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

Abstract

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. KEY WORDS: Salinity · PAT tags · Wet/dry sensor · Geolocation · Atlantic tarpon Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 357: [101][102][103][104][105][106][107][108][109] 2008 poor, due to the relatively high turbidity of coastal ocean waters. In 2006, we initiated use of a new generation of MK-10 PAT tags, manufactured by Wildlife Computers (www.wildlifecomputers.com) and equipped with a wet/dry sensor. In the course of our studies, we noted some interesting features of the recorded wet/dry sensor values that we obtained from a recovered PAT tag (Fig. 1b). We suspected that the variations of wet/dry sensor values were related to the salinity of the coastal ocean environment that the tarpon experienced during movements and migrations. Therefore, we conducted an experiment to calibrate empirical wet/dry sensor values recorded by the tag and compared these to precise salinity measurements obtained from a CTD instrument. In this article, we present the results from those experiments and discuss the potential usefulness of the salinity measurements in both refining light-level geolocation estimates and defining habitat utilization patterns for coastal fishes. MATERIALS AND METHODS Pop-up archival transmitting (PAT) tag.The PAT tag is designed to be attached to a study animal via a tether (Fig. 2). It collects data during the deployment period, and then at a pre-set date and time it pops up (releases from the study animal) and transmits archived data via the Argos satellite system. The PAT tag used in the present study is a new product (MK10) from Wildlife Computers with a new wet/dry sensor, and detailed technical specifications for the tag can be found at www. wildlifecomputers.com. The new wet/dry sensor located at the base of the antenna provides 8-bit analogto-digital conversion for measuring resistance between the sensor and the base metal ring positioned below the float, which determines the wet and/or dry (i.e. in/out of water) status of the tag. Outputs rel...

Vertical movement rates and habitat use of Atlantic tarpon

“…1) facilitated physical recovery of 64 of 158 of our deployed tags (~41%), either by use of a handheld Argos AL-1 PTT Locator System (Com munications Specialists, www.com-spec.com) or by recovery by beach-goers who subsequently returned tags to us. With recovery of the PAT tag the entire archived database can be downloaded from the non-volatile memory to provide high-resolution datasets on depth, temperature, light-level, and wet -dry sensor values (RCS data, used to determine wet or dry status of the tag, and to estimate an approximate salinity following Luo et al 2008a). Ambient light intensity data recorded by PAT tags were first processed using software provided by the manufacturer (Hill & Braun 2001) to derive the initial estimates of geoposition (geographical location) of the tagged tarpon.…”

“…When the tag has 'popped up' and been recovered, the nonvolatile memory can be directly accessed and the entire database can be retrieved using an external power source (Luo et al 2008a).…”

“…An important coastal pelagic species suitable for use of these technologies is the Atlantic tarpon Megalops atlanticus (Ault 2008, Luo et al 2008a. Per haps one of the most storied sport fisheries, it contributes billions of dollars annually to regional USA economies -providing livelihoods to tens of thousands of Americans from Texas to Florida to Virginia (Ault 2008, Mill et al 2010.…”

“…PAT tag technologies are capable of recording accurate high-frequency measurements of ambient water temperature, depth (from pressure), light level, and salinity data that are monitored down to 1 s intervals throughout the period of deployment and stored in the instrument's non-volatile digital flash memory (Arnold & Dewar 2001, Luo et al 2008a. When the tag has 'popped up' and been recovered, the nonvolatile memory can be directly accessed and the entire database can be retrieved using an external power source (Luo et al 2008a).…”

Performance of pop-up satellite archival tags

“…Lutcavage et al 1999, Domeier et al 2005, Wilson et al 2005, residence times (Domeier 2006, Domeier & Nasby-Lucas 2008, and post-release mortality (Do meier et al 2003, Moyes et al 2006, Swimmer et al 2006) of teleost, elasmobranch, and sea turtle species. Refinement of lightbased geolocation methods , Domeier et al 2005, Wilson et al 2007, Galuardi et al 2008, Luo et al 2008) has en hanced the utility of PSATs in marine fisheries research.…”