U.S. Dept Commerce/NOAA/NMFS/NWFSC/Publications Tech Memo-15: Status Review for Oregon's Umpqua River Sea-Run Cutthroat Trout SUMMARY OF BIOLOGICAL INFORMATION ON COASTAL CUTTHROAT TROUT
Cutthroat and rainbow trout are native to western North America. Historically, cutthroat trout were the more broadly distributed species (Behnke 1979, 1992), but in recent years they have been replaced by rainbow trout or other introduced species in many parts of their range. There are 14 extant subspecies of cutthroat trout recognized in the current literature, but all except the O. c. clarki are found east of the temperate rainforest region of the Pacific Northwest ( Fig. 1, Table 2) (Behnke 1979). Because of hybridization with rainbow trout, habitat degradation, and other reasons, many of these inland subspecies have declined in numbers to an extent that they are now protected by state and federal endangered species legislation (Table 2) (Johnson 1987).

O. c. clarki has a karyotype (2n = 68-70, Simon 1963, Gold et al. 1977) that is unique among cutthroat trout subspecies (Gold et al. 1977, Thorgaard 1983, Loudenslager and Thorgaard 1979, Behnke 1992) as well as several unique alleles detected by protein electrophoresis (Leary et al. 1987, Allendorf and Leary 1988). Phenotypically, coastal cutthroat trout differ from all other trout by their profusion of small to medium-size spots of irregular shape (Behnke 1992). In addition, they do not develop the brilliant colors associated with inland cutthroat trout. In sea-run coastal cutthroat trout, spots and colors are further obscured by the silvery skin deposit common to anadromous salmonids. Resident, non-anadromous fish tend to be darker, with a "coppery or brassy" sheen (Behnke 1992).
Table 2. Subspecies of cutthroat trout and their federal and state protection status (modified from Allendorf and Leary 1988). The eight major subspecies are endemic to large geographical areas (Behnke 1979). State abbreviations in italics represent legal protection and non-italicized abbreviations represent fishes of Special Concern according to Johnson (1987): CA = California, CO = Colorado, ID = Idaho, MT = Montana, NM = New Mexico, NV = Nevada, US = United States, UT = Utah, and WY = Wyoming. Common Name           Subspecies           Legal Protection           Major subspeciesBonnevilleCoastalColoradoGreenbackLahontanRio       GrandeWestslopeYellowstoneOncorhynchus clarki utahO. c.       clarkiO. c. pleuriticusO. c.       stomiasO. c. henshawiO. c.       virginalisO. c. lewisiO. c. bouvieriUS, ID, NV, UT, WY--US, CO, UT,       WYUS, COUS, CA, UTCO, NMID,       MTID, MT Minor subspeciesAlvordBear       LakeHumboldtMountainPaiuteSnake       RiverWillow/WhitehorseYellowfinO. c. alvordensisO. c.       subsp.O. c. subsp.O. c. alpestrisO. c.       selenirisO. c. subspO. c. subsp.O.       c. macdonaldiextinctID----US,       CAIDUSextinct
The distribution of coastal cutthroat trout is greater than for any other cutthroat trout subspecies. It extends along the Pacific coast of North America from the Eel River in northern California (DeWitt 1954) to the Prince William Sound area of southeast Alaska, bounded by Gore Point on the Kenai Peninsula (Sumner 1948, 1972; DeWitt 1954; Scott and Crossman 1973; Behnke 1992). The eastern range of the subspecies rarely extends farther inland than 160 km and is usually less than 100 km. The eastern range appears to be bounded by the Cascade Mountain Range in California, Oregon, and Washington and by the Coast Range in British Columbia and southeast Alaska (Fig. 1). As pointed out by Trotter (1989) and Trotter et al. (1993), this range coincides closely with the coastal temperate rain forest belt defined by Waring and Franklin (1979), and even when the fish have access beyond the coastal rainforest, such as in the Columbia River, they penetrate only a limited distance (Sumner 1972; Trotter 1987, 1989). 

Life-History Forms of Coastal Cutthroat TroutThe life history of coastal cutthroat trout is probably the most complex and flexible of any Pacific salmonid (Johnston and Mercer 1976; Johnston 1981; Trotter 1987, 1989). Partly because of their subordinate behavior to other salmonids, cutthroat trout have evolved to exploit habitats least preferred by these other species (Johnston 1981). Unlike other anadromous salmonids, sea-run cutthroat trout do not over-winter in the ocean and only rarely make long extended migrations across large bodies of water. They migrate in the nearshore marine habitat and usually remain within 10 km of land (Sumner 1972, Giger 1972, Jones 1976, Johnston 1981). While most anadromous cutthroat trout enter seawater as 2- or 3- year-olds, some may remain in fresh water for up to 5 years before entering the sea (Sumner 1972, Giger 1972). Other cutthroat trout may never outmigrate at all, but remain as residents of small headwater tributaries. Still other cutthroat trout may migrate only into rivers or lakes (Nicholas 1978b, Tomasson 1978, Moring et al. 1986, Trotter 1989), even when they have seawater access (Tomasson 1978). In the Umpqua River Basin, anadromous, resident, and potamodromous life-history forms have been reported (Trotter 1989, Loomis and Anglin 1992, Loomis et al. 1993). 

Sea-Run or Anadromous O. c. clarki This is the best known life-history form of the subspecies, and most of the biological information presented in the following sections was derived from studies on sea-run individuals. Sea-run trout are the fish petitioned by ONRC et al. (1993) for protection under the ESA. 

Non-Migratory or Resident O. c. clarki Some cutthroat trout do not migrate long distances; instead, they remain in upper tributaries near spawning and rearing areas and maintain small home territories (Trotter 1989). Wyatt (1959) surveyed resident cutthroat trout in the Willamette River (Lookout Creek) and found that in a year less than 3% of the fish moved more than 200 m from their home areas. Resident cutthroat trout appear to be slower growing than potamodromous or anadromous trout (Tomasson 1978, Trotter 1989); they seldom grow larger than 150-200 mm in length and rarely live longer than 2 to 3 years (Wyatt 1959, Nicholas 1978a, June 1981). 

Resident fish in the Umpqua River Basin Resident cutthroat trout have been observed in the upper Umpqua River drainage (Roth 1937, FCO and OSGC 1946 , ODFW 1993a), but, until recently, little specific information has been available on them. In 1992, Waters (1993) radio-tagged what he believed were 25 "resident" cutthroat trout, 154 - 234 mm in length (Table 3), in three tributaries of Rock Creek in the North Umpqua River drainage (Fig. 2) for a study on river flow and winter habitat utilization of cutthroat trout in the North Umpqua River Basin. He found that some of these radio-tagged fish moved over much larger distances than others (Table 3). Fish smaller than 180 mm maintained home ranges that averaged less than 14 m of stream length and moved an average of only about 27 m during the study. Fish larger than 180 mm had home ranges that averaged 76 m and moved an average total distance of about 166 m. One of these larger fish (length 191 mm) was particularly active, had a home range of over 433 m, and moved over 1,305 m during the study. 

Table 3. Date tagged, stream location of tagging, and characteristics of radio-tagged cutthroat trout from a study on the North Umpqua River (Waters 1993).
River-Migrating or Potamodromous O. c. clarki Some cutthroat trout may move within large river basins, but not migrate to the sea. These potamodromous migrations are best documented in rivers with physical barriers to anadromous fish, such as above Willamette Falls in the Willamette River. Historically, the falls apparently barred access of anadromous fish to the upper river, and above this barrier, schools of cutthroat trout were found to migrate from natal spawning areas to mainstem feeding areas and back (Dimick and Merryfield 1945; Nicholas 1978a,b; Moring et al. 1986). Potamodromous cutthroat trout have also been reported as schooling in "large streams above migration barriers in southwest Oregon, e.g., Bald Mountain Creek (Elk Basin), upper Chetco River, upper Silver Creek (Illinois Basin)" (ODFW 1993b). 
Only rarely have potamodromous cutthroat trout been reported below barriers or in locations with access to anadromous fish. In the Rogue River, Tomasson (1978) documented the presence of potamodromous fish that do not enter seawater, but had physical access to the sea and were sympatric with anadromous and resident trout. Tomasson differentiated between the anadromous and non-anadromous fish by chemical analysis of scale tissue. Previously, Bagenal et al. (1973) had developed a technique for the measurement of strontium (Sr) concentrations in fish tissue and had reported large differences between Sr concentrations in the scales of anadromous and non-anadromous brown trout. Tomasson modified these techniques to measure the ratio of Sr to calcium (Ca) in the scales of cutthroat trout. Tomasson reported that there was almost a seven-fold difference between the ratio of these two elements in fresh water and seawater, and he believed that using the ratio of Sr to Ca, rather than simply measuring Sr concentrations, would be more accurate and require less tissue. In preliminary studies, Tomasson (1978) found large and reproducible differences between Sr:Ca ratios from unidentified freshwater and marine fishes. Tomasson also used traditional scale and otolith analysis, length frequency distributions, gonadal dissections, and back calculation of length from scale data to describe the abundance, distribution, and migration patterns of cutthroat trout in the Rogue River. 

In his study, cutthroat trout were collected from the Rogue River estuary and mainstem between 1974 and 1977 and from small upper tributaries in 1977 and 1978. Because of the amount of scale material required for Sr:Ca analysis, most scale samples from the estuary and all scale samples for each tributary had to be pooled. Based upon analysis of the scales, only those from first-time migrants to the estuary, collected at the same time and location, were pooled. 

Tomasson reported that there were differences between Sr:Ca ratios in known resident fish (mean was approximately 1.5 x 10(-3)) and in first-time migrants captured in the estuary (mean was approximately 2.8 x 10(-3)). He found that there was a significant increase in the Sr to Ca ratio with time fish spent in the estuary (from approximately 2 x 10(-3) to 3.2 x 10(-3)). Tomasson concluded that this increase indicated these fish over-summered in seawater. 

In the Sr:Ca analysis of eight samples collected from the lower Rogue River (RKm 5.6 to 44.2), Tomasson found that six of these showed low Sr:Ca ratios (1.10 x 10(-3) to 1.58 x 10(-3)). He considered these fish potamodromous. The other two fish showed high Sr:Ca ratios (2.52 x 10(-3) and 2.97 x 10(-3)), and Tomasson concluded these were anadromous fish. Although all the lower-river fish were collected after spawning should have been completed, only the two (presumably sea-run) fish with high Sr:Ca ratios had definite spawning checks on their scales. Although Tomasson concluded these fish represent two different populations (anadromous and potamodromous), a second interpretation might be that the immature fish were parr that would migrate to seawater in future years. 

Twenty samples from the upper Rogue River (RKm 104 to 252) had low Sr:Ca ratios (0.94 x 10(-3) to 1.70 x 10(-3)), indicating to Tomasson they were freshwater residents and did not have seawater exposure. He "concluded that only rarely, if at all, do anadromous trout migrate above river RKm 104" (Tomasson 1978, p. 34). Tomasson found high Sr:Ca ratios (2.52 x 10(-3)) in scale samples from fish collected from Edison Creek, a stream that empties just above the estuary. He concluded that the fish from this creek had spent some time in the estuary. A short period of rapid growth was also identified from scale analysis. 

Length-frequency distributions were differed between fish captured in the lower Rogue River or estuary and fish captured in the upper river (Tomasson 1978). He found that fish captured in the estuary and lower river had growth peaks at three different times which corresponded to lengths at first entrance to the estuary (140- 150 mm), length at end of first growing season in the estuary (270-310 mm), and length at end of second growing season in the estuary (350-430 mm). Cutthroat trout captured in the upper river had a more uniform, but slower growth. Tomasson concluded that because trout collected in the mainstem appeared to have grown equally well in the mainstem and the estuary, the three peaks indicated that anadromous and potamodromous were intermixed or "superimposed" in the lower river (Tomasson 1978, p. 35). He also concluded that the upper-river length distributions were "indicative of a homogeneous population." However, Tomasson did caution that the lower-river peaks may reflect a sampling problem as more fish were caught outside the growing season in the lower river than in the upper river. 

Although Tomasson was able to identify three different life-history forms in the Rogue River (sea-run, potamodromous, and resident) he emphasized that his study had several shortcomings. The number of scales required for the analysis of Sr:Ca ratios required pooling, and inconsistent results often occurred when the larger samples of scales were analyzed. Tomasson determined that the cause of this inconsistency was precipitation of Sr at certain Ca concentrations. Consequently, Tomasson developed a standard curve of Sr and Ca ratios from large quantities of scales collected from landlocked Willamette River fish. From the standard curve, Tomasson was able to accurately determine Sr:Ca ratios only within a portion of the curve where Sr precipitation was minimal. Because of this, he was limited in his evaluations to only 77 samples (11 from known resident fish, 20 from upper-river fish, 8 from lower-river fish, and 38 from the estuary). 

In summary, Tomasson was the first to identify migratory cutthroat trout with access to seawater, that did not enter the marine habitat, but moved only within a river system (potamodromous). He also was the first to identify potamodromous fish sympatric with sea-run fish, and that sea-run fish in the Rogue River migrated only to the estuary and did not enter the open ocean. However, Tomasson emphasized that the behaviors he had identified in Rogue River cutthroat trout may be unique to cutthroat trout from that river system. He believed the Rogue River had several unique characteristics that might result in different or unusual salmonid behaviors (such as half pounder steelhead). He also emphasized that the purpose of his work was to document the status of cutthroat trout in the river prior to the opening of Lost Creek Dam. The operation of the dam was anticipated to dramatically change some of the physical factors in the riverine environment (such as water temperature and flows) that may have led to some of the unusual behavior of the trout he studied. 

Table of Contents

Potamodromous fish in the Umpqua River BasinPotamodromous fish have only recently been identified in the Umpqua River Basin. No sea-run cutthroat trout had been counted over Winchester Dam in the fall of 1992, when biologists from ODFW conducted a series of radio-tagging studies on large (length 300-400 mm) cutthroat trout in the Steamboat and Canton Creek drainages in the North Umpqua River Basin (Fig. 2). Personnel from ODFW radio-tagged five cutthroat trout from Steamboat Creek and three cutthroat trout from Canton Creek in October 1992 and tracked their movements until February 1993 (Loomis et al. 1993). The fish remained in the tagging area until the fall rains began, at which time they moved upstream 6.5 to 16 km (4 to 10 miles) to over-wintering sites where they remained for the rest of the study (D. Loomis, see footnote 2; T. Loynes see footnote 3). It is unclear whether these fish were sea-run trout that had remained in fresh water after spawning the previous winter or potamodromous fish that spend their entire life cycle in fresh water. It was also possible the radio-tagged fish would migrate to the sea in the future. 

In Waters (1993) radio-tagging study of resident cutthroat trout (length 154- 234 mm) previously discussed in the "Non-migratory or Resident O. clarki" subsection, it was found that fish greater than 180 mm tended to move greater distances than smaller fish, but that some fish, regardless of size, were particularly active (Table 3). Waters (footnote 4), believed that the fish that made more active and longer distance movements may represent either potamodromous fish or future sea-run fish. 

ODFW conducted further and continuing radio-tagging studies beginning in the summer of 1993 on resident fish and in October 1993 on a presumed sea-run cutthroat trout that was trapped while passing Winchester Dam (D. Loomis, footnote 2; T. Loynes, footnote 3). 

Large cutthroat trout have also been observed in the upper Umpqua River by biologists from several agencies (J. Dose footnote 5 ; D. Loomis, footnote 2); T. Loynes, see footnote 3; E. Waters, footnote 4 at times when sea-run trout are not thought to be present or in numbers greater than those of sea-run trout that have been counted across Winchester Dam in that year. But until these reports are published and chemical analyses of scales or other tissues have been conducted to confirm freshwater life histories, it is impossible to determine whether these were potamodromous, resident, or over-wintering anadromous fish. 
Life History of Coastal Cutthroat Trout 
Early Life History Cutthroat trout spawning occurs between December and May and eggs begin to hatch within 6-7 weeks of spawning, depending on temperature. Alevins remain in the redds for a further few weeks and emerge as fry between March and June, with peak emergence in mid-April (Giger 1972, Scott and Crossman 1973). At emergence, fry quickly migrate to channel margins and backwaters with low stream gradients, where they remain throughout the summer (Edie 1975, Glova and Mason 1976). 

In the absence of other species, cutthroat trout prefer to rear in pools (Giger 1972), but when coho salmon are present, the cutthroat juveniles move to less preferred, low gradient riffle areas, where they remain until displaced by winter flows (Glova and Mason 1977, Glova 1987). In winter, the cutthroat trout go to pools near log jams or overhanging banks (Bustard and Narver 1975). 

Parr Movements After emergence from redds, cutthroat trout juveniles generally remain in upper tributaries until they are 1 year of age, when they may begin extensive movement up and down streams. Directed downstream movement by parr usually begins with the first spring rains (Giger 1972) but has been documented in every month of the year (Sumner 1953, 1962, 1972; Giger 1972; Moring and Lantz 1975; Johnston and Mercer 1976; Johnston 1981). As an example, from 1960 to 1963 (Lowry 1965) and from 1966 to 1970 (Giger 1972) in the Alsea River drainage, large downstream migrations of juvenile fish began in mid-April with peak movement in mid-May. Some juveniles (parr) even entered the estuary and remained there over the summer, although they did not smolt nor migrate to the open ocean (Giger 1972). In Oregon, upstream movement of juveniles from estuaries and mainstem to tributaries begins with the onset of winter freshets during November, December, and January (Giger 1972, Moring and Lantz 1975). At this time, these 1-year and older juvenile fish averaged less than 200 mm in length. 

SmoltificationTime of initial seawater entry of smolts bound for the ocean varies by locality and may be related to marine conditions or food sources (Lowry 1965, 1966; Giger 1972; Johnston and Mercer 1976; Trotter 1989). In Washington and Oregon, entry begins as early as March, peaks in mid-May, and is essentially over by mid-June (Sumner 1953, 1972; Lowry 1965; Giger 1972; Moring and Lantz 1975; Johnston 1981). In Alaska, the migration begins in April and peaks in late May or early June (Baade 1957, Armstrong 1971, Jones 1976), although two other additional surges may occur: one in mid-June and one in mid-July. Jones reported that the mid-June rush was composed of outmigrating cutthroat trout over 250 mm and indicated "these were not believed to be initial migrant smolts." Jones also found that the average size of outmigrants in a mid-July peak at Petersburg Creek in southeast Alaska was less than 200 mm. This run occurred at night on moderate stream flows and stopped during extreme high or low stream flows in all years studied. 

Seaward migration of smolts to protected areas appears to occur at an earlier age and a smaller size than to more exposed areas. Johnston (1981) reported that in Puget Sound and the Columbia River, smolts make their first migration at age 2 or 3, with a mean size of about 160 mm. On the less protected Oregon coast, cutthroat trout tend to migrate at an older age (age 3 and 4) and at a size of 200 to 255 mm (Lowry 1965, 1966; Giger 1972). The oldest recorded initial age of seawater entry was a 6-year-old fish that was 280 mm in length from the Alsea River on the Oregon Coast (Giger 1972). 

Timing of smolt migrations in the Umpqua RiverIn the Umpqua River, some information has been gathered on movement of juvenile salmonids from smolt traps operated by ODFW at various locations in the North Umpqua River (Loomis et al. 1993). Trap data from seven locations in the North Umpqua River in 1958 and from three locations in Steamboat Creek between 1958 and 1973 indicate that juvenile movement is similar to that reported by Lowry (1965) and Giger (1972) in other Oregon coastal rivers. Movement peaked in May and June, with a sharp decline in July, although some juveniles continued to be trapped through September and October. It is unknown whether Umpqua River cutthroat trout juveniles migrate from the upper basin areas to the estuary, but it seems unlikely considering the distance (well over 185 km) and the river conditions (average August river temperature at Winchester Dam since 1957 is 23.3°C) (ODFW 1993a). 

Estuary and Ocean MigrationMigratory patterns of sea-run cutthroat trout differ from other Pacific salmon in two major ways: few, if any, cutthroat overwinter in the ocean, and the fish do not usually make long open-ocean migrations, although they may travel considerable distances along the shoreline (Johnston 1981, Trotter 1989, Pauley et al. 1989). Studies by Giger (1972) and Jones (1973, 1974, 1975) indicated that cutthroat trout, whether initial or seasoned migrants, remained at sea an average of only 91 days, with a range of 5 to 158 days. In these studies, the majority of cutthroat trout seemed to migrate in similar patterns from year to year, rarely crossed bodies of water over 8 km in width, and closely followed shorelines, sometimes for up to 71 km. Only in the Columbia River plume have cutthroat trout been documented to move considerable distances offshore, where Dawley et al. (1978, 1979, 1980) and Pearcy et al. (1990) reported cutthroat trout over 27 km offshore. Pearcy et al. (1990) also reported cutthroat trout moved as far as 250 km along the Oregon shoreline. 

Not all sea-run trout populations migrate into the ocean. As previously discussed, Tomasson (1978) concluded from catch data that Rogue River sea-run cutthroat trout did not enter the open sea, but remained in the estuary throughout the summer. All other studies of cutthroat trout (reviewed in Trotter 1989) have found some ocean-migrating component in an anadromous population. Tomasson (1978) speculated that sea-run Rogue River cutthroat trout may remain in the estuary to avoid half-pounder steelhead that reside during the summer in the nearshore ocean margin, where sea-run cutthroat trout usually occur. 

Ocean migrations by Umpqua River cutthroat trout We found no published scientific reports on ocean migrations of Umpqua River cutthroat trout. However, information from the popular fishing literature suggests that Umpqua River cutthroat trout may remain in the estuary longer than has been reported (Giger 1972) for the Alsea, Siuslaw, and Nestucca Rivers: "Anglers who fish the lower [Umpqua River] estuary around Reedsport and Gardner may find fish any time of year, because these anadromous cutthroat rarely enter the open ocean, instead preferring to roam the estuaries" (Shewey 1992, p. 61). However, large numbers of Alsea River hatchery cutthroat trout have been released into Smith River and Scholfield Creek in the Umpqua River estuary for many years (see Table 1), and it would be expected that these fish would follow the migrational timing and pattern evolved in the Alsea River. 

Adult Freshwater Migrations Across the subspecies range, information on the timing of adult upriver migrations of cutthroat trout is based on fish counts across Winchester Dam (the only dam with long-term cutthroat trout counts), angler surveys, limited tagging studies, and trapping and inventory studies. Cutthroat trout may return to freshwater feeding/spawning areas from late June through March. Re-entry timing has been found to be temporally consistent from year to year within streams, but with wide variation between streams (Giger 1972). Return migrations to large rivers seem to consistently occur earlier than to shorter coastal rivers (Giger 1972, Johnston and Mercer 1976, Johnston 1981). It has been suggested that this may be due to adaptation of distinct populations to different environmental conditions, such as distance from seawater to spawning sites (Giger 1972, Johnston and Mercer 1976, Johnston 1981, reviewed in Pauley et al. 1989 and Trotter 1989). 

In small streams, such as Carnation Creek in British Columbia, Sand Creek in Oregon, and Minter Creek in Washington, peak returns occur in December and January, and fish may continue to return through March (Sumner 1953, Anderson and Narver 1975, Johnston 1981). These streams usually have low flows (< 0.6 m3/second) and flow directly into seawater. 

In large river systems in Washington and Oregon, such as the Stillaguamish, Columbia, Cowlitz, and Alsea Rivers, cutthroat trout return migrations usually begin earlier, in late June, and continue through October with peaks in late September and October (Lavier 1963; Bulkley 1966; Hisata 1971, 1973; Duff 1972; Giger 1972; Wright 1973; Tipping and Springer 1980; Tipping 1981, 1986). As an example, Giger (1972) found that the earliest known entrance dates of sea-run cutthroat trout in the Alsea River between 1965 and 1970 ranged from June 23 to July 21. He also noted that these first fish were the "forerunners of larger runs which peaked at later dates..." and that "...smaller numbers of fish were known to enter as late as early October" (p. 11). 

Run-timing in the Umpqua River Basin In the Umpqua River, it is reported (ODFW 1993a) that cutthroat trout historically began upstream migrations in late June and continued to return through January (Fig. 5) with bimodal peaks in late-July and October. Giger (1972) reported a similar return pattern, but with slightly later modal peaks (mid-August and late-October to mid-November) on the Alsea River. 

Giger (1972) suggested that the early run of fish in the Alsea River may consist of older fish, with first time spawners making up the later October-November run. In contrast, at Winchester Dam on the North Umpqua River, observers believe that fish returning in October are larger than those in the August run (D. Loomis, footnote 2; W. Metzler - footnote 6). However, there are no published data on sizes of adult cutthroat trout passing Winchester Dam or from other locations in the North or South Umpqua Rivers. 

Figure 5. Monthly maximum water temperatures for July, August, September, and October. Temperatures were taken at Winchester Dam on the North Umpqua River from 1946 to 1993. 

It is unknown where the fish that compose these two peaks are going (although on-going radio-tagging studies by ODFW should provide information on this question) or whether they represent two runs of fish from a single population, or the returns of two or more different populations. 

Straying In reviewing cutthroat trout life history, Pauley et al. (1989, p. 5) reported that "homing of native sea-run cutthroat is extremely precise (Campton 1980), although hatchery-planted fish may stray as much as 30%, which makes survival rates impossible to determine (Johnston and Mercer 1976)." 

Jones reported (1975, 1976) that in tagging studies from Petersburg Creek in southeast Alaska, many wild fish wandered during their first year's return to fresh water, and were captured in 13 nearby streams. As second year migrants, a much higher proportion of tagged fish were captured in their home stream. Overall, Jones (1976) found that less than 50% of initial returning migrants were sexually mature and suggested that first year fish found wandering to non-natal rivers were on feeding runs. 

In Oregon, Sumner (1953) found that over 95% of returning initial migrant wild females were sexually mature. Giger (1972) found that tagged wild fish from streams in the Alsea River did not stray and were only recaptured in their natal streams. However, over 30% of the tagged hatchery fish entered streams up to 133 km from the release stream. 

Johnston (1981), like Jones, believed wandering cutthroat trout were on feeding runs, and suggested that in localities where a large proportion of first time migrants are not sexually mature, perhaps due to low food availability, they may conduct feeding runs to randomly chosen rivers. In the following year, when a larger proportion of these fish are sexually mature, they will home to natal streams. 

Spawning As reviewed in Trotter (1989) and Pauley et al. (1989), cutthroat trout generally spawn in the tails of pools located in streams with low stream gradient and low flows, usually less than 0.3 m3/second during the summer (Johnston 1981). "You can step across a cutthroat spawning stream, but you have to jump a steelhead stream," R. Dimick, founder of Oregon State University Department of Fisheries and Wildlife, was fond of saying (C. Bond-footnote 7). Spawn timing varies among streams, but generally occurs between December and May, with a peak in February (Trotter 1989). 

It is believed that the choice by cutthroat trout of spawning sites in small tributaries at the upper limit of spawning and rearing sites of coho salmon and steelhead has evolved to reduce competitive interactions and to reduce hybridization with rainbow trout and steelhead. In many drainages where rainbow trout and cutthroat trout coexist, there is believed to be a slight difference in spawn timing between the two species that would also reduce the opportunity for hybridization (Cramer 1940, DeWitt 1954, Sumner, 1972, Glova and Mason 1977, Johnston 1981). However, as discussed later, hybridization between cutthroat and rainbow trout has been documented in locations in Puget Sound where spawning areas and time of spawning overlap (Campton and Utter 1985). 

Cutthroat trout are iteroparous and have been documented to spawn each year for at least 5 years (Giger 1972), although some cutthroat trout do not spawn every year (Giger 1972) and some do not return to seawater after spawning, but remain in fresh water for at least a year (Giger 1972, Tomasson 1978). Spawners may experience high post-spawning mortality due to weight loss of as much as 38% of pre-spawning mass (Sumner 1953) and other factors (Cramer 1940, Sumner 1953, Giger 1972, Scott and Crossman 1973). Still, in one Oregon stream, over 39% of one year's spawning population returned to spawn a second year, 17% returned to spawn a third year, and 12% for the fourth year (Sumner 1953). However, in another stream with an intense sport fishery, only 14% returned to spawn in the second year (Giger 1972). 

Spawning sites in the Umpqua River BasinLittle is known of spawning locations or sites for cutthroat trout in the Umpqua River Basin (D. Loomis, footnote 2; T. Loynes, footnote 3; J. Dose, footnote 5), although T. Loynes observed a possible sea-run cutthroat trout redd near a steelhead redd on Cedar Creek. He also observed presumed sea-run or potamodromous cutthroat trout in Williams Creek, slightly upstream from coho salmon spawning locations and in the same area as steelhead redds. This tributary is blocked by a small falls upstream from the observation point, and cutthroat trout redds dug near the observation point would be accessible to resident, potamodromous, and sea-run cutthroat trout. 

In the Umpqua River Basin there is no information available on how many sea-run cutthroat trout survive spawning and return to spawn a second or third time. Considering the intense fishery for hatchery cutthroat trout in the Umpqua River estuary (Shewey 1992, ODFW 1993a), and the distance the fish would have to travel, it is unlikely that the percentage of ingeminators would be very high. 

Interactions of Cutthroat Trout with Other Salmonids The population structure of cutthroat trout in the Umpqua River cannot be considered in isolation from other salmonids. Cutthroat trout, more than any other salmonid species, are known to change their behavior in the presence of other salmonids (Johnston 1981, Trotter 1989), and there are large populations of steelhead, coho salmon, and rainbow trout in the Basin . Although there are no published studies on the interactions of cutthroat trout with other salmonids in the Umpqua River, there are extensive studies on this issue in other regions (reviewed in Griffith 1988). 

Studies of the fossil record and natural distribution of Pacific salmon and trout show that cutthroat trout were the first salmonid to colonize the western United States (Johnston 1981, Behnke 1992). Many cutthroat populations became well established before other species of salmonids were abundant, and they remained isolated from these other species for thousands of years (Behnke 1979, 1992; Johnston 1981). As an example, the only other native fish historically present with the Yellowstone cutthroat trout (O. c. bouvieri) in Yellowstone Lake (Yellowstone National Park) was the longnose dace (Rhinichthys cataractae) (Gresswell and Varley 1988). In another example, only eight other fish species historically occurred in the Lahontan Basin in Nevada-California along with the Lahontan cutthroat trout (O. c. henshawi) (Behnke 1992). 

Because of this isolation, many interior species of cutthroat trout never competed with other salmonids, and introductions of other salmonids (primarily rainbow trout) into the inland American west resulted in a dramatic decline of many cutthroat trout populations (Behnke 1972a, 1992; Greswell 1988). This decline has been partly caused by habitat modification and destruction (e. g., Clancy 1988), but is primarily attributed to interspecific interactions such as introgressive hybridization (Behnke 1972a, 1992; Allendorf and Leary 1988), predation (reviewed in Marnell 1988), and competition (Griffith 1988). 

However, it is worthwhile noting that one study (Platts 1974) found that westslope cutthroat trout (O. c. lewisi) density peaked at a channel gradient of about 10%, which was higher than for peak densities of bull (Salvelinus confluentus), rainbow, or brook trout. Platts suggested that the cutthroat trout in this study represented populations in gradients least preferred by other salmonids. 

Coastal cutthroat trout are believed to have been less severely affected by these interspecific interactions because they evolved in close contact with other salmonids. This subspecies has developed a variety of habitat partitioning techniques, subordinate behaviors, and a flexible life history, all of which act to reduce competition with other species and help reduce opportunities for hybridization (Johnston 1981, Campton and Utter 1987, Griffith 1988). 

In studies where cutthroat and rainbow trout or steelhead occupied the same watersheds, the cutthroat trout have been found primarily in the headwater tributaries, while steelhead and rainbow trout occupied the larger river reaches (Hartman and Gill 1968, Edie 1975, Hanson 1977, Jones 1978, Nicholas 1978a, Johnson et al. 1986). Nicholas also found that in western Oregon streams, cutthroat trout grew more slowly and matured at an earlier age than did sympatric rainbow trout. They also spawned earlier in the spring and in smaller or different tributaries than did the rainbow trout. Nicholas felt this resource partitioning reduced the opportunity for hybridization and helped maintain the integrity of the cutthroat trout populations. 

In lake studies, Nilsson and Northcote (1981) found that cutthroat trout showed changes in behavior, prey items, and growth in the presence of rainbow trout. In laboratory studies, the rainbow trout were consistently more aggressive and they quickly killed cutthroat trout when they were paired together. The two species successfully coexisted in the natural lake environment. 

Coastal cutthroat trout are not the only cutthroat trout subspecies to have evolved sympatrically with other salmonid species; westslope cutthroat and rainbow trout/steelhead coexist in the Snake River Basin. In a study on abundance and distribution of the two species, Hanson (1977) found that in drainages where both occur, cutthroat trout occupied upper portions of streams, and O. mykiss were found in the lower portions. Hanson also determined that age-0 steelhead displaced previously established age-0 cutthroat, but cutthroat could not displace steelhead. Hanson suggested there is "interactive segregation" where both species co-occur, despite, or because, of the fact that the species apparently have coexisted for thousands of years. 

Coho salmon have also been shown to be dominant to cutthroat trout in field (Giger 1972, Glova 1984) and laboratory studies (Glova 1986). In the absence of coho salmon, cutthroat trout prefer to rear in pools (Giger 1972). However, when coho salmon are present, they are able to dominate cutthroat trout fry because the juvenile coho salmon emerge from redds earlier and have a large body size (Giger 1972). Cutthroat trout juveniles then move to less preferred, low gradient riffle areas, where they remain until winter flows force changes because of displacement (Glova and Mason 1977; Glova 1984, 1987). In winter, the cutthroat trout go to pools near log jams or overhanging banks (Bustard and Narver 1975). 

The effect of these interactions is not clearly understood and may differ depending on a variety of factors. While cutthroat trout may be competitively excluded from preferred rearing habitats by dominant coho salmon (Glova 1984, 1986, 1987) and steelhead (Hartman and Gill 1968), it has been suggested that in some cases this interaction may be positively correlated to sea-run cutthroat trout abundance. In Cumins Creek, a wilderness area on the Oregon coast, cutthroat trout seem to have slower growth and only moderate smolt outmigrations in years with poor coho salmon runs. Coho salmon may be predators on age-0 cutthroat trout, but it has been suggested that this may allow the remaining cutthroat trout to grow faster and may result in better survival of anadromous cutthroat trout (T. Nickelson - footnote 8). 

In the Umpqua River Basin, a variety of native and introduced salmonid species are present, including coho and chinook salmon; brown, brook, and rainbow trout; and steelhead (ODFW 1993a). Considering the precipitous declines experienced by interior cutthroat trout subspecies due to interactions with other salmonid species (Behnke 1992), it might be expected that cutthroat trout in the Umpqua River also have experienced similar negative impacts. However, the mechanisms evolved by the coastal subspecies to reduce opportunities for social interactions and hybridization with other salmonids (Griffith 1988) may have helped isolate the subspecies and allow the persistence of distinct populations. In fact, considering the flexibility of life-history characteristics such as potamodromy, iteroparity, and isolation of spawning habitats, the subspecies may be at a relative survival advantage compared to other salmonid species with more rigid life histories. 

Temperature Tolerance in Cutthroat TroutThe biological significance of the high temperatures and temperature trends in the Umpqua River discussed in the sub-section "River Water Temperature" is unclear. Coastal cutthroat trout are exposed to a wide range of water temperatures across their distribution and, relative to other salmonids, little information on their habitat requirements is available (reviewed in Bjornn and Reiser 1991). Still, like other salmonids, coastal cutthroat trout have evolved to take advantage of temperature regimes in their home ranges. When abrupt changes occur in water temperatures or other physical factors, the fish usually compensate by finding refugia, but abrupt deviations from the normal pattern can adversely affect their survival (Bjornn and Reiser 1991). 

Bell (1986), in experiments on inland cutthroat trout and other salmonids, found that preferred temperatures for spawning and incubation were 6.1°C to 17.2°C for inland cutthroat trout, 2.2°C to 20.0°C for rainbow trout, and 3.9°C to 9.4°C for steelhead. The lethal limit for steelhead was above 24°C (Bell 1986). He also reported that the temperature range in which most Pacific salmon species were able to move upstream if depth and velocity were satisfactory was 7.2°C to 15.6°C, but reached 20.0°C for one stock of summer chinook salmon. 

In a variety of studies (Hunter 1973, Golden 1975, Behnke and Zarn 1976, Behnke 1992), cutthroat trout, like other salmonids, were not usually found in water temperatures higher than 22°C, although they could tolerate temperatures as high as 26°C for brief periods. Typically, the fish appeared stressed when water temperatures rose above 22°C. At 28°C to 29°C the fish lost equilibrium and died, even if temperatures were gradually increased 1°C - 2°C per day (Behnke and Zarn 1976). Juvenile cutthroat preferred water temperatures around 15°C. They also lost equilibrium and died between 28°C and 30°C (Heath 1963). 

Dwyer and Kramer (1975) calculated metabolic rates and scope for activity on inland cutthroat trout from Utah. They found that in their experimental fish, active metabolism and the scope for activity was greatest at 15°C and lowest at 5°C. There was also a decline at 24°C, which the authors believed is near the upper lethal temperature for cutthroat trout. 

Temperature tolerance is difficult to study. Behnke (1992) described rainbow trout in Oregon that over thousands of years appear to have adapted to high water temperatures. He reported that these fish actively feed and apparently thrive in waters of 28.3°C. Other populations do not seem to successfully adapt to high temperatures. In the Firehole River, Yellowstone National Park, introduced rainbow trout have lived for 60-70 years in water temperatures that may reach 29.5°C (Kaya 1977). Adaptation to this warm water might be expected, but in a series of experiments Kaya (1978) found that these rainbow trout survived less than 2 hours at 29.5°C and stopped feeding at 23°C-24°C, even when water temperature was gradually increased. He suggested that the fish, rather than adapting to the hot water, were able to find refuge in cooler water and avoid the higher temperatures. 

GeneticsOnly a few studies, all involving protein electrophoresis, have been made of the genetic structure of coastal cutthroat trout populations. Campton (1981) and Campton and Utter (1987) surveyed natural and hatchery populations in Puget Sound, and Currens et al. (1992) analyzed 11 samples from southern Oregon--10 from the Coquille River and 1 from the Chetco River. Campton and Utter (1985) examined natural hybridization between steelhead and coastal cutthroat trout in northern Puget Sound streams. 

Campton and Utter's (1987) study included 9 locations from Hood Canal in the western Puget Sound Basin and 12 locations in the Skagit and Stillaguamish Rivers in northern Puget Sound. This study examined 25 presumptive gene loci and found that 18 were polymorphic (more than 1 allele in at least 1 population). Campton and Utter found evidence for a substantial degree of genetic differentiation between Hood Canal populations and those in northeastern Puget Sound. Average allele frequencies differed by approximately 0.10 at five gene loci, and numerous rare alleles were restricted to just one of the two regions. Differences between populations within regions were generally smaller in magnitude but were, in many cases, statistically significant. For example, Campton and Utter found only slight differences in average allele frequency between cutthroat trout from the Skagit and Stillaguamish Rivers in northern Puget Sound, whereas populations from Hood Canal could clearly be separated into a northern and a southern group. Within drainages, significant heterogeneity of allele frequencies among streams was found for 7 of 12 loci, and the differences were larger among streams from northern Puget Sound than for Hood Canal. 

Campton and Utter concluded that there is substantial restriction of gene flow between coastal cutthroat trout populations in northern Puget Sound and Hood Canal. This conclusion is consistent with the geographical separation of the two areas. They are on opposite sides of the Puget Sound Basin and separated by over 250 km of shoreline. The authors also believed that the level of genetic similarity in these two regions (Nei's genetic identity > 0.97 for all pairwise comparisons of populations) suggests a common ancestry dating to recolonization of Puget Sound after the last glacial retreat about 10,000 years ago. Campton and Utter speculated that the combination of genetic differentiation at the stream level and relatively high average heterozygosity (about 0.10) could be explained by strong homing fidelity with a low level of incidental straying among nearby streams. 

With two exceptions, all of the samples analyzed by Campton (1981) and Campton and Utter (1987) were believed to represent anadromous cutthroat trout. The two exceptions, however, are informative. Campton and Utter (1987) found that the sample from Howe Creek on northern Hood Canal, which was collected above a barrier to anadromous fish, was distinct genetically from all of the other Hood Canal samples. Similarly, Campton (1981) found that a hatchery sample of resident cutthroat trout originally derived from a lake in the northeastern portion of the Puget Sound Basin (Johnston and Mercer 1976), had "diverged appreciably" (p. 79) from all of the other anadromous wild and hatchery populations he had sampled in the Basin. These results suggest that in some circumstances, substantial divergence can occur between resident and anadromous cutthroat trout. 

In their unpublished report on cutthroat trout in southern Oregon, Currens et al. (1992) examined 44 presumptive gene loci and found 23 that were polymorphic. Their report did not distinguish between resident and sea-run forms, but Currens indicated that some populations had access to the sea, while others were collected above barriers to anadromous migration. All fish were less than 250 mm and one was sexually mature, indicating it was probably a resident fish, as mature sea-run fish are usually larger (K. Currens, footnote 9). Within the Coquille River, Currens et al. (1992) found no apparent geographic structure to the pattern of genetic differentiation. Genetic differences among local populations within tributaries were statistically significant and were as large or larger than differences among populations in different tributaries. With one exception, all samples collected in the Coquille River were more similar to one another than they were to a sample from the Chetco River (over 100 km south of the mouth of the Coquille River). The exception is that fish collected from Slater Creek in the Coquille River were as genetically divergent from other Coquille River samples as they were from the Chetco River sample. 

Currens et al. (1992) interpreted these results as evidence for restricted gene flow at the subpopulation level and reduced size of local populations. Unfortunately, these conclusions must be tempered by consideration of the small samples (mean N = 19, range = 6 to 31). In particular, the outlier sample from Slater Creek consisted of just six individuals and the Checto River sample was only nine fish. 

Future Genetic StudiesSamples for a study of life history and genetic variation in coastal cutthroat trout from California to Alaska were collected in 1993 by the USFS (G. Reeves - footnote 10). Samples were collected from various locations in Oregon, including the North and South Umpqua Rivers. The USFS planned to collect a variety of allozyme, mtDNA, meristic, and life-history data on the samples but has not yet completed sufficient analysis to release any information. 

Genetic Relationship of Life-History FormsIn the context of this status review, a key question that needs to be addressed is whether resident, potamodromous, and sea-run life-history forms are different phenotypes within a single gene pool, or whether they represent genetically differentiated gene pools, each possibly adapted to its specific environment? 

There are no studies that specifically address where sea-run, resident, or potamodromous fish are located in the Umpqua River. ODFW (1993a) identified general locations where cutthroat trout larger than 300 mm have been observed and where resident fish have been observed. The fish found between these two areas may be potamodromous fish (ODFW 1993a; D. Loomis, footnote 2). Resident fish are reported in the upper North Umpqua River, as well as in Canton and Steamboat Creeks. Anadromous cutthroat trout are reported in Sutherlin Creek, Little River, and Rock Creek. The area of the North Umpqua River between the confluence of Rock Creek and Steamboat Creek (Fig. 2) is believed by ODFW (D. Loomis, footnote 2) to contain cutthroat trout that only migrate within the river system. 

It has been suggested (Royal 1972, Edie 1975, Jones 1979) that resident cutthroat trout populations may contribute to and even maintain sea-run cutthroat trout populations. Tomasson (1978) reported that larger juvenile fish were the first to migrate out of natal spawning areas into the mainstem Rogue River. He also found that the larger fish were the first to reach the estuary -- suggesting that anadromous behavior may be correlated with growth. However, in one study that addressed this possibility, that hypothesis was not corroborated (Michael 1983). Michael used mark and recapture methods to investigate whether resident populations in three creeks (Snow, Andrews, and Salmon Creeks) on the Olympic Peninsula contributed to a sea-run population. While his studies were not conclusive due to low return rates and physical problems with fish barriers, the results showed that fin-clipped seaward migrants were the progeny of anadromous fish, not residents. Based upon these results, Michael concluded that offspring of resident cutthroat trout populations make little if any significant contribution to anadromous populations. 

Genetic Studies on Life-History Forms in Other SpeciesAlthough cutthroat trout have not been the focus of extensive studies on the relationship of anadromous and nonanadromous populations (Behnke 1972a, Trotter 1989), this issue has been investigated in other salmonid species, especially brown trout (Salmo trutta), arctic char (Salvelinus alpinus), sockeye salmon (O. nerka), and rainbow trout. Studies on these relationships in other species may provide insight into similar relationships in cutthroat trout. At least three possible genetic relationships between life-history forms have been proposed (Ryman 1983): 
- Alternative life-history forms are genetically isolated and represent   separate populations.   
- Alternative life-history forms are not genetically distinct.   
- Alternative life-history forms are genetically distinct within a local   area, but are more similar to one another than they are to their respective   forms outside of the local area. 

Arctic char: In rearing and transportation studies of arctic char, Nordeng (1983) found that offspring from Norwegian anadromous and nonanadromous ("small" and "large" morphotypes) fish may display morphological characteristics of either or both life-history forms . Nordeng concluded that these life-history forms "belong to the same gene pool" (p. 1372). However, he also found that both environmental and genetic factors contributed to the proportion of different life-history forms in the F1 generation. Similar conclusions have been drawn from life-history surveys (Skreslet 1973, Johnson 1980, Hindar and Jonsson 1982, Jonsson and Hindar 1982). 

Hindar et al. (1986) electrophoretically surveyed three char morphotypes (anadromous, non-migratory or landlocked "dwarf," and "normal" resident) from 15 sites in Norway. They found that the absolute values of Nei's genetic distance between life-history forms and populations were small (0.001). Similar studies on arctic char in Ireland (Ferguson 1981) and Scandinavia (Andersson et al. 1983) reported similar results. All these studies concluded that differentiation among localities explains far more of the total gene diversity than differences between life- history forms. 

Brown trout: Rearing studies (reviewed in Rounsefell 1958 and in Skrochowska 1969) demonstrated that resident brown trout parents can produce sea-run offspring and vice versa. However, Skrochowska concluded that the different life-history forms are not in the same gene pool because although offspring of anadromous and nonanadromous parents were reared in a common hatchery environment, they differed markedly in migration tendency and hybrids of the two life-history forms had an intermediate migrational tendency. Skrochowska also found that resident behavior was associated with slow growth as parr. 

In tagging and transplantation studies, Jonsson (1982) monitored and exchanged brown trout from a land-locked lake with trout from a lake with ocean access. He showed that the trout from the land-locked lake displayed less migrational tendencies (overall movement and direction of movement) than the trout from the lake with sea access. In a later study, Jonsson (1985) found that migrational rates of the fish from the anadromous stock were associated with growth rate. 

Three allozyme studies of brown trout in Europe concluded that genetic differentiation was greater among geographic areas than among anadromous and non-anadromous life-history forms (Ryman 1983, Ferguson 1989, Hindar et al. 1991). While average heterozygosities were similar in the three studies, Hindar et al. reported slightly higher levels in mixed sea-run/resident stocks (about 3%) than in land-locked stocks (about 1%). 

Two recent studies reported significant genetic differentiation between life- history forms in brown trout in the Great Lakes (Krueger and May 1987) and in Norway (Skaala and Naevdal 1989). However, as discussed by the authors, neither of these studies would exclude other causes of genetic differentiation as both studies compared life-history forms from different drainages. 

In a protein electrophoretic study on the zoogeographical origin of brown trout in Russia, Osinov (1984) found greater genetic differentiation between brown trout populations separated by large distances than between anadromous and nonanadromous life history forms or between nonanadromous morphotypes within a region. According to Osinov, a number of previous studies (Berg 1948; Barach 1952; Panov 1958; Sharipov 1970, 1976) on Russian brown trout populations concluded that "as regards the anadromous, brook and lake forms, the brook and lake forms appear to be interchangeable." Osinov does not specifically mention differences between sea-run and freshwater life-history forms. 

Brook trout (Salvelinus fontinalis): McGlade and MacCrimmon (1979) used analysis of morphometric, meristic, and electrophoretic characters to compare populations of brook trout from three sites, only one of which contained anadromous fish (Moisie River estuary, Quebec). Their results show a congruence between allelic frequencies and meristic counts, but not between either of these features and morphometric measurements. The meristic and electrophoretic results showed less diversity between anadromous and non-anadromous forms than between geographically isolated populations. However, morphometric differences among populations from river, lake, and estuarine habitats, were significant, suggesting that "geographically isolated populations of brook trout are, in fact, denizens of particular localities" (McGlade and MacCrimmon 1979, p. 2008). 

Atlantic salmon (Salmo salar): Stähl (1987) reported that the results of cluster analyses of data from protein electrophoretic surveys of European and North American Atlantic salmon support the hypothesis that nonanadromous populations were derived from anadromous stocks in postglacial times. He also found that, within broad geographic regions, anadromous and landlocked forms were genetically more similar to each other than they were to their respective forms between regions. 

Sockeye salmon: In morphological studies of various O. nerka populations, Ricker (1940, 1959) and Nelson (1968 a,b) found that kokanee (non-anadromous sockeye salmon) more closely resembled sympatric sockeye runs than they did other geographically distinct kokanee populations. Further, Ricker (1959, 1972), Scott (1984), and Kaeriyama et al. (1992) found that after transplantations of sockeye into lakes previously barren of the species, kokanee populations became established. 

There is also evidence of genetic divergence between sympatric sockeye and kokanee populations. In a survey of gill raker counts from rivers and lakes in northwestern North America, Nelson (1968b) found differences in gill raker counts between sympatric sockeye and kokanee populations (although McCart (1970) did not find any electrophoretic differences in hemoglobin and muscle myogens between the two life-history forms). Nelson cautions that there was no evidence "that allopatric kokanee differ more from sockeye than those kokanee which are still sympatric and thereby perhaps having gene flow with sockeye" (p. 419). Ricker (1940) has also shown that kokanee in a lake with sockeye may spawn at different times and in different locations. Even when spawning is coincident, male sockeye salmon display a strong preference for spawning only with sockeye, although kokanee males may mate with either sockeye or kokanee females (Hanson and Smith 1967, McCart 1970, Foote and Larkin 1988). 

The most extensive electrophoretic survey of O. nerka life-history forms is of 23 populations from various lakes in British Columbia (Foote et al. 1989). Significant and consistent genetic differences were found between sympatric kokanee and sockeye in three systems where they co-occur. However, kokanee and sockeye from the same lake system always were more similar than were the same form from other lake systems. A similar result was found for sockeye salmon and kokanee from Redfish Lake in Idaho. Redfish Lake sockeye salmon were listed as an endangered species under the ESA in 1991 (NMFS 1991a). Genetic data gathered after the listing determination showed that there are large allele frequency differences at several gene loci between the few remaining sockeye salmon and the more abundant kokanee in Redfish Lake (Waples 1992). However, the genetic differences between the two forms in Redfish Lake are relatively small compared to the differences between Redfish Lake O. nerka as a group and sockeye salmon and kokanee populations from other areas of the Pacific Northwest. 

Steelhead / rainbow trout: In an electrophoretic survey of steelhead and rainbow trout from Washington, Oregon, and Idaho, Allendorf (1975) and Allendorf and Utter (1979) did not find genetic support for division of the species on the basis of life- history forms. The authors concluded that the species O. mykiss was genetically structured into a coastal and inland form, rather than into an anadromous and non- anadromous form. Similar results were also reported by Wilson et al. (1985) from a smaller-scale study on mtDNA variation in steelhead and rainbow trout. 

Sex ratios of different salmonid life-history formsIn a number of surveys of differences between anadromous and resident populations, it has been found that males predominated among resident spawners and females among anadromous spawners. This has been found in chinook salmon (Healy 1991), Atlantic salmon (Myers 1984), arctic char (Nordeng 1983), and sockeye / kokanee (Ricker 1938). If males are less likely to outmigrate than females, this would be an indication that anadromous and resident groups could belong to the same population (Campbell 1977, Jonsson 1985). 

In 1946, Sumner (1972) reported a 3.1 predominance of female to male adult sea-run cutthroat trout at Sand Creek in Oregon, although in other years (1947- 1949) the ratio was only 1.6 to 1 in favor of the females. Although Sumner (1972, p. 24) suggests that "these figures are not 100 percent accurate" due to the difficulty in accurately sexing fish early in the run, he also referenced a 1954 Alsea Hatchery report that gave a similar ratio of 1.9 females to 1 male. Cramer (1940), however, reported a ratio of 1.1 males to 1 female obtained from a random count of spawners from the same hatchery. 

We have no current data on sex ratios among wild or hatchery stocks of cutthroat trout. 

Hatchery Releases in Umpqua River BasinSince the mid-1970s, yearly hatchery production of cutthroat trout in Oregon has ranged from 200,000 to 300,000 smolts per year. Most of these plantings have been from stock derived from the Alsea River (Nickelson et al. 1992). This stock is reared at ODFW's Alsea River and Cedar Creek hatcheries. Alsea River stock are released in 6 to 10 different coastal rivers in Oregon. For example, in 1987 approximately 280, 000 Alsea stock smolts were released into the Alsea River, Salmon River, Siletz River, Smith River, Scholfield Creek, and Siuslaw River. A smaller group of "Nehalem stock" cutthroat trout has also been released, mainly in northern Oregon coastal rivers. In 1993, releases of hatchery cutthroat trout in Oregon were re-evaluated and reduced in some areas (D. Loomis, see footnote 2). In the Umpqua River Basin, Alsea River hatchery fish have been released both in the North Umpqua River below Winchester Dam and in the Smith River and Scholfield Creek at the mouth of the Basin (Fig. 2). 

Hatchery Releases in the North Umpqua RiverThere is less information available on releases of hatchery fish in the North Umpqua River. Between 1961 and 1976, approximately 20,000 cutthroat trout were released per year (Table 1, Fig. 6). The fish were Alsea River hatchery broodstock; smolts were released a few miles below Winchester Dam (ODFW 1993a) at Amacher County Park and Hestness Park (D. Loomis, see footnote 2). No stocking has occurred since 1976, although returns through 1979 could reflect hatchery fish, as cutthroat trout are not semelparous (Fig. 6). 

The effect on native runs of the fish released into the North Umpqua River is unknown. Counts of cutthroat trout passing Winchester Dam increased dramatically during the first 3 years hatchery fish were released below the dam (1961-1963), but were declining steeply before hatchery planting was stopped in 1976 (Fig. 7). For some or all of the years that hatchery fish were released below Winchester Dam, ODFW biologists adipose- or ventral-fin clipped a percentage of the fish released. Unfortunately, fin clip data collected from returning cutthroat trout at Winchester Dam are incomplete and it is unclear whether these marks were consistently recorded at the dam (D. Loomis, see footnote 2). 

Although there are also no quantitative data available on straying rates during the years of hatchery releases near Winchester Dam, ODFW biologists believe that the straying rate was high, since many fin clipped cutthroat trout were found throughout the North and South Umpqua Rivers and in tributaries of the mainstem river (D. Loomis, see footnote 2). 

 Figure 6. Yearly releases of Alsea River Hatchery cutthroat trout below Winchester Dam (bars) compared to the number of adult cutthroat trout (line) passing Winchester Dam, 1956 to 1981 (ODFW 1993a). 
Return-timing of hatchery and natural adults As discussed in a previous section, Adult Freshwater Migrations, ODFW has recorded the upstream movement of cutthroat trout past Winchester Dam annually since 1946 and at 2-week intervals since 1951. Throughout most of this period, Umpqua River cutthroat trout passed Winchester Dam from late June through November, with a bimodal peak in mid-July and mid-October. Figure 7 depicts the seasonal timing of this movement during three periods: 1) before Alsea River hatchery cutthroat trout were planted into the Umpqua River, 1946-1960; 2) during hatchery cutthroat trout plants, 1961-1976; and 3) after terminating the hatchery cutthroat trout plants, 1980-1993 (ODFW, unpubl. data). Because hatchery fish may have continued to return to Winchester Dam during 1977 through 1979, these years are not included in the analysis. The plots indicate the presence of strong bimodality in cutthroat trout migration timing during the first two periods but not the latter. In addition, migration timing shifted to later dates during the period when hatchery fish were planted in the river. 
Because the difference in sample size of the three time intervals analyzed was large (696 in 1951 to 1960, 918 in 1961 to 1976, and 56 in 1989 to 1993), an extension of the median test (Daniel 1978, p. 196) was used to test for differences in migration timing among the three periods. We chose this nonparametric test because of the evidence for strong departure from normality due in the data to bimodality. The extension of the median test employs a chi-square test for homogeneity to evaluate variation in the numbers of fish (across years within periods) that were counted migrating before or after the pooled median migration date. A total of 22,428 cutthroat trout was recorded over the period 1951 to 1993 (excluding fish recorded from 1977 to 1979). Over all samples, the median migration timing occurred during the first two weeks of October. The test was performed after discarding all observations occurring during this interval to minimize the incidence of "ties" in migration timing. The resulting chi square revealed that migrating timing differed significantly among the groups (chi square = 1860.4, 2 df, P < 0.005). 

Figure 7. Bimonthly percentage of adult cutthroat trout passing Winchester Dam, 1951 to 1960 (shaded squares), 1961 to 1976 (circles, broken line), and 1980 to 1993 (unshaded squares). The time periods represent fish counts before hatchery fish were planted below Winchester Dam, during hatchery supplementation, and after hatchery plantings were stopped in 1976. Because hatchery fish may have continued to return to Winchester Dam during 1977 to 1979, these years were omitted from the analysis (ODFW 1993a). 
Individual median tests (Daniel 1978, p. 78), which use the normal approximation, were performed on each pair of the three samples because the extension of the median test does not provide for multiple comparisons. The individual median tests indicated that all three samples differed significantly (minimum T = 10.31, P < 0.001). The order of migration timing was 1978-1993 < 1946-1960 < 1961-1977; thus, the timing shifted to later dates during hatchery plants but, after the plants ceased, returned to earlier dates. Interestingly, migration dates in the years since 1980 have been even earlier than they were before the hatchery plants. This may be due in part to the virtual disappearance of the late peak in returns since 1980. However, the low abundance of cutthroat trout during this period makes it difficult to determine the precise shape of the migration-timing distribution. 
Hatchery Releases in the Lower Umpqua River Hatchery releases occurred in the Smith River from 1975 to the present, and in Scholfield Creek from 1983 to the present (Table 1, Fig. 8). Approximately 12,000 hatchery fish per year have been released into the Smith River and 4,000 per year into Scholfield Creek. These fish are released as smolts and as legal-sized catchable trout prior to or during the trout fishing season (ODFW 1993a). 

There are no reports on straying rate of cutthroat trout from the lower Umpqua River into other Umpqua River tributaries. However, beginning in 1992, all hatchery fish released in Smith River and Scholfield Creek have been fin clipped (ODFW 1993a). To date, no fin-clipped fish have been reported crossing Winchester Dam (D. Loomis, see footnote 2). Still, in 1993, ODFW reassessed their cutthroat trout hatchery program and reduced the number of hatchery cutthroat trout released into the Umpqua River (D. Loomis, see footnote 2). 

Figure 8. Yearly releases of Alsea River Hatchery cutthroat trout into the Smith River and Scholfield Creek (bars) compared to the number of adult cutthroat trout (line) passing Winchester Dam, 1975 to 1993 (ODFW 1993a). 
There are no studies or reports on habitat utilization or competitive interactions between hatchery cutthroat trout released into Smith River or Scholfield Creek and naturally spawned fish from the North Umpqua River Basin. However, studies on cutthroat trout in other estuaries in Oregon (e.g., Alsea, Nestucca, Siuslaw, Rogue Rivers) suggest estuaries are critical areas where juvenile and adult cutthroat trout spend considerable time (Lowry 1965, Giger 1972, Tomasson 1978). It would be likely that naturally spawned fish and Alsea River hatchery fish planted into lower Umpqua River tributaries interact extensively in the Umpqua River estuary. 
Hybridization Between Cutthroat and Rainbow TroutThe interbreeding or introgressive hybridization (often called introgression) of native cutthroat trout with introduced hatchery strains of rainbow trout is often cited as the major cause of the decline of cutthroat trout across the American West (Busack and Gall 1981, Leary et al. 1984, Campton and Utter 1985, Gyllensten et al. 1985, Martin et al. 1985). It is believed this process has compromised the genetic integrity of native populations and resulted in the extinction of two cutthroat trout subspecies (Behnke and Zarn 1976; Behnke 1979, 1992; Allendorf and Phelps 1981; Busack and Gall 1981; Allendorf and Leary 1988). 

The fitness and reproductive success of hybrids between cutthroat and rainbow trout has not been extensively investigated (Busack and Gall 1981, Allendorf and Leary 1988). Studies from hatchery populations have shown that hybrids between these species are often fertile and capable of interbreeding with each other and parental taxa, but may also have lower fitness than the parental taxa (Allendorf and Leary 1988). In one study on a naturally occurring population, Busack and Gall (1981) used meristic and electrophoretic analyses to evaluate two populations of Paiute cutthroat trout (O. seleniris) from California. They found one population to be a hybrid swarm, composed of hybrids between the native trout and introduced rainbow trout. 

Developmental stability as measured by meristic analysis has been used to evaluate the offspring of rainbow trout hybridized with three different subspecies of cutthroat trout. The hybrid juveniles had decreased developmental stability relative to their parental taxa (Leary, et al. 1985). In another study, offspring of crosses between westslope cutthroat and rainbow trout were shown to have had slower growth rates than parental taxa under hatchery conditions (Allendorf and Leary 1988). 

Natural sympatry of rainbow and cutthroat trout is rare, occurring primarily in the coastal cutthroat trout subspecies. It is believed that spatial and temporal separation of spawning have acted as isolating mechanisms to allow the two species to remain distinct in areas of sympatry (Trotter 1989). However, fish that have morphological similarities to both O. c. clarki and O. mykiss have been reported in numerous studies (DeWitt 1954, Needham and Gard 1959, Hartman and Gill 1968, Sumner 1972). Identification of natural hybrids of rainbow and coastal cutthroat trout by protein electrophoresis was first documented by Campton and Utter (1985) from fish collected in two streams from the northern basin of Puget Sound. 

Sumner (1972) reported a number of possible rainbow x cutthroat trout hybrids found along the Oregon coast. He noted that, following planting of inland cutthroat trout into the Higgins Reservoir in Oregon in the late 1940s, a number of fish morphologically intermediate between rainbow and cutthroat trout were found. Sumner also reported a variety of presumed hybrids found in headwater streams at the boundary between the usual spawning areas of steelhead and cutthroat trout in the Tillamook, Miami, Wilson, and Trask Rivers. Possible rainbow x sea-run cutthroat trout were also found from the Nestucca River. These Nestucca hybrids resembled coastal cutthroat trout, but Sumner (1972, p. 85) noted that they were "above average in size" and had larger and coarser scales than cutthroat trout. According to Sumner (1972, p. 86), at one time "many years ago," cutthroat trout x steelhead hybrids were reared at the Alsea Hatchery, and "they were said to have been large for their age...." 

Releases of Hatchery Rainbow Trout in the Umpqua River The potential for introgression of cutthroat with rainbow trout in the Umpqua River Basin is substantial. Intense stocking of hatchery rainbow trout into the watershed began in the mid-1940s (Loomis et al. 1993) and has continued unabated for over 45 years. In 1992, about 533,000 rainbow trout were released in the basin. Although the majority of these fish (476,000) were planted into reservoirs and lakes, 57,000 legal-sized rainbow trout were planted into the North Umpqua River, South Umpqua River, Little River, Cow Creek, and Calapooya Creek. 

Possible cutthroat and rainbow trout hybrids were collected in 1991 from Fish Creek in the North Umpqua River. Meristic analysis indicated that the fish phenotypically resembled rainbow trout (D. Markle - footnote 11 ). No cutthroat and rainbow trout hybrids in the Umpqua River Basin were reported in the 1992 Oregon Wild Fish Management Policy Biennial Progress Report (Chilcote et al. 1992), although both cutthroat and rainbow trout were reported from Fish Creek. Although rainbow trout have been planted into the basin for over four decades, the report only listed two locations throughout western central Oregon with putative cutthroat and rainbow trout hybrid populations, Twomile and Crooked Creeks, neither of which are in the Umpqua River Basin. 

Efforts by ODFW biologists to avoid hybridization of hatchery rainbow trout with cutthroat trout in the Umpqua District have concentrated on stocking non- native rainbow trout with different spawning times than native cutthroat trout (Kinunen and Moring 1976, Loomis et al. 1993). All rainbow trout released into the Basin in 1992 were from two stocks of non-native trout The majority of the these fish, 435,000 or 81.6%, were Oak Springs stock (ODFW stock 53) and were planted as juvenile (fingerling) trout into Diamond Lake near the headwaters of the North Umpqua River. Similar numbers of the strain have been planted into Diamond Lake and other bodies of water in the Umpqua Basin since at least 1975 (Kinunen and Moring 1976, Chilcote et al. 1992, Loomis et al. 1993). Artificial propagation of this stock is thought to have begun in Utah in 1923. Interestingly, while this strain is fall- spawning in the hatchery, in Diamond Lake it reverts to an April-May regimen. 

The other non-native rainbow trout stock planted into the Umpqua Basin in 1992 was from the Cape Cod strain (ODFW stock 72). These fish were stocked as legal-size trout into the North and South Umpqua Rivers as well as into tributaries of the mainstem river. The Cape Cod strain were originally from Massachusetts and were first transported to the Pacific Northwest in 1941 or 1942 (Kinunen and Moring 1976). 

There are numerous populations of naturally spawning rainbow trout in the Umpqua River Basin, but how many of these are originally of hatchery or natural origin is undocumented . Chilcote et al. (1992) listed six rainbow trout populations in the Basin , while Loomis et al. (1993) listed nine. These authorities have identified presumably naturally spawning rainbow trout in the mainstem North Umpqua River, upper North Umpqua River above Soda Springs Dam to Tokatee Lake, Fish Creek, Mowich Creek, Clearwater River, and in several other tributaries (Chilcote et al. 1992, Loomis et al. 1993). In the South Umpqua River, rainbow trout populations have been identified in the mainstem above Galesville Dam, Cow Creek, and other tributaries (Chilcote et al. 1992, Loomis et al. 1993). 

Several tributaries in the Umpqua River Basin contain only rainbow trout and others only cutthroat trout, but there are some tributaries, such as Cow Creek on the South Umpqua River, that contain both (Loomis et al. 1993). In tributaries that contain both cutthroat and rainbow trout, the cutthroat trout often occur in the upper headwater areas and rainbow trout in the lower areas, with a potential hybrid zone in between (J. Dose, footnote 5). We were unable to identify any studies on possible hybridization between rainbow and cutthroat trout from these sites. 
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