I recently watched The Meg with a few friends, a glorious two hours of huge sharks and Jason Statham one-liners. Though it may come as a surprise, the movie wasn’t all that realistic. Some suspension of disbelief is necessary, but one scene that stuck out to me was when Jason Statham used a dart gun to shoot a GPS tracking dart into the dorsal fin of the Meg.
Huge, blood-thirsty shark? Let’s get in the water and shoot it with a tracking dart!
This scene raised many questions for me. Aside from the more general questions like, “what’s this gun usually used for?” and “why’s it just lying around?”, I had some more technology-focused questions.
As someone who works in IoT, my first thought was “well that’s stupid, GPS signals don’t propagate well through water”. My second thought was, “ok well GPS could work if the Meg surfaces, but how would the device communicate? It could use satellite but that has relatively high power consumption so how long would that tracker last on battery?”. My third thought was, “I should write an article about this”.
And so here we are! Fortunately, we don’t have huge, prehistoric sharks to deal with, but we do have many sea and non-sea creatures that we’d like to track, made possible by the power of IoT. In this post I’ll be focusing on aquatic animal tracking since it has many benefits, unique challenges compared to terrestrial animal tracking and interesting IoT approaches to address those challenges.
Why Is Aquatic Animal Tracking Important?
To explain why aquatic tracking is important, you first need to understand what aquatic animal tracking means. When you hear “aquatic animal tracking”, you’re likely to think about it as pure tracking of movement and location (e.g. tracking the Meg with GPS in the above example). However, there are many other data types that are valuable to collect about aquatic animals and about the different environments in which the aquatic animals exist. In addition to location, this data includes temperature, pressure, heart rate, light/fluorescence, magnetic signatures, video and acceleration (among others).
Aquatic animal tracking is important because it enables us to collect invaluable data for scientific understanding, conservation efforts and ecological management. Aquatic animal tracking helps us save animals, save the planet and save ourselves.
To take measures to protect endangered species, we have to know that those species are endangered in the first place. Unlike terrestrial animals, aquatic animals move up and down in the water column and can, therefore, be difficult to locate and estimate populations. Once we’ve identified that a species is endangered, we need to understand how that species operates and how it fits into its ecosystem to design conservation approaches and marine protection areas to help.
Though conservation and protection are ends in themselves, it’s also in our self-interest. By collecting and disseminating animal population data more quickly, we can make management decisions to avoid overexploitation. This prevents us from fishing so much that we wipe out entire populations and don’t have any more fish to fish.
“One of the success stories of biologging came from two small villages in Baja Mexico, said Larry Crowder, a professor of biology at Hopkins Aquatic Station in Monterey, Calif. Crowder told a session at the meeting that tracking loggerhead turtles turned up some surprising information: Fishermen using long lines were unintentionally catching lots of loggerhead turtles.
‘As it turned out, the fishermen didn’t realize they were having a global-scale effect. They didn’t even know the turtles were endangered,’ Crowder said.
After the tags identified the problem, the scientists worked with the fishermen to find a solution: switching to hook-and-line fishing.
More good news is on the way for turtles: A month ago, the National Oceanographic and Atmospheric Administration designated 42,000 square miles (109,000 square kilometers) as critical habitat for pacific leatherbacks — habitat delineated and backed up by data from satellite tracking. “
In addition to gathering crucial insights about the aquatic animals themselves, aquatic animals can also serve as a global sensing system, enabling us to gather data from a variety of environments across the breadth and depth of Earth’s oceans.
Challenges for Aquatic Animal Tracking
There are clear benefits to aquatic animal tracking, but there are also unique challenges in aquatic environments. In terrestrial animal tracking, we can leverage GPS for location data and satellites for collecting that data over broad geographies. However, radio frequency signals don’t propagate well through water (particularly salt water) meaning that signals from both GPS and communications satellites are only useful very close to and above the ocean surface.
There’s also the matter of attaching a tag to a given animal. We’ve come a long way from the 1930s when “researchers used shotguns to shoot stainless steel tubes—bearing an identification number and promise of reward for return—into whales that could be recovered after the marine leviathans had been killed and processed for their blubber.” (‘Marine Skin’ Wearable Tracks Animals Under the Sea). However, many tracking mechanisms are still invasive (involving darts or implants).
Due to the size and weight of tracking devices, they can only be used on larger animals. This is true for terrestrial animal tracking too (think of attaching a tracking device to a small bird, it would make it pretty hard to fly!), but at least there are other methods to track terrestrial animals. Size and weight of devices is also a challenge for early life stages of larger animals, which may be important for understanding breeding and maturation.
IoT Approaches to Aquatic Animal Tracking
In the past, collecting data from tracking devices meant physically retrieving them. Now, global connectivity, cheap sensors, improved batteries and other advances are enabling us to track a greater number and wider variety of aquatic animals. IoT is a big part of this.
One of the most fundamental breakthroughs is that unlike in times past, researchers don’t necessarily have to catch a tagged animal a second time in order to gather all the data accumulated by a tag or tracking device that it’s bearing
For any given IoT solution, the underlying technologies and core features must be tailored to the needs and constraints of the specific use case. Although aquatic animal tracking has its own unique challenges, so too does every IoT application. Here are some of the ways in which aquatic animal tracking addresses its challenges:
To overcome the challenge of communicating in water, given that RF signals don’t propagate well through water, many aquatic animal tracking applications make use of acoustic relays. Acoustic tags attached to the animals being tracked emit acoustic signals (typically ultrasound) which travel through water much better than RF signals. These signals are then received by buoys, which can then use satellite communications to backhaul the data to where it’s needed.
This approach is quite similar in character to other IoT applications. Many IoT applications use one kind of connectivity for “the edge” to collect data from edge devices and then use either a hard connection or a different kind of connectivity to backhaul the data. For example, in agricultural settings, sensors may use a private low-power wide-area network like LoRa to send data to a gateway, then that gateway uses satellite connectivity to communicate data from all those sensors to the cloud.
In this case, the connectivity at the edge is ultrasound rather than LoRa and uses acoustic relays on buoys instead of LoRa gateways.
The acoustic relays can also be used as a positioning system, identifying the position of an animal in a defined space via time-delay-of-signal-arrival triangulation.
While acoustic relays can be invaluable in certain aquatic animal tracking applications, acoustic signals are very limited in range compared to RF signals. This means that many buoys would need to be deployed to cover a large area, which can be expensive and difficult to manage. Enter mobile transceivers:
“an impressive underwater technology called mobile transceiver, made by a company called Vemco. ‘It can be carried by larger animals, say seals, and basically, that seal is transmitting its whereabouts as it moves around the ocean, but any tagged fish or seal, any other tagged animal it encounters, it also records that,’ said Iverson.”
Though relatively new, this technology and approach could enable aquatic animal tracking across much greater geographies by leveraging the animals themselves as mobile tracking platforms.
Pop-up Satellite Tags
Another approach to overcome the challenges posed by limited RF signal propagation and constraints of acoustic relays, is the use of pop-up satellite tags. As the name would imply, after some period of time recording sensor data, the tag detaches itself from the animal and floats to the surface where it uses satellite connectivity to uplink the data stored on the tag.
This approach can be used in conjunction with mobile transceivers to collect data while the tagged animal moves through the ocean, then to get that data back to relevant parties without the need for physical retrieval or reliance on acoustic receivers.
While acoustic relays can help provide location data over time, mobile transceivers and pop-up satellite tags still face the limitation of GPS only being available at the surface. One way to overcome this challenge is to use light-based geolocation. While not as accurate as GPS, for migration patterns or general movement of animals across broad geographies, this can still be enough.
By using sensors on tags to record light data (and often temperature data to augment), we can use varying light levels over time to calculate longitude and latitude readings for the animal. However, this can prove difficult for animals that change depths and requires that the animals are in the photic zone. Light-based geolocation is typically best for terrestrial animals.