DOI: 10.5061/dryad.cvdncjt7p
title: Tracking marine tetrapod carcasses using a low-cost mixed methodology with GPS trackers, passive drifters, and citizen science

description: 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
 coast. Beach surveys and Citizen Science were implemented to recover the
 beached drifters. We recovered 71.83% of non-biological and 27.27% of
 carcasses released. We tracked the movements of 38 carcasses (25 sea
 turtles and 13 cetaceans) with 17 GPS devices. The drifting time, until
 reaching the beach, ranged from 12h to 17 days for carcasses and 12h to
 406 days for bottles. Citizen Science was the most important source of
 recoveries of non-biological drifters, representing 66.67% of the total
 bottles recovered. For carcasses, active search was the most important
 recovery source, representing 64.7% of the total carcasses recovered. Our
 study contributes with new findings about drift patterns of marine
 tetrapods in the SWA and describes an accessible low-cost mixed
 methodology for small and medium-budget projects that can be replicated in
 other coastal regions of the world for tracking a wide range of marine
 tetrapod species.
description: 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 bottles at every point and 15 carcasses (11 seabirds, three
 sea turtles, and one cetacean) at points 1, 3, and 5. However, whenever
 available, more specimens were included (e.g. sea turtles and franciscana
 dolphins, Table S1), maximizing sampling effort. Seabird carcasses were
 not tracked because they have a mean body mass lighter than 2
 kg.