Using an ocean model to predict likely drift tracks of sea turtle carcasses in the north central Gulf of Mexico

Abstract

From March through July 2011, an increased number of Kemp's ridley sea turtles Lepidochelys kempii were reported stranded on the islands, beaches and shorelines of Louisiana, Mississippi and Alabama. Members of the National Sea Turtle Stranding and Salvage Network responded, documenting the location and physical condition of each turtle. This report describes an ocean physical model-based analysis of the spring and summer 2011 Mississippi stranding events. Included within this group of strandings was 1 satellite-tagged moribund Kemp's ridley turtle, initially alive and tagged by the Institute for Marine Mammal Studies for a site fidelity study. Data from this tracking event provided an accurate time sequence of 58 h, during which the animal was presumed to be drifting, based on observed characteristics that were typical of a float- ing carcass. Turtle drift data were combined with output from the America SEAS (AMSEAS) hydrodynamic model to provide an estimate of leeway. The AMSEAS model was then applied to an additional 247 stranded turtles to produce 5 d Lagrangian backtrack drifts to derive mortality source location probability maps. Based on the model presented in this study, the majority of mor- talities appeared to have occurred in eastern Louisiana state waters.