Written by W.G. Duffy, FOMR Board Member
Redband trout Photo Credit: ODFW
In Part Three of this review of redband trout occupying Malheur National Wildlife Refuge I briefly describe the geographic range of the species, its conservation status, and primary threats sustaining its populations in the Harney Basin.
Redband trout occur in a variety of habitats ranging from lakes to streams in forests at higher elevation and high desert streams at lower elevations. The variability of the climate in the Great Basin, with its high summer temperatures and periods of drought punctuated with irregular flooding, adds to the challenges facing these fish. To persist in the Great Basin redband trout have developed the behavioral and physiological ability to survive unpredictable stream flows and lake volumes that lead to fluctuations in alkalinity, and higher water temperatures than are common for other species of trout.
Distribution and Conservation Status
Interior redband trout historically occurred in rivers and streams above the range of anadromy in six western states—Nevada, California, Oregon, Washington, Idaho, and Montana. In Oregon, redband trout once occupied almost 20,000 km of stream habitats while recent estimates
suggests they now occupy about 11,000 km of streams. (55% of historical area). In the 1990’s, the decline in habitats occupied by redband trout, as well as their declining abundance, led to concerns over the ability of the species to persist in the northern Great Basin.
These concerns led in 1997 to the petitioning of the U.S. Fish and Wildlife Service (USFWS) to list Great Basin redband trout as threatened or endangered under the Endangered Species Act. The petitioners argued that habitat degradation, fragmentation, and competition and predation by non-native fish posed significant threats and when combined with prolonged periods of drought, resulted in a decline of redband trout abundance that threatened their continued survival. In 2000, the USFWS found that listing of redband trout in southern Oregon, northeast California and northwest Nevada was not warranted. The USFWS argued that abundance of redband trout in the Great Basin had responded positively to the cessation of regional drought and restoration activities in some basins that had significantly improved aquatic habitat condition.
Within a decade of the USFWS finding in 2005 the Oregon Department of Fish and Wildlife (ODFW) produced a Native Fish Status Report in which they categorized redband trout in the Malheur Lakes basin as potentially at risk of extinction due to habitat fragmentation and a relatively high number of disconnected populations. The same assessment found that redband trout in the Catlow Valley had a high risk of extinction due to intermittent recruitment, small population size and geographic isolation. More recently, in 2015 ODFW found that redband trout in the Malheur Lake and Catlow Valley areas were viable and capable of persisting into the future.
Today the state of Oregon considers redband trout to be a sensitives species. The sensitive species designation by Oregon implies that the species faces one or more threats to their populations or habitats. The American Fisheries Society, the U.S.W.S., the U.S. Forest Service and Bureau of Land Management also classify redband trout as a sensitive species, although their definitions of sensitive may vary.
The geographic range of redband trout in the interior West has not contracted noticeably. The density of stream habitats occupied has, however, been reduced. In Oregon, roughly 55% of the stream distance historically occupied in occupied today.
The conservation status redband trout was disputed by different parties in the 1990’s and early 2000’s. During this period the USFWS was petitioned to list the species but declined to do so. The ODFW subsequently produced three reports that initially voiced concern about possible extinction of redband trout in Oregon, but eventually reached a conclusion that such concern was not warranted. Although not addressed directly, it seems that drought/wet cycles in the climate may have influenced redband trout distribution and abundance and influenced decisions about their conservation status.
Threats to sustaining healthy populations of redband trout in Malheur Refuge and the Harney Basin are the presence of invasive species, quantity and quality of water, invasive species of plants in riparian habitats and climate change. The primary threat to this species on the Malheur Refuge is unquestionably the continued presence of invasive species, especially common carp. Carp have the capacity to negatively affect the entire ecosystem they inhabit; turbidity they create while feeding reduces light penetration in water, eliminating vascular aquatic plants important to waterfowl and their feeding on aquatic invertebrates places them in direct competition with redband trout and multiple species of water birds. Other introduced or invasive species of fish, bullfrogs and plants that invade riparian zones are also problematic.
Modest changes in the hydrological cycle of the Blitzen River and its valley have been documented in recent years. That these changes have been attributed to climate change appears undisputable. The most dramatic changes documented are increases over a 59-year period include March air temperatures increasing 3.5 0f, Snow-Water-Equivalent on 1 April declining by 34% and changes in annual river flow consistent with increased winter rainfall.
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Suggested reading:
Schroeder, R.K., and J.D. Hall, editors. 2007. Redband trout: resilience and challenge in a changing landscape. Oregon Chapter, American Fisheries Society, Corvallis, Oregon.
