Inspecting substrate Assessing Shoal Bass Habitat Use in the Lower Flint River from with a drop camera Sonar survey Low-cost Side Scan Sonar and Electrofishing Data Image 1 Flint River Lower Flint River Basin • mean width 102 m • mean depth 4.4 m Adam J. Kaeser, Thomas L. Litts, and Travis Ingram • gradient <0.001% Red box defines 124-km Shoal bass Georgia Department of Natural Resources Image 2 extent of map study area Micropterus cataractae

Shoals are Important, Complex Habitats Evolution of the Lower Flint River Habitat Map Is Shoal 566 (a Spawning Site) Unique?

• Shoals (i.e., shallow, boulder-strewn areas with swift currents) are areas Map scale ~1:8000 Principal Components Analysis (PCA) of high biological diversity and productivity, used by shoal bass and other Patch Variables endemic species in the Flint River (e.g., Alabama shad, Gulf sturgeon) PC1= Shoal Size • Shoal habitat quality likely differs on a variety of characteristics and Variable PC1 PC2 PC3 Eigen- Cumulative Length 0.93 -0.01 0.04 Gradient PC value % Variance scales, but an assessment of such characteristics at the landscape scale Area 0.93 0.04 0.01 PC2= Isolation (i.e., throughout the river) is unfeasible using traditional approaches 1 2.83 0.40 Ratio -0.62 -0.06 0.21 Gradient (with larger • Adult shoal bass are difficult to sample, but appear to migrate long 2 1.11 0.56 % expo 0.35 -0.04 0.74 distances to specific shoals where they form spawning aggregations. Edge 0.69 -0.28 -0.02 distant shoals) 3 0.95 0.70 Narrowing the search for spawning sites by identifying key spawning site Dist near 0.29 0.73 -0.38 PC3= % Exposed Area near -0.10 0.70 0.45 characteristics may improve our ability to collect and tag adult shoal bass 2007 NAIP image of a Flint River reach with sonar survey Gradient for research and management investigations. Panel 1 route highlighted, each point contains depth data PCA Plots ‐ Patch Variables An Area of Shoal Habitat Each point Boulder (exposed) represents a Shoal 566 shoal Shoal 566 Does shoal 566 Shoal Size + appears to be:

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exhibit unique

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patch-level t •Larger in size

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characteristics? s I •More isolated

Image 3 Sonar image map layer overlaid on the river channel, •More exposed Panel 2 interpreted at ~1:300 scale to define substrate class boundaries during low water OBJECTIVES: 1) map and characterize shoal habitat throughout the than most other lower Flint River using our low-cost, sonar habitat mapping approach shoals + 2) identify shoal characteristics associated with spawning site selection 3) use this information to screen and identify other potential spawning Exposed

locations % Mapping Habitat Throughout the River Isolation +

• Sonar survey conducted April 2008 Boulder substrate polygons = shoals Sonar during high water (Panel 1, Image 1) shadow PCA Plots ‐ Neighborhood Variables • Sonar data geoprocessed using our Boulder Substrates classified, each color represents a different (shoal) class in the scheme (e.g., lime = limestone bedrock, tools to create sonar image map layers Panel 3 red = no data beyond sonar range) in ArcGIS 9.x (Panel 2)

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• Major substrate classes digitized, t

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e Shoal 566 appears classified, and accuracy assessed n Does Shoal 566 e

Rocky g Sand o to have: (Panel 3, Image 2) exhibit unique r fine e

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• Aerial imagery from summer 2007 (cobble) neighborhood H •Higher Average used to classify portions of boulder characteristics? Max, Avg Depth + and Maximum (i.e., shoal) substrate as exposed during low flows (Panel 4, Image 3) Sonar image revealing distinct substrates Depth within 250 •PCs 1-4 Account m buffer Map Results Shoal Distribution and Abundance for 62% of •Greater range • 124 km river map produced by Variance and variability in summer intern 2007 NAIP obtained during extreme low flows used to identify Depth, Lower • 607 shoals (boulder polygons) exposed portions of boulder substrate patches (shown here in red) substrate

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represented in map, with several Minimum Depth,

areas of high concentration (e.g., Rf and Less Sand, and boulder km 35-60, see adjacent figure) More Edge in its Rocky • Classification accuracy for boulder neighborhood of was very high (94%) 2 How to use this Lf ‐, Rb and Mx + m Extracting Characteristics from the Habitat Map than other shoals • 13.4% of boulder substrate information? exposed during extreme low flows Patch Level Variables Neighborhood Variables • Size (area) • Mean, Min, Max, SD, Range of A Spawning Aggregation found at Shoal 566 • Shape (perimeter) Patch= individual boulder Neighborhood= 250 m Will these associations help us locate substrate polygons mid-channel radius around shoal centroid • During spring 2009, a large group of adult shoal bass Shoal 566 • Edge:Area ratio depth additional spawning areas? was located during electrofishing efforts aimed at • Whether the distinct characteristics of shoal 566 and its neighborhood truly relate to capturing adult fish for a tag-return, exploitation study • Edge within 15 m • Additional shoal buffer area (Rb) spawning habitat selection or are merely coincidental requires further investigation • Subsequent sampling of the area revealed that these fish • Two sets of shoals (one set similar and another dissimilar to shoal 566) have been moved between a deep, outside bend of the river (a • % Exposed •Area of each identified using PCA scores; these shoals will be sampled to determine if other staging area), and a shoal located on the inside bend additional • Distance to spawning aggregations of shoal bass can be located ~250 m upstream Shoal 566 substrate class nearest shoal • Beyond shoal bass, the generated data set of shoal characteristics is available for • Observations in early May suggested that the group had present future studies involving Alabama shad and Gulf sturgeon, two species that selectively moved from the staging area to the shoal site to spawn (centroid-centroid) •Total edge spawn over coarse, rocky substrate • Why so many fish chose to spawn at this site, and how • Size (area) of (heterogeneity) far they traveled to do so, are important questions nearest shoal *For more information on low-cost, sonar habitat mapping contact Adam at [email protected]