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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...
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.
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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OGC WMS Service;
Tags: 2015,
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SouthwesternRegion,
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Table showing human and natural landscape factors used for the 2015 national assessment of stream fish habitat.
Relative condition of fish habitat in streams of the Eastern Gulf of Mexico States. Histogram shows percentage of total stream length in each condition class.
Integrating data into a spatial framework After acquiring data, variables were attributed to a national stream coverage for use in assessment following Wang et al. (2011). The National Hydrography Dataset Version 1 (NHDV1) is a 1:100,000 scale representation of streams from throughout the conterminous United States. The NHDV1 identifies stream reaches as sections of streams occurring between confluences (Figure 2). We attributed all data to stream reaches (i.e., fish data, fragmentation metrics by dams) or to local catchments and 90m buffers draining to stream reaches (i.e., human land uses, mining activities, impervious surfaces, etc.). Local catchments (watersheds) and buffers are the land areas draining directly...
Spatial scales to which data were attributed for Hawaii inland stream assessment. Units include local catchments (A), network catchments (B), and downstream main channel catchments (C).
Map of the risk of current fish habitat degradation of inland streams of the Mid-Atlantic States region.
Identifying disturbances to fish habitat The approach for identifying disturbances to fish habitat was based on the assumption that greater intensities and types of human landscape disturbances would most likely lead to more disturbed stream fish habitat (e.g., Danz et al. 2007, Esselman et al. 2011). Twenty-two human landscape variables were identified for the Alaska assessment, with 21 variables used in the southeast and 19 in greater Alaska. We grouped variables into six sub-indices representing specific types of disturbances including: urban land use, agricultural land use, stream fragmentation, point source pollution, infrastructure, and active mines. Each sub-index of disturbance was represented by 2 to...
Integrating data into a spatial framework Greater Alaska For most of Alaska excluding the southeast portion of the state, watershed boundaries for individual stream reaches were unavailable, and the highest resolution spatial units available for assessment were 12-digit USGS hydrological units (HUC-12s). Greater Alaska includes 12,824 HUC-12s that partially follow watershed boundaries; however, boundaries are also intended to capture roughly similarly-sized regions vs. entire upstream landscape areas draining to streams (Figure 11). After acquiring data, variables were attributed to HUC-12s for the greater Alaska assessment. Southeast Alaska For the southeast portion of Alaska, watersheds were delineated from...
Map of the risk of current fish habitat degradation of inland streams of the Central Midwest States.
Map of the risk of current fish habitat degradation of inland streams of the Central Mississippi River States.
Map of current habitat degradation of Hawaii
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Map of the risk of current fish habitat degradation of inland streams of the Southeast States.
Data on stream fishes were provided for use in the 2015 assessment by the Hawaii Division of Aquatic Resources. Data were collected from 1992 to 2010, and assemblages were sampled using standardized visual surveys (Higashi and Nishimoto 2007). Fish data indicated presence or absence of nine native taxa in stream reaches including five fluvial fish species, two shrimp species, a gastropod, and two species of native flagtails (treated as a single taxonomic group analytically) that periodically enter the stream from the nearshore coastal environment (Table 6). Fish presence-absence data were available for 403 perennial stream reaches throughout the five main Hawaiian Islands. Many different human landscape factors...
Table displays native stream taxa included in the 2015 assessment.
Map of the risk of current fish habitat degradation of inland streams of the Southwestern States.
Creating cumulative habitat condition scores Greater Alaska All six sub-indices of disturbance scores in each HUC-12 were summed together to yield a cumulative habitat condition index (CHCI) score for each HUC-12. The maximum value for the CHCI was 6, indicating that a HUC-12 was in the worst condition class for each sub-index of disturbance, while the minimum value of the CHCI was 0, indicating that a HUC-12 was in the best condition class for each sub-index of disturbance. We followed methods applied for the conterminous US and created condition classes using Jenk’s natural breaks. With the exception of the HUC-12s that received a CHCI score of <0.001, which were given a priory assignment of “very low” risk of...
Map of the risk of current fish habitat degradation of inland streams of the Upper Midwest States.
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