winter   steelhead extends from the vicinity of Cape Blanco in southern Oregon to the   Klamath River Basin (inclusive) in northern California. These are essentially   the boundaries of a prominent geologic feature known as the Klamath Mountains   Province. Both winter- and summer-run steelhead are included in this ESU, as   well as populations sometimes referred to as "fall-run" in California. Within   this geographic area, most steelhead populations show a declining trend in   abundance, and 10 stocks have been identified in independent stock assessment   reports as being at moderate or high risk of extinction. Furthermore, the   declines are even more dramatic when only natural fish (progeny of naturally   spawning fish) are considered. We conclude that steelhead within this ESU are   likely to become endangered in the foreseeable future.     ACKNOWLEDGMENTS   This review was conducted, in effect, as a continuation of the status   review for Illinois River winter steelhead (Busby et al. 1993). Although the   legal requirements for responding to the Illinois River winter steelhead   petition were fulfilled by the initial status review, which concluded that the   petitioned population was not a "species" under the Endangered Species Act,   the National Marine Fisheries Service Directorate initiated this extended   status review, and the authors of this Technical Memorandum would like to   acknowledge their support.  As with all ESA status reviews, information submitted by agencies,   organizations, and individuals was invaluable. The authors acknowledge the   efforts of all who contributed to the Administrative Record.  The biological review team for this status review included: Peggy Busby,   Dr. David Damkaer, Robert Emmett, Dr. Stephen Grabowski, Dr. Jeffrey Hard, Dr.   Orlay Johnson, Dr. Conrad Mahnken, Gene Matthews, Dr. Michael Schiewe, Dr.   Thomas Wainwright, William Waknitz, Dr. Robin Waples, Laurie Weitkamp, Dr.   John Williams, and Dr. Gary Winans.     INTRODUCTION   In May 1992, the National Marine Fisheries Service (NMFS) received a   petition (ONRC et al. 1992) to list southwest Oregon's Illinois River winter   steelhead (Oncorhynchus mykiss) as a threatened or endangered "species" under   the U.S. Endangered Species Act (ESA) of 1973 as amended (U.S.C. 1531 et   seq.). A status review completed in May 1993 (Busby et al. 1993, NMFS 1993)   concluded that winter steelhead of the Illinois River, a tributary to the   Rogue River (Fig. 1), did not by itself constitute a species under the ESA.   However, it was also concluded that steelhead from the Illinois River are part   of a larger Evolutionarily Significant Unit (ESU) whose boundaries remained to   be determined. Whether the larger ESU that contains Illinois River winter   steelhead would merit protection under the ESA could not be determined until   the nature and extent of the ESU were identified and additional information   about patterns of abundance in coastal steelhead was compiled.  On 20 May 1993, NMFS published a Federal Register notice (NMFS 1993)   initiating a status review of coastal steelhead populations in California,   Oregon, and Washington for the purpose of identifying ESU(s) in these areas   and determining whether listing under the ESA was warranted for any identified   ESU. The present report summarizes information considered in this status   review relative to the ESU that includes Illinois River winter steelhead.  The biological species Oncorhynchus mykiss includes several forms   of nonanadromous and anadromous trout, including rainbow trout, redband trout,   and steelhead (the name applied to the anadromous form of the species).   Taxonomy of O. mykiss, and the relationship between the various   forms, has been well studied, yet remains challenging (e.g., Kendall 1920,   Snyder 1940, Behnke 1992). Behnke (1992) proposed that there are seven or   eight subspecies within O. mykiss (Table   1). Figure 1. Map showing the Illinois River and other key   geographic locations discussed in this status review. See Figure   2 for detail.     Table 1. Proposed taxonomy of various forms   (subspecies) of Oncorhynchus mykiss (Behnke 1992).    Scientific nameCommon name and commentsRainbow trout of coastal basinsO. mykiss irideusCoastal rainbow trout from Alaska to California         (anadromous form is called steelhead)O. mykiss mykissKamchatka rainbow trout or mikizha (anadromous form is         called steelhead)Redband trout of northern inland basinsO. mykiss gairdneriColumbia redband trout of the Columbia and Fraser River         Basins east of the Cascades, including Kamloops trout (anadromous form         is called steelhead)Redband trout of eastern Oregon basinsO. mykiss newberriiUpper Klamath redband trout (including Upper Klamath       Lake)(no name given)Oregon desert basin redband trout (other than Upper         Klamath Lake)Redband trout of the Sacramento BasinO. mykiss aguabonitaCalifornia golden troutO. mykiss gilbertiKern and Little Kern River golden troutO. mykiss stoneiSacramento redband trout (McCloud River     subspecies)  Two major genetic groups of O. mykiss are presently recognized:   the inland and coastal groups, separated by the Cascade crest (Huzyk and   Tsuyuki 1974, Allendorf 1975, Utter and Allendorf 1977, Okazaki 1984,   Parkinson 1984, Schreck et al. 1986, Reisenbichler et al. 1992). Both inland   and coastal steelhead occur in British Columbia, Washington, and Oregon; Idaho   has only inland steelhead; California has only coastal steelhead. Based on   Schreck et al. (1986), the demarcation between coastal and inland steelhead in   the Columbia River Basin occurs between the Hood River and Fifteenmile Creek   in Oregon and between the Klickitat River and Rock Creek in Washington (i.e.,   in the vicinity of The Dalles Dam). These genetic groups apply to both   anadromous and nonanadromous forms of O. mykiss; that is, rainbow   (redband) trout east of the Cascades are genetically more similar to steelhead   from east of the Cascades than they are to rainbow trout west of the Cascades.   Behnke's (1992) terminology for subspecies of O. mykiss reflects this   genetic difference. Coastal rainbow trout of North America, as well as coastal   steelhead, are placed in the subspecies O. m. irideus (Behnke 1992).   The inland Columbia redband trout of the Columbia and Fraser River Basins, as   well as inland steelhead, are placed in the subspecies O. m.   gairdneri (Behnke 1992). Illinois River winter steelhead fall within the   coastal group, subspecies O. m. irideus.  Present distribution of coastal steelhead in Washington, Oregon, and   California extends from the U.S.-Canada border south to Malibu Creek,   California. Within this distribution are two major life-history types:   summer-run (summer steelhead) and winter-run (winter steelhead). These   run-types are primarily differentiated by time and duration of spawning   migration and state of sexual maturity at the time of river entry. Summer   steelhead enter fresh water between May and October, in a sexually immature   condition. After several months in fresh water, summer steelhead mature and   spawn. Winter steelhead enter fresh water between November and April with   well-developed gonads and spawn shortly thereafter. Both summer and winter   steelhead are found in some drainages, including the Rogue River Basin of   southwest Oregon. The Illinois River is generally considered to have only   winter-run steelhead.     Scope of Present Status Review   The environmental and biological information developed in the Illinois   River winter steelhead status review (Busby et al. 1993) indicated that the   ESU that contains that population might extend somewhat north of the Rogue   River Basin and south into northern California. Therefore, the present status   review concentrates on environmental and biological information for that   geographic area.     KEY QUESTIONS IN ESA EVALUATIONS   Two key questions must be addressed in determining whether a listing under   the ESA is warranted:   1) Is the entity in question a "species" as defined by the ESA?     
2) If so, is the "species" threatened or endangered?
     The "Species" Question   As amended in 1978, the ESA allows listing of "distinct population   segments" of vertebrates as well as named species and subspecies. However, the   ESA provided no specific guidance for determining what constitutes a distinct   population, and the resulting ambiguity led to the use of a variety of   criteria in listing decisions over the past decade. To clarify the issue for   Pacific salmon, NMFS published a policy describing how the agency will apply   the definition of "species" in the ESA to anadromous salmonid species,   including sea-run cutthroat trout and steelhead (NMFS 1991). A more detailed   description of this topic appeared in the NMFS "Definition of Species" paper   (Waples 1991). The NMFS policy stipulates that a salmon population (or group   of populations) will be considered "distinct" for purposes of the ESA if it   represents an evolutionarily significant unit (ESU) of the biological species.   An ESU is defined as a population that 1) is substantially reproductively   isolated from conspecific populations and 2) represents an important component   in the evolutionary legacy of the species. Information that can be useful in   determining the degree of reproductive isolation includes incidence of   straying, rates of recolonization, degree of genetic differentiation, and the   existence of barriers to migration. Insight into evolutionary significance can   be provided by data on genetic and life-history characteristics, habitat   differences, and the effects of stock transfers or supplementation efforts.     Hatchery Fish and Natural Fish   Because artificial propagation of Pacific salmonids has been widespread for   many years, the influence of hatchery fish needs to be considered in most ESA   status reviews. NMFS policy stipulates that in determining whether a   population is distinct for purposes of the ESA, attention should focus on   "natural" fish, which are defined as the progeny of naturally spawning fish   (Waples 1991). This approach directs attention to fish that spend their entire   life cycle in natural habitat and is consistent with the mandate of the ESA to   conserve threatened and endangered species in their native ecosystems.   Implicit in this approach is the recognition that fish hatcheries are not a   substitute for natural ecosystems.  The decision to focus on natural fish is based entirely on ecosystem   considerations; the question of the relative merits of hatchery vs. natural   fish is a separate issue. Fish are not excluded from ESA consideration simply   because some of their direct ancestors may have spent time in a fish hatchery,   nor does identifying a group of fish as "natural" as defined here   automatically mean that they are part of a listed ESU. For a discussion of   artificial propagation of Pacific salmon under the ESA, see Hard et al.   (1992).     Thresholds for Threatened or Endangered   Status   The ESA (sec. 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." Neither NMFS nor the   U.S. Fish and Wildlife Service (USFWS), which share authority for   administering the ESA, has an official policy interpreting these definitions   in terms of thresholds for considering ESA "species" as threatened or   endangered. An information document on this topic (Thompson 1991) published by   NMFS suggests that conventional rules of thumb, analytical approaches, and   simulations may all be useful in making this determination. There is   considerable interest in incorporating the concepts of population viability   analysis (PVA) into ESA threshold considerations for Pacific salmon. However,   available PVA models generally require substantial life-history information   that is not available for most Pacific salmon populations, so quantitative PVA   is not practical at this time.  Therefore, NMFS considers a variety of information in evaluating the level   of risk faced by an ESU. Important factors 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.  In evaluating these factors, the role of artificial propagation is an   important issue. Because of the ESA's emphasis on conserving species in their   native ecosystems, threshold determinations must focus on the status of   natural fish.  Artificial production may have direct or indirect impacts on the status of   a population through direct supplementation of numbers, by altering the   genetic composition of the population, or through ecological interactions   (competition, predation, disease transmission, etc.) between   artificially-produced and natural fish. A mixture of artificially-produced and   natural fish in a population also makes assessment of the natural fish   difficult: abundance and viability of the natural stock is difficult to   estimate unless artificially-produced fish are clearly marked, and trends in   the natural stock can be obscured by the infusion of artificially-produced   fish and their progeny into the natural population. An important question for   many natural populations is the following: Is natural production sufficient to   maintain the population without the constant infusion of artificially-produced   fish?  According to the ESA, the determination 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 (recognizing, of   course, that natural demographic and environmental variability is an inherent   feature of "present conditions").     SUMMARY OF INFORMATION RELATING TO THE SPECIES   QUESTION   In this section, we summarize biological and environmental information that   is relevant to determining the nature and extent of the ESU that includes   Illinois River winter steelhead. Information presented in this section forms   the basis for conclusions regarding the species and threshold questions, which   are addressed in the following section.     Environmental Features   Ecoregions and Zoogeography   Many efforts have been made to describe and classify the distributions of   the Earth's plant and animal species and their habitats. These have resulted   in the development of several classification schemes for continental and   marine environments.  Bailey (1976, 1980), Omernik and Gallant (1986), and Omernik (1987) used   geologic, edaphic, climatic, and vegetational patterns to delineate ecoregions   for the United States. Franklin and Dyrness (1973) used similar information to   delineate physiographic provinces for Oregon and Washington. Most recently,   the Forest Ecosystem Management Assessment Team (FEMAT) delineated aquatic and   terrestrial physiographic provinces for the northern spotted owl region (USFS   and BLM 1994).  Zoogeographic regions and provinces in the marine environment have been   described using climate and faunal distribution. Allen and Smith (1988)   discussed the marine zoogeographic literature and presented zoogeographic   regions and provinces and marine life zones for the North Pacific Ocean and   Bering Sea. Within the Oregonian Province, Allen and Smith (1988, p. 144)   found that Cape Mendocino, California "is an important southern limit (at   least in abundance) of many northern species" of marine fish.  Ichthyogeography--Snyder (1907) may have been the first to   attempt to categorize the freshwater ichthyofauna of Oregon and California   into geographic groups. Based on phenotypic characteristics and assemblages of   fluvial fish species, Snyder (1907) identified three ichthyofaunal groups for   the coastal area between the Columbia and Sacramento Rivers: Columbia River   Fauna, Klamath River Fauna, and Sacramento River Fauna. The Columbia River   faunal group included basins north of the Rogue River. The Klamath River   faunal group included the Rogue and Klamath River Basins. The Sacramento River   faunal group included rivers south of the Klamath Basin.  Moyle (1976) discussed the zoogeography of inland fish of California. He   noted that the Klamath smallscale sucker (Catostomus rimiculus) is common to   both the Rogue and Klamath Rivers, yet the Rogue River "lacks other Klamath   fishes, such as speckled dace [Rhinichthys osculus] and marbled sculpin   [Cottus klamathensis], and contains reticulate sculpin [C. perplexus], a   species abundant in coastal streams further north" (Moyle 1976, p. 15). Moyle   considered coastal streams of northern California (south of the Klamath River)   to be part of the Sacramento River inland fish fauna, as did Snyder (1907).   Moyle specifically noted that "the Mad, Eel, Bear, Navarro, Gualala, and   Russian rivers, as well as three tributaries to Tomales Bay (Walker,   Papermill, and Olema creeks) all contain freshwater fishes derived from the   Sacramento-San Joaquin River system" (p. 17).  Hughes et al. (1987) described ichthyogeographic regions in Oregon based on   the distribution of 68 native fish species. They found a similarity between   these ichthyogeographic regions and the physiographic provinces of Franklin   and Dyrness (1973) and the aquatic ecoregions of Omernik (1987). Hughes et al.   concluded that seven ichthyogeographic regions could be delineated in Oregon.   Coastal steelhead are known from all of these regions except the Blue   Mountains region, which contains inland steelhead, and the Endorheic Lakes   region of eastern Oregon, which contains redband trout.  Physiographic and zoogeographic classification of southwest   Oregon--With respect to the above, the Illinois River (Rogue River   Basin) of southwest Oregon falls within the Coast Range and Sierra Nevada   ecoregions of Omernik (1987) and the Klamath Mountains physiographic region of   Franklin and Dyrness (1973) and FEMAT (USFS and BLM 1994). The Rogue River   Basin is within the Rogue River/Sierra Nevada ichthyogeographic region of   Hughes et al. (1987) and the Klamath/Siskiyou and Franciscan aquatic   ecosystems physiographic provinces of FEMAT (USFS and BLM 1994). The Rogue   River Basin shares some inland ichthyofaunal commonalities with the Klamath   River to the south, as well as with some streams to the north (Snyder 1907,   Moyle 1976, Behnke 1992). Each of the studies cited above has consistently   delineated an ecoregion, that includes the Illinois River, that largely   corresponds with a geological feature known as the Klamath Mountains   Geological Province.   Klamath Mountains Geological Province   The Klamath Mountains Geological Province includes a complex of mountain   ranges in southwest Oregon and northwest California (Fig.   2). Collectively, these are called the Klamath Mountains; they include the   Trinity Alps, Salmon Mountains, Marble Mountains, and Siskiyou Mountains   (Wallace 1983). Ecologically, the region is classified in the Marine Division   of the Humid Temperate Domain (Bailey 1980); however, it exhibits influence   from the warmer, drier Mediterranean Division (Atzet   - footnote 1). This region includes diverse localized climates including   cool, wet coastal areas and hot, dry interior valleys that receive less   precipitation than any other location in the Pacific Northwest west of the   Cascade Range (Franklin and Dyrness 1973). For example, average annual   precipitation in the interior Rogue River valley ranges between 30 and 94 cm   (Oregon Water Resources Committee 1955), while at Cave Junction in the middle   Illinois Valley it is 152 cm, and Gold Beach at the mouth of the Rogue River   receives 229 cm (USFS 1989).  The Siskiyou Mountains include northern extensions of geological formations   typical of those found in the California Coast Ranges and the Sierra Nevada   (Franklin and Dyrness 1973). The unusual geology and climate result in   vegetation which "combines elements of the California, north coast, and   eastern Oregon floras, with a large number of species indigenous only to the   Klamath Mountains region" (Franklin and Dyrness 1973, p. 130).   Figure 2. Map of the southern Oregon-northern California area.   Shaded area is the Klamath Mountains Geologic Province (modified from Irwin   1966 and Walker and MacLeod 1991).  California Current System  The rivers and streams of California, Oregon, and Washington drain into the   California Current system of the eastern North Pacific Ocean. This current   system includes the California Current, the California Undercurrent, and the   Davidson Current (Hickey 1989). The prevailing California Current has a   southerly flow. The California Undercurrent (or Countercurrent) flows   northward on the continental slope. Both the California Current and California   Undercurrent are strongest in summer (Hickey 1989). The Davidson Current is a   north-flowing seasonal surface current, existing in winter and early spring   (Doyle 1992).  Upwelling--Upwelling occurs when warm, nutrient poor   surface waters are driven offshore by wind stress and are replaced by cold,   nutrient-rich subsurface water. On the Oregon coast, prevailing winds from   September through March are from the southwest. At the end of March, wind   direction shifts, typically coming from the northwest, and Ekman transport   causes surface water to move offshore and deep water moves up to replace it   (Ingmanson and Wallace 1973, Neshyba 1987). These wind patterns result in   summer upwelling and winter downwelling.  The strength and consistency of upwelling south of Cape Blanco yields   highly productive waters. This is demonstrated in satellite imagery, described   by Pearcy (1992), that shows chlorophyll-rich water extending several hundred   kilometers offshore south of Cape Blanco to approximately 33øN latitude   (Thomas and Strub 1989).  In-Stream Water Temperature   Data from the U.S. Geological Survey for coastal streams in Oregon and   northern California demonstrate that with decreasing latitude there is an   upward trend in water temperature (Table 2). There appears to be a   geographical break-point in the average high water temperature south of the   Mad River, California.     Table 2. Average daily high water-temperatures (°C), by month, recorded by   U.S. Geological Survey for selected coastal streams in Oregon and California.   Streams are listed from north to south (Hydrosphere 1993).      StreamRecordinglocationMonth (January-June)Month(July-December)Year*Years ofrecordNumber ofyearsrecordedOregonSiuslaw RiverMapletonJan: 6.7 Feb: 7.5 Mar: 8.9 Apr: 10.5         May:14.8 Jun: 18.8Jul: 22.5 Aug: 22.6 Sep: 18.7 Oct: 13.5         Nov: 9.1 Dec: 7.513.41970-8211Umpqua RiverElktonJan: 5.9 Feb: 6.9 Mar: 9.0 Apr: 11.6 May:         15.6 Jun: 19.9Jul: 23.7 Aug: 23.4 Sep: 19.9 Oct: 14.4         Nov: 9.1 Dec: 6.313.81971-9121Rogue RiverAgnessJan: 5.9 Feb: 7.2 Mar: 8.8 Apr: 11.2 May:         15.1 Jun: 19.4Jul: 22.7 Aug: 22.3 Sep: 18.7 Oct: 13.5         Nov: 9.0 Dec: 6.713.41961-8828CaliforniaSmith RiverCrescent CityJan: 7.5 Feb: 8.2 Mar: 9.0 Apr: 10.6 May:         13.7 Jun: 17.6Jul: 20.4 Aug: 20.4 Sep: 17.9 Oct: 13.6         Nov: 10.2 Dec: 8.013.11966-8116Klamath RiverKlamathJan: 6.8 Feb: 7.7 Mar: 9.0 Apr: 11.5 May:         14.4 Jun: 18.6Jul: 22.4 Aug: 22.2 Sep: 20.1 Oct: 16.2         Nov: 11.4 Dec: 7.514.01966-8116Redwood CreekOrickJan: 7.5 Feb: 8.8 Mar: 9.6 Apr: 11.6 May:         15.8 Jun: 20.5Jul: 22.2 Aug: 21.4 Sep: 19.6 Oct: 14.9         Nov: 9.9 Dec: 8.114.21966-7914Mad RiverArcataJan: 7.8 Feb: 9.3 Mar: 10.2 Apr: 12.6         May: 16.2 Jun: 18.8Jul: 21.5 Aug: 21.2 Sep: 19.6 Oct: 16.0         Nov: 11.6 Dec: 8.714.51962-7916Eel RiverScotiaJan: 8.2 Feb: 9.0 Mar: 10.5 Apr: 12.8         May:16.8 Jun: 19.9Jul: 21.7 Aug: 21.6 Sep: 20.5 Oct: 16.9         Nov: 12.5 Dec: 9.115.01962-8220Mattole RiverPetroliaJan: 8.7 Feb: 10.0 Mar: 11.7 Apr: 14.0         May: 17.8 Jun: 22.1Jul: 23.4 Aug: 22.5 Sep: 21.1 Oct: 16.7         Nov: 12.3 Dec: 9.915.91966-7913Noyo RiverFort BraggJan: 8.5 Feb: 9.6 Mar: 10.8 Apr: 12.8         May: 16.4 Jun: 18.8Jul: 20.3 Aug: 19.8 Sep: 18.3 Oct: 14.2         Nov: 11.2 Dec: 8.914.11966-7914Navarro RiverNavarroJan: 8.7 Feb: 10.1 Mar: 11.7 Apr: 13.8         May: 18.4 Jun: 21.5Jul: 22.4 Aug: 21.7 Sep: 20.0 Oct: 16.2         Nov: 11.9 Dec: 8.915.41966-7913Garcia RiverPoint ArenaJan: 10.6 Feb: 11.4 Mar: 12.6 Apr: 14.5         May: 17.1 Jun: 18.7Jul: 19.6 Aug: 19.6 Sep: 18.8 Oct: 16.7         Nov: 13.6 Dec: 11.215.41964-7916Russian RiverGuernevilleJan: 9.9 Feb: 11.6 Mar: 13.3 Apr: 16.2         May: 20.3 Jun: 23.6Jul: 25.6 Aug: 24.6 Sep: 22.3 Oct: 18.2         Nov: 13.6 Dec: 10.317.51964-8219 *The average of the   monthly values.      Table   of Contents