Tracking marine tetrapod carcasses using a low-cost mixed methodology with GPS trackers, passive drifters, and citizen science

Drift experiments are essential to understand stranding patterns and to estimate the mortality of beached animals. Most studies do not use telemetry technology due to the high costs of this methodology. The objective of this paper is to describe the possibilities of tracking marine tetrapod carcasses with a low-cost and replicable methodology. The study was conducted in the Southern Subtropical Shelf (~ 28º–34º S), a highly productive and key ecological region of the southwestern Atlantic Ocean (SWA). 

We designed and tested a low-cost mixed methodology including Global Positioning System trackers, passive drifters (reused glass bottles), and Citizen Science (through instant message platform and email) for tracking carcasses of marine tetrapods. We performed four drift experiments, during the four seasons of 2019. We released 787 drifters (600 non-biological and 187 carcasses of seabirds, sea turtles, and cetaceans) at sea, at five equally separated distances (5–25 km) from the coa..., We used a commercial vehicular GPS tracker (©TKSTAR TK905, Figure S2a) to monitor the trajectories of the carcasses of sea turtles and franciscana dolphins. The device works with a GSM network and GPS satellites and can locate and monitor any remote target by Short Message Service (SMS), Application (APP), and the Internet (technical specifications are presented in Supplementary Material S1). In order to extend battery life, the device was connected to a 5000mAh power bank (©XTRAX, Figure S2c).
In 2019, we conducted four drift experiments (summer, autumn, winter, and spring) in the State of Rio Grande do Sul, Southern Brazil, to refine the estimates of at-sea mortality of marine tetrapods, using a commercial vessel (length: 16m, beam: 5.5m; Figure S3). The drifters were released at sea at five points at different distances from the beach (Table S2). Points were numbered from 1 to 5 from the coast to offshore. The standard composition of drifters by release point was the following: 30 bo...,