Why do Argos satellite tags stop relaying data?

Abstract

Satellite tracking of animals is very widespread across a range of marine, freshwater, and terrestrial taxa. Despite the high cost of tags and the advantages of long deployments, the reasons why tracking data from tags stop being received are rarely considered, but possibilities include shedding of the tag, damage to the tag (e.g., the aerial), biofouling, battery exhaustion, or animal mortality. We show how information relayed via satellite tags can be used to assess why tracking data stop being received. As a case study to illustrate general approaches that are broadly applicable across taxa, we examined data from Fastloc‐GPS Argos tags deployed between 2012 and 2019 on 78 sea turtles of two species, the green turtle ( Chelonia mydas ) and the hawksbill turtle ( Eretmochelys imbricata ). Tags transmitted for a mean of 267 days ( SD = 113 days, range: 26–687 days, median = 251 days). In 68 of 78 (87%) cases, battery failure was implicated as the reason why tracking data stopped being received. Some biofouling of the saltwater switches, which synchronize transmissions with surfacing, was evident in a few tags but never appeared to be the reason that data reception ceased. Objectively assessing why tags fail will direct improvements to tag design, setup, and deployment regardless of the study taxa. Assessing why satellite tags stop transmitting will also inform on the fate of tagged animals, for example, whether they are alive or dead at the end of the study, which may allow improved estimates of survival rates.

Global collision-risk hotspots of marine traffic and the world’s largest fish, the whale shark

“…To examine this possibility further we analyzed the final locations of all tracked whale sharks in relation to vessel densities. While transmitters can fail and cease transmitting for a number of reasons unrelated to mortality ( 32 , 33 ), we reasoned that normal technical failure or loss of satellite transmitters would 1) occur randomly along a shark’s trajectory rather than 2) being more frequently associated with areas of higher vessel activity. We tested both these possibilities (see Methods ) and found that the overlap of actual last locations of sharks within busiest routes (characterized as ≥90th percentile of unique vessel counts within grid cells; 31 vessels for the 2011 to 2014 annual mean) was greater than for randomly selected potential “last” locations ( n = 348 locations; overlap coefficient, OC = 0.065, P < 0.001, 95% CI: [0.041, 0.042]) ( Fig.…”

Social media mining and photo-identification detects the shift of long-term seasonal foraging habitat for a juvenile loggerhead sea turtle

“…Foraging site fidelity is either confirmed via traditional capturemark-recapture (CMR) methods using flipper tags and/or satellite tracking. The latter is typically able to detect site fidelity of relative short time periods, typically only up to couple of years, constrained by the limited duration of satellite tracking devices (Hays et al ., 2021). On the other hand traditional CMR studies on (neritic) foraging grounds are able to document individual histories spanning multiple decades (Rees et al ., 2013; Shimada et al ., 2020).…”

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.…”