Pop-up satellite archival tags (PSATs) are used to track movements of (usually large, migratory) marine animals. A PSAT (also commonly referred to as a PAT tag) is an archival tag (or

data logger A data logger (also datalogger or data recorder) is an electronic device that records data over time or about location either with a built-in instrument or sensor or via external instruments and sensors. Increasingly, but not entirely, they a ...

) that is equipped with a means to transmit the collected data via the Argos satellite system. Though the data are physically stored on the tag, its major advantage is that it does not have to be physically retrieved like an archival tag for the

data Data ( , ) are a collection of discrete or continuous values that convey information, describing the quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted for ...

to be available making it a viable, fishery independent tool for animal behavior and migration studies. They have been used to track movements of

ocean sunfish The ocean sunfish (''Mola mola''), also known as the common mola, is one of the largest bony fish in the world. It is the type species of the genus ''Mola'', and one of five extant species in the family Molidae. It was once misidentified as th ...

marlin Marlins are fish from the family Istiophoridae, which includes between 9 and 11 species, depending on the taxonomic authority. Name The family's common name is thought to derive from their resemblance to a sailor's marlinspike. Taxonomy T ...

blue shark The blue shark (''Prionace glauca''), also known as the great blue shark, is a species of requiem shark, in the family Carcharhinidae and the only member of its genus which inhabits deep waters in the world's temperate and tropical oceans. Ave ...

bluefin tuna Bluefin tuna is a common name used to refer to several species of tuna of the genus ''Thunnus''. {{Animal common name Commercial fish Thunnus Fish common names ...

swordfish The swordfish (''Xiphias gladius''), also known as the broadbill in some countries, are large, highly migratory predatory fish characterized by a long, flat, pointed bill. They are the sole member of the Family (biology), family Xiphiidae. They ...

and

sea turtles Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. The seven existing species of sea turtles are the flatback, green, hawksbill, leatherback, loggerh ...

to name a few species. Location, depth, temperature, oxygen levels, and body movement data are used to answer questions about migratory patterns, seasonal feeding movements, daily habits, and survival after catch and release, for examples. A satellite tag is generally constructed of several components: a data-logging section, a release section, a float, and an antenna. The release sections include an energetically popped off release section or a corrosive pin that is actively corroded on a preset date or after a specified period of time. Some limitations of using satellite tags are their depth limitations (2000m), their costs ($499–$4000+), their vulnerability to loss by environmental issues (

biofouling Biofouling or biological fouling is the accumulation of microorganisms, plants, algae, or small animals where it is not wanted on surfaces such as ship and submarine hulls, devices such as water inlets, pipework, grates, ponds, and rivers that ...

), or premature release through ingestion by a

predator Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

. There are two methods of underwater

geolocation Geopositioning is the process of determining or estimating the geographic position of an object or a person. Geopositioning yields a set of Geographic coordinate system, geographic coordinates (such as latitude and longitude) in a given map datum ...

that PSATs employ. The first method is through light based geolocation which uses the length of the day and a noon time calculation to estimate the tags location while underwater. This method has a functional depth limitation of light penetration which can be as shallow as a few meters to upwards of hundreds of meters. Geolocation estimates based on light are usually coupled with additional satellite data like

sea surface temperature Sea surface temperature (or ocean surface temperature) is the ocean temperature, temperature of ocean water close to the surface. The exact meaning of ''surface'' varies in the literature and in practice. It is usually between and below the sea ...

or other available data input such as bathymetry, land avoidance, and physical limitations of the tagged animal. The other method available is through measuring ambient light and the

Earth's magnetic field Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from structure of Earth, Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from ...

. This method has a functional depth limitation equivalent of the maximum depth limitation, generally 1800m. Magnetic based geolocation is generally not coupled with additional satellite data or other inputs, and relies on the Earth magnetic field for latitude estimations and light (noon time) for longitude estimations.

General information

Pop-up satellite tags range in length from about and weigh 36-108 grams in air. A tag must be small compared to the size of the animal, anywhere from 3-5% of the total fish weight, so that it does not interfere with normal behavior. These tags record information such as temperature, magnetics, acceleration, light level, oxygen levels and pressure at set intervals of a few seconds to several hours. Data are often collected for several weeks or months, but with new advances in memory technology microSD cards tags can store data for centuries. PSATs record data in

non-volatile memory Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data. Non-volatile memory typ ...

so that data are retained even if the power source fails. When the PSAT releases from the animal on which it was attached, it floats to the surface, and begins to transmit data to the Argos satellites at a frequency of 401.65 MHz +/-. Therefore, the tag does not have to be physically recovered for the data to be obtained. Summarized data illustrating where the fish's migration started and ended is usually recovered from the tag within about seven days; however, tags can transmit significant amounts of oceanic data for months after they release from the fish. Limitations of PSAT technology are that it is subject to loss by malfunction of the power source, environmental effects such as biofouling, ingestion by a

, its depth limitation and cost. Most PSATS have internal

software Software consists of computer programs that instruct the Execution (computing), execution of a computer. Software also includes design documents and specifications. The history of software is closely tied to the development of digital comput ...

designed to detect damaging or sub-optimal conditions that will trigger an early release and transmission of data. For example, PSATs can withstand pressures to depths of depending on the model. If data indicate no change in pressure (depth) for a period of time, this could trigger an early release due to premature release (a tag pulling out of the fish early) or death of the animal to which it was attached. Such internal checks can alert researchers to unexpected or undesirable events. Ingestion by a predator is more difficult to detect in the sense of forcing a tag to report; however, in data processing it is indicated by an immediate loss of light and an increase in temperature that stabilizes while it is inside the predator.Kerstetter, DW, Polovina, JJ, Graves JE. Evidence of shark predation and scavenging on fishes equipped with pop-up satellite archival tags. Fish. Bull. 102:750–756 (2004).

Types

Using light level

The most popular method of determining an animal's location underwater requires the tag to acquire light levels throughout the day. Observing the length of the day, from when the tag observed the first light until the last light, the tag can determine its latitudinal location (with accuracy exceeding 1 degree). From the length of day the tag computes the noon time which is converted to a longitude location (with accuracy averaging about 0.5 degree or 30–50 nautical miles). This method of geolocation is suitable for animals that inhabit clear waters near the surface. At depths or in turbid waters, light based geolocation does not work as well due to light attenuation. It also does not work well during the equinoxes when the length of day is globally uniform. Manufacturers of this technology include Wildlife Computers, Microwave Telemetry, and Lotek Wireless. Star-Oddi is in the development phase of a pop-up satellite tag as well.

Using Earth’s magnetic field and light level

Another approach to geolocation couples light and magnetics. This method measures the total Earth's

magnetic field A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...

for latitude estimations while using light based noon time detection for longitude. These tags measure the Earth's magnetic field on their built-in magnetometers throughout the day and then take the average value as the tag's daily location. Average accuracy of this method is approximately 35 nautical miles. Manufacturers of this technology include Desert Star Systems.

References

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