WCT Multi-State Assessment February 10, 2003 



(1996) estimate and our estimate was likely due to differences primarily in the Missouri River 

 system discussed above. 



Rieman and Apperson (1989) estimated that WCT were historically present in approximately 

 10.900 miles of streams in Idaho, while we estimated that over 18,000 miles were historically 

 occupied. Much of this discrepancy is likely due to mapping scale differences. 



Lee et al. (1997) and Thurow et al. (1997) assessed the status of native fishes in the upper and 

 middle portions of the Columbia River basin including delineating historical ranges. For WCT 

 their designation of historical range was similar to ours for Idaho and Oregon, but they included 

 more 4"' code HUC's in Washington on the east side of the Cascade Mountains, including the 

 Yakima. Wenatchee. and Naches basins, than either we or the U.S. Fish and Wildlife Service 

 (1999) included. Our estimation for the distribution of native WCT populations in Washington 

 was based on their known presence prior to the proliferation of hatchery stocking. Though it is 

 possible that this assessment underestimates the historical distribution of WCT. historical 

 presence of native WCT populations outside of Lake Chelan, the Methow and Pend Oreille River 

 basins cannot be documented with available information (Williams 1998). Van Eimeren (1996) 

 also included these basins within the historical range of WCT in his assessment. 



Current Distribution 



WCT currently occupy about 33,500 miles in 7,071 tributaries throughout their historical range. 

 The U.S. Fish and Wildlife Service (1999) estimated that WCT occupied about 23.000 miles in 

 4.275 tributaries. The differences between these two estimates are likely due to several reasons. 

 First, more populations of WCT have been documented in the four- year period between 1998 

 and 2002. Second, our assessment provided more detailed information that was gathered and 

 summarized more consistently than was available to the FWS when they conducted their earlier 

 status review. Third, the scale at which we collected and summarized information was finer than 

 the scale at which some data were provided to the FWS. 



Mclntyre and Rieman (1995), citing Rieman and Apperson (1989). estimated that WCT 

 populations whose abundance were at least 50% of potential occupied only 1 1% of historical 

 range in Idaho. We estimated that WCT occupied almost 96% of historical range in Idaho and 

 that stream segments that supported WCT "Slightly Below" to "Near" habitat capacity occupied 

 about 50% of historical range. We are uncertain why these two different assessments had such a 

 large difference; however, it is likely that different biologists made different interpretations. For 

 example, Rieman and Apperson (1989) noted that biologists classified WCT populations in the 

 Middle Fork Salmon River drainage as depressed, because they occurred at relatively low 

 densities. Our assessments of abundance were tied to habitat potential. In the Middle Fork 

 Salmon drainage, wilderness designation results in habitat generally being regarded as pristine. 

 However, wilderness streams located in the central Idaho batholith have inherently low 

 productivity, thus where stream productivity is expected to be low due to underlying 

 geology, WCT will also be relatively low, even though their abundance is at or near 

 capacity. Additionally. WCT in the Middle Fork Salmon have been managed with catch and 

 release regulations since the 1970s, and harvest is not affecting population abundance. In 

 addition, since publication of the Rieman and Apperson (1989) report, a substantial number of 

 new field studies have been initiated in Idaho WCT habitats that provided abundance data, 



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