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The small isolated populations that characterize the current status of Apache trout tend to score relatively well in the CSI Genetic Purity and Disease Vulnerability indicators because most populations are isolated above small instream barriers and therefore are clearly separated from downstream non-native fishes. These same populations, however, score low on Population Extent and Life History Diversity because of the small, fragmented nature of their habitat. Seven of 35 existing populations meet persistence criteria, which includes sufficient habitat and population size to support an effective population of 500 fish. No habitats or populations are large enough to support a migratory life history except for a few small reservoirs where fish may ascend streams tributary to the lake for spawning. CSI indicator scoring is summarized in Table 1.
Habitat conditions for Apache trout typically scored higher than for most other native trouts in the West. Habitats are managed by the U.S. Forest Service (Apache-Sitgreaves National Forest) or White Mountain Apache Tribe. Almost no private land exists within the historic range. Riparian and stream degradation from livestock grazing are problems in certain subwatersheds, but road densities are low, flow regimes largely are undisturbed, and overall watershed conditions and water quality are quite good within most of the historic range.
Despite these relatively positive findings about habitat quality across the species’ historic range, reports about the lack of monitoring and enforcement of livestock grazing programs continues to be a cause for concern. Further fine-scale investigation of grazing management and localized habitat conditions are warranted.
Historically, Apache trout occurred in well-connected stream systems that included small headwater streams but also larger mainstem rivers. The interconnected nature of such populations provided natural resilience to disturbances such as flood, drought, or wildfire. If a headwater stream was degraded by such a disturbance, the fish could move downstream and then recolonize the upstream habitat once it recovered. But under existing conditions, Apache trout are unable to escape such threats because movement is blocked by dams and other instream barriers.
Trout Unlimited is encouraging efforts by the Arizona Game and Fish Department, U.S. Forest Service, White Mountain Apache Tribe, and U.S. Fish and Wildlife Service to reestablish larger, interconnected metapopulations for Apache trout. A larger reconnected population is currently proposed for the West Fork of the Black River on national forest land. Additional metapopulations are desired on tribal and national forest lands. Reestablishing these larger metapopulations would involve removal of existing instream barriers, creation of a new barrier downstream, and likely non-native fish control efforts. However, once established, these larger populations would be much more resistent to disturbances, including brown trout invasion, and would have a better chance of surviving impacts resulting from climate change.
Rapid climate change poses a substantial risk for Apache trout. Small populations are inherently vulnerable to global warming and climate change, especially through greater intensity and duration of drought and wildfire. Severe drought conditions are likely to become commonplace in this portion of Arizona by midcentury. As noted by NOAA meterologist Martin Hoerling and Jon Eischeid, “by about 2050, average moisture balance conditions will mimic conditions experienced only rarely at the height of the most severe historical droughts.” Already, the drought of 2002-2003 significantly reduced existing populations in many streams.
Expanding populations by increasing available downstream habitat is important in most drainages. Larger streams not only support more fish but also larger fish, which have higher reproductive capacity and improve the population’s ability to survive and to resist brown trout invasions. However, barriers also play a vital role deflecting non-native fish invasions but need increased monitoring and maintenance to ensure their long-term effectiveness. Thus, fishery managers face tradeoffs in their use and maintenance of artificial barriers.
Apache trout remain threatened with extinction and should retain their status as a threatened species pursuant to the Endangered Species Act. The primary concern is increased vulnerability of remaining small, fragmented populations, particularly to drought and wildfire.
Prepared by Jack E. Williams, TU, 12/1/2008
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