State Space Model for Light Based Tracking of Marine Animals: Validation on Swimming and Diving Creatures

Abstract

Determining light-based geolocations of electronically tagged marine animals by using irradiance measurements in an integrated random walk movement model is presented for improving the precision of the reconstructed geographical tracks. The model avoids making any irradiance threshold assumptions, or constraining the movement of the tag between dawn and dusk, which has limited the efficacy of previous models. Unlike previous models which relied on using previously calculated raw geolocations from outside sources, the new model uses irradiance data to produce the most probable track. The model generates two estimates of geographic positions per day (at dawn and dusk). Prior to this study, the model has been successfully evaluated for tags mounted on moorings, drifters, and in simulated cases. This paper documents the application of the model to wild caught swimming and diving mako sharks and blue marlin. The reconstructed tracks via the new model are compared to tracks adjusted using sea-surface temperature and to very accurate satellite-based tracks. The model performs well for the tested tags, which is surprising as these are pop-off satellite archival tags (PSATs), from which only a small fraction of the light record around approximately dusk and dawn is stored. The integrated model was vastly superior to classical purely light-based methods in all cases.