Written by Dr. Michelle Heupel
I love gizmos. There are so many cool machines in the world now that make life more interesting and entertaining, and in science they let us do things we couldn’t even have dreamed of in the past. In this post I want to tell you about some of the cool tools that we can use to help learn about what sharks are doing.
This is my area of research and we have some of the best gizmos around. If we want to track the long-range movements of sharks the go-to gizmo is the satellite tag. This comes in two types. One that gives positions every time the shark comes to the surface and one that records data to send back to you later. Heather Marshall is using both of these tags if you’ve seen her posts. The first tag is one that you attach to the dorsal fin and has a small antenna on it. The unit has a sensor on it that tells it when it is out of the water and then it sends a signal to the satellites to say “here I am!”. Researchers use these tags on all kinds of animals, not just sharks, including turtles and marine mammals. The second satellite tag is what we call a pop-off tag. It looks like a microphone and gets attached to the back of the shark. This tag records the light level so it can tell when it is day or night, has a depth sensor to tell how deep the shark was swimming and a temperature sensor. It records data for a programmed time and then like the name suggests it pops itself off the shark, floats to the surface and sends back its data. These tags are usually programmed to record for up to a year. We can use the data from both of these tags to see how far a shark has moved and learn about their diving patterns.
John Tyminksi from Mote Marine Lab releasing a blacktip shark with a pop-off satellite tag off the coast of Florida.
If you want to track a shark that lives in a relatively small space then you can use passive acoustic tracking. This is mostly what I do. We put listening stations (or receivers) in our study sites. Then we go out and catch some sharks and put a transmitter in them. The transmitters send out an ID code for the shark and can also report temperature and depth. The receivers sit and listen for a shark to swim by and record the information from its transmitter. This way I can track where my sharks are for really long periods because acoustic transmitters can last for years, some of them last as long as 10 years.
The earliest tracking of sharks was done by active acoustic tracking where you attach a transmitter and then follow the shark in the boat with a hydrophone (an underwater microphone) for as long as possible. We still do this if we want to know detailed movements of sharks. It is hard work though and most people can only last a few days before the track is terminated. This means we only get short bits of information about movements of the individuals tracked. However, this method gives really detailed information about what the sharks are doing and in that respect is better than some of the other approaches depending on your research question.
Understanding how much energy it takes for a shark to swim or how often they really eat are difficult questions to answer. People have been thinking about these things for a long time. To test the energy needs of sharks we have to put them in a tank, make them swim against a current and then measure how much oxygen they use from the water. There are some new approaches coming though that might help answer some of these questions. Chris Lowe, (California State University Long Beach – look him up!) did an interesting study where he fitted a transmitter to the tail of a shark to see how many times the tail moved. Kind of like a pedometer you can buy to count how many steps you take, except for sharks. New transmitters are coming out that can tell us about the acceleration of sharks. This tells us when they make burst speed swimming movements or other behaviours. These tags have been used to look at nurse shark mating behaviour (Nick Whitney, Mote Marine Laboratory) and to look at energy needs of great white sharks (Jayson Semmens, University of Tasmania). Other researchers are trying to build transmitters that will tell us when sharks eat. All of these tools and toys tell us a little bit more about what sharks are doing out in the wild.
Technology keeps evolving and I have no doubt we will keep seeing cool new gadgets and gizmos not only in our daily lives, but also in the daily lives of sharks. We have so much more to learn and I can’t wait to see what the next set of gizmos can tell us.