Calibrating PSAT tridimensional acceleration data for the estimation of fish swimming speed and activity

Background Understanding marine species distribution and habitat use contributes to the development of effective population conservation and management. Data from biotelemetry can provide valuable insights on individual movement, behaviour and swimming speed. These data can link movement ecology and ecophysiology, thereby describing life strategies from a bioenergetic perspective. Technical limitations often constrain the use of biologgers over large spatial and temporal scales in free-ranging marine animals, hindering detailed examination of movements over seasonal or annual migrations, for instance. Pop-up Satellite Archival Tags (PSATs) equipped with triaxial accelerometers offer a promising solution to these challenges in aquatic animals by providing a platform recoverable at-sea to aid the collection and interpretation of high frequency, year-long accelerometry data. Results Using two approaches, this study calibrated the relationship between PSAT tridimensional tilt and speed of movement, while addressing potential limitations related to interpreting movement rates via PSAT accelerometry. First, we tested five PSATs under different attachment designs, attachment positions, and flow rates in a controlled calibration flume tank experiment. We found that properties of the tags and attachment had a minor effect except at no and low flow, and that an asymptotic model accurately described the relationship between tilt and flow speed. Second, we analysed field data from 43 tagged Atlantic halibut ( Hippoglossus hippoglossus ) and two stationary moored PSATs in the Gulf of St. Lawrence (Canada). We found that slow swim speeds up to a threshold of about 0.25 m s ^− 1 could not be distinguished from tag movement caused by ocean currents; however, above this threshold average swimming speed was related to halibut fork length. Conclusion This study validates the reliability of PSATs accelerometry data for estimating moderate and fast, but not slow swimming speeds, across long-term movements of halibut. Further research is needed to accurately characterize slow swimming speeds given variability in tag inclination even in the absence of movement, and confounding with water current-induced values. PSAT accelerometry offers prospects for investigating species distribution, life strategies and habitat selection from a bioenergetic perspective through an individual-focused approach for the wide diversity of aquatic taxa that can be equipped with PSATs.