Select a quick link TRRP staff contact list Calendar of events Remaining 8 - MEIR Lewiston-Dark Gulch project Hatchery project Indian Creek project Hocker Flat pilot project Canyon Creek Complex Boat Ramp elevations

Trinity River

Restoration Program

Program Administration

 

 

Wildlife Resources

	Wildlife Communities of the Trinity River Mainstem
	Regional Setting
	Local Setting
	Special-Status Wildlife of the Mainstem Trinity River

Although the primary focus of the TRRP is on anadromous salmonids, the Trinity River is important to many species of wildlife. Riparian habitats in unregulated rivers in northwestern California support diverse vertebrate and invertebrate communities. These species are adapted to and depend on annual flood events to create river and floodplain habitats, such as seasonally flooded marshes and side channels, early successional willow vegetation, and shallow, low water-velocity areas along the main channel (i.e., backwater and edgewater pools) (68; 39; 50; 51). Many wildlife species also have adapted their breeding, migration, and foraging cycles to the natural flow cycles of the river (38). Growth, development, behavior, and survival of ectothermic animals (amphibians, reptiles, invertebrates) are highly dependent on temperature. Thus, the timing and temperature of water releases could have significant effects on many species.

Little pre-TRD information exists on riparian-associated wildlife species in the Trinity River Basin. Many sensitive wildlife species occur in riparian habitats along the mainstem Trinity River today and likely occurred prior to the construction of the Trinity and Lewiston Dams: foothill yellow-legged frog (California species of special concern [CSSC]); western pond turtle (CSSC; bald eagle (Federal ESA-listed threatened); osprey (CSSC; yellow warbler (CSSC; willow flycatcher (State threatened); yellow-breasted chat (CSSC; and black-capped chickadee (CSSC (68; 39; 6). There are also three bat species (pallid, little brown myotis, and Townsend's western big-eared [CSSC]) that are typically associated with riparian habitats, but their historical and current status in the Trinity River Basin is unknown (6).

Two sensitive and highly aquatic species have been studied in the Trinity River Basin: the foothill yellowlegged frog (Rana boylii) and the western pond turtle (Clemmys marmorata) (39; 50; 51; 52). Foothill yellow-legged frogs are active during spring, summer, and fall along the river margins and in flowing side channels, and probably hibernate in the winter. Eggs are deposited between April and June in shallow, low-velocity areas along rocky, sparsely vegetated river bars (38). Upon metamorphosis, most juveniles migrate upstream, probably as a compensating mechanism for downstream drift of larvae (11). Surveys of foothill yellowlegged frogs on the Trinity River found that their distribution is related to the distribution of early successional riparian and gravel-bar habitats (38). Greater numbers of frogs were found in reaches farther downstream from the dam, where the gravel bar habitats are in greater abundance. The loss of open, rocky, shallow river bars in the upper river has probably contributed to a decline in foothill yellowlegged frog populations (38), and the absence of these habitats may deter young frogs from migrating upstream where habitat is less suitable.

Yellow-legged frog egg and larvae survival depends on timing and volume of runoff events (38). From the onset of oviposition, yellow-legged frogs require a minimum of 15 weeks to metamorphose (11), and are extremely vulnerable to fluctuating flows during this period. Unhatched eggs subjected to a high-flow event are generally washed away (38). Larva that hatch prior to a high-flow event are more likely to survive depending on the rate of fluctuation. Rapidly ascending or descending water levels can decrease survival because larvae have difficulty tracking rapidly changing water levels and cannot find appropriate habitat before they are washed away or stranded (38).

It is suspected that yellow-legged frogs use environmental cues such as temperature and rainfall patterns to initiate or suspend breeding activities (38). Thus, in an unregulated river the frogs are effectively able to avoid depositing eggs during periods of highly fluctuating flows, which are so detrimental to eggs and larvae. On the Trinity River, however, yellow-legged frogs are often subjected to releases that are not in sync with their environmental cues, resulting in high egg and larvae mortality (38).

In summer, water temperatures of TRD releases are generally lower than what yellow-legged frogs have adapted to on the Trinity River. Low temperatures retard egg and larvae development, and prolong the period in which they are vulnerable to fluctuating flows and to predators.

Since the construction of TRD, yellow-legged frogs in the upper river have been subjected to decreasing habitat availability, unpredictable timing and volume of releases, and lower summer water temperatures. Thus, frogs have probably had to deposit eggs in faster, deeper water more vulnerable to scouring flows; oviposition has often occurred during periods when eggs and larvae are likely to be washed away or stranded; and the eggs and larvae have taken longer to develop in the cooler water extending the vulnerable period. Also, upstream migration may have been reduced due to sparse upstream habitat.

Western pond turtles are found in and along pool and glide habitats of the main channel, and smaller hatchlings and juveniles are found in backwater pools, shallow river margins, and side channels with vegetation. The lower end of side channels (the alcove) is often scoured during large floods, providing deep slow-velocity pool habitat adjacent to the main channel. These pools are important foraging and thermoregulation sites for western pond turtles (50). Backwater eddies (a common attribute of alcoves) trap logs and other debris, which are used for aerial basking by western pond turtles when air temperatures are greater than water temperatures (11). The limited mixing of backwater areas with the mainstem allows surface temperatures to get considerably higher in backwater areas than the mainstem during the summer. This warm surface layer is utilized by western pond turtles for "water basking" when air temperatures become too warm for aerial basking. Mats of submergent vegetation commonly associated with backwater areas are particularly attractive to western pond turtles because they maintain even warmer surface-water temperatures, help turtles maintain their position, and provide immediately accessible cover (11). Standing water associated with more isolated backwater areas also provide an abundance of nekton (zooplankton fauna), a major food source for juvenile pond turtles (11).

Cooler summer water temperatures probably also affect western pond turtles by slowing growth, and by altering behavior and habitat selection (40). Cooler water temperatures may shorten the turtles' active period, increase aerial basking activity, or force turtles to seek warmer waters in shallower or more isolated backwaters. Warmer winter water temperatures would also affect pond turtles, which may overwinter on land or in water, or remain active in water during the winter, depending on temperatures (11).

Since the construction of TRD, the loss of alternate point bars has resulted in fewer deep pool microhabitats used for refuge and also has reduced shallow edgewater used for rearing. Densities of western pond turtles in the mainstem Trinity River (2.6 turtles/acre) are very low in comparison to densities on the unregulated South Fork Trinity River (5 turtles/acre) and unregulated Hayfork Creek (up to 300 turtles/acre), a tributary to the South Fork Trinity River (50; 52). Additionally, the age structure for these two locations differs from that of the mainstem, which has a more adult-biased population than either of the other two (50; 52). These differences indicate population declines on the mainstem owing to changes resulting from the dams.

In summary, downstream from Lewiston Dam, there have been many changes in riverine and riparian habitats owing to TRD operations. Habitat features such as seasonally flooded marshes and side channels, shallow river margins, cold-water holding pools, and bank undercuts have been reduced or eliminated.

Species that depend on flood-maintained habitats (e.g., foothill yellow-legged frogs, western pond turtles) have been negatively impacted by reductions in flows. The post-project reductions in summer water temperatures may also affect development rates and other physiological functions of ectothermic wildlife such as amphibians and reptiles (6).

Wildlife Communities of the Trinity River Mainstem

Regional Setting

Many wildlife species that inhabited river and riparian habitats prior to construction of the Trinity and Lewiston dams still occur along the mainstem of the Trinity River. However, species associated with early-successional stages or riparian vegetation or those taxa that require greater riverine structural diversity likely occurred in greater abundance prior to construction of the dams. Species common to the Mainstem prior to dam construction likely included:

• Rough-skinned newt (Taricha granulosa)
• Pacific coast aquatic garter snake (Thamnophis couchi)
• Foothill yellow-legged frog (Rana boylei)
• Western pond turtle (Clemmys marmorata)
• American Dipper (Cinculus mexicanus)

Riverine taxa that foraged on abundant salmon and steelhead runs (e.g., black bear [Ursus americana], Bald Eagle [Haliaeetus leucocephalus], and other scavengers) were also common along the pre-dam Trinity. However, the current flow regime has established conditions favoring upland habitat at the expense of early successional wetland and aquatic habitat. This shift in habitat types is hypothesized to be the primary causative factor in the current depressed populations of aquatic, semi-aquatic, and wetland wildlife species compared to terrestrial species. Species such as the western pond turtle have declined since completion of the dams in response to diminishing instream habitat. In contrast, species that favor mature, late-successional riparian habitats, such as the northern goshawk (Accipiter gentilis) and black salamander (Aneides flavipunctatus), prefer the current mature conditions.

Local Setting

Wildlife species commonly found along the Mainstem of the Trinity River and their associated plant communities are listed below.

Plant Community	Associated Wildlife Species
Klamath Mixed Conifer	Mountain Quail (Oreortyx pictus) Sharp-shinned Hawk (Accipiter striatus) Cooper's Hawk (Accipiter cooperii) Long-eared Owl (Asio otus) Western red bat (Lasiurus blossevillii) Western gray squirrel (Sciurus griseus) Virginia opossum (Didelphis virginiana) Gray fox (Urocyon cinereoargenteus) Black bear (Ursus americanus)
Montane Hardwood-Conifer	Sharp-shinned Hawk (Accipiter striatus) Mountain Quail (Oreortyx pictus) California Quail (Callipepla californica) Mourning Dove (Zenaida macroura) Western Scrub-jay (Aphelocoma californica) Virginia opossum (D. virginiana) Vagrant shrew (Sorex vagrans) Black-tailed jackrabbit (Lepus californicus) Gray fox (U. cinereoargenteus)
Montane Riparian Riparian Wet Meadow Riparian Wetland	Western skink (Eumeces skiltonianus) Rubber boa (Charina bottae) Northern Flicker (Colaptes auratus) Common Yellowthroat (Geothlypis trichas) Song Sparrow (Melospiza melodia) Vagrant shrew (S. vagrans) Beaver (Castor canadensis) Raccoon (Procyon lotor) Striped skunk (Mephitis mephitis)
Fresh Emergent Wetland Seasonal Wet Meadow	Black salamander (A. flavipunctatus) Western toad (Bufo boreas) Pacific chorus frog (Pseudacris regilla) Rubber boa (C. bottae) Striped racer (Coluber constrictor) Western aquatic garter snake (Thamnophis couchi) Black Phoebe (Sayornis nigricans) Water shrew (Sorex palustris) Shrew-mole (Neurotrichus gibbsii) Raccoon (Procyon lotor)
Riverine	Bullfrog (R. catesbeiana) Western pond turtle (C. marmorata) Mallard (Anas platyrynchos) Great Blue Heron (Ardea herodias) Osprey (Pandion haliaetus) Belted Kingfisher (Ceryle alcyon) Beaver (C. canadensis) River otter (Lutra canadensis)

Special-Status Wildlife of the Mainstem Trinity River

Below is a list of special-status species of wildlife, and their general habitat affinities in habiting or potentially inhabiting the mainstem of the Trinity River and proposed bridge and restoration sites. Special-status species of wildlifeinclude those taxa that are:

• Designated as Rare, Threatened, or Endangered by state or federal governments
• Proposed for rare, threatened, or endangered status by state or federal governments
• State or federal Candidate species
• Species of Concern by the U.S. Fish & Wildlife Service (USFW)

Common name	Scientific name	Special Status			General habitat
		FED	ST	BLM
AMPHIBIANS
Foothill yellow-legged frog	Rana boylii	SC	SSC	S	Cool, fast-moving streams and rivers with rocky substrate in chaparral, forests, and woodlands.
REPTILES
Western pond turtle	Clemmys marmorata marmorata	SC	SSC	S	Rivers and streams with slow-moving water or pools and some canopy cover. Require basking sites such as partially submerged logs, rocks, or exposed mud banks.
BIRDS
Cooper's Hawk	Accipter cooperi	-	SSC	-	Nests in riparian areas and oak and conifer woodlands; forages at woodland edges.
Northern Goshawk	Accipiter gentiles	SC	SSC	-	Rare permanent resident and confirmed breeder in Trinity County. Hunts birds and small mammals in flight. Typically nests in north-facing conifer forests near water.
Sharp-shinned Hawk	Accipter striatus	-	SSC	-	Nests in riparian areas and oak and conifer woodlands; forages at woodland edges.
Golden Eagle	Aquila chrysaetos	-	SSC	S	Rare permanent resident in Trinity County. Nests on cliffs and tall trees on hillsides; forages over open grasslands or early successional stage vegetation. Suitable foraging habitat occurs on gravel bars and open areas along the river.
Yellow-billed Cuckoo	Coccyzus americanus	-	C	E	Obligate riparian nesters; only breed in streamside forests, especially those dominated by mature willow and cottonwood stands. Most nesting occurs within relatively large patches of riparian forest, usually 25 to 100 acres in extent.
Yellow Warbler	Dendroica petechia	-	SSC	-	Nests and forages in dense riparian scrub habitat.
Little Willow Flycatcher	Empidonax traillii brewsteri		SC	E	Rare summer resident in wet meadow and montane riparian habitats at 2,000 to 8,000 ft elevation.
American Peregrine Falcon	Falco peregrinis anatum	D	E	CFP	Rare permanent resident and confirmed breeder in Trinity County. Forages over marshes and grasslands on flying birds up to duck size. Nesting habitat includes high, protected cliffs and ledges near water. May forage 5 km or more from nesting area.
Bald Eagle	Haliaeetus leucocephalus	T	E	-	Forages on live and dead fish and nests in large trees or snags. Requires large bodies of water including ocean shorelines, lake margins, and large, open river courses for foraging, nesting and wintering habitat.
Yellow-breasted Chat	Icteria virens	-	SSC	-	Nests and forages in dense riparian habitat with mature riparian tree species (e.g., willow, cottonwood).
Osprey	Pandion haliaetus	-	SSC	-	Utilizes similar habitat as the bald eagle, often competing for foraging and nesting resources. Forages on live and dead fish and nests in large trees or snags. Requires large bodies of water including ocean shorelines, lake margins, and large, open river courses for foraging, nesting and wintering habitat.
Bank Swallow	Riparia riparia	SC	T	-	Colony nester restricted to isolated places where fine-textured or sandy, vertical bluffs or riverbanks are available in which to dig nesting cavities.
Northern Spotted Owl	Strix occidentalis caurina	T	-	-	Prefers multiple-story canopy dominated by big trees with cavities or broken tops; frequently in mixed conifer habitats. Most often in old-growth or mixed old-growth and mature trees.
MAMMALS
California wolverine	Gulo gulo	SC	T	-	Scarce resident of North Coast Mountains in Trinity County, typically at elevations > 1600 feet. Den in caves, cliffs, hollow logs, cavities in the ground, under rocks; may dig dens in snow, or use old beaver lodges. Forages in open to sparse treed habitats on ground, in trees, burrows, among rocks, in/under snow, and shallow water.
American marten	Martes americana	SC	-	-	Dens and forages in old-growth forests or mixed stands of old-growth and mature trees. May use riparian corridors for movement.
Pacific fisher	Martes pennanti	SC	SSC	S	Dens and forages in old-growth forests or mixed stands of old-growth and mature trees. May use riparian corridors for movement.
Pale Townsend's big-eared bat	Corynorhinus townsendii pallescens	SC	SSC	S	Uncommon, but occurs through out California in all but alpine habitats. Most abundant in mesic habitats. Hibernation sites are usually cold but not below freezing; maternity sites are warm.
Small-footed myotis bat	Myotis ciliolabrum	SC	-	S	Occurs in a wide variety of habitats, primarily in relatively arid wooded and brushy uplands near water from sea level to 8900 feet. Forages in arid habitats.
Long-eared myotis bat	Myotis evotis	SC	-	S	Uncommon but widespread in California. Has been found in most habitats, but prefers coniferous woodlands. Roosts singularly in buildings, crevices, spaces under bark, and in snags. Forages among trees, over brush, usually in close association with water.
Fringed myotis bat	Myotis thysanodes	SC	-	S	Mesic habitats, roosting in caves, mines, tunnels, and buildings. Maternity roosts can have 200 individuals. Roosts typically in valley foothill hardwood and hardwood-conifer habitats from 4000 - 7000 feet, but forages in open, early successional stage habitats near water.
Long-legged myotis bat	Myotis volans	SC	-	S	Occurs throughout the Coast Range from Oregon to Mexico and in most of the Sierras, but is absent from the arid Central Valley. Most common in woodland and forest habitat above 4000 ft. Roosts in rock crevices, buildings, under tree bark, in snags, mines and caves. Trees are the most important day roosts.
Yuma myotis bat	Myotis yumanensis	SC	-	S	Forages over water such as ponds, streams, stock tanks in open woodlands. Roosts in buildings, caves, mines, abandoned swallow nests, bridges, and rock crevices. Common and widespread in California.
FED = Federal ST = State of California BLM = U.S. Bureau of Land Management E = Endangered T = Threatened SC = Species of Concern SSC = Species of Special Concern D = Delisted (status to be monitored for 5 years) S = Sensitive CFP = California Fully Protected species S = BLM Sensitive