Download Paiute Plan - Living Assessment

California Trout’s Paiute Cutthroat Trout Recovery Project
Working Outline
Purposes
 To restore and delist the Paiute Cutthroat Trout (PCT) from the Endangered
Species Act
 To inspire and engage California Trout’s donors in order to increase their
financial support
 To expand and deepen conservation partnerships with agencies, NGOs, and
foundations
 To pave the way for opening California Trout’s Tahoe/Truckee regional office
this year
Background1
PCT are listed as “threatened” pursuant to the Endangered Species Act and are native to
just a single drainage, Silver King Creek, in eastern California. Silver King Creek is a
tributary of the East Fork of the Carson River. PCT historical distribution is exceedingly
limited. They are thought to have existed in only 14.7 kilometers of habitat from the base
of Llewellyn Falls downstream to Silver King Canyon and including three small tributary
creeks in the drainage, Tamarack Creek, Tamarack Lake Creek, and the lower reaches of
Coyote Valley Creek downstream of barrier falls.
PCT are thought to occupy a total of 18.6 km of stream with a core habitat of 12.9 km.
California Department of Fish and Game (DFG) population assessments found
approximately 1,020 adult fish in the six streams currently inhabited by PCT in the Silver
King Drainage. While most populations are stable, they remain heavily fragmented and
have no chance of interbreeding without human intervention, thus reducing the effective
population size and seriously limiting the genetic viability of the species.
The biggest threats to the persistence of PCT are 1) alien trout, 2) loss of genetic
diversity, and 3) habitat loss.
Alien trout. Alien trout are the principal threat to the continued persistence of the
PCT. They impact PCT through competition for resources and habitat, predation, and by
hybridization. The introduction of non-native rainbow, golden and Lahontan cutthroat
trout into the historic range of the PCT below Llewellyn Falls has resulted in the
extirpation of PCT. PCT are subject to both competition and predation from alien trout.
PCT readily hybridize with rainbow trout and Lahontan cutthroat trout, resulting in loss
of genetic integrity and phenotypic distinctiveness.
Loss of genetic diversity. A study by Cordes et al (2004) found PCT to be the
most genetically limited and narrowly distributed native trout in the state of California.
Genetic distances between the current populations of PCT show that there are three
genetic groups within PCT, but Cordes et al (2004) surmise that this differentiation is due
to founders effects and genetic drift, which are more representative of PCT’s stocking
histories than natural variation within the subspecies. Most of the transfers consisted of
This section is drawn from Dr. Peter Moyle’s State of Salmonids draft life history account for
Paiute Cutthroat Trout.
1
small numbers of fish and the creeks with similar genetic strains had similar stocking
histories (Cordes et al 2004). Nielsen and Sage (2002) found no distinctive alleles
differentiating PCT from LCT, but did see that PCT had gone through a genetic
bottleneck. It is likely that the first isolation of PCT when it diverged from LCT
represented a genetic bottleneck and that subsequent stocking and culling of stocks to
eliminate hybridization has further amplified the situation. Additionally, there is no
population that currently possesses all of the alleles known to PCT, so further transfers to
maintain what is left of genetic diversity may be required. The loss of genetic diversity
due to small populations and lack of metapopulation connectivity combined with the loss
of genetic diversity due to introgression from other species of trout represent the largest
threats to PCT.
Habitat loss. Right now (2008), the 23 km of stream habitat in which PCT persist
are in reasaonably good condition, with limited or no grazing affecting the stream banks
and light human use. However, this could change if grazing allotments are renewed or if
a catastrophic fire swept through one or more of the basins. Thus the limited habitat by
itself represents a reason for careful management because conditions can change so
quickly.
Conservation
The populations of Paiute cutthroat trout are small but reasonably stable because they are
entirely located in streams in remote national forest lands (Toiyabe, Sierra, and Inyo
NFs). The habitat closest to their native range is all in the Carson-Iceberg Wilderness as
well. However, additional protection is needed by expanding their range back into their
historic habitats.
Part of the management actions listed in the 2004 USFWS Recovery Plan is
removal of non-native trout in the waters between Llewellyn Falls and Silver King
Canyon. This was to be done using the piscicide, rotenone, which has resulted in years of
lawsuits and no progress in restoring PCT below Llewellyn Falls. Opposition to the
poisoning of the creek comes in part from anglers who value the healthy fishery of wild
(though non-native) trout that thrives in the excellent habitat below the falls. There is also
concern that endemic invertebrates may occur in that reach and rotenone is toxic to them
as well as fish. Additionally, the area is habitat for two species of amphibians that are
candidates for listing under the Endangered Species Act, the mountain yellow-legged
frog (Rana mucosa), and the Yosemite toad (Bufo canorus); there is fear that the rotenone
treatments could harm them, though the USFWS plans include removal of any
amphibians found in the reach prior to treating the creek (USFWS 2004). Recent reviews
of toad sampling indicate that most toads in the Silver King basin are western toads (Bufo
boreas), although a few hybrids with Yosemite toads may exist. No pure Yosemite toads
have been found in the Silver King Creek basin (William Somer, DFG, pers. comm.). It is
unlikely that the candidate species amphibians occur in high densities below Llewellyn
Falls because non-native trout predation is one of the factors in their decline throughout
their range. The current distribution of PCT and mountain yellow-legged frogs overlap in
Silver King Creek basin. The two organisms co-evolved in the basin, so it is likely they
can coexist. The two species also co-occur in all four of the out of basin populations of
PCT (N.F. Cottonwood Creek, Cabin Creek, Sharktooth Creek, and Stairway Creek). The
Recovery Plan includes treatment of Tamarack Lake (in the upper Silver King drainage)
to rid it of trout for the benefit of the two amphibian species (USFWS 2004).
The many unauthorized transfers both of PCT and the non-native trout that
threaten them have been both a scourge and a savior. By 1924, the PCT in their native
reach (below Llewellyn Falls) were already introgressed with LCT, rainbow trout, and
golden trout. In 1949, another unauthorized transfer introduced rainbow trout above the
falls. If it had not been for the 1946 stocking in Cottonwood Creek and introduced
populations within Silver King basin in Fly Valley and Four Mile Creeks, PCT could
well have been lost. Introductions, hybridization, and culling have occurred repeatedly
throughout the 20th century. Table 2 below shows the complicated stocking history of
PCT in the last 150 years and identifies management actions that have taken place during
that time. Current PCT populations are fairly stable, but the lack of genetic diversity of
existing stocks, extirpation from their native range, lack of connectivity among
populations, and small effective population sizes continue to hamper recovery efforts.
The 2004 PCT Recovery Plan lists reintroduction of PCT to their native range below
Llewellyn Falls and eradication of non-native salmonids there as one of the criteria for
delisting the species. Efforts on the part of CDFG, US Fish and Wildlife Service, and US
Forest Service to eradicate alien trout in lower Silver King Creek with piscicides have
been blocked by litigation for several years, but USFWS is in the process of completing
an environmental scoping document to move forward with a chemical treatment. If
treatments are successful, then the process of restocking PCT in lower Silver King Creek
can begin. Further conservation plans by CDFG and USFWS include monitoring and
maintaining all existing populations of PCT and their habitat as well as continued
protection of all existing PCT populations from alien trout incursions. The limited
historical range of PCT and the fact that this habitat is publicly owned and suffers from
very limited degradation gives the species a good chance of recovery. However, the small
geographic range and limited genetic diversity of PCT make it vulnerable to inbreeding
depression, stochastic events, and illegal introductions of alien trout.
Restoring PCT to their historic habitat will more than double the number of fish in
the Silver King basin, provide greater connectivity of habitat, restore the PCT as the
principal aquatic predator to re-establish natural processes, and help to isolate PCT in the
basin from the threat of non-native trout introductions. In short, PCT have a good chance
at recovery if alien trout can be kept out of their, their range can be expanded, and their
habitat protected.
Trends:
Short term: PCT populations have remained fairly stable since 1998. They
currently inhabit more miles of stream than they did historically, but the populations are
heavily fragmented and cannot interbreed. Non-native trout exist below Llewellyn falls
and 56 years of restoration and conservation efforts could be unraveled by a single illegal
introduction of non-native fish into current PCT habitat.
Long term: Though PCT have a far more limited distribution than LCT, their
habitat is in reasonably good condition and is all on public land (US Forest Service)
which simplifies recovery efforts considerably. Their dependence on humans for
reproduction is limited, though continued transfers will be required in order to maximize
the remaining genetic diversity in the populations. Monitoring and removal of any alien
trout must continue indefinitely to protect genetic integrity of the remaining fish. Climate
change may pose a threat to PCT populations in the future, but the alpine nature of their
native habitat could potentially buffer them from the effects of warming or loss of
snowpack. The out-of-basin populations at Cottonwood and Cabin Creeks may be more
at risk because of the arid nature of the White Mountains.
Status: 2. PCT have a high likelihood of extinction in their native range within the next
50 years without continued intense monitoring and management. All populations are
small and isolated, so therefore subject to illegal introductions of alien trout and local
natural and man-made disasters.
PCT were listed as endangered under the Endangered Species Preservation Act of
1966 on March 11, 1967. However, they were subsequently downgraded to threatened
under the Endangered Species Act of 1973 (on July 16, 1975) to facilitate management
activities and to allow limited recreational fishing (USFWS 2004). The 2004 USFWS
Recovery Plan’s goal is to restore PCT to their native range in Silver King Creek and
continue to monitor and protect all existing populations. The status determination (Table
1) is for the effective wild populations, including introduced populations.