Draft Imnaha Subbasin Summary November 30, 2001 Prepared for the Northwest Power Planning Council Subbasin Team Leader

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Limiting Factors



Fish


Four tiers of information have been considered for review of limiting factors to fish populations in the Imnaha subbasin, each differing in relative scale and species considerations: (1) regional documentation for review of non-species specific factors limiting production of resident and anadromous fish in the subbasin as a whole, (2) past subbasin specific research documents and current professional judgment for review of species specific factors limiting populations in specific portions of the subbasin, (3) information compiled by the Northwest Power Planning Council as part of the subbasin planning process for review of reach specific limiting factor information related to spring chinook, fall chinook and steelhead, and (4) the 1998 §303(d) list compiled by ODEQ for review of reach specific factors limiting beneficial use(s) including support of cold water biota and/or salmonid spawning.

Subbasin Scale – Regional Sources

Anadromous fish production in the Imnaha River subbasin is currently being limited by out-of-subbasin factors. It is generally accepted that hydropower development on the lower Snake River and Columbia River is the primary cause of decline and continued suppression of Snake River salmon and steelhead (IDFG 1998; CBFWA 1991; NPPC 1992; NMFS 1995; 1997a; NRC 1995; Williams et al. 1998). This limiting factor has the effect of keeping yearly effective population size (Nb) low, increasing genetic risk and demographic risk of localized extinction.

Adult escapement of anadromous species remains low even given significant hatchery production/reintroduction efforts. Smolt-to-adult survival rates remain below the 2%-6% needed for recovery (IDFG 1998) mainly due to dams on the lower Snake and Columbia rivers. The dams cause direct, indirect, or delayed mortality, mainly to emigrating juveniles (IDFG 1998, Nemeth and Kiefer 1999) and have been estimated to cause an average mortality of 15% per dam to immigrating adults (Chaney and Perry 1976). Low adult abundance has resulted in stocking at variable rates between years, depending on the availability of brood fish. In addition, bull trout production may be limited by reductions in available forage due to loss of anadromous fish production (CBFWA 1999).

Hatchery influences to fish populations are not addressed here as limiting factors due to the debatable and often site specific nature of hatchery influences to existing fish stocks. Hatcheries play a significant role in meeting social and recovery goals of the Blue Mountain Province. Co-mangers have restructured Imnaha spring chinook programs to support recovery (ODFW 1996, see Artificial Production section). The general body of science regarding hatcheries as recovery tools suggest that natural spawning by hatchery fish can provide benefits as well as pose risks to wild populations (IMST 2001, ISAB 2001, and Brannon 2001). It is clear that hatcheries can provide a production boost for a host population, potentially preserving a population or rescuing it from a production bottleneck. The risks hatchery intervention pose to wild populations tend to be site specific and include management associated (i.e. over-harvest of weak stocks in mixed stock fisheries), genetic (i.e. artificial selection inbreeding and outbreeding depression) and ecological impacts (i.e. increased competition) (Busby et al. 1996; Evans et al. 1997; U.S. Fish and Wildlife Service and Nez Perce Tribe 1995). Given the current state of our knowledge of these benefits and risks, hatchery programs should be used appropriately considering site-specific needs to insure recovery goals are achieved.


Subbasin Specific Scale


Out of basin factors are the primary contributors limiting production and stability of key fish species in the Imnaha (NPT et al. 1990), however in-basin factors have additionally contributed to reductions in salmonid life history stages. Elevated summer water temperatures, insufficient water quantity in portions of the Sheep Creek system, areas of inadequate riparian vegetation, low pool frequency in some tributaries, inadequate habitat diversity in various stream reaches and excessive rates of sedimentation at times due to mass-wasting events and some land management activities (e.g. roads) are commonly cited as the primary in-basin factors limiting Imnaha fish production, distribution and population stability (Ashe et al. 2000; Huntington 1994; Mason et al. 1993; Mobrand and Lestelle 1997; USDA Forest Service 1994; Wallowa-Whitman National Forest 1998). However, factors limiting local fish production or survival may differ from those defined across broader scales, limiting factors in a given location may vary between species.

The following discussion identifies limiting factors by life stage of key salmonid species (spring/summer chinook, steelhead, and bull trout) in the Imnaha subbasin. Tables 27-29 summarize this discussion at a subbasin-specific scale, stratified by life history stage. Much of the spring chinook discussion is taken from Mobrand and Lestelle (1997) and Ashe (et al. 2000), while the assessment of summer steelhead is largely based on documents by USDA Forest Service (1998a; 1998b) and the discussion on bull trout comes primarily from personal communications with [Error in text –CBFWA] (ODFW), and documents by Buchanan et al. (1997), and USDA Forest Service (2000).

Table 29. In-basin factors limiting various life history stages of spring/summer chinook populations in the Imnaha subbasin (summarized from Ashe et al. 2000; Mobrand and Lestelle 1997; Mundy and Witty 1998)



Location

Spring/summer chinook

Adult Passage

Spawning and Incubation

Colonization and summer rearing

Fall redistribution and overwintering

Smolt Migration

Lower Imnaha1/

Temperatures may limit late season migration

Icing conditions limit fall chinook success same years only

Temperatures, habitat diversity, sediment, channel stability







Big Sheep Cr.2/

Temperatures and/or flow may limit late season migration

Low flows, high summer temperatures, shade/canopy

Low flows, high temperatures poor habitat diversity







Little Sheep Cr.3/

Spring/summer chinook not present in Little Sheep Cr.

Upper Imnaha4/














1/Reach defined from mouth (RM 0.0) to Big Sheep Creek confluence (RM 22.3) and all associated tributaries

2/Reach defined from mouth (RM 0.0) to headwaters and all associated tributaries

3/Reach defined from mouth (RM 0.0) to headwaters and all associated tributaries

4/Reach defined from confluence of Big Sheep Creek (RM 22.3) to headwaters and all associated tributaries

Table 30. In-basin factors limiting various life history stages of summer steelhead populations in the Imnaha subbasin (from Huntington 1994; USDA Forest Service 1994; USDA Forest Service 1998a; USDA Forest Service 1998b)




Location1/

Summer steelhead

Adult Passage

Spawning and Incubation

Colonization & summer rearing

Fall redistribution & overwintering

Smolt Migration

Lower Imnaha

Temperatures exceed PACFISH & NMFS standards (only applies to fish entering v. early in the fall)


Temperatures exceed PACFISH & NMFS standards; Excessive sediment in the

mainstem below 9 points Cr



LOD<20 pieces/mi. but close to natural potential







Big Sheep Cr.







Low flows







Little Sheep Cr.

Temps exceed PACFISH & NMFS standards




Low flows; Temperatures exceed PACFISH & NMFS standards







Upper Imnaha




Sediment is excessive in some perennial headwater tribs.










1/Refer to Table 29 for reach description
Table 31. In-basin factors limiting various life history stages of bull trout populations in the Imnaha subbasin (from USDA Forest Service 1999; USDA Forest Service 2000a; Buchanan 1997; M. Hanson, personal communication, April 2001)


Location1/

Bull trout

Adult Passage


Spawning and Incubation

Colonization and summer rearing

Fall redistribution and overwintering

Lower Imnaha







  • High stream temperatures below Fence Creek

  • Reduced amount and/or quality of riparian veg.

  • Reduced amount and/or quality of riparian veg.

Big Sheep Cr.

  • Loss of connectivity due to WVI Canal

  • Low flows resulting from irrigation withdrawals

  • High sediment below the WVI canal

  • Decreased sinuosity due to riprapping/bank stabilization assd. w/ road construction

  • Reduced amount and/or quality of riparian veg.

  • Temperatures >24C during June-August

  • Decreased sinuosity due to riprapping/bank stabilization assd. w/ road construction

  • Reduced amount and/or quality of riparian veg.

Little Sheep Cr.

  • Blocked access to upper Little Sheep Creek through the WVI Canal

  • Low flows resulting from irrigation withdrawals

  • Sediment from recent fires, logging & road construction

  • Decreased sinuosity due to riprapping/bank stabilization assd. w/ road construction
  • Reduced amount and/or quality of riparian veg.


  • Decreased sinuosity due to riprapping/bank stabilization assd. w/ road construction

  • Reduced amount and/or quality of riparian veg.

  • Water withdrawals reduce summer and fall flows in the upper reaches

Upper Imnaha




  • Sedimentation resulting from landslides/fires in the NF







1/Refer to Table 29 for reach description

Spring chinook
Adult passage

Wallowa County and Nez Perce Tribe (1993) and Huntington (1994) identified high stream temperatures in the lower Imnaha to be a potential concern for the success and timing of upstream migrating adult chinook salmon. Mobrand and Lestelle (1997) also noted temperature increases from historic levels in the lower river corridor (below Freezeout Creek, RM 29.4) yet did not specifically identify the change as a factor limiting productivity. The patient-template analysis of the mainstem suggests that the relative productivity (survival) of Imnaha chinook salmon has been reduced due to losses in key life history stages, including pre-spawning adults (Mobrand and Lestelle 1997). Pre-spawning life history stages have been compromised in the mid to lower reaches of the river by losses in habitat diversity and streambed instability (Mobrand and Lestelle 1997). Upon review of the available information, Ashe (et al. 2000) proposes that while high stream temperatures may stress the fish, migration will not be prohibited and rates early season migration as excellent and late season migration conditions to be fair to good.

Wallowa County and the Nez Perce Tribe (1993), Huntington (1994), and Mobrand and Lestelle (1997) identify summer temperatures, flows and sediment loads as potential problems for spring chinook migration into Big Sheep Creek. Upon review of the available information, Ashe (et al. 2000) rates early season migration conditions as “excellent” and late season migration conditions as “fair to poor” (based on temperatures and possible flow concerns).



Spawning and incubation

In their patient-template analysis, Mobrand and Lestelle (1997) found that the quantity of key chinook habitat has declined in certain portions of the subbasin, and specifically that insufficient substrate size in the mid portions and upper reaches of the Imnaha (up to RM 67) was the primary factor limiting chinook spawning and egg incubation success. Losses of appropriate sized substrate have resulted from upstream channel simplification and bank armoring caused by “stream cleaning” and land use activities (Ashe et al. 2000).

Recent improvements, such as livestock exclosures and woody debris reintroduction by the USFS, have improved gravel accrual rates in the mainstem Imnaha River (Ashe et al. 2000). By the mid 1990’s, reaches of the Imnaha upstream of the national forest boundary were considered to have sufficient amounts of woody material, and had gravel bars beginning to form behind logjams. Spawning and incubation conditions were considered to be good to excellent in the upper Imnaha (Ashe et al. 2000).

Spring chinook spawning and incubation life history phases are limited in the upper half of Big Sheep Creek (Mobrand and Lestelle 1997). Although the quantity of spawning and incubation habitat in Big Sheep Creek is comparatively small, losses over time have been substantial (Mobrand and Lestelle 1997). Factors contributing to these declines include changes in water temperature regimes, channel stability, habitat diversity, and, to a lesser extent, flow regimes and sediment load (Mobrand and Lestelle 1997). USDA Forest Service (1998b) found that stream temperatures were slightly below environmental potential (at risk) throughout much of the Big Sheep Creek drainage, although the analysis was focusing on summer steelhead. High water temperatures and low water levels prevent Little Sheep Creek from being suitable chinook spawning habitat (NMFS 2001). Ashe (et al. 2000) summarizes chinook spawning and rearing conditions in the Big Sheep Creek watershed as “fair to excellent in the upper watershed above Coyote Creek (RM 20.4) and fair to poor below Coyote Creek.


Colonization and summer rearing

Spring chinook fry colonization and summer rearing life history stages have been reduced from historic levels in the mid to lower reaches of the Imnaha (Mobrand and Lestelle 1997). Habitat conditions that support these particular stages have been compromised by increased water temperatures, small losses in habitat diversity, and increased channel instability (Mobrand and Lestelle 1997). Ashe (et al. 2000) does not consider these losses to significantly threaten chinook production however, and rates colonization and summer rearing in the Imnaha as “good to excellent”.

In Big Sheep Creek, fry colonization and summer rearing life history stages have been reduced through losses of habitat diversity, elevated temperatures, predators, competitors, flows and sediment loads in the lower 35 stream miles (Mobrand and Lestelle 1997). Colonization and summer rearing life history stages in Little Sheep Creek are not identified as limited since chinook production in the drainage has likely never been significant in relation to the rest of the subbasin (Mobrand and Lestelle 1997). Ashe (et al. 2000) rates colonization and summer rearing conditions as “good to excellent above Coyote Creek (RM 20.4) and fair to poor below Coyote Creek”.



Fall redistribution and overwintering

Overwintering survival in the upper Imnaha may be reduced due to anchor ice formation or ice floes (refer to Appendix F) (Ashe et al. 2000; NPPC 1990). Ashe (et al. 2000) defines fall redistribution and overwintering life history phases of chinook salmon to range from good to excellent in the lower Imnaha, and fair to good in the upper Imnaha, based on temperatures.

Fall redistribution and overwintering life history stages of chinook may be limited in the lower portion of Big Sheep Creek due to land use activities and the presence of a channel-confining road (Big Sheep Creek Road) (Gaumer 1968). Conditions for fall redistribution and overwintering of spring/summer chinook are considered to be fair to excellent from the 39 Road bridge to the mouth (Ashe et al. 2000).


Smolt migration

The emigration of chinook smolts from the Imnaha subbasin does not appear to be limiting the productivity of the population as a whole (Ashe et al. 2000). This is especially true during the early part of the migration between March and April. Smolts that outmigrate later than April are more likely to encounter elevated temperatures, such as in the lower Imnaha and in lower Big Sheep Creek, which may delay or postpone emigration (Gaumer 1968). Ashe (et al. 2000) summarizes smolt outmigration conditions to be excellent in the early part of the migration and good in the latter part of the migration for both the mainstem and for Big Sheep Creek.

Summer steelhead2
Adult passage

Stream temperatures in the lower portion are considered by the Wallowa-Whitman National Forest to be “at environmental potential (properly functioning)” but overall, do not meet PACFISH and NMFS matrix criteria (refer to USDA Forest Service 1998a, pp. 32-33 for PACFISH and NMFS criteria). It is highly unlikely however, that temperatures prohibit steelhead migration into the subbasin, unless fish enter very early in the fall (late summer). Most adult steelhead migration into the subbasin occurs during the winter and spring months when water temperatures are low. Extremely low water temperatures and icing may limit steelhead migration into the Imnaha in winter months. Most migration occurs during periods of increased streamflow during the months of December through April. Modifications to the floodplain and riparian areas on private land in the lower-middle reaches of the mainstem Imnaha, and riparian removal in the upper-middle reaches (below the Imnaha River Wood Development), are considered to be areas where stream temperatures are “at risk” (Wallowa-Whitman National Forest 1999).

Spawning and incubation

Steelhead spawning and incubation life history phases below Nine Points Creek on the mainstem Imnaha may be limited by unstable cobble and gravel bars, which resulted from excessively high amounts of bedload movement caused by storm events in 1992 and 1997 (USDA Forest Service 1998a). Some perennial headwater streams that feed the upper Imnaha may not be suitable for steelhead spawning and incubation due to high amounts of fine sediment produced through various land management activities and natural erosion patterns (USDA Forest Service 1998a), however the majority of these streams are in a condition that is suitable to support spawning and rearing life history stages. The primary factors considered to affect steelhead spawning and rearing habitat are the livestock allotments and roads in mid-elevation areas on the Forest (B. Knox, ODFW, personal communication, May, 2001).

USDA Forest Service (1998b) suggests that low flows may limit rearing and spawning in Big Sheep Creek, however, due to their spawn timing (April through mid-June), it is likely that flows would be sufficient for steelhead spawning success. Conversely, spawning success in certain reaches of the Big Sheep watershed may be limited by excessively high flows. Modification of upland vegetation through the Canal Fire (1989), Twin Lake Fire (1994), timber harvest, windstorms, and insect outbreaks has changed runoff characteristics in portions of the drainage, based on flow characteristics of the gaging station at the town of Imnaha (USDA Forest Service 1998b). Changes to upland vegetation have also accelerated sheet and rill erosion in five subwatersheds within the Big Sheep Creek drainage, and has caused gully erosion to increase in three subwatersheds (USDA Forest Service 1998b). Although increased sediment deposition in low gradient reaches has been noted, the removal of the hydropower facility on Little Sheep Creek in 1997 is suspected to flush a proportionate amount of stored sediment during spring runoff (NMFS 2001; USDA Forest Service 1998b).

Water temperatures, turbidity/sediment, substrate and peak/base flows are considered to be either at risk or not properly functioning within portions of Little Sheep Creek (NMFS 2001), and may limit steelhead spawning and incubation life history stages. Areas with sufficient amounts of temperature-ameliorating vegetation are present in some portions of Little Sheep Creek, but are limited in others, mainly due to the presence of the adjacent highway and livestock encroachment of the riparian area.


Colonization and summer rearing

Summer steelhead fry colonization and summer rearing life history stages in the mainstem Imnaha have been reduced from historic levels. The reductions have resulted from a decreased amount of suitable habitat caused by reduced water quality and channel/habitat simplification. Excessive stream temperatures, inadequate amounts of large organic material, insufficient pool frequency and quality, and extreme peak/base flows are among the primary constraints to steelhead colonization and summer rearing (USDA Forest Service 1998a). These conditions are most pronounced in stream reaches bordered by private land or inholdings, or in areas where riparian vegetation has been removed or modified (USDA Forest Service 1998a). For example, summer rearing habitat near Nine Point Creek, a reach influenced by the encroachment of a powerline right-of-way, may be periodically unsuitable, as the seven-day moving maximum stream temperatures recorded during July and August of 1994 (71F and 72F respectively) were at or near lethal limits (USDA Forest Service 1998a).

Cultivation, farming, and pasturing have further reduced the riparian component, specifically the cottonwood communities, resulting in an “at risk” rating (USDA Forest Service 1998a). The lack of woody material input to the stream channel in these areas has in turn simplified the system both hydraulically and biologically. In an effort to address large organic debris (LOD) deficiencies, the Wallowa-Whitman has completed bioengineering work along three stream miles, in which woody material was anchored to the streambank (i.e. hard structures), and has completed work along 13 stream miles, in which woody material was merely reintroduced to the channel (i.e. soft structures) (Platz, Wallowa-Whitman National Forest, personal communication, May, 2001).

Because steelhead fry colonization and summer rearing life history stages are largely reliant upon diverse, sufficiently deep, cool and productive habitat types (Bjornn and Reiser 1991), the lack of these in the lower portions of the Big and Little Sheep Creek drainages may pose a limiting factor to production. USDA Forest Service (1998b) defines large woody material throughout lower Big Sheep Creek and lower and middle Little Sheep Creek to be below natural potential (“at risk”) based on PACFISH guidelines and NMFS habitat matrices. A combination of natural landscape characteristics and riparian habitat modification has contributed to the rating. Similarly, pool quality and frequency were rated as “at risk” and did not meet PACFISH guidelines or NMFS criteria for anadromous habitat; the ratings however, excluded pocket pools, which often comprised up to 30 percent of the channel (USDA Forest Service 1998b). Nevertheless, pool frequency, pool quality, large organic matter, stream flow and stream temperatures, are generally least favorable for summer steelhead colonization and summer rearing life history stages in the lower elevation reaches of the Big Sheep Creek drainage.



Fall redistribution and overwintering

The primary constraints to fall redistribution and overwintering life history stages of steelhead in the mainstem Imnaha are related to habitat availability and flow. Similar to summer rearing life history phases, overwintering juvenile steelhead require relatively complex habitat types, like that often provided by in-channel organic debris (Bjornn and Reiser 1991). In select areas where riparian reserves have been altered such as along private lands bordering some of the lower mainstem reaches, or channels modified through riprapped banks, dredging, and elimination of off-channel refugia. (USDA Forest Service 1998a) the diversity of overwintering habitat has been reduced or eliminated, and hence has constrained the potential productivity of these life history phases. The elimination of riparian reserves and their inherent insolation capacity combined with wintertime base flows may also restrict overwintering success, since stream temperatures may become low enough to freeze and/or for anchor ice to form.

Adult and juvenile steelhead that utilize Big and Little Sheep Creek during winter months--December through February--are subject to a reduction in available habitat due to anchor ice buildup and ice floes (USDA Forest Service 1998b). Icing conditions in the smaller perennial tributaries are prevalent throughout the watershed because of low flow conditions (refer to Appendix G).



Smolt migration

Since juvenile steelhead outmigration timing (early April through mid-June) generally coincides with periods of high flow and reduced temperatures, smolt migration life history stages are for the most part not limiting population persistence.

Bull Trout
Adult passage

The fluvial and resident forms of bull trout that reside in the Imnaha rely on an unobstructed path both to and from spawning, rearing, and overwintering areas. Seasonal migration barriers, including periods of reduced water quality, insufficient flows and/or degraded habitat pose a potential threat to bull trout connectivity between neighboring subpopulations in the Imnaha River and Sheep Creek (USDA Forest Service 2000a). On National Forest Service lands, the Wallowa Valley Improvement Canal blocks upstream migration of bull trout on Big Sheep, McCully, Ferguson, Canal, Redmont and Salt Creeks (USDA Forest Service 2000a). On Little Sheep Creek, the ODFW satellite fish hatchery facility represents a human-made physical barrier during adult bull trout migration; however, all non-target fish species are passed.

In the Little Sheep subwatershed, ODFW biologists believe that the influence of the WVI canal and periodic influx of bull trout from upper Big Sheep Creek are currently maintaining the population in Little Sheep Creek (unpublished ODFW habitat surveys). The resident populations that reside in the steep gradient streams above the canal (refer to section 1B-Fish), are connected via the canal system, but are classified as “Functioning at Risk” due to periodic losses in connectivity (reduced flow during non-irrigation seasons) and small population sizes (USDA Forest Service 2000a). Migration barriers also occur on McCully Creek and Big Sheep Creek, and when combined with downstream losses of migrants through the canal, the current habitat designation also is considered to be “Functioning at Risk” (USDA Forest Service 2000a).



Spawning and incubation

Although the majority of bull trout spawn in areas upstream from those affected by recent storm events, the large quantity of bedload material moved during the 1997 flood is a likely source of fine sediment in the mainstem Imnaha River below Nine Points Creek (USDA Forest Service 2000a), and may influence the quantity and quality of bull trout spawning and incubation habitat occurring in downstream reaches. Bull trout spawning and incubation life history forms may also have been impacted from an August, 1992 event, during which a thunderstorm triggered a debris flow in a tributary to the North Fork Imnaha. A debris fan formed at the confluence of the tributary, causing the thalweg of the North Fork to shift (USDA Forest Service 2000a). The change in the North Fork channel morphology, combined with the material deposited in the fan produced more sediment than the stream could carry, and may have smothered many incubating bull trout in downstream redds. The impacts of the January 1997 flood event on bull trout were likely similar, in that incubating bull trout in many of the Imnaha tributaries were either flushed, smothered, displaced or eliminated by the high flow velocities and excessive bedload movement accompanying the event. The Wallowa-Whitman National Forest rates the upper Imnaha as “Functioning Appropriately” in relation to sediment and embeddedness, while the lower Imnaha is considered to be “Functioning at Risk” (USDA Forest Service 2000a).

Spawning habitat in Big Sheep Creek, below the Wallowa Valley Improvement Canal, has been impacted from excessive sediment produced by the 1989 Canal fire and through a variety of other land use activities (Buchanan et al. 1997), however a relationship between spawning/incubation success of bull trout has not been established. Nutrient additions, once supplied in great abundance through the decomposition of anadromous fish carcasses, are currently considered to be in short supply. The affects of this reduction on newly emerged bull trout fry may be realized in a reduced number of macroinvertebrate prey items that may potentially nourish this particular life history stage (Rieman and McIntyre 1993).



Colonization and summer rearing

Because colonizing and summer rearing life history forms of bull trout are closely associated with large organic debris (Rieman and McIntyre 1993), the presence or absence of woody material provides an effective surrogate for the assessment of this particular life history stage. The Wallowa-Whitman National Forest examined amounts of woody material (>12 inches in diameter and >35 feet in length) throughout the subbasin prior to 1991 and again following the January 1997 flood event (1998). Although survey results were inconclusive for many reaches, the event appears to have had mixed effects. Three of the five reaches, for which comparisons can be made, lost woody material following the storm, while one gained and one remained constant. From an overall rating standpoint, the amounts of wood occurring in the Upper Imnaha and Sheep Creek watersheds are rated as “Functioning Appropriately” while the Lower Imnaha has been rated as functioning at risk (refer to previous discussions in steelhead and spring chinook LF sections).

Woody debris in Lick Creek, a tributary to Big Sheep Creek, has been reduced through logging activities, campground use, road construction, and fire (ODFW 1993 cited in Buchanan et al. 1997).



Overwintering

The upper Imnaha watershed where most resident bull trout reside is in near pristine condition. Fluvial froms overwinter in the lower Imnaha and Snake Rivers where large pools are abundant.

The downward population trend of spring chinook in the Imnaha subbasin may be affecting bull trout abundance since chinook represent a preferred prey item with which bull trout have evolved.


Stream Reach Scale – NPPC Data

Constraints to production of chinook salmon and steelhead trout in the Imnaha subbasin were delineated for individual stream reaches during the earlier subbasin planning process (Nez Perce Tribe et al. 1990). In the Imnaha subbasin, three individual constraints were defined for spring chinook salmon, one constraint was defined for fall chinook salmon, and three for summer steelhead, any of which may inhibit spawning, rearing or migration of these species.

One major weakness of this database is its failure to address constraints in areas not currently being used by anadromous species at the time the data was compiled. For example, it does not address constraints in areas of historical distribution (i.e., Little Sheep Creek for chinook salmon), and does not attempt to delineate potential constraints in areas that might be made accessible to either species in the future. Addressing these issues would require considerable time to replicate the methods and analyses used in developing the original database, and has therefore not been attempted.

Strength(s) of the database include the fact that constraints to chinook salmon and steelhead trout have not likely changed much in the past 10 years, except in very localized areas having had significant restoration effort. The database should therefore still provide a good understanding of current constraints to anadromous production in the Imnaha subbasin.

As defined in the NPPC database, spring chinook salmon production in the Imnaha subbasin is predominantly constrained by ice floes or icing conditions (22 stream miles) in the upper subbasin, and constrained by inadequately screened diversions (12 stream miles) and/or channelization (12 stream miles; Table 32). Constraints to spring chinook salmon production for individual stream reaches throughout the Imnaha subbasin are presented in Appendix F.

The only factor considered by subbasin planners to constrain fall chinook production in the lower Imnaha are excessively low winter water temperatures (22.3 stream miles of 22.3 stream miles are considered to be limiting production; Table 33). Constraints to fall chinook salmon production for individual stream reaches throughout the lower Imnaha subbasin are presented in Appendix H.


The same three factors limiting Imnaha spring chinook production are also considered to be constraining steelhead trout production. Unscreened or poor diversion/channelization (26.7 stream miles), channelization (12.3 stream miles) and ice floes/icing conditions (12.8 stream miles; ) are considered to be the primary factors affecting summer steelhead. The occurrence of these problems is generally similar to those affecting spring chinook. Constraints to summer steelhead production for individual stream reaches throughout the Imnaha subbasin are presented in Appendix G.

Table 32. Summary of stream miles where spring chinook use is constrained in the Imnaha subbasin (defined by NPPC and downloaded from Streamnet.org). Numbers in parenthesis represent the estimated total stream miles with habitat suitable for spawning, rearing, and/or migration by spring chinook. Numbers in corresponding “constraint” rows represent the estimated number of lineal stream miles affected






Assessment Unit



Constraint



Lower Imnaha1

Big Sheep Creek2

Little Sheep Creek3

Upper Imnaha4

Total




(46.0)

(52.8)

(0.0)

(49.1)

147.9

Unscreened or poor diversion/ channelization

0.0

12.4

0.0

0.0

12.4

Channelization

0.0

12.3

0.0

0.0

12.3

Ice floes/icing conditions

0.0

0.0

0.0

22.0


22.0

1/Reach defined from mouth (RM 0.0) to Big Sheep Creek confluence (RM 22.3) and all associated tributaries

2/Reach defined from mouth (RM 0.0) to headwaters and all associated tributaries


3/Reach defined from mouth (RM 0.0) to headwaters and all associated tributaries

4/Reach defined from confluence of Big Sheep Creek (RM 22.3) to headwaters and all associated tributaries
Table 33. Summary of stream miles where fall chinook use is constrained by various factors in the Imnaha subbasin (defined by NPPC and downloaded from Streamnet.org). Numbers in parenthesis represent the estimated total stream miles with habitat suitable for spawning, rearing, and/or migration by spring chinook. Numbers in corresponding “constraint” rows represent the estimated number of lineal stream miles affected




Assessment Unit1




Constraint

Lower Imnaha

Big Sheep Creek

Little Sheep Creek

Upper Imnaha

Total




(22.3)

(0.0)

(0.0)

(0.0)

(22.3)


Low winter water temperatures

22.3

0.0

0.0

0.0

22.3

1/Refer to Table 32 for reach delineation

Table 34. Summary of stream miles where steelhead trout use is constrained in the Imnaha subbasin (defined by NPPC and downloaded from Streamnet.org). Numbers in parenthesis represent the estimated total stream miles with habitat suitable for spawning, rearing, and/or migration by steelhead trout. Numbers in corresponding “constraint” rows represent the estimated number of lineal stream miles affected






Assessment Unit1




Constraint

Lower Imnaha1

Big Sheep Creek

Little Sheep Creek

Upper Imnaha

Total



(130.9)


(92.1)

(51.3)

(121.5)

(395.8)

Unscreened or poor diversion/ channelization

0.0

26.7

0.0

0.0

26.7

Channelization

0.0

12.3

0.0

0.0

12.3

Ice floes/icing conditions

0.0

0.0

0.0

12.8

12.8

1/Refer to Table 32 for reach delineation

Stream Reach Scale - §303(d)

Oregon Department of Environmental Quality (ODEQ) has defined beneficial uses, which include salmonid spawning and/or cold water biota for the majority of streams within the Imnaha subbasin. Pollutants limiting these beneficial uses may have a limiting impact on salmonid or other fish populations throughout the subbasin. The ODEQ maintains the §303(d) list for stream reaches with impaired beneficial uses. Since the affected stream reaches and associated pollutants have already been identified and summarized in the water quality section of this report, the reader is referred to that section for the limiting factors discussion.

Wildlife Limiting Factors


The following list identifies the primary factors in the Imnaha subbasin currently considered to limit the overall production of terrestrial vertebrates. A brief discussion follows.


  • Loss of ponderosa pine communities

  • Loss of prairie grassland ecosystems

  • Loss of classified wetlands

  • Noxious weeds

  • Loss of legacy resources

  • Roads

  • Loss of marine derived nutrients

Loss of ponderosa pine


Timber harvest and fire suppression have reduced the prevalence of ponderosa pine forests in the region (Quigley and Arbelbide 1997). Since ponderosa pine is a valuable timber species, large mature stands were among the first to be harvested after European settlement. Fire suppression further reduced the extent of ponderosa pine in the subbasin. The thick bark of ponderosa pine allows it to withstand ground fires better than the thin-barked true firs. In areas with a short fire return interval firs never had an opportunity to become established. Fire suppression allows the shade-tolerant forest fir species time to establish in the understory of ponderosa pine forest. In the continued absence of fire these species eventually become dominant when the canopy becomes dense enough that the shade-intolerant ponderosa pine seedlings cannot survive (Johnson 1994). This decline has probably reduced the suitability of the subbasin for ponderosa pine dependent wildlife including flammulated owl, white-headed woodpecker, and black-backed woodpecker.

Loss of prairie grasslands

The vast ranges of fescue and Agropyron bunchgrasses that dominated the lowland areas of the subbasin have been altered by a history of heavy grazing. Native grasslands in the Columbia basin are thought to have been less heavily grazed before settlement than those in the Great Plains region of the country; this made them more susceptible to damage when Euro-american settlers introduced large herds of sheep and cattle during the late 1800s and early 1900s. Removal of the original perennial grass cover left the soil vulnerable to erosion by wind and water, altered hydrologic regimes, and aided grassland colonization by annual grasses and noxious weeds (Quigley and Arbelbide 1997; Black et al.1997 updated 2001).


Loss of classified wetlands


Riparian areas contain higher wildlife species diversity and abundance, than any other habitat type. The unique characteristics present in healthy riparian areas that contribute to this diversity include structural complexity, connectivity with other ecosystems, abundance of food and water, and a moderate microclimate (Knutson and Naef 1997). The ability of many riparian zones of the Imnaha subbasin to support wildlife species and to protect aquatic habitats has been reduced.

Road construction and livestock grazing have impacted the quality of remaining riparian habitat in the subbasin. Roads are commonly constructed parallel to stream and river courses for scenic reasons and ease of construction. The construction of these roads results in the removal of riparian vegetation and alters the development of meanders, side channels, and attached wetlands that provide important habitat for fish and aquatic wildlife (Knutson and Naef 1997). Cattle spend 20-30% more time in riparian areas than elsewhere on their range, because of the abundant forage, availability of water, and protection from the elements these areas provide, magnifying their impacts on these habitats (Knutson and Naef 1997).



Noxious weeds

The introduction of non-native plant species to the Imnaha subbasin has reduced the subbasin’s ability to support its native wildlife and plant species. Introduced plants in the subbasin often outcompete native plant species and alter ecological processes reducing habitat suitability (Quigley and Arbelbide 1997). The designation “noxious” is applied to the most destructive of these invaders. Thirty-two introduced plant species are legally recognized as “noxious” in Wallowa county, many of these species have been documented to occur in the Imnaha subbasin (Table 35). The lower Imnaha subbasin is the most impacted by noxious weeds.

Table 35. Noxious weed species of Wallowa County, Oregon (University of Montana 2001)



Genus

Species

Common Name

Genus

Species

Common Name

Anchusa

officinalis

common bugloss

Equisetum

arvense

field horsetail

Artemisia

absinthium

absinth woodworm

Euphorbia

esula

leafy spurge

Cardaria

draba

hoary cress

Hyoscyamus

niger

black henbane

Carduus

nutans

musk thistle

Hypericum

perforatum

St. Johnswort

Cenchrus

longispinus

longspine sandbur

Kochia


scoparia

Kochia

Centaurea

diffusa

diffuse knapweed

Linaria

dalmatica

dalmatian toadflex

Centaurea

maculosa

spotted knapweed

Linaria

vulgaris

yellow toadflax

Centaurea

solstitialis

yellow starthistle

Onopordum

acanthium

Scotch thistle

Chondrilla

juncea

rush skeletonweed

Polygonum

sachalinense

giant knotweed

Chrysanthemum

leucanthemum

oxeye daisy

Rubus

discolor

Himalaya blackberry

Cirsium



bull thistle

Senecio

jacobaea

tansy ragwort

Cirsium

arvense


Canada thistle

Silene

latifolia

white catchfly

Conium

maculatum

poison hemlock

Solanum

rostratum

Buffalobur

Convolvulus

arvensis

field bindweed

Sonchus

arvensis

perennial sowthistle

Cynoglossum

officinale

houndstongue

Taeniatherum

caput-medusae

Medusahead

Daucus

carota

wild carrot

Tribulus

terrestris

Puncturevine



Loss of late successional


Snags and downed wood are structural elements, common in mature forests, with significant importance to wildlife. The prevalence of these elements has been dramatically reduced through the removal of older trees that might soon die and create snags, fire suppression, and increased access to these elements during salvage harvest or fire wood collection (Wisdom 2000)

Roads

The transportation system of the Imnaha subbasin is a potential limiting factor to wildlife populations. More than 65 species of terrestrial vertebrates in the interior Columbia River basin have been identified as being negatively affected by road-associated factors (Wisdom 2000). Road-associated factors can negatively affect habitats and populations of terrestrial vertebrates both directly and indirectly (Table 36). Motorized access facilitates firewood cutting, and commercial harvest, which can reduce the suitability of habitats surrounding roads to species dependent on large trees, snags, or logs (USDA Forest Service 2000b). Roads aid in the spread of noxious weeds and can facilitate the spread of competitive species into otherwise unsuitable habitat. Roads increase the amount of edge habitat in the landscape increasing habitat suitability for edge dependent species like the brown-headed cowbird. Populations of reptiles which using roads for thermal regulation, wide ranging forest carnivores, and migrating amphibians are particularly vulnerable to the effects of road mortality. Wisdom (2000) identified 13 factors that were consistently associated with roads in a manner deleterious to terrestrial vertebrates.

Table 36. Thirteen road-associated factors with deleterious impacts on wildlife (Wisdom 2000)

Road-associated Factor

Effect of Factor in Relation to Roads

Snag reduction

Reduction in density of snags due to their removal near roads, as facilitated by road access

Down log reduction

Reduction in density of large logs due to their removal near roads, as facilitated by road access

Habitat loss and
fragmentation

Loss and resulting fragmentation of habitat due to establishment and maintenance of road and road right-of-way

Negative edge effects

Specific case of fragmentation for species that respond negatively to openings or linear edges created by roads

Over-hunting

Nonsustainable or nondesired legal harvest by hunting as facilitated by road access

Over-trapping

Nonsustainable or nondesired legal harvest by trapping as facilitated by road access

Poaching

Increased illegal take (shooting or trapping) of animals as facilitated by road access

Collection

Collection of live animals for human uses (e.g., amphibians and reptiles collected for use as pets) as facilitated by the physical characteristics of roads or by road access


Harassment or disturbance
at specific use sites

Direct interference of life functions at specific use sites due to human or motorized activities, as facilitated by road access (e.g. increased disturbance of nest sites, breeding leks or communal roost sites)

Collisions

Death or injury resulting from a motorized vehicle running over or hitting an animal on the road

Movement Barrier

Preclusion of dispersal, migration or other movements as posed by a road itself or by human activities on or near a road or road network

Displacement or avoidance

Spatial shifts in populations or individual animals away from a road or road network in relation to human activities on or near a road or road network

Chronic negative interaction
with humans

Increased mortality of animals due to increased contact with humans, as facilitated by road access

Nutrient Flow Reduction

Spawning salmon populations form an important link between the aquatic, riparian, and terrestrial communities. Anadromous salmon help to maintain ecosystem productivity and may be regarded as a keystone species. Salmon runs input organic matter and nutrients to the trophic system through multiple levels and pathways including direct consumption, excretion, decomposition, and primary production. Direct consumption occurs in the form of predation, parasitism, or scavenging of the live spawner, carcass, egg, or fry life stages. Carcass decomposition and the particulate and dissolved organic matter released by spawning fish deliver nutrients to primary producers (Cederholm et al. 2000). Cederholm identified nine wildlife species that have (or historically had) a strong consistent relationship with salmon; of these the common merganser, harlequin duck, osprey, bald eagle, Caspian tern, black bear, and northern river otter occur in the Imnaha subbasin. Eighty-three other wildlife species were identified as having a recurrent or indirect relationship with salmon, and many of these also occur in the Imnaha subbasin (Cederholm et al. 2000). The golden eagle, bald eagle, peregrine falcon, and bank swallow are among those that are state or federally listed/candidate species.




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