Implications of location accuracy and data volume for home range estimation and fine-scale movement analysis: comparing Argos and Fastloc-GPS tracking data

The advent of Fastloc-GPS is helping to transform marine animal tracking by allowing the collection of high-quality location data for species that surface only briefly. We show how the improved location accuracy of Fastloc-GPS compared to Argos tracking is expected to lead to far more accurate home range estimates, particularly for animals moving over the scale of a few km. We reach this conclusion using simulated data and home range estimates derived from empirical tracking data for green sea turtles (Chelonia mydas) equipped with Argos linked Fastloc-GPS tags at three different foraging areas (western Indian Ocean, Western Australia, and Caribbean). Poor-quality Argos locations (e.g., location classes A, B) produced home range estimates ranging from 10 to 100 times larger than those derived from Fastloc-GPS data, whereas high-quality Argos locations (location classes 1–3) produced home range estimates that were generally comparable to those derived from Fastloc-GPS data. However, the limited number of Argos class 1–3 locations obtained for all three turtles—an average of 14.6 times more Fastloc-GPS locations were obtained compared to Argos class 1–3 locations—resulted in blurred patterns of space use. In contrast, the high volume of Fastloc-GPS locations revealed fine-scale movements in striking detail (i.e., use of discrete patches separated by just a few 100 m). We recommend careful consideration of the effects of location accuracy and data volume when developing sampling regimes for marine tracking studies and make recommendations regarding how sampling can be standardized to facilitate meaningful spatial and temporal comparisons of space use.