Read more about this series here.

Marine tags are relatively unique in the biologging space. While there are many different technologies available for terrestrial telemetry studies as radio waves and satellites do not transmit through water, there are much fewer options when it comes to aquatic species. Weight is no longer the main consideration but rather drag. 

The other important factor for biologging marine species is how often the tag will be at the water's surface. Marine mammals or turtles or fish species that surface regularly often use tags which come equipped with a sensor for when the tag is out on the water and thus is safe to transmit data using radio or satellite waves. For other species different solutions are needed. 

I spoke with Lucy Hawkes and Jessica Rudd of the University of Exeter and Samantha Andrzejaczek with the Hopkins Marine Stations about their experiences with choosing tags for marine species to try to find out how researchers navigate these issues. 

Samantha Andrzejaczek’s biologging experience 

Samantha Andrzejaczek spoke to me first about her experience working with tags from Custom Animal Tracking Solutions (CATS) for her PhD. Her PhD looked into the Fine-scale movement of tiger sharks and sandbar sharks. For which she used CATS Diary and CATS Cam tags. 

The CATS Diary tag consists of a full tri-axial IMU (accelerometer, gyroscope and magnetometer) and light sensor with the option of adding GPS, pressure and temperature sensors. The CATS Cam tags are wireless video recorders that can be controlled by the Diary tags. This aspect of the tag meant that the tags were initially used as part of a documentary filming the interactions of tiger sharks with other animals.

These tags were chosen by the CEO of CATS who was very involved with the creation of the documentary and provided the tags they would use. Samantha was involved with deploying the tags for the documentary and worked closely with the CATS CEO. After the documentary was finished, the tags were donated to Samantha’s department for her to use during her PhD. 

This method is quite unusual as the first step of the project process was to get the tags. This meant that the project could be developed around what the tech was capable of as opposed to the tech being chosen around the projects. The tags could collect huge amounts of data using their different sensors, allowing in-situ measurements of animal trajectory and locomotion to be calculated. This data was used to publish a paper on the fine scale vertical and horizontal movements of tiger and sharks and the video was used to study the shark’s prey interactions. 

Photo credit: Alex Kydd

Since completing her PhD she has started working at Hopkins Marine Station which studies a number of shark species as part of a long term monitoring program which uses satellite tags for tracking multiple species. Speaking with Samantha about the types of tags she uses now, it appears that she uses a common tag type for studying marine species.

As far as studying marine species which do not surface regularly the generally accepted tag used is a PSAT or Pop-Up Satellite Archival Tags; a tag that determines location using the light levels of the ocean and the time of noon. After a predetermined length of time within the tags battery life it will “pop-up” off the animal and float to the surface and either transmit the data through satellites or simply alert the researcher that the tag is detached so it can be retrieved and the data manually collected. These are ideal for longer term studies as they can have a deployment length of multiple years. 

The company of choice for PSAT tags is Wildlife Computers. Although Samantha said that in her experience, there is no real difference between the different models of PSAT tags, Wildlife Computers are still used the most and are her preferred tag for her chosen study species of great white sharks. 

This is because they have an integrated data centre with their products so that the data can be uploaded and analysed within the same platform making understanding patterns across species easy. This is also the reason that they tend to be the more expensive options for tags.

“I usually just say we work with Wildlife Computers’ tags, and it’s nice because we deploy them all different kinds of animals and you analyse it in the same way so you can have the same workflow when working on different species, even though you might have the same questions or like you're thinking about it in a different way depending on the species.” - Samantha Andrzejaczek

Photo credit: Alex Kydd

Jessica Rudd's biologging experience

Jessica Rudd from the University of Exeter and her supervisor Lucy Hawkes seconded the idea about Wildlife Computers tags being the most widely used within marine species biologging. Jessica’s recent work had focused on the post release behaviour of bluefin tuna and with short term deployments of PSAT tags from Wildlife Computers. 

These tags have been very successful for her project as the multi sensor data was very useful in retrieving the depth and spatial data from the tag. Though with other collaborators she was also using acoustic transmitters to track multiple different species including basking sharks and tuna. Acoustic transmitters track marine species as a tag contains a unique sound which connects to an acoustic receiver on the ocean floor. 

Lucy Hawkes' biologging experience

Both Samantha and Jessica, as part of larger projects, had not been heavily involved with the decision making of their tags, so I spoke with Lucy Hawkes who as a senior researcher had experience with choosing biologging tech for the bluefin tuna among other marine and avian species. 

On choosing a tag, she said that often there are relatively limited tags for researchers to choose from and that the main way in which she had found tags for her projects was through word of mouth. 

“It's definitely that like Venn diagram of what tags could I use and there just often isn't that many options on the on the take away menu and then and then you often talk to others, you know from conferences or in your department or collaborators and say, did you ever use an ecotone tag and they go, Oh yeah, they're great. And you go. OK, thanks. Or it's often word of mouth. I think that does the vast majority of the work.” - Lucy Hawkes

In choosing the acoustic tags they would use as part of the bluefin tuna project. There were only two options: Innovasea tags and Thelma Biotel tags. In this case the decision was made as a part of the European Tracking Network to go with only acoustic tags  Thelma Biotel had a higher commitment towards data sharing which was important for the collective research interests. 

In terms of the actual technical process for deciding tags, when writing a project proposal, the researcher would need to have an idea of what type of biologger they were going to use and would reach out to the companies that supplied these tags to get an idea of price. Lucy said that in the study of birds and marine species there are usually only three or less companies which supply the tags so that allows for each one to be contacted individually. 

Biologgers are, generally speaking, very expensive with a single PSAT tag from Wildlife Computers costing over $5000. However, Lucy stressed to me that in fact biologging itself is what is expensive. With the cost to get licences, additional equipment, accessing boats, the staff to actually tag and the amount of time all these things take, the price of the tag is just seen as one part of the cost to do business. 

This also means that it is more important than ever that the tag works, which also explains the prevalence of Wildlife Computers in the space. Once a tag has been widely adopted by researchers it is seen as tried and tested and thus a good choice for studies.  

“You go to a fish tracking conference, you're gonna see Wildlife Computers, and then what are you gonna buy when, when you come to think of A tag, you think; a tag, a tag… Wildlife Computers…. But I think, that kind of product placement and making them be centred in the front of your mind is really important because I think that's a large part of how we choose stuff. Yeah. It's definitely that and I don't think price really comes into it.” - Lucy Hawkes 

This helps us get a greater picture of the biologging space and emphasises what we have seen earlier with how wider networks of researchers collaborate to help each other find technology solutions and the role that cost plays in choosing and deploying tags on marine species. 

Thank you to Samantha Andrzejaczek, Jessica Rudd and Lucy Hawkes for speaking to me about their experiences with finding and using marine tags for their studies. 

Look out for the next article in my series on biologging technology where we discuss developing custom technology for a koala tracking project!  

Banner photo credit: Abraham Sianipar