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The Kern River basin drains the southern extent of the Sierra Nevadas in California. The system was connected to the San Joaquin River and first occupied by ancestral rainbow trout around 10,000 years ago. As the connection to the San Joaquin River valley and Tule Lake dried up and natural barriers within the system developed, three distinct forms of trout evolved through isolation: the California golden trout (Oncorhynchus mykiss aguabonita) found in the South Fork Kern River and Golden Trout Creek basins, the Little Kern golden trout (Oncorhynchus mykiss whitei) found in the Little Kern River, and the Kern River rainbow trout (Oncorhynchus mykiss gilberit) found in the mainstem and tributaries of the Kern River.
Because its natural range spans two basins in the Kern River system, California golden trout were initially split into two taxonomic forms: the Volcano Creek golden trout, found in Golden Trout Creek (formerly called Volcano Creek), a tributary of the mainstem Kern River; and the South Fork Kern golden trout. Subsequent investigations determined that the two populations were once connected and only isolated thousands of years ago by a lava flow that diverted the headwaters of the South Fork Kern River west into the mainstem Kern. Since the region was settled in the late 1800s, California golden trout have been translocated above natural barriers into the headwater streams and alpine lakes of its native drainages and throughout the Sierra Nevada Mountains and western US. The alpine lakes and mainstem South Fork Kern River were also stocked with non-native trout and, by the mid-1960s, California golden experienced widespread hybridization. Additional stress to the subspecies came from habitat degradation associated with livestock grazing.
Beginning in 1968, California Department of Fish and Game began a series of restoration activities designed to return the subspecies to its historic range. The primary activities included the construction of three barriers in the upper South Fork Kern – the Ramshaw, Templeton, and Schaeffer barriers – and repeated piscicide applications above the barriers to eliminate non-native rainbow and brown trout. Additional efforts were intended to mitigate the effects of livestock grazing and recreational uses in the basin. Recent efforts focused on eradicating non-native trout from the alpine lakes in Golden Trout Creek and reconstructing the South Fork Kern barriers. Nonetheless, genetic studies led by the Genomic Variation Lab at the University of California, Davis confirm that hybrid California golden trout remain widely distributed throughout both basins. Management of the introgressed and remnant pure populations remains the primary conservation challenge.
Our CSI analysis incorporated data from the 2008 SOS: California’s Native Fish Crisis report, the Genomic Variation Lab, the 2004 Conservation Assessment and Strategy for the California Golden Trout, and the retrospective Restoration of the California Golden Trout 1966 -2004 and information from Molly Stephens (University of California, Davis), Christy McGuire (California Department of Fish and Game), and Lisa Sims (US Forest Service). We are grateful for these contributions to our understanding of this subspecies. A complete list of data sources is provided in the framework documentation.
Our CSI analysis considers populations with introgression values exceeding 0.20 as functionally extirpated. Although the catchments occupied by these populations may contain pure individuals and valuable genotypes, the consensus among management agencies is that conservation efforts should be focused on populations with introgression levels less than 0.10 – 0.20. Data for several CSI indicators affecting California golden trout are unavailable or uncertain, including: a clear understanding of the historic distribution (confounded by the history of translocations), a complete picture of the natural barriers in the system, and abundance data that would allow comparisons of productivity between different streams. This CSI summarizes information at the catchment scale (2,000 – 16,000 acres), a finer scale than the typical CSI.
Key CSI Findings
- Populations of California golden trout currently occupy all of the historical distribution in Golden Trout Creek and 17 percent of the historic distribution in the South Fork Kern River. Additional non-historic habitat outside the natural distribution and above natural barriers within the natural distribution is currently occupied. Introgressed populations occur in Strawberry Creek and below the Templeton barrier in the South Fork Kern River.
- Populations in the Golden Trout Creek basin and in the South Fork Kern River above the Templeton barrier have the highest population integrity scores. Additional information on population density and natural barriers will further inform the population integrity analysis.
- Habitat integrity scores are high due to the occurrence of the subspecies on protected public lands and the absence of sources of acute anthropogenic habitat degradation. Instream habitat conditions are not mapped within the CSI and the legacy of grazing, logging, and recreation disturbance may not be fully reflected in high habitat integrity scores.
- The primary source of lower watershed condition and water quality scores is the road network found in a limited number of catchments.
- California golden trout are at low risk to the future threats of resource extraction, energy development, and land conversion. Several catchments contain timber resources, geothermal resources, and/or private land with development potential.
- Introduced species and changes in fire regime and winter flooding associated with potential climate change represent the largest threat to the future security of the subspecies.
Our CSI analysis shows that the range-wide conditions related to species distribution are moderately high for current populations of California golden trout. All of the historically occupied catchments in Golden Trout Creek are currently occupied, but only 17 percent of historic South Fork Kern River catchments are currently occupied. An additional non-historic, pure population exists in Cottonwood Creek, an adjacent Owens River drainage (other populations with unknown pedigree and purity scattered across the Sierra Nevada Mountains and the western US are not considered in this analysis). In Golden Trout Creek and above the Schaeffer barrier in the South Fork Kern River, the subspecies occupies a stream network and catchment area nearly equivalent to the size and extent of its historic distribution. Most populations occupy streams second order or higher – Barigan Stringer, Salt Lick Creek, Dry Creek, Kern Peak, Johnson Creek, Long Stringer, and Little Cottonwood Creek are notable exceptions - suggesting that the subspecies may persist in relatively stable environmental conditions. The lack of information on the historic distribution of the subspecies adds some uncertainty to the range-wide conditions analysis.
Most population integrity scores for California golden trout are high. Because of indications of small amounts rainbow trout introgression in all populations, most populations have moderately high genetic purity scores. Populations in Dry Creek, Long Stringer, and the South Fork Kern River below Templeton barrier have the lowest genetic purity scores. The presence of introgressed individuals and artificial barriers in the mainstem South Fork Kern River lowers population extent scores (additional information on natural barriers would lower population extent scores). All populations are generalized as persisting at high densities (estimated at 482 fish/mile; field information on the density of individuals would further inform this indicator). Disease vulnerability scores reflect the absences of any known debilitating pathogens in the basin. Based on the criteria described by Rieman and others and Hilderbrand and Kershner, the California golden trout do not meet the desired persistence threshold of 5 populations per basin. Two equivalent populations exist in each Golden Trout Creek, Cottonwood Creek, and the South Fork Kern River above the Templeton barrier, with one additional population below the Templeton barrier.
Most habitat integrity scores are high. With the exception of the Smith Meadows, Troy Meadow, Jackass Creek, and Kennedy Peak catchments, at least 60% of all catchments are formally protected within the Golden Trout, South Sierra, or Domeland Wilderness areas. All catchments score high for watershed connectivity except those populations impacted by artificial barriers: the Upper South Fork Kern (above Ramshaw barrier), the South Fork Kern at Schaeffer (between the Templeton and Schaeffer barriers) and Beck Meadow Creek. Though detrimental to the connectivity of California golden trout populations, these barriers do currently serve to isolate the subspecies from rainbow trout, brown trout, and highly introgressed golden trout downstream. Few roads and minimal converted lands exist within the distribution of California golden trout: accordingly, all catchments receive high watershed condition scores (Troy Meadow, Smith Meadow, and Kennedy Peak catchments contain moderate road densities). High water quality scores reflect the lack of acute anthropogenic stressors, such as agriculture, oil and gas wells, and active mines. Several catchments have low water quality scores as the result of road networks within the riparian zones of perennial or intermittent streams. Long Canyon and Pine Creek have at least ¼ mile of road within the riparian zone of every mile of stream. Kennedy Peak, Sacatar Canyon, and North Fork Cottonwood Creek have at least 1/10 mile of road within the riparian zone. With few canals and no existing dams, all catchments score high for flow regime. The CSI lacks a specific indicator for addressing instream habitat conditions and the legacy effects of over a century of logging and cattle and sheep grazing may not be fully reflected in the total habitat integrity score. Nonetheless, the lack of the primary anthropogenic sources of habitat degradation that typically affect salmonids suggests that the California golden trout occurs within a landscape within which population restoration would be particularly appropriate and successful.
The CSI analysis of future security suggests the California golden trout is at moderate risk. Because the majority of the subspecies’ distribution lies within the Inyo or Sequoia National Forest, there is minimal risk of land conversion. Resource extraction risks are limited to portions of the Smith Meadows, Little Trout Creek, and Troy Meadow catchments, which are suitable for intensive forest management. Similarly, energy development risk is low with the exception of geothermal resources previously leased in the Smith Meadows, Monache Creek and Meadows, Snake Creek, and South Fork Kern at Schaeffer catchments. The logistics of moving these resources around the surrounding wilderness areas may ultimately preclude their development.
The primary predicted threats to future security come from climate change and the persistence of introduced species in the system. The CSI considers a + 3°C climate change scenario for each species. Our analysis suggests that the California golden trout is at highest risk to increased winter flooding associated with rain-on-snow events in the lower portions of Golden Trout Creek and the upper portions of the South Fork Kern. The subspecies is at high risk to the effects of altered fire regimes associated with earlier spring warming in mid-elevation zones in the western portion of the South Fork Kern basin and low risk in the higher elevation Golden Trout Creek basin and the northern portion of the South Fork Kern. California golden trout are at moderate risk to drought (except in the North Fork Cottonwood Creek catchment, where risk is low). Based on its historic distribution relative to air temperature, the subspecies is at low to moderate risk to increased summer temperatures, except for high risk in the lower mainstem South Fork Kern River and its west-draining tributaries below Kennedy Meadows.
Recommendations to increase resistance and resilience to climate change include a reduction of other remaining stressors, restoration of any riparian, wetland, and wet meadow areas that are not in high condition, and partial reconnection of stream systems to allow greater fish movement within the native range. However, restoring connectivity also may increase risk from non-native fish introductions and thus must proceed with caution.
The South Fork Kern River below the Templeton barrier, lower reaches of Golden Trout Creek, and the mainstem Cottonwood Creek drainages receive the lowest possible introduced species scores due to the continued presence brown trout, rainbow trout, or golden trout with introgression values of at least 0.50. Additionally, catchments connected to Kennedy Meadows are impacted by the continued stocking of triploid rainbow trout. Because of the history of unauthorized trout introductions in the Kern system, the remaining catchments received moderate scores.
Total CSI scores and conservation strategies are consistent with the current management direction for California golden trout. The purest populations in the Golden Trout Creek and upper South Fork Kern River basins should remain the conservation and protection focus. Because introgressed individuals persist in the both systems, however, population restoration/reintroduction activities should be directed at eliminating or managing non-native trout or highly introgressed golden trout. The existing barriers on the mainstem South Fork Kern River will not serve their intended, isolating function if highly introgressed individuals persist in Strawberry Creek or the mainstem South Fork Kern above the barriers. The proposed Dutch John barrier would provide additional habitat for California golden trout to occupy downstream of the existing barriers. The primary conservation value of the Cottonwood Creek basin populations may be as a source of unique genetic material from pure individuals. New information regarding fish densities and population extents may further refine CSI scores for population integrity and provide additional guidance for restoration activities. Local knowledge will be required to direct habitat restoration activities designed to mitigate instream habitat degradation associated with historical land uses.
Trout Unlimited strongly supports the continued restoration efforts of California Department of Fish and Game, the U.S. Forest Service, University of California - Davis, and California Trout. These entities have made great strides in the conservation of California golden trout since coordinated efforts began in the late 1960s. Consistent with CSI findings related to habitat and population integrity, expanding the available habitat and managing the introgression exposure for the purest populations of California golden trout should remain a top priority. Because it occurs almost entirely on public lands with the highest protection status, there is a significant opportunity to ensure the subspecies’ persistence.
Prepared by Kurt Fesenmyer, TU, 4/6/2009
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