FISHERIES SURVEYS IN THE SOUTH FORK AMERICAN RIVER DOWNSTREAM OF SLAB CREEK DAM AND IOWA CANYON CREEK, 2010 Prepared for: Sacramento Municipal Utility District Power Generation Department 6201 S Street Sacramento, California Prepared by: ECORP Consulting, Inc. 2525 Warren Drive Rocklin, California 95677 May 2011
TABLE OF CONTENTS 1.0 INTRODUCTION... 1 1.1 Project Purpose and Study Area... 1 1.2 Previous Studies... 2 2.0 METHODS... 2 2.1 Station Selection... 2 2.2 Data Collection... 3 2.2.1 Aquatic Habitat... 3 2.2.2 Fisheries... 3 3.0 RESULTS... 6 3.1 Aquatic Habitat Mapping... 6 3.1.1 SFAR ¼-Mile Reach... 6 3.1.2 Lower Iowa Canyon Creek... 10 3.2 Sampling Station Descriptions... 10 3.2.1 Sampling Station 1: SFAR Upstream from Iowa Canyon Creek Confluence... 10 3.2.2 Station 2: SFAR Downstream from Iowa Canyon Creek Confluence... 13 3.2.3 Lower Iowa Canyon Creek Sampling Station... 13 3.3 Fish Community SFAR and Iowa Canyon Creek Sampling Stations... 13 3.4 Fish Biomass and Condition Factor SFAR and Iowa Canyon Creek Stations.. 16 3.5 Direct Observation Surveys SFAR Stations... 20 4.0 DISCUSSION... 20 4.1 Comparison with Previous Fisheries Studies... 22 5.0 CONCLUSIONS... 24 5.1 South Fork American River... 24 5.2 Iowa Canyon Creek... 26 6.0 LITERATURE CITED... 27
LIST OF FIGURES Figure 1. Habitat Mapping Areas, SFAR Reach and Lower Iowa Canyon Creek...4 Figure 2. Aquatic Habitats Mapped Within the SFAR Reach...7 Figure 3. Locations of Fisheries Sampling Stations Within the SFAR Reach and in Lower Iowa Canyon Creek...12 Figure 4. Rainbow Trout Length-Frequency for South Fork American River, Slab Creek and Iowa Canyon Creek; September 201...17 Figure 5. Brown Trout Length-Frequency for South Fork American River, Slab Creek and Iowa Canyon Creek; September 2010...17 LIST OF TABLES Table 1. Results of habitat mapping conducted within the SFAR, August 2010...8 Table 2 Average instream habitat characteristics for each habitat type within the SFAR, fall 2010...9 Table 3. Results of habitat mapping conducted within lower Iowa Canyon Creek, August 2010...11 Table 4. Fish population estimates by species and age class for the SFAR stations, September 2010...14 Table 5. Results Fisheries population and biomass estimates per 100 m for SFAR and Iowa Canyon Creek stations, September 2010...15 Table 6. Condition factors for rainbow and brown trout collected at SFAR and Iowa Canyon Creek stations, September 2010...18 Table 7. Average condition factors by age class for rainbow and brown trout collected at SFAR and Iowa Canyon Creek stations, September 2010...19 Table 8. Results of snorkel surveys conducted in large pools within the SFAR...20 Table 9. Extrapolated results of snorkel surveys (fish per 100 m) conducted in the SFAR, August 2010...22 LIST OF ATTACHMENTS Attachment A Estimated age of all trout species collected at South Fork American River Slab Creek Dam Reach, Station 1, Station 2, and Iowa Canyon Creek.
1.0 INTRODUCTION This report presents the results of the 2010 fish sampling surveys conducted for the Sacramento Municipal Utility District (SMUD) in support of the proposed New Slab Creek Powerhouse Project (Project). The Project consists of modification of SMUD s existing Upper American River Project (UARP), a 688 MW hydroelectric project consisting of eight powerhouses. The smallest is Slab Creek Powerhouse, a 0.4 MW facility lying at the base of Slab Creek Reservoir Dam on the South Fork American River (SFAR). This powerhouse generates power from the 10/36 cfs minimum release requirements under the existing license. Under the new UARP license, higher and more variable minimum releases ranging between 63 and 415 cfs will be released from Slab Creek Reservoir. Preliminary engineering feasibility studies have demonstrated the value of adding a new powerhouse at Slab Creek Reservoir to take advantage of the new minimum releases. However, the size of the release valve at the base of Slab Creek Reservoir Dam, which feeds into the existing powerhouse, limits the volume of water to approximately 260 cfs. Under the new license, SMUD will also provide boating flows below Slab Creek Reservoir of up to 1,500 cfs. Currently, boating flows can only be provided by spilling water over Slab Creek Dam. Alternatively, boating flows could be realized by boring a new hole through the base of the dam and installing a larger pipe and release valve. SMUD has determined the White Rock Tunnel Adit 3, a short tunnel that connects to the White Rock Tunnel, is the optimal location for a new powerhouse that can facilitate the minimum and boating releases required under the new license. Under SMUD s proposal, a valve inserted into the White Rock Tunnel bulkhead would deliver water into a penstock leading to the new powerhouse at the end of the adit. The powerhouse would be located on the banks of the SFAR, directly downstream of Iowa Canyon Creek. A new bridge crossing the lowermost section of Iowa Canyon Creek would provide vehicular access to the new powerhouse. 1.1 Project Purpose and Study Area The Project area is focused on the SFAR just below the Slab Creek Reservoir Dam in Section 25 of Township 11 North, Range 12 East of the Slate Mountain, California USGS 7.5-minute topographic quadrangle map. Elevations in the Project area range from approximately 1,640 1,800 ft (500 550 m). Electrofishing surveys were performed at two locations within the SFAR located immediately downstream of Slab Creek Reservoir Dam, and at one location in Iowa Canyon Creek. Snorkel surveys were also conducted in pool habitats in the SFAR. The objectives of the study were to document the current fish community present in wadeable and non-wadeable habitats within the ¼-mile reach of SFAR between Slab Creek Reservoir Dam and the proposed new powerhouse location, as well as in Iowa Canyon Creek, where the new bridge will be constructed to access the powerhouse, and to calculate population estimates (where appropriate) for each of the fish species present. Results of the fisheries surveys are discussed relative to results of a companion report from the current study describing benthic macroinvertebrate (BMI) communities (ECORP 1
2011). Also, results of these recent fisheries surveys are compared to earlier studies (2002-2004 and 2007), which described the aquatic habitat and associated fish and BMI communities. 1.2 Previous Studies Fisheries sampling was previously conducted within the SFAR Slab Creek Dam Reach in 2002, 2003, and 2004 (DTA and Stillwater Sciences 2004) and in 2007 (Stillwater Sciences 2008) as part of the UARP relicensing studies. A single snorkel station was sampled in 2002, and one electrofishing station was sampled both in 2002 and 2003. A more comprehensive snorkel survey was conducted in 2004, extending 4.0 miles (mi) above Chili Bar Reservoir. In 2007, snorkel surveys were conducted at 14 stations in June, August, and November; beginning approximately 0.65 mi upstream of Chili Bar Reservoir and extending 5.3 mi upstream. The results of these surveys (Stillwater Sciences 2008) indicated the presence of nine fish species within the 8.0 mile Slab Creek Dam Reach, which begins just below Slab Creek Reservoir Dam and continues downstream to the White Rock Powerhouse. In general, species abundance and diversity was greatest in the lower portion of the Reach, declining with distance upstream. Although none of the previous sampling stations were located within the ¼-mile reach associated with the Project, results of these studies provide value in comparison to the results of the 2010 surveys. 2.0 METHODS 2.1 Station Selection Two electrofishing sampling stations were selected within the SFAR ¼-mile reach to provide an assessment of the fish community in the wadeable portion of the reach, which was limited to the downstream sampling site. Iowa Canyon Creek enters the ¼-mile reach along the right bank (looking upstream) of the river, about 420 meters (m) (1,380 feet [ft]) downstream of the dam and within the wadeable portion of the reach. Iowa Canyon Creek generally flows northwesterly through heavily wooded areas and has a relatively steep overall gradient. The lower 500 m of the creek flows over several bedrock outcrops resulting in a series of waterfalls / cascades prior to entering the SFAR. The original creek sampling site was located in the lower 150-m of the creek; however, flow in this lower section of the creek became subsurface at the bottom of the lowest waterfall in mid-july and could not be sampled. Subsurface flow eventually percolated through the SFAR river bank, entering the river at a point approximately 30 m downstream of the dry channel mouth. The dry creek bed forced the relocation of the sampling station away from the general area of the proposed bridge across Iowa Canyon Creek. A secondary station was selected above the waterfall and cascade segment, in a perennial flow segment of the creek directly upstream of the Slab Creek Reservoir Road crossing, approximately 585 m (1,900 ft) upstream of mouth of the creek. Electrofishing station lengths were targeted at 100 m; however, the presence of non-wadeable deep pool habitat near the downstream end of the ¼-mile reach limited the length of Sampling 2
Station 2 (downstream of Iowa Canyon Creek) to 70 m. The Iowa Canyon Creek station was approximately 120 m in length. In addition to the electrofishing stations, snorkel surveys were conducted within all nonwadeable pool habitats within the ¼-mile reach. 2.2 Data Collection Data collected at each sampling station included basic site information (project name, station name, time, date, stream / watershed name, GPS coordinates, and crew members), water quality (see BMI report, ECORP 2011), habitat assessment parameters, and photo-documentation. 2.2.1 Aquatic Habitat A field-based habitat assessment was performed in the SFAR ¼-mile reach and lower Iowa Canyon Creek on 27 August 2010, during fall low flow conditions. The aquatic habitat assessment followed methods outlined in the California Department of Fish and Game (CDFG) California Salmonid Stream Habitat Restoration Manual (Flosi, et al. 2010). Although lower Iowa Canyon Creek was dry at the time, level IV habitat types were estimated for low flow conditions, per Flosi, et al. 2010. Stream habitat mapping within the ¼-mile reach extended from the base of Slab Creek Reservoir Dam downstream approximately 578 m, which included a section of the river downstream of the adit tunnel (approximately 85 m) (Figure 1). In lower Iowa Canyon Creek, habitat mapping extended from the confluence with the SFAR upstream approximately 165 m to the first waterfall/cascade (see Figure 1). The linear distance of each habitat unit was measured using a 100-m tape. Physical stream parameters were recorded on field data sheets for each habitat unit, including wetted channel width, water depth, substrate composition, and aquatic cover. Other channel characteristics included stream vegetation, canopy cover and overhanging cover. Incidental observations of fish and other aquatic species were also documented. 2.2.2 Fisheries Fish community sampling was performed on 26 and 27 August and 7 and 8 September 2010 using two methodologies; backpack electrofishing and direct observation (snorkel survey). Backpack electrofishing was conducted during September in representative riffle, run and shallow pool habitats occurring immediately upstream (Sampling Station 1) and immediately downstream (Sampling Station 2) of the Iowa Canyon Creek confluence with the SFAR. Since the sampling station in Iowa Canyon Creek was not situated within a section of the creek affected by the proposed project, only qualitative sampling was conducted to provide an assessment of the trout population structure, relative abundance, and overall fish condition. 3
Figure 1. Habitat Mapping Areas, SFAR Reach and Lower Iowa Canyon Creek Map Features SFAR Bypas Reach Iowa Canyon Creek Location: N:\2010\2010-026 SMUD\002_Lower_Slab_Creek_Powerhouse\MAPS\Vegetation\Habitat\LSC_Reaches.mxd (ekeethe 4/29/2011) 2010-026.2 Lower Slab Creek Powerhouse 1 " = 160 ' S c a le i n F e et 0 200 Ch p Photo Source: USGS June 2007 USGS 7.5' Quadrangle: Slate Mountain Map Date: 4/29/2011
Backpack electrofishing was performed using standard methods identical to those performed during the relicensing studies (multi-pass depletion method). Block nets were set at the upper and lower station boundaries to prevent fish movement into and out of the station during sampling. Fish were collected during multiple passes (minimum of two) using Smith-Root backpack electroshockers in pulsed DC mode. Captured fish were held in live cars outside the electrofishing station until each pass was completed. Fish were then processed after each pass for length (mm) and weight (0.1 g) measurements and fish scale samples were collected for assessment of age and growth. After processing the catch from the final sampling pass, all fish were carefully redistributed throughout the sampling site. Snorkel surveys were conducted during August in four pools associated with the 100 m SFAR Sampling Station 1 (pools 1, 2, 2a, and 3), and in six pools associated with the 70 m SFAR Sampling Station 2. These six pools include Pool 4, which is located within Sampling Station 2, and pools 5, 6, 7, 8 and 8a located just downstream of the station. Surveys were conducted by three biologists using snorkel gear, each moving upstream in separate lanes from the bottom to the head of each pool. When a fish or school of fish was observed, each snorkeler provided the species observed, relative length(s), and number of each species to a shore-based observer who recorded all data. Only those fish that passed downstream of each individual snorkeler were counted. After completing each pool, the combined results from the three snorkelers were recorded. Due to the lack of deep pool habitat in Iowa Canyon Creek, fish sampling was only conducted by backpack electrofishing. Age determination was completed through analysis of collected scale samples from both rainbow and brown trout. Scale samples were mounted on slides and examined independently by two biologists on a microfiche reader to determine age. The age determinations were compared to the length-frequency analyses of each trout species per station to determine final size classes for each species age group. Population and biomass estimates were then calculated by species and life stage (i.e., 0+ age class and base population, which is defined as fish in age class 1+ and older) using the MicroFish 3.0 software that calculates maximum-likelihood population estimates from removal-depletion sampling data (Van Deventer and Platts 1986). The condition factor (K) for each individual fish was calculated according to the following formula: K= W x 100 L 3 Where W is the fish weight in grams, and L is its length in cm. 5
3.0 RESULTS 3.1 Aquatic Habitat Mapping Aquatic habitat mapping was conducted within the ¼-mile reach, extending downstream from just below the tailout of the dam plunge pool, and within the lower portion of Iowa Canyon Creek (see Figure 1). 3.1.1 SFAR ¼-Mile Reach A total of 498.2 m of the SFAR was mapped during this study. Results of habitat mapping conducted within the SFAR in August 2010 are provided graphically in Figure 2, and all data are presented in Table 1. Average instream habitat characteristics for each habitat type within the SFAR study area are presented in Table 2. Within the ¼-mile reach, the SFAR channel is of moderate gradient (4 to 7 %) and generally stable due to the dominance of bedrock and large boulder substrates. Riparian vegetation is generally sparse along the right bank (looking downstream), but is relatively extensive along the left bank, ranging from 2 to 20 m in width, and composed primarily of willow, alder and blackberry. A total of 14 habitat units were identified within the reach for a total distance of 498.2 m (see Table 2 and Figure 2). Due to the high level of disturbance that occurs at the base of the dam associated with spill events and the general lack of usable aquatic habitat; the plunge pool at the base of the dam was not included in the overall assessment of aquatic habitat and is not considered any further in this text. Pool habitat was the dominant feature (50 % of the total length) within this 498 m reach. With the exception of one bedrock lateral scour pool, all of these features were mid-channel pools. Run and run / pocket water habitat combined (18 %) was the next most abundant habitat type within the reach followed by high-gradient riffles (15 %) and step-runs (11 %). The remaining habitat types were low-gradient riffles (3 %) and cascades (3 %). The pools ranged in length from 9 to 105 m, and from 9 to 20 m in width. Under the 36 cfs flow that occurred during habitat mapping, pool depth was generally less than 2 meters, although the two largest pools were 5 and 7 m deep. Many of the pools are associated with bedrock outcroppings, as reflected by the percent bedrock values (up to 50 percent). Similar to other habitat types within the ¼-mile reach, boulder substrates dominate the reach, ranging from 40 to 95 percent. Cobble substrate was often co-dominant. Fine sediments, including gravel, were generally present in low abundance. Fish cover in the pools is generally abundant, consisting primarily of surface turbulence, boulder edge, and depth. The largest pool lies roughly in the middle of the reach, over which spans a pedestrian bridge (see Figure 2). This single large pool is 105 m in length, thereby comprising 1/5 of the entire reach, 20 m at its widest and as much as 7 m deep. It essentially demarcates the two distinct geomorphic areas within the ¼-mile reach. Upstream of the large pool, lies a river segment dominated by a right bank lateral bar of rock 6
Figure 2. Aquatic Habitats Mapped Within the SFAR Reach Map Features Reach Habitat Type High Gradient Riffle 57 m 31 m 74 m 80 m Low Gradient Riffle L. Scour Pool - Bedrock Formed Mid-Channel Pool Run Run/PW Location: N:\2010\2010-026 SMUD\002_Lower_Slab_Creek_Powerhouse\MAPS\Vegetation\Habitat\LSC_ReachHabitatType_v1.mxd (ekeethe 4/29/2011) 48 m 9 m 10 m 2010-026.2 Lower Slab Creek Powerhouse 60 m 9 m 21 m 38 m 25 m 16 m 1 " = 160 ' 105 m S c a le i n F e et 0 200 Ch p Photo Source: USGS June 2007 USGS 7.5' Quadrangle: Slate Mountain Map Date: 4/29/2011
Table 1 Results of habitat mapping conducted within the SFAR, August 2010. Habitat Unit Depth (m) Substrate (%) Cover Photo No. GPS Coord. No. Type Characteristics 1 MCP Length (m.) Avg. Width (m.) Max Avg Silt Sand Gravel Cobble Boulder Bedrock Pool at bottom of reach 48.2 13 5.0 1.5 1 1 5 8 50 35 0 10 5 1 4 1 1 1 6 N/A 5 2 CAS HGR elements 9 10.2 0.8 0.4 1 1 3 5 50 40 0 5 5 0 4 0 1 5 2 35 Pocket water 3 MCP elements 9.2 8.9 1.5 1.1 0 0 1 4 65 30 0 5 4 0 3 0 0 4 4 N/A 10 Fish 4 Run/POW 49.8 23 1.1 0.6 1 0 14 10 75 0 0 15 2 1 4 0 1 2 4 20 Station 2 5 MCP Boulder formed 10.2 12.2 1.3 1.0 1 0 1 3 95 0 0 20 3 0 4 0 0 2 3 N/A 5 6 CAS HGR elements 3 12 1.0 0.8 20 80 7 LSBk 20.8 14 1.3 0.9 0.5 0.5 9 15 65 10 0 15 2 1 3 0 1 2 4 10 Fish 8 POW Elements of run/hgr 38.5 15.8 0.9 0.4 0 0 3 17 80 0 0 5 5 0 5 0 1 4 2 25 Station 1 9 SRN 25.5 15.4 1.0 0.6 1 0 4 20 75 0 0 5 1 0 3 0 1 2 3 15 10 LGR Pool tailout/pock. water/hgr 17 17.5 0.8 0.4 0 0 5 10 85 0 0 5 4 0 4 0 1 2 2 25 11 MCP Bridge over pool 105 20 7.0 2.5 0 0 0 10 40 50 0 10 1 0 4 0 1 1 5 N/A 2 12 HGR 74 10 0.7 0.4 0 0 0 20 70 10 0 0 2 0 3 0 0 2 1 35 13 MCP 57 15 2.2 1.3 0 0 0 15 70 15 0 0 1 0 4 0 0 1 5 N/A 5 14 SRN Elements of HGR 31 10 1.3 0.5 0 0 0 20 70 10 0 0 2 0 3 0 0 2 1 35 RIFFLE / CASCADE FLATWATER MAIN CHANNEL POOL SCOUR POOL BACKWATERPOOLS Cover Categories 0 = 0 (LGR) Low Gradient Riffle (POW) Pocket Water (TRP) Trench Pool (CRP) Corner Pool (SCP) Secondary Channel Pool % (HGR) High Gradient Riffle (GLD) Glide (MCP) Mid-Channel Pool (LSL) L. Scour Pool - Log Enhanced (BPB) Backwater Pool - Boulder Formed 1 = 1-10% (CAS) Cascade (RUN) Run (CCP) Channel Confluence Pool (LSR) L. Scour Pool - Root Wad Enhanced (BPR) Backwater Pool - Root Wad Formed 2 = 11-20% (BRS) Bedrock Sheet (SRN) Step Run (STP) Step Pool (LSBk) L. Scour Pool - Bedrock Formed (BPL) Backwater Pool - Log Formed 3 = 21-30% (DRY) Dry Sidechannel (EDW) Edgewater (LSBo) L. Scour Pool - Boulder Formed (DPL) Dammed Pool 4 = 31-40% Concrete Canopy (%) Instream: Surface Turbulence Undercut Boulder LWD Riparian Veg (OV) Bubble Curtain Depth Pool Tail Embeddedness Exposed Boulders 8
Table 2 Average instream habitat characteristics for each habitat type within the SFAR, fall 2010. Aquatic Habitats Depth (m) Substrate (%) Percent of Total Habitat Within the Reach Type Average Length (m) Average Wetted Width (m) Average Maximum Silt Sand Gravel Cobble Boulder Bedrock Concrete Pool Run / Pocket Water Step-Run High Gradient Riffle Low Gradient Riffle Cascade Total Sampling Reach 498.2 14.2 0.9 13.0 0.4 0.2 3.5 12.6 68.5 15.4 57.0 15.0 10.0 13.0 3.0 2.0 Mid-Channel Pools 45.9 13.8 1.5 3.4 <1.0 <1.0 1.4 8.0 90.0 Lateral Scour Pool 20.8 14.0 0.9 1.3 1.0 9.0 15.0 75.0 Run / Pocket Water 44.0 19.5 0.5 1.1 1.0 8.0 13.0 78.0 Step-Run 28.0 13.0 0.5 1.3 2.0 20.0 78.0 High Gradient Riffle 74.0 10.0 0.4 0.7 20.0 80.0 Low Gradient Riffle 17.0 17.5 0.4 0.8 5.0 10.0 85.0 Cascade 6.0 11.0 0.6 0.9 1.0 1.0 13.0 85.0 RIFFLE / CASCADE FLATWATER MAIN CHANNEL POOL SCOUR POOL BACKWATERPOOLS (LGR) Low Gradient Riffle (POW) Pocket Water (TRP) Trench Pool (CRP) Corner Pool (SCP) Secondary Channel Pool (HGR) High Gradient Riffle (GLD) Glide (MCP) Mid-Channel Pool (LSL) L. Scour Pool - Log Enhanced (BPB) Backwater Pool - Boulder Formed (CAS) Cascade (RUN) Run (CCP) Channel Confluence Pool (LSR) L. Scour Pool - Root Wad Enhanced (BPR) Backwater Pool - Root Wad Formed (BRS) Bedrock Sheet (SRN) Step Run (STP) Step Pool (LSBk) L. Scour Pool - Bedrock Formed (BPL) Backwater Pool - Log Formed (DRY) Dry Sidechannel (EDW) Edgewater (LSBo) L. Scour Pool - Boulder Formed (DPL) Dammed Pool (WET) Wet Sidechannel (PLP) Plunge Pool 9
waste (some of it concrete blocks left from dam construction), and a left bank composed of bedrock, high gradient riffle, and pool habitat. High gradient riffles are dominant, comprising approximately 2/3 of the segment, with the balance represented by pools. Downstream of the large pool, the SFAR passes through a lower gradient segment with a more diverse set of habitat types including pools, low gradient riffle, step-runs, and pocket water. 3.1.2 Lower Iowa Canyon Creek Results of habitat mapping conducted in lower Iowa Canyon Creek cannot be presented graphically due to vegetative cover; however, habitat data are provided in Table 3. A total of 17 habitat units were identified in lower Iowa Canyon Creek. The study reach extended from the confluence with the SFAR upstream 165 m to the first waterfall/cascade (see Figure 1). Heavy vegetative cover along most of Iowa Canyon Creek precluded the use of an aerial photograph to map stream habitats. Within the Iowa Canyon Creek reach, the dominant instream habitats by length were: cascades/high gradient riffles (35.5 %), main channel pools (23.2 %), and step-pools (19.3 %). The remaining habitats consisted of low-gradient riffles (11.7 %) and step-runs (10.3 %). Boulder, bedrock, and broken concrete comprised 62.1 percent of all substrates, with 17.5 percent cobble, 10.5 percent sand, and 9.9 percent gravel. The overall gradient for lower Iowa Canyon Creek averaged between 17 to 18 percent, and the gradient in the lower 10 m of the creek was 22 percent. Canopy cover averaged 60.6 percent for the reach. 3.2 Sampling Station Descriptions 3.2.1 Sampling Station 1: SFAR Upstream from Iowa Canyon Creek Confluence Sampling Station 1 is located approximately 347 m (1138.5 ft) downstream of Slab Creek Reservoir Dam (NAD83 coordinates Easting 10S 699529 and Northing 4293939) at an elevation of 1,640 ft above mean sea level (Figure 3). Gradient within this 100-meter (m) long site ranged from 0.5% to 4%. Mean wetted and bank-full widths were 15.6 m and 27.1 m, respectively, with a mean depth of 29 cm. Riparian vegetation consisted of alder and willow with an understory of blackberry, forbs and grasses, and wild grape. This station was comprised of four major habitat units that included elements of several microhabitat types. The top of this station consists of a large pool tailout with elements of low gradient riffle and pocket water (17 m). Below the pool tailout is a series of step-runs, which also include elements of riffle and pocket water microhabitat (25.5 m). Immediately downstream of the step-run habitat is pocket water with elements of run and riffle habitat (38.5 m); and a bedrock lateral scour pool (20.8 m) occurs at the bottom of the station. To provide a more representative estimate of the substrate composition in each habitat unit within the station, the percentage of each substrate type within each habitat unit was weighted by the length of that habitat unit. The resulting substrate composition was 76.5 % boulder, 16.2 % cobble, 4.8 % gravel, and 2.0 % bedrock, with trace amounts of fines (0.5 %). Cobble embeddedness was generally low, averaging 12.2 %. Surrounding land use includes forest and recreational areas. 10
Table 3 Results of habitat mapping conducted within lower Iowa Canyon Creek, August 2010. Habitat Unit Depth (m) Substrate (%) Cover Photo No. GPS Coord. No. Type Characteristics Length (m.) Avg. Width (m.) Max Avg. Silt Sand Gravel Cobble Boulder Bedrock Concrete Canopy (%) Instream: Surface Turbulence Undercut Boulder LWD Riparian Veg (OV) Bubble Curtain Depth Pool Tail Embeddedness Exposed Boulders 1 CAS/HGR Plunge pool 25 3 2 8 20 70 100 2 Pool 5 6 20 25 25 30 30 3 LGR 3.5 3.5 2 18 80 0 4 MCP 5.8 5 5 10 30 55 25 5 CAS 1 2 5 15 80 100 6 HGR 21 2.5 2 3 30 70 80 7 MCP Plunge pool 4 5 5 5 20 70 100 8 MCP Plunge pool 9.5 3 5 5 20 70 100 9 LGR 9 4 20 10 10 60 30 10 MCP 4.9 4 20 10 5 50 15 50 11 SRN 17 4 15 20 20 45 25 12 MCP 9 6 25 10 20 20 25 50 13 LGR 6.8 5 10 10 25 45 10 10 14 STP 11.8 2.5 15 10 10 10 30 25 100 15 CAS 6 2.5 10 5 70 15 80 16 HGR 5.5 3 5 10 10 75 100 17 STP Plunge pool series 20 2 1.6 0.8 20 20 20 40 90 Note: Discharge from sub-surface flow into SFAR is 15-30 meters ds of main channel of Iowa Canyon Creek. 164.8 Gradient 20-25% at confluence with SFAR, with the remainder of the reach at 17-18%. RIFFLE / CASCADE FLATWATER MAIN CHANNEL POOL SCOUR POOL BACKWATERPOOLS Cover Categories (LGR) Low Gradient Riffle (POW) Pocket Water (TRP) Trench Pool (CRP) Corner Pool (SCP) Secondary Channel Pool 0 = 0 % (HGR) High Gradient Riffle (GLD) Glide (MCP) Mid-Channel Pool (LSL) L. Scour Pool - Log Enhanced (BPB) Backwater Pool - Boulder Formed 1 = 1-10% (CAS) Cascade (RUN) Run (CCP) Channel Confluence Pool (LSR) L. Scour Pool - Root Wad Enhanced (BPR) Backwater Pool - Root Wad Formed 2 = 11-20% (BRS) Bedrock Sheet (SRN) Step Run (STP) Step Pool (LSBk) L. Scour Pool - Bedrock Formed (BPL) Backwater Pool - Log Formed 3 = 21-30% (DRY) Dry Sidechannel (EDW) Edgewater (LSBo) L. Scour Pool - Boulder Formed (DPL) Dammed Pool 4 = 31-40% (PLP) Plunge Pool % = 41-50% (WET) Wet Sidechannel 11
Figure 3. Locations of Fisheries Sampling Stations Within the SFAR Reach and in Lower Iowa Canyon Creek Map Features Electrofishing Stations Snorkel Survey Area Iowa Canyon Creek Station Station 1 Station 2 Iowa Canyon Creek Channel Mouth S c a le i n F e et 0 50 100 150 200 250 500 1 " = 250 ' Location: N:\2010\2010-026 SMUD\002_Lower_Slab_Creek_Powerhouse\MAPS\Site_Vicinity\LSC_Fisheries_SiteVicinity_Aerial.mxd (ekeethe 4/29/2011) Location of Subsurface Emergence (Iowa Canyon Creek) Slab Creek Reservoir Road Iowa Canyon Creek Station USGS 7.5' Quadrangle: Slate Mountain 2010-026.2 Lower Slab Creek Powerhouse Photo Source: USGS June 2007 Map Date: 4/29/2011
3.2.2 Station 2: SFAR Downstream from Iowa Canyon Creek Confluence This 70 m long station is located approximately 449 m (1,473 ft) downstream of Slab Creek Reservoir Dam (NAD83 coordinates Easting 10S 699458 and Northing 4293896) at an elevation of 1,630 ft above mean sea level (see Figure 3). Gradient in Station 2 ranged from 0.5% to 8.0%. Mean wetted and bank-full widths were 18.1 m and 33.8 m, respectively, with a mean depth of 36 cm. Riparian vegetation consisted of alder and willow with an understory of blackberry, forbs and grasses, and wild grape. This station was also comprised of four major habitat units with elements of several microhabitat types. The top of this station is a cascade with elements of riffle and step run (3 m), below which is a relatively large mid-channel pool, with complex microhabitats (10.2 m). Adjacent to the pool is a run-pocket water complex (49.8 m) with riffle elements. The bottom of the station consists of another mid-channel pool, with pocket water and riffle elements (9.2 m). To provide a more representative estimate of the substrate composition in each habitat unit within the station, the percentage of each substrate type within each habitat unit was weighted by the length of that habitat unit. The resulting substrate composition within Station 2 consisted of 76.8 % boulder, 9.9 % gravel, 8.7 % cobble, and 3.8 % bedrock, with trace amounts of fines (0.8%). Mean cobble embeddedness was identical to that in Station 1 (12.2 %). Surrounding land uses includes forest and recreational areas. Both Stations 1 and 2 are readily accessible to anglers. 3.2.3 Lower Iowa Canyon Creek Sampling Station The Iowa Canyon Creek fish sampling station was approximately 150 m in length, and was located 585 m (approximately 1,900 ft) upstream of the confluence with the SFAR (see Figure 3). This alternate sampling location was selected due to the lack of surface flow (flow was subsurface in the lower 165 m [540 ft] of the creek during the survey period). Within this sampling reach, stream gradient ranged from 0 to 2%, bank-full widths ranged from 8 to 10 m (26 to 33 ft), wetted width averaged about 3.5 m (11 ft), and depth averaged approximately 25 cm (0.8 ft). Riparian vegetation consisted primarily of willow, alder, and conifers with understory of blackberry, various forbs and grasses. Stream habitats within the 150 m reach included low gradient riffles, runs, glides, and step-pools; and substrates consisted primarily of gravel (50%), cobble (35%), and boulder (8%); with very little sand and fines (5% combined) or bedrock/concrete (2% combined). 3.3 Fish Community SFAR and Iowa Canyon Creek Sampling Stations Three fish species were collected within the ¼-mile reach during the electrofishing surveys; rainbow trout (Oncorhynchus mykiss), brown trout (Salmo trutta), and Sacramento sucker (Catostomus occidentalis). Fish population estimates by species, age class, and station for the SFAR are reported in Table 4. Fish population and biomass estimates per 100 m by species, age class, and station for the SFAR reach and Iowa Canyon Creek stations are ummarized in Table 5. Numbers of fish collected at each of the SFAR stations and at the Iowa Canyon Creek station during each pass are included in Attachment A, as are estimated ages for all fish from scale analysis. 13
Table 4 Fish population estimates by species and age class in the SFAR Stations, September 2010 Species Site Length (m) Pass 1 Pass 2 Estimate Std Err Station 1 Rainbow trout - 0+ 100 4 0 4.0 0.00 Rainbow trout - Base 100 5 2 7.0 0.95 Brown trout - 0+ 100 1 0 1.0 0.00 Brown trout - Base 100 6 0 6.0 0.00 Species Site Length (m) Pass 1 Pass 2 Pass 3 Estimate Std Err Station 2 Rainbow trout - 0+ 70 2 3 0 5.0 0.79 Rainbow trout - Base 70 2 2 0 4.0 0.54 Brown trout - 0+ 70 0 0 0 0.0 na Brown trout - Base 70 2 2 2 8.0 5.73 Sacramento sucker 70 1 0 0 1.0 na 14
Table 5 Fisheries population and biomass estimates per 100 m for SFAR Reach and Iowa Canyon Creek stations, September, 2010. Species Population Estimate / Site Population Estimate / 100m Percent of Population Avg Biomass (g) Biomass / Site (g) Biomass / 100m (g) Station 1 Age 0 Rainbow 4 4 36.4 2.0 8.0 8.0 Base Rainbow 7 7 63.6 59.4 416.0 416.0 Age 0 Brown Trout 1 1 14.3 5.5 5.5 5.5 Base Brown Trout 6 6 85.7 112.0 671.7 671.7 Station 2 Age 0 Rainbow 5 7 55.6 3.4 17.2 24.6 Base Rainbow 4 6 44.4 35.0 139.8 199.7 Age 0 Brown Trout 0 0 0.0 0.0 0.0 0.0 Base Brown Trout 8 11 100.0 88.8 710.7 1015.2 Total Sacramento Sucker 1 1 45.5 45.5 65.0 Iowa Canyon Creek Age 0 Rainbow 16 16 61.5 2.9 45.6 N/A Base Rainbow 10 10 38.5 16.7 166.5 N/A * Population estimate is actual catch 15
Rainbow and brown trout base populations were generally low, but similar at Station 1. The brown trout base population was greater than the rainbow trout base population at Station 2. Rainbow trout base population estimates (extrapolated to fish per 100 meters) were 7 (Station 1) and 6 (Station 2) fish/100 m. Brown trout base population estimates were 6 fish/100 m (Station 1) and 11 (Station 2) fish/100 m. Young-of-the-year (Age 0+) rainbow trout were estimated at 4 and 7 fish per 100 meters at Station 1 and Station 2, respectively. Age 0+ brown trout were nearly absent, with only one collected at Station 1. Rainbow and brown trout length-frequency analyses (Figures 4 and 5) show the presence of multiple year classes for both species. Only one Sacramento sucker was collected, for a population estimate of 1 fish/100 m at Station 2. 3.4 Fish Biomass and Condition Factor SFAR and Iowa Canyon Creek Stations Biomass estimates per 100 m at both SFAR stations were higher for brown trout than for rainbow trout, resulting from the fact that average weight per fish was substantially higher for brown trout than rainbow trout (see Table 5). Brown trout base population biomass was estimated at 1,015.2 g/100 m (Station 2) and 671.7 (Station 1) g/100 m. In contrast, rainbow trout base population biomass was estimated at 416.0 g/100 m (Station 1) and 199.7 (Station 2) g/100 m. The Sacramento sucker biomass estimate of 65.0 g for the SFAR is based on 1 fish collected at Station 2; no suckers were collected from Station 1. Iowa Canyon Creek fisheries consisted entirely of rainbow trout. Qualitative sampling resulted in a catch of 26 fish comprised of young-of-the-year (age 0+) and juvenile (age 1+) rainbow trout (see Table 5). Age 0+ fish accounted for 61.5 percent of the population in Iowa Canyon Creek, indicating that a self-sustaining rainbow trout population is present in the reach upstream of the lowest waterfall/cascade located approximately 165 m from the mouth of the creek. Observations obtained during the amphibian and BMI surveys indicated similar numbers of rainbow trout in the lower portion of the creek between the road crossing and the lowest waterfall/cascade. The average rainbow trout base population biomass (16.7 g) was nearly half that observed in SFAR Station 2 (35.0 g) and less than one third of that observed in SFAR Station 1 (59.4 g) since only age class 1+ fish were captured during the sampling effort (see Table 5). Condition factors for individual rainbow and brown trout collected at SFAR and Iowa Canyon Creek (rainbow trout only) stations are provided in Tables 6 and 7. Condition factors for rainbow trout ranged from 0.70 to 1.14 at SFAR Sampling Station 1, from 0.92 to 1.14 at Sampling Station 2, and from 0.84 to 1.21 in Iowa Canyon Creek. Condition factors for brown trout ranged from 0.90 to 1.08 at SFAR Sampling Station 1, and from 0.89 to 1.08 at SFAR Sampling Station 2. No brown trout were collected from Iowa Canyon Creek. Average condition factors at age for rainbow trout appeared to be somewhat higher at Sampling Station 2, ranging from 1.01 to 1.14, as compared to those at Sampling Station 1 (0.93 to 1.02). In 16
contrast, average condition factors at age for brown trout were generally higher at Sampling Station 1, ranging from 0.94 to 1.07, as compared to those at Sampling Station 2 (0.89 to 1.01). 17
18
Table 6 Condition factors for rainbow and brown trout collected at SFAR Reach and Iowa Canyon Creek stations, September 2010. Station 1 Station 2 Iowa Canyon Creek Length (mm) Weight (g) CF* Length (mm) Weight (g) CF Length (mm) Weight (g) CF Rainbow trout Rainbow trout Rainbow trout 56 2.0 1.14 46 1.0 1.03 57 1.7 0.92 57 1.7 0.92 61 2.1 0.93 58 2.1 1.08 61 1.6 0.70 68 3.2 1.02 62 2.3 0.97 66 2.7 0.94 72 3.8 1.02 63 2.1 0.84 135 22.9 0.93 88 7.1 1.04 63 2.5 1.00 146 29.9 0.96 111 15.1 1.10 64 2.8 1.07 146 30.5 0.98 143 30.1 1.03 64 2.7 1.03 152 37.3 1.06 147 29.3 0.92 64 2.6 0.99 153 39.1 1.09 179 65.3 1.14 66 2.9 1.01 217 104.1 1.02 66 3.1 1.08 250 152.2 0.97 68 3.4 1.08 68 2.9 0.92 Brown trout Brown trout 69 3.0 0.91 83 5.5 0.96 117 14.2 0.89 70 3.4 0.99 97 9.8 1.07 158 41.6 1.05 72 3.7 0.99 217 104.2 1.02 196 74.6 0.99 76 4.4 1.00 232 112.4 0.90 223 120.2 1.08 100 11.1 1.11 237 119.3 0.90 226 112.0 0.97 101 11.5 1.12 247 151.5 1.01 268 170.4 0.89 102 10.4 0.98 253 174.5 1.08 102 10.6 1.00 102 11.5 1.08 108 15.3 1.21 119 16.8 1.00 138 24.3 0.92 138 27.8 1.06 138 27.2 1.03 *Condition Factor 19
Table 7 Average condition factors by age class for rainbow and brown trout collected at SFAR Reach and Iowa Canyon Creek stations, September 2010. Age 0+ Age 1+ Age 2+ Age 3+ Rainbow trout Reach Station 1 0.93 1.00 1.02 0.97 Reach Station 2 1.01 1.02 1.14 - Iowa Canyon Creek 0.99 1.05 - - Brown trout Reach Station 1 0.96 1.07 0.94 1.04 Reach Station 2-0.97 1.01 0.89 Iowa Canyon Creek - - - - 3.5 Direct Observation Surveys SFAR Stations In total, 45 rainbow trout, 1 brown trout, 62 Sacramento sucker (mostly post-larval), and 9 crayfish were counted during direct observation (snorkel) surveys of 10 habitats units (Table 8). The majority of rainbow trout observed were between 6 and 12 inches in length, distributed throughout all habitat units. Young- of-the-year rainbow trout (< 3 inches) were observed in four pools, but in smaller numbers, as were 3-6 inch and >12 inch trout. Two schools of post-larval Sacramento sucker were observed, ranging from 29 to 35 fish per school, for a total of 59 fish. Nearly all suckers were young-of-the-year fish (< 3 inches). Snorkelers reported seeing few benthic macroinvertebrates on rocks, boulders, and submerged woody debris. The invasive algae Didymosphenia geminate (i.e., Didymo) was observed to be ubiquitous on larger substrate within the sampled habitat units. 4.0 DISCUSSION Based on the overall results of the fish sampling efforts (electrofishing and snorkel observations), the population estimates for the two stations in the SFAR are conservative. Periodic conductivity readings recorded within the river during the spring and summer of 2010 were extremely low, ranging from a high of 40 µs/cm in May to a low of 20 µs/cm in August. Actual conductivity during electrofishing in early September was measured at 22µS/cm. Multiple salt blocks were placed in the river upstream of Stations 1 and 2 prior to and during electrofishing to increase conductivity; however, the conductivity rose only to about 27 µs/cm. Because of the low conductivity, fish were often not held in the electric field long enough to be captured, and were observed swimming past the netters. In addition, the deep habitats, complex substrates and high water velocities (due to high stream gradient) increased the difficulty of capturing fish at the two SFAR sampling stations. As a result, actual abundance and biomass levels are likely higher than the calculated estimates for each station. Nevertheless, despite these considerations, population numbers appear to be low throughout the SFAR ¼-mile reach. 20
Table 8 Results of snorkel surveys conducted in the SFAR Reach, 26-27 August, 2010. Rainbow Trout Brown Trout Sac. Sucker Crawfish Pool Number Length (m) Pass <3 in. 3-6 in. 6-12 in. >12 in. <3 in. 3-6 in. 6-12 in. >12 in. <3 in. 3-6 in. 6-12 in. 1 57 1 1 2 1 4 2 1 2 1 3 4 2 105 1 2 1 0 1 3 2 5 0 1 1 6 2a 17 1 2 35 1 37 2 1 30 1 31 3 21 1 6 1 2 7 2 6 1 2 7 4 10 1 3 1 1 1 5 2 2 1 1 1 4 5 48 1 4 1 1 1 6 2 4 1 1 0 6 6 11 1 2 2 1 4 2 2 2 1 4 7 15 1 3 3 2 3 3 8 12 1 3 1 20 1 25 2 29 1 30 8a 8 1 1 3 4 8 2 1 3 4 8 Total Pass 1 11 8 22 3 0 0 0 0 55 2 1 7 109 Total Pass 2 10 5 23 2 0 0 0 1 59 2 1 9 112 Total Fish 21
4.1 Comparison with Previous Fisheries Studies Historically, the 8-mile Slab Creek Dam Reach supported rainbow trout, Sacramento sucker, speckled dace (Rhinichthys osculus), hardhead (Mylopharodon conocephalus), California roach (Hesperoleucus symmetricus), Sacramento pikeminnow (Ptychocheilus grandis) and sculpin (Cottidae sp.), all of which still exist within this reach. Additional species now present include the introduced brown trout and smallmouth bass (Micropterus dolomieui). During the UARP relicensing, electrofishing and/or snorkeling sampling was performed throughout the reach in 2002, 2003, 2004, and 2007. The closest relicensing sampling station to the ¼-reach was Site SCD-F1, located 2.75 miles downstream of Slab Creek Dam. In 2002, five habitats were sampled at this site by snorkel surveys, including riffle, run, and pool habitat units (DTA and Stillwater Sciences 2004). Rainbow trout, brown trout, Sacramento sucker, and sculpin were observed at this sampling site, with rainbow trout the dominant species numerically. The species composition from 2002, similar to the rainbow trout assemblage described by Moyle (2002), is nearly identical to that of the 2010 sampling in the ¼-mile reach with the exception of the presence of sculpin. Subsequent relicensing studies examined fish species distribution throughout the entire Slab Creek Dam Reach. During the 2004 and 2007 snorkel surveys, species distribution through the reach was strongly associated with water temperature (Stillwater Sciences 2008). A longitudinal temperature gradient was present during the three seasons of monitoring (June through November), ranging from 10.5 to 13.8 C at RM 7.85 (just below the ¼-mile reach), and from 10.4 to 20.2 C at RM 0.75 (just above Chili Bar Reservoir). A fish community comprised of the species listed in the above paragraph reflects the change from the coldwater rainbow trout assemblage to a warm water transition community referred often to as the sucker-pikeminnowhardhead assemblage (Moyle 2002). Hardhead were most abundant in the lower half of the Slab Creek Dam Reach (downstream of RM 3.9) due, in part, to more favorable water temperatures. Hardhead were not observed in the ¼-mile reach, likely due to cool water temperatures that are present year round. Comparison of electrofishing results with snorkel survey results The snorkel survey results by pool were extrapolated to numbers of fish per 100 m so they could be compared to the electrofishing data (Table 9). Fish per 100 m were calculated for both Age 0+ and base population segments. Only base population data are compared due to the inherent variability in age 0+ populations. Extrapolated rainbow trout base populations in the ten pools surveyed ranged from 4.8 to 87.5 fish per 100 m, and averaged 22.4 fish per 100 m which is approximately three times the number of fish per 100 m calculated for electrofishing sampling station 1 (7 fish per 100 m) and (6 fish per 100 m) (see Table 5). This is at least partially due to higher quality of deep pool habitat as compared to overall riverine habitat for adult rainbow trout. However, the results could also be an artifact of the data, since fish abundance was low during both electrofishing and snorkel surveys, and variance of fish abundance can be pronounced when extrapolating data to reflect a number per 100 m. However, of the ten pools surveyed, rainbow trout abundance (fish per 100 m) was similar to the electrofishing results in six pools, ranging from 4.8 to 11.8 fish per 100 m. Numbers of brown trout and Sacramento 22
Table 9 Extrapolated results of snorkel surveys (per 100m) conducted in the SFAR Reach, August, 2010. Pool Number Length (m) 1 57 2 105 2a 17 3 21 4 10 5 48 6 11 7 15 8 12 8a 8 Pop. Segment Rainbow Trout Brown Trout Sac. Sucker Rainbow Trout per 100/m Brown Trout per 100/m Sacramento sucker per 100/m Age 0 1 0 1.8 0.0 0.0 Base 3 0 5.3 0.0 0.0 Age 0 0 0 0.0 0.0 0.0 Base 5 1 4.8 1.0 0.0 Age 0 0 0 35 0.0 0.0 205.9 Base 2 0 11.8 0.0 0.0 Age 0 6 0 28.6 0.0 0.0 Base 1 0 4.8 0.0 0.0 Age 0 3 0 30.0 0.0 0.0 Base 1 0 1 10.0 0.0 10.0 Age 0 0 0 0.0 0.0 0.0 Base 5 0 1 10.4 0.0 2.1 Age 0 0 0 0.0 0.0 0.0 Base 4 0 36.4 0.0 0.0 Age 0 0 0 0.0 0.0 0.0 Base 3 0 20.0 0.0 0.0 Age 0 0 0 29 0.0 0.0 241.7 Base 4 0 1 33.3 0.0 8.3 Age 0 1 0 12.5 0.0 0.0 Base 7 0 87.5 0.0 0.0 23
sucker were too low to provide a meaningful comparison between electrofishing and snorkel survey data. 5.0 CONCLUSIONS 5.1 South Fork American River The combined results of electrofishing and snorkel surveys indicate that the fish community currently present within the SFAR ¼-mile reach is generally low in diversity and abundance. The findings of the current study suggest at least four factors may be affecting fish populations within the SFAR ¼-mile reach. These factors include: (1) a relatively cold thermal regime; (2) limited food production; (3) limited spawning habitat; and (4) the presence of the invasive alga, Didymo, which covered the majority of larger substrates (boulders and bedrock primarily) in a vegetative carpet. The thermal regime within the ¼-mile reach is likely contributing to the low diversity of fish observed in 2010. This assessment is based on information gathered from a 4-year water temperature monitoring program performed during the years 2001 through 2004 as part of UARP relicensing (DTA 2005). Under this program, two monitoring stations were located within the ¼-mile reach: one directly downstream of the dam and the other approximately ⅛-mile downstream, just below the pedestrian bridge spanning the river. Daily temperature statistics from these sampling sites reveal a thermal regime characterized by normal seasonal fluctuation, limited daily variability, and relatively cold water during summer months. Winter temperatures range between 3 and 6 C, while summer temperatures range between 12 and 16 C. The limited daily variability is driven by the fact that water emanating from the dam has no daily variability given its origin from the reservoir hypolimnion and given the short distance between the dam and monitoring station 1/8-mile below it. This classic cold tailwater condition directly below the dam explains, in part, the low diversity of the fish community, which stands in stark contrast to the greater diversity of fish in the lower portion of the Slab Creek Dam Reach, where summer water temperatures frequently exceed mean daily values of 20 C. The limited presence of low-gradient riffle with suitable sized substrate is also potentially contributing to the low diversity and abundance of fish in the ¼-mile reach. Low-gradient riffles with gravel and cobble substrate are the primary food-producing habitats of coldwater trout streams, and the low representation of this habitat type in the reach, particularly in the segment upstream of the large pool, has the strong potential to influence food availability in the reach. Another structural feature potentially limiting food production in the reach is the prevalence of boulders (representing 67 % of the substrate), many of which are exposed. Although these habitat conditions do provide cover for trout and other species, they are less conducive for BMI production. Similarly, allochthanous input from riparian vegetation is likely low given the sparse riparian vegetation within the reach, as is insect drift from upstream sources given the close proximity of the dam. A higher percentage of low gradient riffle habitats with moderate organic input (along with the presence of more complex habitats) are generally necessary to develop a diverse and abundant BMI community. Condition factor values for rainbow trout were generally moderate (K > 1.0) throughout the study area, however approximately 55 percent of all rainbow trout in Sampling Station 1, and 38 percent in Iowa Canyon Creek, exhibited values less 24
than 1.0 (see Attachment A). The relatively low abundance of fish combined with relatively low to moderate rainbow trout condition factors, generally support the conclusion that trout food production is limited in this reach. The presence of the invasive alga Didymo is also potentially contributing to the issue of limited food availability. This alga species was observed covering larger substrates within most of the ¼-mile reach (especially large cobble, boulder, and bedrock substrate) with a thick vegetative layer. Smaller substrates throughout the reach, such as small cobble and gravel, generally lacked or had very little Didymo. Results of concurrent BMI surveys (ECORP 2011) indicate that Didymo may adversely influence the abundance and diversity of prey organisms that are preferred by trout (e.g., grazer organisms including caddisfly and mayfly larvae), which could not utilize the otherwise suitable substrate. Didymo does not appear to be a food source for these invertebrates. However, this alga may favor generally tolerant organisms such as some of the midges, which use vegetation as substrate or simply thrive within the algal matrix. The midges in the ¼-mile reach were mostly filter feeders or collector-grazers and accounted for 53 to 76 percent of the collected organisms. The EPT taxa (which are preferred trout prey) accounted for 15 to 28 percent of the organisms collected in the ¼-mile reach, which is low in comparison to Iowa Canyon Creek where Didymo were not observed and EPT taxa accounted for greater than 60 percent of the community (albeit in a targeted riffle sample). Additionally, the ¼-mile reach exhibits reduced EPT Index (%) and Sensitive EPT Index values, compared to values of these same metrics from surveys conducted in 2002 and 2003 when Didymo may not have been present to the extent observed in 2010 (ECORP 2011). Black flies (Simuliidae) are usually abundant in streams with substrates that are dominated by boulder and bedrock with overlaying laminar flow; however, Didymo also tends to favor these types of habitats. Based on the BMI results, Didymo appears to preclude or limit the presence of these taxa. In fact, black flies were only a minor component of the SFAR benthic community, and large colonies of black fly larvae that usually occur in streams with large substrates and laminar flows were not observed. This condition suggests that trout prey abundance may be suppressed in the SFAR, not only by the paucity of food-producing riffle habitat, but also by the presence of Didymo which limits available substrates and appears to suppress prey abundance in less productive habitats. The predominance of bedrock and coarse substrates throughout the ¼-mile reach, combined with the small percent of gravel and fines (4.1 %), likely limit trout spawning. This is particularly true of the reach segment upstream of the large pool, where high-gradient riffle habitat directly downstream of the dam is very low in gravel deposits that can be used for trout spawning purposes. It is likely that only limited spawning occurs in the reach, and probably takes place in the lower gradient segment of the reach downstream of the pool, where smaller substrates are more likely to deposit behind boulder and other instream features. Additionally, Iowa Canyon Creek has the potential to deposit gravel in SFAR in the lower segment below the large pool. Other factors associated with the effects of impoundments (Slab Creek Dam) on downstream aquatic habitats and species also may be influencing the fish community within the ¼-mile reach. These factors include regulation of flows (e.g., limited flow variation exists within the reach) and 25