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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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Table showing human and natural landscape factors used for the 2015 national assessment of stream fish habitat.
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 current habitat degradation of Hawaii
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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.
After acquiring data, variables were attributed to a stream coverage for use in assessment following Wang et al. (2011). The Hawaii Fish Habitat Partnership (HFHP) stream layer (Tingley et al. in prep) is a modified version of the 1:24,000 National Hydrography Dataset that consists of 11,436 intermittent and perennial stream reaches across the five largest Hawaiian Islands (Hawai’i, Maui, Moloka’i, O’ahu, Kaua’i). The HFHP stream layer distinguishes stream reaches as sections of streams occurring between confluences, headwaters and confluences, and confluences and pour points, following the definition of stream reaches in the contiguous United States. Each reach has an associated local catchment (watershed), upstream...
The approach for identifying disturbances to fish habitat was based on the assumption that greater intensities and types of human disturbances would most likely lead to more disturbed stream fish habitat (e.g., Danz et al. 2007, Esselman 2011). Twenty human landscape variables were identified for the Hawaii assessment (Table 2). We grouped variables into seven categories representing specific types of disturbances including: agricultural land use, urban land use, former plantation lands, point source pollution, density of ditches, stream fragmentation, and 303d listed streams. Disturbance sub-indices were then created for each category of disturbance variables for each spatial scale (i.e., local catchments, network...
303(d) list - A list established by the Environmental Protection Agency of impaired waters based on total maximum daily loads of pollution under Section 303(d) of the Clean Water Act Alkalinity – the capacity of water to neutralize an acid and higher levels are found in water bodies that are exposed to limestone Anadromous – adult fish live in the sea and return to fresh water to spawn Anchialine pools - unique brackish water environments that form in lava fields near the ocean and are fed by both fresh groundwater and salty seawater Anthropogenic –environmental change caused or influenced by people, either directly or indirectly Ballast water – water carried in the hull of a ship for stability when empty and...
The largest of the eight main Hawaii Islands— Hawai’i, Maui, Molokai, O’ahu, and Kaua’i—have well-defined watersheds and perennial streams. There are 376 perennial streams on these islands, most of which start high in the mountains and high numerous waterfalls before they reach the ocean. Forty large stream systems form small stream-mouth estuaries at their confluence with the ocean. These estuaries are critical transition points for migratory fish species and represent the connecting point between inland and coastal systems. They are also important nursery habitat for many coastal marine reef fish during key life stages. Furthermore, Hawaii’s aquatic resources are considered to be absolutely...
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To create the cumulative habitat condition index (CHCI) for streams of Hawaii, we first standardized and summed disturbance sub-indices described above within each of the three spatial scales to create three habitat condition indices (HCI) for each stream reach. Based on the assumption that urban land use can have excessive negative effects on stream habitat compared to other disturbances and at the request of the HFHP, the urban sub-index was upweighted in each spatial scale by a factor of 2. The CHCI was developed by summing HCI scores across spatial scales for each stream reach and standardizing from 0 (best condition) to 1 (worst condition). We followed methods applied for the contiguous U.S. and created condition...
Key elements of the 2015 national assessment of stream fish habitats follow the 2010 assessment, including: 1) the idea that 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 Hawaii. Note that the stream assessment for Hawaii is conducted within the five main Hawaiian islands: Hawai’i, Maui, Moloka’i, O’ahu, and Kaua’i.
Steps for 2015 hawaii assessment of stream fish habitats.
Classifying Stream Reaches in Hawaii based on Ecological Potential Besides influences of human landscape factors on stream organisms, many “natural” landscape factors also affect distributions and abundances of species found in different stream habitats. To account for those influences, we used an analytical approach to create groupings of perennial stream reaches with similar natural landscape characteristics that were found to be influential to distributions of nine native stream taxa including fish, shrimp, and snails (Table 2). This approach, referred to as classification, is driven by relationships between natural landscape factors and stream organisms and does not account for influences of anthropogenic factors....
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