U.S. Dept Commerce/NOAA/NMFS/NWFSC/Publications NOAA-NWFSC Tech Memo-10: Status Review for Illinois River Winter Steelhead Population Trends
Regional Overview of Steelhead Abundance 

Three substantial reviews of North American steelhead abundance have been undertaken, by Sheppard (1972), Light (1987), and Cooper and Johnson (1992). 

Sheppard (1972) reviewed historical commercial catch records from the 1890s through the 1960s. Total U.S. commercial steelhead catch declined from an average of 2,700,000 kg in the 1890s to an average of 370,000 kg in the 1960s--a sevenfold decline. Sheppard attributed most of this decline to restrictions on the fisheries rather than decline in abundance. For the period from 1945 to 1962, however, the Oregon coastal fishery was primarily an Indian gill-net fishery with relatively stable effort, so statistics for that fishery do provide an index of abundance. This fishery declined from an average of 38,100 kg in 1945-49 to an average of 1,500 kg in 1958-62. The fishery was discontinued in 1962 due to declining stocks. 

Sheppard (1972) also reviewed trends in sport catch of steelhead. Steelhead sport fishing statistics were first formally collected after World War II, when Washington (1948) and then Oregon (1952) instituted punchcard systems. California began using questionnaires to estimate steelhead catch in 1953 but discontinued regular reporting after 1956. In both Washington and Oregon, number of anglers and total steelhead sport catch increased roughly twofold from 1953 to 1969, the last year included in Sheppard's study. 

Finally, Sheppard (1972) provided rough estimates of total regional average adult steelhead runs in the early 1970s: California, 400,000; Oregon, 357,200; Washington, 606,400; Idaho, 42,500; British Columbia, 112,000; total, 1,528,000. These estimates were based on an expansion of total sport and commercial catch, assuming a 50% catch rate. Sheppard's overall assessment was that North American steelhead abundance remained relatively constant from the 1890s through the 1960s, although there had been significant replacement of natural production with hatchery production in California, Oregon, and Washington. 

Light (1987) attempted to estimate total average run size for the mid-1980s based on sport harvest data, dam counts, and other resource agency information (Table 12). The coastwide total of 1.6 million is similar to Sheppard's estimate 15 years earlier. 

Cooper and Johnson (1992) focussed on recent regional trends in steelhead abundance, using catch and hatchery returns as indices. They did not attempt an overall abundance.Table 12.estimate. They noted a recent (1985 to 1991) decline in steelhead returns (both hatchery and wild) in British Columbia, Washington, and Oregon, and they suggested common factors that might be responsible for that decline, including a combination of low ocean productivity in the Gulf of Alaska, competition for food due to increased salmonid hatchery smolt releases and increased pink and sockeye salmon stocks, and catch of steelhead in high-seas driftnet fisheries (primarily in unauthorized fisheries). 

Historical Abundance in Southern Oregon 

Information on steelhead abundance in southern Oregon before the 1950s is sketchy, coming primarily from Rivers' (1957, 1963) studies of Rogue River basin steelhead. Regarding late 19th-century fisheries in the Rogue River basin, Rivers (1963, p. 56) reported that 
cutthroat and downstream migrant steelhead were abundant and   easily caught by the hundreds from streams all through the settled portions of   the basin.... The headwaters of the Applegate River, the Illinois River,   Jumpoff Joe Creek, and Grave Creek were sections of the basin preferred for   trout fishing because of the easy access afforded by mining roads. Specifically regarding the Illinois River, he reported (p. 55) interest in sport fishing for steelhead in the Applegate and   Illinois sections of the drainage was limited. A few people fished the   Applegate, but up to 1941, there were less than 25 people known to fish the   Illinois River for steelhead. The anglers were attracted by the concentration   of fish at the Illinois Falls ladder. Rivers (1957) estimated that the steelhead catch for 1950-56 in the Illinois River averaged zero for spring run (early summer-run), 10-40 for fall run (late summer-run), and 1,400-1,800 for winter run. 
Abundance of Illinois River Winter Steelhead 

Two sources of data on abundance of Illinois River steelhead are available: angler catch estimates generated by ODFW from returns of salmon/steelhead punchcards covering the period 1952-91 (Tables 13 and 14), and records of juvenile steelhead caught in irrigation diversion traps, primarily for the period 1975-91. The diversion trap records (ODFW 1992c) have not been consistently kept, the traps are operated differently in different seasons and years, and the trap catches are affected by changes in river flow and irrigation practices; thus, the records do not provide a reliable indication of population trends and will not be discussed. 

Interpreting population abundance from the angler catch data presents several problems. First, numbers of fish caught do not directly represent abundance, which must be estimated from catch by applying assumptions about fishing effort and effectiveness. Fishing effort is largely determined by socioeconomic factors, including fishery regulations. Fishing effectiveness is a function of both the skill of the anglers and environmental conditions which affect behavior of both fish and anglers. Both effort and effectiveness may exhibit long-term trends and interannual fluctuations that can obscure the relationship between catch and abundance. Second, estimates of catch may not be accurate. In Oregon, catch is estimated from returns of punchcards corrected for nonreporting bias. While catch estimates are generated separately for each stream basin, the bias correction is calculated statewide and may not be accurate for any particular stream due to local variations in the tendency to return punchcards. Third, when fishing effort varies across a river basin, catch may reflect only local abundance rather than the total basin population. All three of these problems have been discussed for the Illinois River basin by Cramer (1992), who argued that catch estimates are not a good index of steelhead abundance in that system. We discuss each problem briefly below. 

Variation in fishing effort and effectiveness--One letter received by NMFS from a local angler (Williams 1992) suggested that fishing pressure in the Illinois River has declined substantially and that this decline could account for the decline in catch. To our knowledge, no accurate records of fishing effort on the river are available to evaluate this claim. For comparison, statewide salmon and steelhead fishing effort (as indexed by number of punchcards issued) has been relatively constant since the late 1970s (Fig. 4), and winter steelhead catch rates (calculated by comparing catch estimates with dam passage counts) for the upper Rogue and upper North Umpqua Rivers have shown only small variation over the last several years (Fig. 5). 

Nonreporting bias--Catch data can be used to develop population abundance estimates and population trend estimates. While it is probable that reporting rates in the Illinois River basin differ from the statewide average, this would only result in a general bias in estimates of total catch, making estimates of total population abundance questionable. We have no indication of whether there is any local trend in reporting rate that would result in a bias in population trend estimates. 

Local variation in fishing effort--A substantial problem with catch data in the Illinois River basin is that fishing effort is concentrated in the upper river near Cave Junction, and there is very little fishing in the lower river. We have no good information regarding historical or present distribution of steelhead spawning throughout the basin. From catch data, we cannot conclude whether spawning in the lower river tributaries represents a substantial portion of the total population. Cramer (1992) argued that the lower river represents better spawning habitat than the upper river, and that "steelhead populations in these streams could be near carrying capacity even when catch for the basin as a whole is at record low levels." While this is possible, we have no evidence to suggest that lower river stocks operate independently of upper river stocks. Without definite knowledge of factors influencing the populations, we must either assume that upper river trends reflect abundance in the total basin, or conclude that it is impossible to determine population trends from available data. 

The following analysis assumes that catch trends reflect trends in overall population abundance. We recognize that variations in effort and effectiveness introduce a certain amount of error, and that the index does not adequately represent the complete river basin, but believe that changes in catch still provide an indication of trends in population abundance. 

The trend in catch of Illinois River winter steelhead over the historical record has been downward, when expressed as either absolute catch or relative to total Rogue River or statewide steelhead catches (Fig. 6). This implies that there are specific local factors causing a decline beyond the recent regional declines in steelhead abundance. Analysis of returns-per-spawner indicates that production has been below replacement in most years (Fig. 7), and fitting an exponential trend to the catch time series (Fig. 6A) indicates an average decline of about 5.5% per year over the entire record (1956-90). 

Because there are no direct estimates of catch rate for the Illinois River, only rough estimates of total run size can be calculated, and those only for the upper river where the fishery is concentrated. Kenaston (1989) classified the Illinois River steelhead fishery as "low intensity" and applied an average exploitation rate of 0.08 which was estimated for other low intensity winter steelhead fisheries (upper North Umpqua River and upper Rogue River) to estimate total run size for the Illinois River for 1981-85. In recent years, estimated exploitation rate for these fisheries has ranged from 0.04 to 0.14, with a mean of 0.09 (Fig. 5. If the steelhead exploitation rate in the total upper Illinois River is comparable to these fisheries, then the upper Illinois River steelhead run size would be in the range of 7 to 25 times the annual catch. 

Abundance of Steelhead in Southern Oregon 

To provide some perspective on Illinois River steelhead abundance, we briefly reviewed other steelhead stocks in southern Oregon (south of Cape Blanco). There are seven main steelhead rivers in this area: Elk, Pistol, Rogue, Applegate, Illinois, Chetco, and Winchuck. Of these, four (Elk, Pistol, Illinois, and Winchuck) are managed for "wild" production and should have little or no direct hatchery influence (Nickelson et al. 1992), although there may be some effect of straying and unaccounted hatchery plants. We considered the hatchery-influenced rivers (Rogue, Applegate, and Chetco) separately from the "wild" coastal rivers. 

Rogue, Applegate, and Chetco Rivers--The presence of Cole Rivers Hatchery, which releases smolts of both summer and winter steelhead into both the Rogue and Applegate Rivers, makes evaluation of trends in naturally spawned stocks difficult. We have no direct estimates of "natural" spawning runs for the Applegate River, but overall catch (hatchery and natural fish combined) for both summer and winter runs have been steady over the last 20 years (Fig. 8). Overall catch of both runs in the Rogue River has been steady or increasing (Fig. 8), and available "wild" fish counts at Gold Ray Dam (up to 1987) indicate that this is true of both hatchery and naturally-spawned fish. The Chetco River supports a considerable winter steelhead fishery and is stocked with steelhead from Elk River Hatchery. We have no data to separate hatchery from naturally-spawned fish, but the overall trend in catch has been level (Fig. 8). 

Elk, Pistol, and Winchuck Rivers--These rivers, along with the Illinois River, represent the majority of southern Oregon steelhead production outside of the hatchery-influenced rivers. All have predominantly winter-run steelhead. Elk River steelhead catches (Fig. 9) have experienced a decline similar to that for the Illinois River stock (Fig. 6). The Pistol and Winchuck Rivers have maintained low, fluctuating steelhead catches, with no apparent trend (Fig. 9). 
DISCUSSION AND CONCLUSIONS
In this section, we address the two key questions raised at the start of this status review: Do Illinois River winter steelhead represent a species as defined by the ESA? and, if so, is the species threatened or endangered? We begin by summarizing evidence developed in the status review that is relevant to the two criteria that must be met for a population to be considered an ESU, and hence a species under the ESA. 
Reproductive Isolation
Straying Rates 

As the petitioners pointed out, the high degree of homing fidelity of Pacific salmon and steelhead allows for the possibility that individual spawning populations can experience substantial reproductive isolation. This general argument, however, provides no specific evidence that this has occurred with Illinois River winter steelhead. We are not aware of current or historical data on straying rates of natural steelhead either into or out of the Illinois River. 

Barriers to Migration 

The Illinois River Falls (RKm 64) is a convenient landmark for separating the Illinois River into upper and lower sections. Important spawning grounds for steelhead are found in the upper section, but it is not clear whether this was the case prior to modification of the falls to improve fish passage earlier in this century. It is possible, as the petitioners speculated, that the falls historically acted as an isolating mechanism by selecting against strays that might not arrive at the proper time and might not have the ability to surmount the barrier. Again, however, we found no direct evidence that this was the case. 

Steelhead that spawn in the upper parts of the river are separated by as much as 120 km from the confluence of the Illinois and the Rogue Rivers, and this may contribute to reproductive isolation of steelhead spawning above Illinois River Falls. However, there is evidence that streams in the lower Illinois River may be an important source of steelhead smolt production. These areas are considerably closer to (and hence potentially less isolated from) steelhead spawning areas in other river systems. 

Genetic Data 

Data from several studies provide evidence for some level of genetic differentiation between steelhead from north and south of Cape Blanco. However, a protein electrophoretic survey conducted as part of this status review failed to find evidence for genetic distinctiveness of steelhead from four locations throughout the Illinois River basin. This finding is consistent with results reported by Hatch (1990) for steelhead from Lawson Creek, a lower Illinois River tributary. 

Life History Traits 

The 2-week shift in time of peak spawning for steelhead from the Illinois River relative to some other populations in the Rogue River basin may reflect reproductive isolation. However, this shift is relatively small; in fact, it is no larger than year-to-year differences in spawn timing observed in Rogue River summer steelhead. A longer time series of data is necessary to determine whether spawn timing of Illinois River winter steelhead differs consistently from steelhead in nearby drainages. 

In other life history characteristics (e.g., smolt age, age and size at first spawning, and absence of half-pounders), Illinois River winter steelhead appear to differ somewhat from Rogue River steelhead. Again, this may reflect reproductive isolation between steelhead from the two rivers. Alternatively, these differences may simply reflect habitat differences between the Illinois and Rogue Rivers, since it is known that these and other life history traits can be strongly influenced by environmental conditions. A large hatchery program for Rogue River steelhead has been in operation for several decades, and it is also possible that artificial propagation has affected life history parameters in Rogue River steelhead, thus contributing to observed differences from Illinois River winter steelhead. 

Finally, with respect to these life history characteristics, Illinois River winter steelhead are similar to most other coastal steelhead populations from outside the Rogue River basin. Thus, the degree to which Illinois River winter steelhead are isolated from these other populations is unclear. 

Summary 

Available information does not make a strong case for reproductive isolation of Illinois River winter steelhead. Genetic data fail to show that Illinois River winter steelhead as a.group are distinct from other coastal steelhead populations. Although this does not prove that Illinois River winter steelhead are not reproductively isolated, it does mean that evidence to support reproductive isolation must be found elsewhere. Other lines of information are largely inconclusive in this regard. Straying data for naturally spawning steelhead in the region are largely nonexistent. Geographic features such as the Illinois River Falls are potential isolating mechanisms, but evidence that they operate in this way is lacking. Although other explanations are possible, life history characteristics suggest some degree of reproductive isolation from Rogue River steelhead is likely. However, these same characteristics fail to show differences between Illinois River winter steelhead and other coastal steelhead populations. 
Evolutionary Significance
Habitat Characteristics 

Adaptations to environmental conditions such as elevated water temperature may contribute substantially to ecological/genetic diversity of species such as Pacific salmon and steelhead, which have a limited tolerance for water above about 18�C. Water temperatures in at least some sections of the Illinois River appear to be higher than are found in some nearby coastal streams. However, other coastal rivers (e.g., the Umpqua River) have temperature profiles similar to those in the Illinois River. Furthermore, in light of reports that steelhead from the Rogue River historically entered the lower Illinois River in temporary search of cooler water, present water temperatures in the Illinois River may not be a good indication of historical temperature patterns. 

Phenotypic and Life History Traits 

Many of the life history traits cited by the petitioners as evidence for reproductive isolation are also important to consider with respect to the contribution of Illinois River winter steelhead to ecological/genetic diversity of the species O. mykiss. For example, the half-pounder life history has a limited distribution and is considered unusual. Although it is not well understood why this life history is common in some steelhead populations, it appears to represent an evolutionary adaptation that may contribute substantially to ecological/genetic diversity of the biological species. In contrast to other Rogue River basin steelhead populations that have been studied, Illinois River winter steelhead lack this trait. It could be argued that this indicates ecological/genetic differentiation between steelhead from the Illinois and Rogue Rivers. However, in other drainages where half-pounders occur (e.g., the Klamath and Eel River drainages), it is not clear that all tributaries have half-pounder runs, so the Illinois River may not be unique in this respect. Furthermore, as half-pounders occur only in certain rivers in southern Oregon and northern California, Illinois River winter steelhead are similar to most other coastal steelhead populations in lacking this trait. Other life history traits identified by the petitioners show a similar pattern: Illinois River winter steelhead are somewhat different from Rogue River steelhead, but not distinctive in comparison with other coastal steelhead populations. 

Genetic Data 

It is generally presumed that genetic characters detected by protein electrophoresis are largely neutral with respect to natural selection and therefore do not provide direct evidence about important adaptations. Nevertheless, the occurrence of substantial genetic differences at neutral markers would suggest that there has been ample opportunity for selection to foster.adaptive differences at other parts of the genome. Genetic data for Illinois River winter steelhead provide no evidence to suggest such adaptive differences. 

Effects of Artificial Propagation 

Although Illinois River winter steelhead are generally considered to be the best remaining example in Oregon of an indigenous, "wild" steelhead run, we found records of introductions of hatchery fish from outside the basin. Nevertheless, the hatchery releases were few and did not involve large numbers of fish. Furthermore, many of the releases involved early life history stages of steelhead whose survival rate was likely very low. Absent any information to the contrary, it is reasonable to assume that the permanent effects of these hatchery releases on population structure of Illinois River winter steelhead have been small. 

The very limited scale data for Illinois River winter steelhead also are consistent with the theory that straying of hatchery fish into the Illinois River occurs at a low rate. 

Summary 

Several phenotypic and life history characteristics show modest differences between Illinois River winter steelhead and steelhead from the Rogue River. These differences suggest that either a) there are some genetic differences between steelhead from the two rivers, b) the natural environments of the two rivers differ in at least some respects, or c) artificial propagation has affected life history parameters of Rogue River steelhead, thus causing them to differ from Illinois River winter steelhead. In any case, in the larger context of coastal steelhead from southern Oregon and northern California, it is the Rogue River fish, rather than the Illinois River winter steelhead, that appear to be somewhat anomalous. That is, steelhead from the Illinois River appear to be somewhat distinctive in comparison to Rogue River steelhead, but not in comparison to other coastal steelhead populations. 
Conclusions
At best there is weak evidence that Illinois River winter steelhead experience substantial reproductive isolation from other coastal steelhead populations. In several respects, Illinois River winter steelhead differ somewhat from Rogue River steelhead, but in these same characteristics, steelhead from the Illinois River are similar to most other coastal steelhead populations. We therefore conclude that although Illinois River winter steelhead may be locally distinctive within the Rogue River basin, they do not by themselves represent an evolutionarily significant unit of the biological species Oncorhynchus mykiss. 

Because Illinois River winter steelhead are therefore not a "species" as defined by the ESA, the question of whether they should be listed as threatened or endangered under the Act need not be addressed. Nevertheless, steelhead from the Illinois River are undoubtedly part of a larger ESU whose boundaries remain to be determined. Whether the larger ESU that contains Illinois River winter steelhead would merit protection under the ESA cannot be determined until the nature and extent of the ESU are identified and additional information about patterns of abundance in coastal steelhead is compiled. This status review, therefore, should be viewed as the first step in a process to define the larger ESU and determine whether it qualifies for protection under the ESA. 
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