Drivers of realized satellite tracking duration in marine turtles

Abstract

Background Satellite tags have revolutionized our understanding of marine animal movements. However, tags may stop transmitting for many reasons and little research has rigorously examined tag failure. Using a long-term, large-scale, multi-species dataset, we evaluated factors influencing tracking duration of satellite tags to inform study design for future tracking studies. Methods We leveraged data on battery status transmitted with location data, recapture events, and number of transmission days to probabilistically quantify multiple potential causes of failure (i.e., battery failure, premature detachment, and tag damage/fouling). We used a combination of logistic regressions and an ordinary linear model including several predictor variables (i.e., tag type, battery life, species, sex, size, and foraging region). Results We examined subsets of data from 360 satellite tags encompassing 86,889 tracking days deployed on four species of marine turtles throughout the Gulf of Mexico, Caribbean, and Bahamas from 2008 to 2019. Only 4.1% of batteries died before failure due to other causes. We observed species-specific variation in how long tags remain attached: hawksbills retained 50% of their tags for 1649 days (95% CI 995–1800), loggerheads for 584 days (95% CI 400–690), and green turtles for 294 days (95% CI 198–450). Estimated tracking duration varied by foraging region (Caribbean: 385 days; Bahamas: 356; southern Gulf of Mexico [SGOM]: 276, northern Gulf of Mexico [NGOM]: 177). Additionally, we documented species-specific variation in estimated tracking duration among foraging regions. Based on sensor data, within the Gulf of Mexico, across species, we estimated that 50% of tags began to foul after 83 95% CI (70–120) days. Conclusions The main factor that limited tracking duration was tag damage (i.e., fouling and/or antenna breakage). Turtles that spent most of their time in the Gulf of Mexico had shorter tracking durations than those in the Bahamas and Caribbean, with shortest durations observed in the NGOM. Additionally, tracking duration varied by species, likely as a result of behaviors that damage tags. This information will help researchers, tag companies, permitting agencies, and funders better predict expected tracking durations, improving study designs for imperiled marine turtles. Our results highlight the heterogeneity in telemetry device longevity, and we provide a framework for researchers to evaluate telemetry devices with respect to their study objectives.

Why do Argos satellite tags stop relaying data?

“…Diagnostic data provided strong evidence that battery exhaustion was the main reason why tags stopped relaying data in our study, echoing findings reported by some others (e.g., Hanson et al, 2013;Hofman et al, 2019). In contrast, Hart et al (2021) concluded that damage to their satellite tags was the main reason why data relay stopped. Based on the drop in tag battery voltage, Hart et al (2021) concluded that only 4.1% of their satellite tags attached to turtles stopped relaying data due to battery failure.…”

“…In contrast, Hart et al (2021) concluded that damage to their satellite tags was the main reason why data relay stopped. Based on the drop in tag battery voltage, Hart et al (2021) concluded that only 4.1% of their satellite tags attached to turtles stopped relaying data due to battery failure. However, since the batteries fail quickly, often direct information on the drop in battery voltage is not received via Argos, as we showed here, with the detection of the battery voltage drop being more frequent when more battery status diagnostic information was received.…”

Ecological Trap or Favorable Habitat? First Evidence That Immature Sea Turtles May Survive at Their Range-Limits in the North-East Atlantic

“…For two other individuals, biofouling was not indicative of tag failure, but the decrease in swimming speed might suggest that the turtles could have died due to cold-stunning in winter. The rapid growth of immature loggerhead turtles could also explain a premature tag detachment (Hays et al, 2021), leading to a shorter tag life (mean: 145 ± 152 days, range: 18-679 days) compared to other studies based on adult individuals, e.g., loggerheads retain 50% of their tags for 584 days (Hart et al, 2021). For future deployments, we recommend a careful battery management based on a severe duty cycling to extend tag life in immature individuals (Christiansen et al, 2016).…”

“…The algorithm accounted for the Argos quality to predict the daily locations using Argos error ellipses for the tags deployed after 2011, while the location classes (0, 1, 2, 3, A or B) were used for the remaining tags. Following Hays et al (2021) and Hart et al (2021), assessment of tag failure was conducted on the data available using the three following metrics: battery voltage, wet/dry switches and the number of Argos transmissions.…”

Loggerhead marine turtles (Caretta caretta) nesting at smaller sizes than expected in the Gulf of Mexico: Implications for turtle behavior, population dynamics, and conservation

“…We fitted platform terminal transmitters (PTTs; SPOT5, SPOT6, or SPLASH10; Wildlife Computers, Redmond, WA) to loggerhead females after they nested (n = 110 turtles), according to established protocols (NMFS-SEFSC, 2008) and methods outlined in Hart et al (2014Hart et al ( , 2018bHart et al ( , 2021; methods were approved by Institutional Animal Care and Use Committee Protocol (see Acknowledgments for more details). All tagged turtles were released within 2 hr at their capture location.…”