| .AQUATIC BIOLOGICAL RESOURCES |
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Aquatic Foodbase and Trout:
Greatly increased, post-dam water clarity has allowed the development of extensive aquatic vegetation and aquatic invertebrates in the river, particularly from the dam to Lees Ferry (Stevens et al. 1997). Recent monitoring and research by Northern Arizona University have demonstrated that exposure of shorelines during drawdowns or fluctuating flows greatly reduces aquatic foodbase biomass, and potentially affecting the Lees Ferry trout fishery. The Arizona Game and Fish Department and GCMRC convened a trout symposium in the spring of 2000, and the results are available through AGFD. The trout population in the Lees Ferry reach has recovered since the early 1990s, and fishing conditions are generally good to excellent. Over the past decade, medium sized rainbow trout have become extremely abundant in the reach between the Paria River and about Mile 40.
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Endangered Fish:
The Colorado River is known both for its remarkably high proportion of endemic fish (fish found nowhere else), and the poor condition of its native fishery. Of the eight native species in Grand Canyon, 50% have been extirpated, including: Colorado pikeminnow (Ptychocheilus lucius), razorback sucker (Xyrauchen texanus), bonytail chub (Gila elegans), and roundtail chub (Gila robusta). Humpback chub (Gila cypha) are federally endangered, and great efforts are being taken to manage the river specifically for this species, including the costly prolonged low constant flows in the summer of 2000. This species consists of a population of about 8,000 adult fish, about half of which live in the lower Little Colorado River, and most of the other half live in the mainstream near the LCR confluence. Mainstream fish near the LCR run up that tributary to spawn. Several other non-breeding concentrations occur throughout the mainstream. Several larval humpback chub were reported downstream from Lava Falls in 2000 for the first time in post-dam history. This may indicate that the summer low flows were beneficial to native fish.
The other three native fish species include: bluehead sucker (Pantosteus discobolus), flannelmouth sucker (Catostomus latipinnis), and speckled dace (Rhinichthys osculus) remain fairly common, but their population dynamics and status are poorly known. For a description of the life history of the humpback chub and other endangered fish, visit the GCMRC website (http://www. gcmrc.gov).
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| .TERRESTRIAL BIOLOGICAL RESOURCES |
Riparian Vegetation:
Riparian vegetation provides habitat and food resources for many species of concern in the Colorado River corridor downstream from Glen Canyon Dam. Five zones of vegetation are observed along the river: the hydro-riparian marsh zone (HRZ), the lower riparian zone (LRZ; "New High Water Zone"), the middle riparian zone (MRZ), the upper riparian zone (URZ; "Old High Water Zone"), and the desert zone. The extent of vegetation cover in the lower four belts changes dramatically through the 13 geomorphic reaches. Narrow reaches encompass approximately 40% of the river corridor and are characterized by steep rocky or bedrock banks with sparse to no riparian vegetation. Extensive riparian vegetation cannot develop in narrow reaches because little sand or suitable germination sites exist, grain size is generally larger, and stage-to-discharge relationships are steeper (more stage gain per unit increase in discharge). In contrast, wide reaches have lower gradient banks, less exposed bedrock, more sand bars, and abundant riparian vegetation. Debris-fan eddy complexes suport HRZ (marsh) habitats in low velocity, near-shore and return current channel settings, LRZ sand bar habitats, and fine-grained URZ terraces. The distinctive vegetation composition on these surfaces is similar within geomorphic settings.
Riparian vegetation assemblages are strongly related to flood and inundation frequency, and grain-size. Riparian vegetation development takes place in response to changes in these state variables, and over time; however, vegetation development does not occur as a perfect stage-for-time replacement process, because of variability in life history traits of the more than 700 plant species that occur in the river corridor.
The HRZ (8-25,000 cfs stage): An overall increase in the number and area of marsh patches was detected from aerial surveys and river studies from 1986 through 1995, then decreased by 20-35% as a result of the 1996 Test Flow, and remained low until 2000, when low flows allowed some vegetation expansion on lower terraces. Many of these new vegetation patches were scoured by the September 31,000 cfs flow. These data demonstrate that redevelopment of fluvial marshes takes place over a 5-10 yr time period in specific riverside habitats (i.e., rarely scoured near-shore and return channel habitats). High productivity is strongly related to invasibility by non-native plant species, and this the case both in the HRZ and the LRZ.
The LRZ (ca 18,000-45,000 cfs stage): Lower riparian zone vegetation develops in a variety of geomorphic settings and grain-sizes, including sand bars, channel margins, debris fans, and, sparsely, on rocky talus slopes. This zone is dominated by tamarisk, coyote willow, arrowweed, seep-willows, and numerous grasses and herbs. URZ vegetation is gradually invading this zone, but this invasion is retarded by higher flood frequency because URZ dominants (mesquite and catclaw) are less flood tolerant than the phreatophytes that generally dominate the LRZ. Non-native tamarisk establishment takes place on sand bars after May and June high flow events, and when flows are constant and low (such as 2000). Therefore, much tamarisk establishment occurred in 2000, and many of those plants have so far survived the return to higher flows.
The MRZ (45,000-125,000 cfs stage): This sparsely vegetated zone exists in a dynamic state, with establishment of fast-growing river plants after high floods (most of which soon perish from desiccation) offset by the downslope invasion of slow-growing, flood intolerant desert plant species (i.e., cacti, creosotebush, brittlebush), which are eliminated by high flows.
The URZ (125,000-300,000 cfs stage): This belt of pre-dam vegetation exists upslope from the 10-yr pre-dam flood return stage (125,000 cfs). The dominant woody species (mesquite, catclaw, netleaf hackberry) are long-lived (100-750 yr in age at least), and are highly resilient, having persisted through large pre-dam flows. Detailed studies in the mid-1980s failed to demonstrate any relationship between flooding and growth or integrity of URZ vegetation.
Endangered Kanab Ambersnail:
Like the humpback chub, the endangered Kanab ambersnail population at Vaseys Paradise does not appear to face any immediate threat, but is at risk because its population exists at a single site. The Arizona Game and Fish Department has attempted to establish 3 populations of this diminutive landsnail outside the river corridor in Grand Canyon National Park: Mile 47.5R, Elves Chasm, and Lower Deer Creek Spring. It remains to be seen whether this population introduction effort will succeed.
Southwestern Willow Flycatcher:
iIn Grand Canyon, the population status, breeding season distribution, nesting habitat, and nest characteristics of endangered southwestern willow flycatcher (SWWF) are documented in a series of published papers (Brown 1987; Brown and Johnson 1987; Brown et al. 1987; Brown 1988a,b; Brown and Trossett 1989; Sogge et al. 1995), and monitoring reports from 1976 to 1995 (Carothers and Sharber 1976; Brown 1991; Sogge and Tibbitts 1992, 1994; Sogge et al. 1993, 1995; Tibbitts et al. 1994). As elsewhere in Arizona, SWWFs in Grand Canyon nest preferentially in relatively wide stands of tamarisk and rarely in native trees, occasionally with a scattered overstory of taller trees (Brown and Trossett 1989, Tibbitts et al. 1994). Nest sites usually have nearby exposed sand bars or fluvial marshes. SWWF nests are typically 3.5 to 7 m above the ground and several m below the canopy and nest sites have dense canopy from 0 to 4 m above the ground (Brown 1988a; Tibbitts et al. 1994). SWWF usually nest over moist or wet soil, or over water. The last successful breeding record for SWWF in upper Grand Canyon occurred in 1996, although more than a dozen active territories have been detected in the past few years in lowermost Grand Canyon downstream from Mile 245.
Other Bird Species of Concern:
Several other bird species in Grand Canyon are of special concern. Although bald eagles were downlisted to threatened status by the U.S. Fish and Wildlife Service two years ago, they continue to be managed as an endangered species for the next three years. Wintering bald eagles first began to concentrate in Grand Canyon in the early 1980s, particularly in Marble Canyon and near Nankoweap Creek (Mile 53). Bald eagles are commonly seen from November through March, and as many as 29 birds have been seen simultaneously at Nankoweap Creek. Unlike other situations, bald eagles are extremely sensitive to human disturbance in Grand Canyon.
Peregrine falcons have become common in the region since the early 1980s, and it is unusual not to see at least one on a Grand Canyon river trip. Grand Canyon presently hosts the largest breeding population of peregrine falcons of any single land management unit, with perhaps as many as 100 pairs. Osprey and belted kingfisher also are species of concern in Arizona, and these species migrate through the region but are not known to breed here. Neotropical migrant birds are abundant along the river from April through July, with nearly 30 species breeding in LRZ and URZ vegetation. One of the better places for a quiet float to hear and see many of these colorful songbirds is from Mile 196 to Parashant (Mile 198).
Extirpated Species:
In addition to the four extirpated native fish, several terrestrial vertebrates have declined precipitously or disappeared from the Colorado River corridor in Grand Canyon during post-dam time. These include: northern leopard frog, zebra-tailed lizard, California condor, southwestern willow flycatcher, badger, Colorado River otter, and muskrat. Along with gray wolf and jaguar, this list demonstrates that large national parks are not sufficient to protect native biodiversity, and that surrounding lands must be included in wildlife management. In testimony to this fact is the on-going effort to restore extirpated California condor to northern Arizona. A mulitagency and stakeholder program has released more than two dozen immature condors onto escarpments in northern Arizona, and these individuals soon may begin to breed again in Grand Canyon.
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| .CULTURAL RESOURCES |
Cultural resources along the Colorado River corridor include archaeological sites and traditional cultural resources such as springs, landforms, sediment and mineral deposits, many plants and animals, and traditional cultural properties. Many of these resources may be affected by the operations of Glen Canyon Dam. Current information concerning cultural resources is based on a number of previous investigations within the river corridor in Glen and Grand canyons conducted by the NPS and various tribal groups. Inventories by the NPS during the 1990s located approximately 475 sites in the river corridor from Glen Canyon Dam to Separation Canyon. These sites range back in age to before 1000 BC, and provide evidence of at least five cultures, including Desert, early to middle Puebloan, Paiute, Pai, and Navajo. Comprehensive overviews of previous investigations are included in Ahlstrom et al. (1993) and Fairley et al. (1994).
Under the Adaptive Management Program, several Native American tribes also conduct annual cultural river trips to identify and monitor resources with particular importance, and recommend appropriate preservation or recovery alternatives. Participating tribes include the Hopi, Hualapai, Navajo, Southern Paiute, and Zuni tribes. Sites in the Furnace Flats and Lower Canyon reaches appear to sustain the highest frequencies of physical and visitor related impacts (Leap et. al. 1998), and the tribes request that visitors respect their values by not disturbing Grand Canyon archeological sites.
Archaeological resources that are contained in alluvial terraces may erode because lower terrace erosion. The 1996 Test Flow presented an opportunity to evaluate the possibility of terrace restoration through high flows, and it had a neutral or beneficial effect, meaning that habitat building flows may provide system-wide mitigation for cultural resource sites.
Many plant species are culturally significant to the various tribes, and are monitored. These ethnobotanical resources generally appear to be in a favorable condition, although non-native plant species appear to be increasing in some settings.
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| .RELEVANT LITERATURE |
See the GCMRC website at http://www. gcmrc.gov for the references cited here. Additional recent works include:
Myers, T., C. Becker, and L. Stevens. 1999. Fateful journey: injury and death on Colorado River trips. Red Lake Books, Flagstaff (520)774-4923.
Patten, D.T. and L.E. Stevens. Restoration of the Colorado River ecosystem using planned flooding. A Special Feature in the journal, Ecological Applications. In press.
Webb, R.H., J.C. Schmidt, G.R., Marzolf, and R.A. Valdez, editors. 1999. The controlled flood in Grand Canyon. American Geophysical Union Geophysical Monograph 110: 1- 367.
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