Beach geomorphology and Kemp’s Ridley (lepidochelys kempii) nest site selection along Padre Island, Tx, USA
Culver, Michelle F.
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The Kemp’s ridley sea turtle (Lepidochelys kempii) is the most endangered sea turtle species in the world, largely due to historic take of eggs at the primary nesting beach in Mexico, loss of juveniles and adults incidental to fisheries operations, and the limited geographic range of its nesting habitat. In the USA, the majority of nesting occurs along Padre Island in Texas. There has been limited research regarding the connection between beach geomorphology and Kemp’s ridley nesting patterns, but studies concerning other sea turtle species suggest that certain beach geomorphology variables, such as beach slope and width, influence nest site selection. This research addresses the literature gap by quantifying the terrestrial habitat variability of the Kemp’s ridley and investigating the connection between beach geomorphology characteristics and Kemp’s ridley nesting preferences on Padre Island, Texas, USA. Beach geomorphology characteristics, such as beach slope and dune peak height, were extracted from airborne topographic lidar data collected annually along the Texas coast from 2009 through 2012. The coordinates of observed Kemp’s ridley nests from corresponding years were integrated with the geomorphic data, which was then statistically analyzed using generalized linear models and random forest models. These models were successful in predicting Kemp’s ridley nest presence. The top generalized linear models explained 40-46% of nest presence variability with a relatively low prediction error. The final random forest model was superior in performance in comparison to the generalized linear models, with a true positive rate above 85%. Nest elevation, distance from shoreline, maximum dune slope, and average beach slope were the significant variables in the top two generalized linear models and the relatively most important variables in the random forest model, with elevation and distance from shoreline being the most influential in each. Kemp’s ridleys nested at a median elevation of 1.04 m above mean sea level and a median distance from shoreline of 12.79 m, which corresponds to the area directly below the potential vegetation line, which is defined as the lowest elevation where dune plants may persist. Kemp’s ridleys also exhibited a preference for a limited range of the study area and avoided nesting on beaches with extreme values for maximum dune slope, average beach slope, and beach width. This study provides new information regarding Kemp’s ridley terrestrial habitat and nesting preferences that have many applications for species conservation and management.