Indicator: Migratory Fish Connectivity

Aug 10, 2020
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This indicator is an index capturing how far upstream migratory fish have been observed. It also includes adjacent areas where habitat access could be restored through fish passage and hydrological barrier removal efforts.

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.

Input Data

Southeast Aquatic Connectivity Assessment Project (SEACAP)

Watershed Boundary Dataset (September 2015 release)

– Estimated Floodplain Map of the Conterminous U.S. from the EPA EnviroAtlas (see this factsheet for more information)

Mapping Steps

1) We used HUC 12 watershed boundary dataset polygons to dissect the polygons representing functional catchments (from the Southeast Aquatic Connectivity Assessment Project), using the Intersect function in ArcGIS. This sliced up the functional catchments into HUC12 sized pieces and reduced the area selected in step 2.

2) We performed the following spatial intersections to associate the linework representing presence/absence for diadromous species with the sliced up functional network catchments: 4 = All HUC12 sliced functional catchments that intersected with the linework depicting presence of Gulf or Atlantic Sturgeon3 = All HUC12 sliced functional catchments that intersected with the linework depicting presence of Alabama shad, American shad, blueback herring or striped bass (and that were not already identified as having Gulf or Atlantic Sturgeon presence).2 = All HUC12 sliced functional catchments that were adjacent to the diadromous fish associated catchments listed above1 = All remaining HUC12 sliced functional catchments

3) We converted the polygon layer created above to a raster with 30 m cell size using the ArcGIS “Polygon to Raster” tool with a cell assignment type of “maximum combined area”.

4) We intersected the above raster with the EPA Estimated Floodplain map to limit the results to the floodplain associated with each functional network.

Final indicator values

Indicator values were assigned as follows:

4 = Presence of Gulf or Atlantic sturgeon (high)

3 = Presence of Alabama shad, American shad, blueback herring, or striped bass

2 = Adjacent to presence of migratory fish connectivity index species

1 = Migratory fish connectivity index species not adjacent/not observed (low)

**Definitions **

Functional Network: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. Functional Catchments:

SEACAP also developed a functional river network layer (final SEACAP report, page 9). A functional river network is a 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.

Estimated Floodplain map:

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-meter 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.”

Known Issues

– Does not account for smaller dams/culverts.

– Overestimates species ranges in some areas (e.g., above Blewett Falls and High Rock Dam in the Pee Dee, upstream of Rocky Mount, NC).

– Underestimates species ranges in other areas (e.g., Atlantic Sturgeon range upstream of the confluence of the Altamaha river)

– In certain cases, when calculating adjacency to presence of migratory fish connectivity index species, GIS processing steps may erroneously include in a species’ range stream segments that are nearby, but not hydrologically connected.

– 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 Kerr Lake are missing from the estimated floodplain dataset.

–This indicator does not account for the habitat quality of the connections.

Disclaimer: Comparing with Older Indicator Versions

There are numerous problems with using South Atlantic indicators for change analysis. Please consult Blueprint staff if you would like to do this (email

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.

EPA EnviroAtlas. 2018. Estimated Floodplain Map of the Conterminous U.S.

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generated using ADIwg mdTranslator 2.17.1
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Content date:
2020-08-15 04:00:00 (lastRevision Date), 2020-08-15 04:00:00 (Release Date), 2019-08-15 04:00:00 (Start Date), 2021-08-15 04:00:00 (End Date)
Rua Mordecai(Point of Contact), Amy Keister(Point of Contact), Hilary Morris(Point of Contact), U.S. Fish and Wildlife Service(Point of Contact), Southeast Conservation Adaptation Strategy (SECAS)(Point of Contact), 2020-08-15(lastRevision), 2020-08-15(Release), Indicator: Migratory Fish Connectivity,,
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U.S. Fish and Wildlife Service
Landscape Conservation Cooperative Network
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The South Atlantic Conservation Blueprint is a living spatial plan to conserve natural and cultural resources for current and future generations in the face of future change. It spans parts of six states, from Virginia to Florida, including U.S. waters to 200 miles offshore. The Blueprint...