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Key elements of the 2015 national assessment of stream fish habitats follow the 2010 assessment, including: 1) the idea that distributions and numbers fishes reflect the quality of habitat in which they live; and 2) human landscape factors pose a risk to the condition of stream habitat, and indirectly, to fishes. The 2015 inland stream assessments for the contiguous United States, Alaska, and Hawaii all followed five broad steps (Figure 1) that are described in detail below for the inland stream assessment for Alaska. Note that analytical details for the Alaska assessment differed in southeast Alaska as compared to the remainder of the state (referred to as greater Alaska) due to differences in the resolution of...
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Accounting for natural variation With the exception of differences in spatial units, assessments for greater Alaska and southeast Alaska were conducted similarly across regions. Because stream fish assemblage data were not available for the state, no steps were taken to account for natural variation in stream habitats for either southeast or greater Alaska. This represents an important need for future work.
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State-wide data on fish populations were limited in Alaska for use in this assessment, as was a detailed spatial (mapping) framework that fully characterizes watersheds throughout the state at the time this assessment was conducted. Because of these factors, we modified our assessment methods to account for these limitations. Twenty-one landscape disturbance variables were assembled from medium-sized watersheds throughout the state (i.e., 12-digit hydrologic unit code watersheds). Variables were then assigned to one of six categories based on their disturbances to stream habitats. Categories include: urban land use, agricultural land use, point source pollution and water quality, barriers to fish movement, human...
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In the mostly arid Southwestern United States, water availability (hydrology – a key fish habitat process), wildfires, and grazing intensity are important disturbances that are known to have major, negative effects on fish habitats. While this assessment indicated that many of the streams in this region are in good condition, a number of key habitat variables (i.e. water availability, wildlife frequency and intensity, and grazing intensity) could not be directly included in this assessment because national datasets of these disturbances and their measured variable are unavailable. Their absence from this assessment, along with absences of other disturbances, has likely produced an overestimation of habitat condition...
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Table showing human and natural landscape factors used for the 2015 national assessment of stream fish habitat.
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