PSAT Tags

PSAT

Today let’s talk about PSATs, I’m not talking about the scholastic test you have to take to get into a program. I'm talking about the high tech tools we use to tag fish, elasmobranchs, and marine mammals.  If you caught our recent podcast feature on the CCA’s CCA CAL Podcast, you might have heard Jake briefly talking about PSAT tags. At the R/V Pilar we are already regularly tagging fish using spaghetti tags, but we would really love to be tagging swordfish with PSAT tags. With the timing of the podcast, and the tag’s importance to us, we thought it would be the perfect opportunity to talk about them in a little more depth.

What is a PSAT?

PSAT stands for Pop-up Satellite Archival Tag. As the name suggests these are devices that connect to satellites and transmit information, allowing researchers to collect data from the animal in real time as it surfaces. Compare these with the spaghetti tags we primarily use and it's easy to see the massive benefits of using a PSAT to collect data. A spaghetti tag is a small plastic tag with a serial number on it. While you are able to create a data point for an individual in a population, it doesn’t go much further than that unless someone else collects the same fish and you can see how it has grown and changed over time. A PSAT tag is constantly collecting data from the same fish and will continue to do so until the batteries are exhausted. PSAT tags allow you to see a much broader picture for an individual that you don’t get to see with some of the other types of tags. 

What kind of data do PSATs collect?

PSAT’s collect and record archival data as the animal goes about it’s life. Some of the environmental data it collects are pressure, water temperature, DO (dissolved oxygen), salinity, light, direction, speed, and location. Some tags have the ability to sense when significant events like random bursts of speed or rapid dives occur, and can adjust the frequency of its data collection. Researchers have the ability to determine what parameters they want to monitor and how frequently they want each of the parameters to be sampled. While PSAT’s allow researchers to access the data, thanks to the ARGOS satellite system, the tags themselves have the space necessary to store all the data. Once the tag pops back up to the surface the researchers are able to collect it and will have a hard copy of the data that is on the tag. 

What kind of animals do PSATs work best on?

PSAT’s are used in situations where it is hard to track an animal. A species can be hard to track for a variety of reasons, such as having a broad range, migration, fast swimmers, deep divers, species that stay at depth for long periods of time. Teleosts (bony fish), elasmobranchs (sharks and rays), and marine mammals (whales, dolphins, seals, etc.) are all groups of animals that fit the above criteria and are easily tracked with PSATs. Another criteria that it is important to think about for using a PSAT, is if the species is heavily fished. If it is, you run the risk of not being able to get the tag back. Here at the R/V Pilar a lot of our focus is on billfish, and because of their speed, extensive migrations, they make excellent candidates for PSATs. 

How do PSATs work?

Let’s say you just brought in a Blue Marlin, and have a PSAT you want to use. The tag will be secured to the fish by inserting a small anchor made of surgical grade material below the fish’s skin. An attachment strap made of monofilament loops around a metal pin (which is connected to a battery) and connects the tag to the anchor. At a preprogrammed date and time, the battery will turn on and the attached pin will dissolve allowing the pop-up part of the tag to float to the surface. Thanks to the attached battery, the tag can transmit its location for up to 2 weeks so the researchers can retrieve it.   

One of the exciting reasons to use a PSAT is because researchers are able to get data that is transmitted from the satellite, but this will only occur if the fish is close enough to the surface for transmission. 

Photo: Audun H. Rikardsen / Finn Økland.

What does a PSAT tag cost? 

You know that saying, you get what you pay for? Well that is definitely the case when it comes to tags. Spaghetti tags are extremely affordable, to the point they are given away at little to no cost, but as previously mentioned they only provide a quick snapshot of a fish’s life history. PSAT tags on the other hand, give you such a vast array of data about the fish and its life history, that you would expect it to have a larger price tag. DesertStar is one of the well known companies that makes some of these high tech tags and the cost per tag can vary a good bit, based on what you are looking to study. Their SeaTag is their flagship tag. It’s modular and reusable and the cost for a single one of these starts at $2,500.  But before you gasp in horror at that price, consider that this ARGOS tag can measure depth, temperature, acceleration, magnetic field (direction), location, light, has self controlled sampling abilities, and has enough storage for a century’s worth of 1 minute interval data samples. That tag may have more storage space than the computer I’m typing this article on.  Now the SeaTag is just one option from one of the companies making these types of tags. Several of the others, while they don’t have as many capabilities, have a lower price point which can decrease with quantity purchased. 

How long have PSATs been around?

PSATs have been around for nearly 3 decades. The first tag was introduced in 1997 by a company called Microwave Telemetry. The original PSAT was a bit different than the ones we look to use today. Initially, the tags were limited in the data they could collect. According to Juerg M Brunnschweiler’s article in the Journal of Ecosystem and Ecography, at the time the tags were “single-point, pop-up satellite tags with limited temperature data collection capability.” 

Are there any scientific studies that have used PSATs? 

Since these tags have been around since 1997, there have been numerous studies done utilizing them. While the tags themselves are very efficient, you might be surprised to learn that some of these studies take time. Tagging a fish and collecting the data is the easiest part, catching the fish is where things get hard. If you have ever spent time trying to catch billfish you know they can be elusive. 

To give you an idea of how tricky it can be, let’s take a look at the numbers of swordfish in this study, published in Fisheries Direct. For 7 years (from June 2014 to July 2021) there were only 26 individual swordfish captured. Of all the individuals captured, only 11 of them were able to be released with PSAT’s. That is a lot of work for a small dataset.  If you are interested in checking out some other studies that have utilized PSAT’s, check out these studies: 

An investigation into swordfish stock structure using satellite tag and release methods

Maximising the value of transmitted data from PSATs tracking marine fish: a case study on Atlantic bluefin tuna

THE ATLANTIC-WIDE RESEARCH PROGRAMME FOR BLUEFIN TUNA (GBYP Phase 12) Final report on tagging activities in the Celtic Seas Area

Why are PSAT tags important? 

So many of the species that we use PSAT tags to study, we know very little about because of the extreme aspects of their lifestyles. Tagging them allows us to study parts of their basic ecology we aren’t otherwise privy to. The more we can learn about them, what roles they play in their ecosystems, if they are resilient in the face of changing oceans, the better we are able to help make policies that will keep their populations sustained.