OREGON CHUB RESEARCH IN THE WILLAMETTE VALLEY Paul Scheerer Oregon Department of Fish and Wildlife Corvallis, Oregon 97333

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1 OREGON CHUB RESEARCH IN THE WILLAMETTE VALLEY Paul Scheerer Oregon Department of Fish and Wildlife Corvallis, Oregon Oregon chub Oregonichthys crameri are endemic to the Willamette Valley of western Oregon. This species was formerly distributed throughout the Willamette Valley in off-channel habitats such as beaver ponds, oxbows, stable backwater sloughs, and flooded marshes (Snyder 1908) (Figure 1). These habitats usually have little or no water flow, silty and organic substrate, and considerable aquatic vegetation and cover for hiding and spawning. In the last 90 years, these habitats have disappeared rapidly because of changes in seasonal flows resulting from the construction of dams throughout the basin, channelization, revetments, diking, drainage of wetlands, and agricultural practices. By 1967, the channel length of Willamette River had been drastically reduced (Sedell and Froggatt 1984). This loss of habitat combined with the introduction of non-native species to the Willamette Valley such as largemouth bass Micropterus salmoides, smallmouth bass Micropterus dolomieui, crappie Pomoxis sp., bluegill Lepomis macrochirus, and western mosquitofish Gambusia affinis has resulted in a sharp decline in Oregon chub abundance. The reduction of suitable habitat and the restricted distribution of the Oregon chub resulted in a determination of "endangered" status under the federal endangered species act (Markle and Pearsons 1990; Rhew 1993). In the late 1980 s, researchers at Oregon State University became concerned about the status of Oregon chub populations and collected information regarding their distribution and natural history (Pearsons 1989; Markle et. al. 1991). The Oregon Department of Fish and Wildlife Aquatic Inventories Project conducted surveys throughout the Willamette River Valley in (Scheerer et. al. 1992; 1993; 1994; 1995; 1996; 1998; 1999; Scheerer and Jones 1997) (Figure 2). The surveys provided information on the distribution and abundance of Oregon chub, the distribution of native and non-native species, the characteristics of historic Oregon chub habitats, the characteristics of potential reintroduction sites, and the status of Oregon chub reintroductions. In June 1996, we initiated a study to collect additional information regarding life history, population dynamics, aquatic communities, and habitat parameters necessary to determine the factors that limit Oregon chub populations and to aid in the recovery of this species (Scheerer 1997; Scheerer and Apke 1998; Scheerer et. al. 1999). 1

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4 Objectives Objective 1: Objective 2: Determine the status of Oregon chub in the Willamette Valley. Estimate the abundance of selected Oregon chub populations. Investigate off-channel habitats for the presence of previously unknown Oregon chub populations and describe the habitat characteristics of these locations. Investigate factors that favor abundant Oregon chub populations and determine factors limiting Oregon chub abundance. Evaluate habitat variables and faunal characteristics of Oregon chub sites to identify key variables that influence Oregon chub abundance. Task 2.1: Task 2.2: Task 2.3: Task 2.4: Monitor temperature profiles, water chemistry, and composition of aquatic vegetation across the range of Oregon chub locations. Quantify population abundance of Oregon chub and other fish species at selected sites. Monitor and evaluate natural fluctuations in Oregon chub abundance and fish and amphibian community structure. Monitor spawning activity and juvenile Oregon chub abundance to determine timing of spawning, timing of emergence, and patterns of natural mortality. Relate these factors with water temperature, photoperiod, and other environmental variables. Determine the age structure and length-at-age relationships of selected Oregon chub populations. Objective 3: Update and develop maps showing suitable Oregon chub habitat in the Willamette Valley. Identify the current distribution of Oregon chub in the Willamette Valley. Identify potential habitat restoration and potential reintroduction sites. RESULTS Oregon Chub Distribution Historically, Oregon chub were found throughout the Willamette River drainage from Oregon City to Oakridge (Figure 1). The historical records note collections from the Clackamas River, Molalla River, Mill Creek, Luckiamute River, North Santiam River, South Santiam River, Calapooia River, Long Tom River, Muddy Creek, McKenzie River, Coast Fork Willamette River, Middle Fork Willamette River drainages, and the mainstem Willamette River. Current distribution is limited to populations in the Santiam River, Muddy Creek(s), Camous Creek, and the Middle Fork Willamette River drainages (Figure 3). Most of the these populations are located in the Middle Fork Willamette River (11 populations) and Santiam River (5 populations) drainages (Table 1). There are seven other locations where Oregon chub were collected at one time or another between , yet were absent during subsequent sampling conducted more recently. 4

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7 Status of Oregon Chub Populations and Trends in Their Abundance In 1989, researchers at Oregon State University sampled 22 of 29 known historic sites and collected Oregon chub from only three locations (Markle et. al. 1991). We later collected Oregon chub from eight of the 29 known historic sites. Three of these eight sites were locations that were not sampled in 1991, and small numbers of Oregon chub were collected from two locations where they reported none. Oregon chub have been reintroduced into four new habitats since Three introductions occurred prior to 1989, although none were highly successful and only one persists to date. Currently, there are 22 known locations that contain Oregon chub, including the five introduced populations. The Oregon Chub Recovery Plan (U.S. Fish and Wildlife Service 1998) sets recovery goals for downlisting the species to threatened and for delisting the species. The criteria for downlisting the species to threatened is to establish and manage 10 populations of at least 500 adult fish. All populations must exhibit a stable or increasing trend for 5 years and at least three populations must be located in each of the three sub-basins (Middle Fork Willamette River, Santiam River, Mid-Willamette River tributaries). The abundance of populations of adult Oregon chub has been estimated at selected locations throughout the Willamette Valley since 1992 (Scheerer et. al. 1999) (Table 1), using a modified Peterson estimate (Ricker 1975). Currently there are nine populations totaling 500 or more individuals and six of these have exhibited a stable or increasing trend for at least 5 years. Seven of the nine populations totaling 500 or more individuals are located in the Middle Fork Willamette drainage (5 natural populations and 2 introduced populations). Certain populations of Oregon chub have remained relatively stable from year to year, while others have fluctuated substantially. Several populations in the Middle Fork Willamette River drainage showed significant increases in abundance in 1997 (Sites 1, 5, 6, 7). The population introduced into Middle Fork Willamette Site 4 steadily increased in abundance between 1994 and 1997, then declined substantially in In the Santiam River drainage, the Oregon chub population in Site 2 declined following the 1996 floods and continues to be depressed. The abundance of the Oregon chub population at the Santiam Site 1 declined substantially in Non-native fish invaded both locations during the 1996 floods and may be responsible for these declines. Aquatic Communities We described the fish and amphibian communities present at locations containing Oregon chub to determine whether abundant Oregon chub populations are more likely to occur in habitats with certain faunal assemblages. We also noted the occurrence of native western pond turtles, a sensitive species with similar habitat requirements. The fish species found most frequently at locations containing Oregon chub, excluding those sites where chub were introduced, were redside shiners (91%), sculpins (77%), speckled dace (73%), northern squawfish (59%), threespine sticklebacks (55%), and largescale suckers (45%) (Table 2). A fish community containing Oregon chub, redside shiners, speckled dace, and sculpins occurred at 59 percent of the locations. Native amphibians (ex. redlegged frogs and northwest salamanders) and western pond turtles were more common at locations that support large populations of Oregon chub. Nonnative bullfrogs, common in off-channel habitats throughout the Willamette Valley, were notably absent from three of the four locations that support the most abundant naturally occurring Oregon chub populations (Middle Fork Willamette Sites 2, 3, 5). Bullfrogs prey on juvenile turtles and redlegged frogs and are believed to be a major factor in their decline (Holland 1994; Blaustein et. al. 1995). We collected bullfrogs from two sites in for diet analyses. Prey items included 7

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9 aquatic and terrestrial insects, snails, a garter snake, a northwest salamander, and juvenile bullfrogs. No fish were identified in the stomach contents (Scheerer 1997, Scheerer and Apke 1998). Non-native fish are widely distributed in the Willamette Valley and are a major threat to Oregon chub populations. The presence of non-native fish in Oregon chub habitat appears to limit the abundance of Oregon chub at those sites where they coexist. In locations where naturally occurring Oregon chub populations total fewer than 400 individuals, non-native fish were present in 11 of 19 sites (63%). In locations where Oregon chub populations total more than 400 individuals, non-native fish were present in only two of the eight sites (25%). Recent flooding in 1996 redistributed non-native fish in the Willamette Valley. In the Santiam River drainage, non-native fish were collected for the first time, or increased in abundance, following the 1996 floods. The Oregon chub populations at these locations subsequently declined and have remained depressed. In 1995 and 1996, non-native fish were found in the Middle Fork Willamette Site 7. Non-native fish were not collected from this location between , nor were they collected in The Oregon chub population abundance at this location was very low in 1995 and 1996 and increased dramatically in The site is small and has a year round connection to the adjacent reservoir. In addition, two locations where Oregon chub were collected between , but were absent in (Middle Fork Willamette Site 14 and Santiam River Site 3), were invaded by non-native fish (Table 2). The fish communities present at Oregon chub locations are, in part, determined by the connectivity of the site to adjacent water bodies. Our data suggests that the more connected a site is to the adjacent river or reservoir, the greater the chance that non-native fish will invade the site. Those sites that are isolated from the adjacent river or reservoir (Middle Fork Willamette River Sites 2, 3, and 5) tend to have fewer species of fish present and larger populations of Oregon chub (Table 3). Sites that experience frequent connection to the river (Santiam River Sites) have higher species richness, are more likely to contain non-native fish, and support smaller Oregon chub populations. Comparisons between sites with low and high connectivity showed that species richness was significantly higher, number of species of non-native fish was significantly higher, and Oregon chub abundance was significantly lower at locations with high connectivity (Table 4). Similar results were found for comparisons between basins. The sites in the Middle Fork Willamette River basin, which are typically more isolated, have significantly larger Oregon chub populations and significantly lower species richness than sites in the Santiam River basin. The relative abundance (dominance) of certain fish species can also influence the abundance of Oregon chub at that location. Beginning in 1997, we obtained estimates of the population abundance and densities for all species of fish that occur at locations containing abundant populations of Oregon chub. These estimates allow us to monitor changes that occur in the community structure from year to year and relate these changes to changes in environmental conditions. Oregon chub were the dominant fish species at most of the locations that support abundant populations of Oregon chub ( Middle Fork Willamette River Sites 1, 2, 3, 5, 7 and Santiam River Site 1) (Scheerer et. al. 1999). Oregon chub were one of the least abundant fish species present at two locations that support only small populations of Oregon chub (Mid-Willamette Site 1 and the Santiam Site 2). Water Temperature and Water Chemistry Monitoring We monitored water temperature and water chemistry at locations containing Oregon chub, and at potential reintroduction sites, beginning in We collected this information to 9

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11 Table 4. Comparisons of species richness, number of species of non-native fish, and population abundance between Oregon chub locations with high and low connectivity and between basins. Species Richness Non-native Fish Oregon chub abundance Sites N mean st. dev. mean st. dev. mean st. dev. High connectivity ,383 Low connectivity , ,525 Species Richness Non-native Fish Oregon chub abundance Basin N mean st. dev. mean st. dev. mean st. dev. Santiam Mid-Willamette M. Fk. Willamette ,747 1, 3 1, Means are significantly different at 0.99 level. 2 Means are significantly different at 0.95 level. 3 Means are significantly different at 0.90 level. 11

12 assist in determining whether temperature and/or water quality might limit the abundance of Oregon chub at a location, or limit the suitability of a potential reintroduction site for Oregon chub. Water temperature regimes could limit the abundance of Oregon chub in several ways. Temperatures exceeding the upper lethal tolerance for Oregon chub would negatively affect survival rates. Temperatures that remain below the threshold where spawning has been observed might limit production at that location. Spawning activity in Oregon chub has been observed at temperatures exceeding 16 o C. For those sites with available data, we tallied the total number of days between May 1 and August 31 (the time period when spawning has been observed) when the maximum pond temperature exceeded 16 o C in 1997 and 1998 (Table 5). No pattern was evident from this data. Many of the locations that support abundant Oregon chub populations had a large number of days when the temperature exceeded 16 o C. However, there were some notable exceptions to this trend. For example, Middle Fork Willamette Site 9 had 91 days in 1997 and 104 days in 1998 when the maximum temperature exceeding 16 o C, yet the site supports only a small population of Oregon chub. Conversely, Middle Fork Willamette Site 5 supports a large population of Oregon chub (~3,030), yet has a very cool temperature regime. There were distinct differences in the temperature profiles between locations (Scheerer et. al. 1999). In several locations (Middle Fork Willamette Sites 5 and 8, Santiam Site 2) the maximum water temperatures remained cool throughout the summer (<18 o C). These sites have substantial springs or ground water inflow that keep the site from drying up during the summer and maintain cool pond temperatures. At other locations (Middle Fork Willamette Sites 1, 4, 6, and 7, Mid- Willamette Sites 1 and 2), water temperatures are warmer (20-26 o C) for much of the summer. No temperatures approaching the upper lethal maximum temperature of 31 o C for Oregon chub (Scheerer and Apke 1998) were recorded at any site. Certain temperature regimes may also favor non-native fish and amphibians. For example, spawning activity for non-native centrarchid fishes generally occurs at temperatures exceeding 20 o C (Scott and Crossman 1973) and bullfrogs are more successful colonizing sites where summer water temperatures exceed 20 o C (Holland 1994). Conversely, cool temperature regimes can limit the ability of centrarchid fishes and bullfrogs to colonize a site. Overwinter mortality has been found to be size dependent in juvenile basses (Oliver et. al ; Post et. al. 1998). In cooler environments, spawning may be delayed and growth may be slowed, such that juvenile bass do not have enough energy stores to survive the winter. Bass typically do not feed when temperatures drop below 12 o C. Several locations that support large Oregon chub populations, where non-native fish and bullfrogs are absent (Middle Fork Willamette Sites 2, 3, 5), have cooler temperature regimes (<20 o C). Water chemistry and macroinvertebrate communities (an index of water quality) were monitored at numerous Oregon chub sites, reintroduction sites, and potential reintroduction sites in 1996 and 1997 (Scheerer 1997, Scheerer and Apke 1998). The parameters measured included temperature, dissolved oxygen, ph, specific conductance, redox potential, and total dissolved solids. The water chemistry measurements were similar at all of the locations and were typical of low gradient Willamette Valley streams and ponds. The macroinvertebrate communities were also similar at all of the locations and characteristic of those found in high quality lentic environments (Merritt and Cummins 1984). Oregon Chub Spawning Activity and Requirements We observed spawning activity of Oregon chub in the field and in the laboratory to determine when breeding occurs in Oregon chub populations and to describe the temperature and photoperiod requirements that influence the onset and duration of spawning activity. This information will be used to assess the suitability and productive potential of a site for Oregon chub. 12

13 Table 5. Number of days between May 1 - August 31 when water temperature was at least 16 o C. These numbers represent the approximate number of days when temperature was suitable for Oregon chub to spawn Number of Days >16 o C Site Name Abundance Middle Fork Willamette 1 5, Middle Fork Willamette 2 4, Middle Fork Willamette 3 3, Middle Fork Willamette 4 1 3, Middle Fork Willamette 5 3, Santiam 1 1, Middle Fork Willamette 6 1 1,400 n/a 109 Middle Fork Willamette 7 1,280 n/a 74 Mid-Willamette Mid-Willamette Santiam Mid-Willamette n/a 112 Middle Fork Willamette 8 ~ Middle Fork Willamette 9 ~ These are locations where Oregon chub were introduced. 2 The abundance estimates for these locations were not obtained from mark-recapture techniques and represent a rough approximation. 13

14 Spawning behavior in the field was observed in shallow vegetated areas of the ponds (Middle Fork Willamette Sites 2 and 3), during the months of June, July, and August, at temperatures ranging from 16 o -21 o C (Scheerer and Apke 1998). Laboratory spawning experiments were initiated in June No spawning behavior was observed in 1997 (Scheerer and Apke 1998) and the experiments were repeated in The experiments consisted of five treatment groups and three replicates per treatment (five fish per replicate). Each tank was observed twice daily to monitor spawning behavior and activity. The control treatment was exposed to a natural photoperiod and natural temperature regime. The temperature was adjusted weekly to mimic conditions in Middle Fork Willamette Site 3, the site from which the fish were collected. One treatment was exposed to a natural photoperiod and a constant temperature (12-13 o C). One treatment was exposed to a natural photoperiod and a constant temperature (16-17 o C). One treatment was exposed to a natural photoperiod and a constant temperature (20-21 o C). One treatment was exposed to a 13.5 hour photoperiod and a constant temperature (20-21 o C). One treatment was injected with ovaprim, a hormone used to induce spawning, and exposed to a constant temperature (20-21 o C). The first spawning activity was observed in the o C treatments, beginning the week of June 7 (day 53 of the experiment) and continued through the week of August 24 (Figure 4). The first spawning activity was observed in the o C treatments during the week of June 14 (day 58) and continued through the week of August 10. The first spawning activity was observed in the control treatments beginning the week of July 20 (day 94), when the temperatures reached 18 o C. Spawning activity in the control treatments continued through the week of August 10. No spawning activity or visible gamete development was observed in the o C treatments, the treatments exposed to the 13.5 hour photoperiod, or the treatments injected with the ovaprim hormone. Eggs were collected from natural vegetation in one control treatment on July 31 and August 11 and from one o C treatment on July 28. Eggs were adhesive and measured approximately 1 millimeter in diameter. Cannibalism of eggs was observed in the same o C treatment on July 27, 28, 31, and August 9. Cannibalism of the eggs may explain why no eggs were found prior to July 31 despite numerous observations of spawning activity prior to this date. The eggs that were collected were placed in a o C tank for incubation; none of these eggs hatched. Oregon chub larvae (n=4) were collected from a control treatment on September 2, 10 days after the last spawning activity was observed in that treatment. We designed a field study to determine periods of peak spawning activity and the relative survival of Oregon chub broods. Initially, we tried to obtain this information by monitoring larval and juvenile abundance throughout the breeding season. We tested several methods for collecting juvenile Oregon chub including the use of dip nets, small mesh minnow traps, plankton nets, and a lift net. Catch rates were typically low and variability was high (Scheerer and Apke 1998). Currently, we are using otolith analyses to determine approximate hatch dates from collections of juvenile Oregon chub. First, we validated that otoliths could be used to accurately age juvenile Oregon chub. We found that juvenile Oregon chub deposited one increment per day on their otolith (Number of increments deposited = X number of days post marking; r 2 =.997). Hatch dates are estimated by counting daily growth increments and backcalculating from the date the juveniles were collected (Hoff et al. 1997). Approximate hatch dates were determined for samples collected in August and October 1997 from Middle Fork Willamette Site 2 (Figure 5). The earliest hatch date was from the week of May 10. The range of hatch dates extended from the week of May 10 through the week of August 2 when temperatures exceeded 16 o C. The range of hatch dates from August sample was from the week of May 10 through the week of July 12. The range of hatch dates from the 14

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17 October sample was from the week of June 21 through the week of August 2. The early (validation) sample was not a random collection; only the smallest larvae present were collected. No fish younger than 3 weeks old were collected at either sampling period. Actual spawning dates are assumed to be approximately 3-7 days earlier than the hatch dates, based on studies of redside shiners (Weisel and Newman 1951). These data suggest that peak spawning occurred between the first of June and the end of July The data also suggests that fish hatched after mid-july survived better (represent a larger proportion of October sample) than fish hatched prior to mid-july. We collected larval samples in 1998 from this same location and from Middle Fork Willamette Site 5 in 1997 and When analysis of larval samples is completed in 1999, we will compare peak spawning dates and relative brood survival between years and locations. Population Age Structure Length frequency histograms for Oregon chub do not show good separation of length categories (age classes) at any location (Scheerer et. al. 1999). In 1997 and 1998, we collected Oregon chub for aging from four locations. Five fish, covering the range of sizes present at each location, were collected each month beginning in November Analyses are incomplete at this time. Fish ages were determined for samples collected in 1998 from one location, Middle Fork Willamette Site 2. Fish ages ranged from 0+ to 6+ years old with the majority being <4+ years old (89%). There was considerable overlap in length distributions for fish larger than 36 mm in total length (Table 6, Figure 6). Overlap of lengths between age classes is common in cyprinids (Mann 1991). Even though fish in each age class were collected over a period of up to 12 months, there was little difference in the size of fish of a given age collected at different months during the year. Therefore, we pooled all fish of a given age to calculate the mean length-at-age for each age class. The growth rate of Oregon chub increases for the first two years, presumably when maturation occurs, then appears to level out. The annular mark on the otoliths of Oregon chub from this location was formed during January or February. Monitoring Reintroductions and Habitat Restoration Projects Monitoring reintroductions of Oregon chub and habitat enhancement projects is essential to our understanding of Oregon chub colonization rates (rates of expansion) and the limiting factors and carrying capacities of suitable habitats. In 1994, 573 Oregon chub were introduced into Middle Fork Willamette Site 4. The pond was drained in 1993 and the remaining water in the pond was treated with rotenone to poison the non-native fish (largemouth bass, western mosquitofish, crappies). In May 1994, we thoroughly snorkeled and seined the pond and collected/observed no fish. In September 1995, we estimated the population of Oregon chub to be approximately 3,500 fish. We also found that the rotenone treatment was ineffective; western mosquitofish were abundant. Meffe (1983, 1984) found chemical treatments to be ineffective in the removal of western mosquitofish in attempts to recover Sonoran topminnows Poeciliopsis occidentalis in Arizona. In 1997, the Oregon chub population expanded to 7,200 fish and the western mosquitofish population totaled 87,600 fish. In 1998, the Oregon chub population declined to 3,500 fish, western mosquitofish continued to be abundant, and adult largemouth bass were found. The bass are presumably the result of an illegal introduction. The rapid increase in size of the Oregon chub population from was encouraging, and illustrates the potential of Oregon chub to expand when habitat conditions are suitable. However, the recent decline in Oregon chub abundance, the presence of largemouth 17

18 Table 6. Mean length at age of Oregon chub collected from Middle Fork Willamette Site 2 in Age (years) Mean Length (mm) 95% Confidence Intervals Range n lower upper

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20 bass, and the rapid expansion of the western mosquitofish population are concerns. The effects of these non-native fish on the Oregon chub population will be monitored in future years. In 1996, 500 Oregon chub were introduced into the Middle Fork Willamette Site 6, which consists of a series of beaver ponds. Speckled dace, western pond turtles, and bullfrogs were found in the pond prior to the reintroduction. We estimated 480 Oregon chub and 2,200 speckled dace in 1997 and 1,400 Oregon chub and 4,330 speckled dace in A habitat enhancement project (Mid-Willamette Site 2), located on private property in the Mid-Willamette basin, was completed in September A spring fed, 0.8 hectare, shallow water pond was constructed. The pond is located adjacent to a similar 0.8 hectare pond that was created in Oregon chub were introduced into the older (1994) pond in October 1997 (n=200) and May 1998 (n=300). Survival of these fish was high (October 1998 estimate = 460) and three fish were collected from the newer (1997) pond. The ponds are connected during the rainy winter months. The vegetation in the new pond became well established during the summer of 1998 and we introduced 73 Oregon chub into this pond in October The introduced fish were Oregon chub that were reared in captivity and used in the laboratory spawning experiments. Oregon chub were introduced into Mid-Willamette Site 6 in The pond was drained in 1997 to remove non-native fish. A small number of fish (n=60) were transferred from Mid- Willamette Site 1 (1998 population estimate = 600 Oregon chub) to Mid-Willamette Site 6. These sites are located in the same basin and the transfer was made to expand this population and reduce the risk of extinction. Since most of these introductions are relatively recent, few conclusions can be made at this time. Oregon chub have the ability to increase rapidly in abundance if the conditions are suitable. Currently 13 potential reintroduction sites for Oregon chub have been identified and are being evaluated (Scheerer et al. 1999). Oregon Department of Fish and Wildlife guidelines restrict introductions to protected sites within the historical range of Oregon chub, that are secure from imminent or future threats of habitat destruction and invasion by warmwater fish, and are likely to fulfill all life history requirements for Oregon chub. DISCUSSION Populations of Oregon chub Oregonichthys crameri, endemic to the Willamette Valley, have been drastically reduced. Factors in the decline of this fish include changes in flow regimes and habitat characteristics resulting from the removal of large snags for river navigation, the construction of flood control structures, channelization, diking, revetments, agriculture, and the drainage of wetlands. The Oregon chub is further threatened by predation and competition by non-native fish species such as largemouth bass, smallmouth bass, crappies, bluegills, and western mosquitofish. In 1974, Dr. Carl Bond, Oregon State University fisheries professor, first noted the apparent decline of Oregon chub populations in the basin (Bond 1974). In 1993, the Oregon chub was listed as "endangered" under the federal endangered species act. (Rhew 1993). Flood control dams have had a major impact on the flow regimes of the Willamette River. By 1968, eleven major impoundments were completed in the basin. These impoundments were constructed for flood control and hydropower production. The dams further reduced the available Oregon chub habitat (side channels, oxbows, sloughs) in the Willamette Valley. Many of the current populations of Oregon chub are located in close proximity to, and are influenced by the operation of these dams. In addition, the flood control reservoirs provide habitat for non-native fishes, many of which are threats to Oregon chub population survival. The distribution of non-native fishes in the 20

21 Willamette basin is broad and has been expanding over the last decade (Kin Daily, ODFW Warmwater Fish Biologist, personal communication). Non-native fish were collected from 40 percent of the 415 sites that we sampled in the Willamette basin between , and were generally absent from locations that support large populations of Oregon chub. Several Oregon chub locations were either invaded by non-native fish during this period, or risk invasion by nonnative fish. The habitat adjacent to and affected by the fluctuations in the reservoirs is generally not suitable for Oregon chub. Hiding and spawning cover (aquatic vegetation) is often lacking when reservoir water levels are dropped, and the chub are exposed to predation by non-native fish that live in the reservoirs. The reservoirs also act as a migration barrier to Oregon chub that attempt to colonize new areas. The Oregon Chub Recovery Plan was completed in 1998 and set recovery goals for Oregon chub (U.S. Fish and Wildlife Service 1998). The criteria for downlisting the species from endangered to threatened requires a total of 10 populations exceeding 500 individuals per population. These populations must exhibit a stable or increasing trend of abundance for a period of at least five years and at least three of these populations must be in each of the three major subbasins (Santiam, Middle Fork Willamette, and Mid-Willamette Rivers). The criteria for delisting this species requires a total of 20 populations exceeding 500 individuals per population. These populations must exhibit a stable or increasing trend of abundance for a period of at least five years and at least four of these populations must be in each of the three major subbasins. In 1998, there were nine Oregon chub populations that exceeded 500 individuals and six of these exhibited a stable or increasing trend in abundance for at least five years. All six were naturally occurring populations. Currently, most known populations of Oregon chub are concentrated in the Middle Fork Willamette River and Santiam River drainages. Oregon chub are known to inhabit 11 locations in the Middle Fork Willamette River drainage. The largest populations of Oregon chub in the Willamette Valley are located in this drainage. Three of these are introduced populations. Oregon chub are known to inhabit five locations in the Santiam River drainage. The populations at three of these sites were discovered in and only a few Oregon chub (n=2-5) were collected. In recent years, the abundance of Oregon chub has declined substantially at several locations in the basin. In addition, no Oregon chub were collected in 1998 from three locations where they were previously found in small numbers. Non-native fish invaded several Santiam River sites during the February 1996 floods and are likely responsible for the declines in Oregon chub abundance at these locations. Efforts to recover Oregon chub in recent years have focused on reintroductions of Oregon chub into suitable, secure habitats and restoring or enhancing Oregon chub habitats (Scheerer et. al. 1999). By expanding the distribution of this species to secure locations in the valley, we not only reduce their risk of extinction, but also increase the probability their recovery. Oregon chub have been successfully introduced into five locations in the Willamette Valley. Two of these introduced populations totaled more than 1,000 Oregon chub in We conducted studies of the natural history and habitat requirements of Oregon chub to identify those factors that have the strongest influence on Oregon chub abundance. Relationships of specific habitat parameters and community components to Oregon chub abundance were evaluated using correlation and multiple regression analyses. The variables most highly correlated with Oregon chub abundance were the number of days during the summer when the water temperature exceeded 16 o C, the summer surface area of the site, and the presence of western pond turtles (Scheerer et. al. 1999). A multiple regression model was then developed where variables were added to the model in a stepwise fashion. In the model, summer surface area and total vegetated area explained the majority of the variation in Oregon chub population abundance. 21

22 Laboratory and field spawning investigations found that Oregon chub spawn in the summer months (June-August) when temperatures exceed 16 o C. The juvenile hatch date distribution for samples collected in August and October 1997 from Middle Fork Willamette Site 2 showed that late-hatched Oregon chub survived in greater proportion than early-hatched fish, suggesting that conditions in June and early July were not favorable for optimal juvenile survival. The studies of fish assemblages showed that Oregon chub are the dominant species at locations that support abundant Oregon chub populations (Scheerer et. al. 1999). However, the species richness varied considerably between populations. Recent studies indicate that most variation in fish assemblages is correlated with the geographic position of wetlands (Snodgrass et. al. 1996). The authors report that wetland drying frequency and connectivity determine the presence and absence of fishes, and variation in fish communities depends on the colonization rates and relative abundance of the species in source pools. We found a strong relationship between species richness and the connectivity of the site to the adjacent river system. Sites with low connectivity had fewer species of fish present, were less likely to contain non-native fish, and supported larger populations of Oregon chub. Sites that experience frequent connection to the river had higher species richness, were more likely to contain non-native fish, and supported smaller Oregon chub populations. Oregon chub evolved with few native predators, in a Willamette River that had abundant off-channel habitat and frequent floods. Currently, flooding is suppressed, non-native fish are widespread, and Oregon chub are severely limited in their ability to successfully colonize new locations. Nonetheless, the status of Oregon chub has improved since This improvement is due to the discovery of additional, previously unknown populations, and successful reintroductions. We have also gained valuable life history information that assists us in protecting Oregon chub populations, enhancing and protecting Oregon chub habitat, and selecting suitable reintroduction sites. Unfortunately, threats from habitat destruction and nonnative fish persist and continue to hamper recovery efforts. 22

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