Salinity measurements from pop-up archival transmitting (PAT) tags and their application to geolocation estimation for Atlantic tarpon

A new wet/dry sensor was developed by the satellite-based pop-up archival transmitting (PAT) tag manufacturer to determine the wet and dry status of a tag, designed to indicate whether or not to initiate uplink transmissions to overhead satellites to extend tag battery life. We discovered that the wet/dry sensor can also be used to measure the salinity of coastal waters after we recovered a PAT tag showing oscillating readings of wet/dry sensor values that mimicked tidal cycles. We conducted a calibration experiment on 6 PAT tags to evaluate the stability, resolution, and accuracy of the sensor to obtain salinity measurements. Our results indicated that the wet/dry sensor was stable, and the resolution and accuracy of the sensor were good at low salinities (<20 psu), but relatively poor at high salinities. We then provide an example showing how the salinity information can be used to improve geolocation estimation for a large coastal marine fish, the Atlantic tarpon Megalops atlanticus.