A riverscape perspective for modeling flood-driven suitable spawning habitat for Alligator gar in the Lower Guadalupe River floodplain, Texas

Abstract:

Flood inundation processes provide necessary access to floodplain habitats for a variety of floodplain dependent spawning fish. The riverscape perspective provides a framework for linking species specific flow-ecology relationships to suitable habitat conditions using spatially-explicit modeling techniques. We developed a flood inundation driven habitat suitability model to assess the available spawning locations for Alligator gar (Atractosteus spatula) over a 250 km segment of the Lower Guadalupe River, Texas. We modeled flows from 500 m³s^-1 up to 5,000 m³s^-1 and processed these for suitable spawning depths (0.2-2m) and connectedness between the river and suitable floodplain vegetation types derived from the Texas Ecological Mapping Systems. We analyzed the hydrology for frequency, timing, and duration of these flows to examine how the spatially-derived suitable habitats related to the temporal aspects of the flow occurrence during the suitable spawning season of May-July for the period of 1935-2020. Reduced flood-pulse and peak flows from dams, floodplain land cover conversions (to agriculture, timber, urban development), and physical barriers (livestock fences and weir gates) prevent access and disrupt reproductive success. These anthropogenic factors, along with over-harvesting, threaten the health and integrity of Alligator gar. The management and conservation of these species depends on collaboration of multiple stakeholders including private floodplain landowners. Spatially and temporally informed riverscape models, similar to this example, can provide valuable tools for designing conservation strategies for floodplain-dependent species.