Gulf Migratory Fish Connectivity (Southeast Blueprint Indicator)

Reason for Selection Migratory fish presence reflects uninterrupted connections between freshwater, estuarine, and marine ecosystems. Aquatic connectivity benefits diadromous fish and is considered a high priority for the integrity of aquatic ecosystems. Larger diadromous fish, like sturgeon, are often more sensitive to disruptions in aquatic connectivity. Smaller fish can make better use of fish ladders and other fish passage measures than larger fish. Input Data * [Southeast Aquatic Connectivity Assessment Project] (SEACAP); see [the final report] for more information SEACAP developed linear spatial data on the presence of priority diadromous species. These layers are modified versions of the NHDPlus Version 2. These data were altered to contain presence of Alabama shad using data from the Atlantic States Marine Fisheries Commission (produced for the ASMFC by the Biodiversity and Spatial Information Center at North Carolina State University, Alexa McKerrow), and expert knowledge of the SEACAP Workgroup. SEACAP also developed a functional river network layer ([final SEACAP report], page 9). A functional river network is defined by those stream reaches that are accessible to a hypothetical fish within that network. The functional river network is defined by lines (streams). SEACAP also calculated “functional catchments,” which are polygons that represent the catchment area that is associated with each of those functional networks. Note: A catchment is the local drainage area of a specific stream segment based on the surrounding elevation. Catchments are defined based on surface water features, watershed boundaries, and elevation data. It can be difficult to conceptualize the size of a catchment because they vary significantly in size based on the length of a particular stream segment and its surrounding topography—as well as the level of detail used to map those characteristics. To learn more about catchments and how they’re defined, check out these resources: * [An article from USGS explaining the differences between various NHD products] * The glossary at the bottom of [this tutorial for an EPA water resources viewer], which defines some key terms * [National Oceanic and Atmospheric Administration (NOAA) Gulf Sturgeon Critical Habitat] * Estimated Floodplain Map of the Conterminous U.S. from the [Environmental Protection Agency’s (EPA) EnviroAtlas]; [see this factsheet] for more information; [download the data] The EPA Estimated Floodplain Map of the Conterminous U.S. displays “...areas estimated to be inundated by a 100-year flood (also known as the 1% annual chance flood). These data are based on the Federal Emergency Management Agency (FEMA) 100-year flood inundation maps with the goal of creating a seamless floodplain map at 30-m resolution for the conterminous United States. This map identifies a given pixel’s membership in the 100-year floodplain and completes areas that FEMA has not yet mapped” (EPA 2018). * U.S. Geological Survey (USGS) [Watershed Boundary Dataset] (WBD), accessed 8-11-2020: HUC6s, HUC12s; [download the data] * [Base Blueprint 2022 extent] * [Southeast Blueprint 2023 extent] Mapping Steps * Combine all the linework for Gulf Sturgeon using the ArcPy Data Management Merge function. This includes line data from SEACAP and the NOAA critical habitat. Add and calculate a field showing that these are sturgeon lines. * Combine all the linework for the Alabama shad, American shad, or striped bass from SEACAP using the ArcPy Data Management Merge function. Add and calculate a field showing these lines represent the above species. * Assign the values from the two sets of linework above to HUC12s using two separate ArcPy Analysis Spatial Join functions. * Add and calculate a new field. If it intersects a sturgeon line, give it a value of 2. Otherwise, if it intersects the other species linework, give it a value of 1. * Covert the HUC12s from polygons to a 30 m raster using the field above. * Convert the polygon layers from the Gulf sturgeon critical habitat to 30 m rasters and give those pixels a value of 2. * Combine the two rasters above using the ArcPy Spatial Analyst Cell Statistic “MAX” function. * Clip the resulting layer to the EPA estimated floodplain. * Use the HUC6 layer to remove from the resulting raster areas outside the Gulf drainage where those 4 species ranges occur. The Atlantic drainages are represented in the Blueprint by the Atlantic Migratory Fish Habitat Indicator. * Use the HUC6 layer to add zero values to the above raster representing the Gulf range of the 4 species listed above. Zero values are intended to help users better understand the extent of this indicator and make it perform better in online tools. * Clip to the spatial extent of Base Blueprint 2023. * As a final step, clip to the spatial extent of Southeast Blueprint 2023. Note: For more details on the mapping steps, code used to create this layer is available in the [Southeast Blueprint Data Download] under > 6_Code. Final indicator values Indicator values are assigned as follows: 2 = Presence of Gulf sturgeon 1 = Presence of Alabama shad, American shad, or striped bass 0 = Not identified as Gulf migratory fish habitat (east of the Mississippi River) Known Issues * This indicator does not account for smaller dams/culverts that serve as barriers to fish passage. * Where the SEACAP linear spatial data interests a dam, the indicator can extend to reservoirs that are not accessible to fish due to fish passage barriers (e.g., Ross R. Barnett Reservoir in MS). * The EPA Estimated Floodplain layer sometimes misses the small, linear connections made by artificial canals, especially when they go through areas that wouldn’t naturally be part of the floodplain. As a result, some areas (like lakes) that are connected via canals may appear to be disconnected, but still receive high scores. * While this indicator generally includes the open water area of reservoirs, some open water portions of reservoirs are missing from the estimated floodplain dataset. * Estuaries where Gulf sturgeon are not present are often underprioritized because data for the other species do not extend into the estuaries. * This indicator does not account for instream habitat quality, which can also be a barrier to fish passage. * This indicator likely underestimates the value of some areas for American eel. That species is not included in the indicator due to a lack of integrated regionwide data depicting how far upstream American eels have been observed. Disclaimer: Comparing with Older Indicator Versions There are numerous problems with using Southeast Blueprint indicators for change analysis. Please consult Blueprint staff if you would like to do this (email [hilary_morris@fws.gov]). Literature Cited Martin, E. H, Hoenke, K., Granstaff, E., Barnett, A., Kauffman, J., Robinson, S. and Apse, C.D. 2014. SEACAP: Southeast Aquatic Connectivity Assessment Project: Assessing the ecological impact of dams on Southeastern rivers. The Nature Conservancy, Eastern Division Conservation Science, Southeast Aquatic Resources Partnership. [[https://secassoutheast.org/pdf/SEACAP_Report.pdf]]. EPA EnviroAtlas. 2018. Estimated Floodplain Map of the Conterminous U.S. [[https://enviroatlas.epa.gov/enviroatlas/DataFactSheets/pdf/Supplemental/EstimatedFloodplains.pdf]].