To better understand the behaviors and patterns of sharks in the oceans, scientists and conservationists will catch and tag sharks. These tags record or transmit information about how a shark lives. This in turn can help us better understand how to protect endangered species and ensure the survival of a vital part of most marine ecosystems.
How Are Sharks Caught for Tracking?
You might be wondering how sharks are selected and caught for tracking. First, you should know that this is a process that is designed to be as stress-free and quick as possible for the safety of the sharks. If a shark at any time seems too stressed to be tagged, they are released immediately.
Sharks are caught with bait and hooks that are specially designed to allow for the safety of the shark. A special line allows for sharks to continue to be able to swim in such a way that they can survive while they await being brought in. Special hooks that prevent deep hooking are used, and these make hook removal easy. Some shark species are cradled against the side of a boat for quick and stressless tagging. If a shark needs to be brought onboard, water pumps are used to keep it oxygenated and cool.
Everyone on board involved in the processes knows how to work fast so that the shark can return to the ocean safely as soon as possible. For shark species particularly prone to stress like hammerhead sharks, an abridged version of tagging is done to reduce the amount of time the shark is captive. The well-being of the shark always takes precedence over the collection of information.
What Are Sharks Tracked With?
There are a few ways sharks are tracked. Depending on the shark or the data being collected, different tags will be attached and used. These tags are either clipped to a shark’s dorsal fin or surgically attached to or inside of the shark. Some tags can even be attached via a dart so that the shark never has to be caught. Tags can be short-term or long-term and may have to be removed by eventual recapture or will be pre-programmed to pop off themselves at a given time.
Types of Shark Tags
There are two primary types of shark tags, transmitter tags, and data logging tags. Some tags are capable of both transmitting information and keeping a more detailed onboard log. Tags gather information not only about the track a shark takes in the ocean, but also about the water's depth or pressure, temperature, and light.
Transmitter tags use either sound waves or radio waves to relay information to receptors either in a nearby boat, underwater receiver stations, or satellites.
Acoustic pinger tags emit an ultrasonic ping that is picked up by a vessel equipped with a hydrophone. Don’t worry, the shark can’t hear the ping. The vessel can then follow the shark using the hydrophone to pick up the pinger signals. This is called active tracking and is used to follow sharks for a short amount of time physically.
Passive Acoustic Tag
A passive acoustic tag works the same as an acoustic pinger except that it is designed to work over months and years. Instead of a vessel, underwater receivers listen 24 hours every day for pings from passing tagged sharks. These receivers are stationed all along the ocean floor and have a receiving distance of about 1km. When a receiver records a ping, a unique ID is saved along with the time and any other data. The collected data from all these receivers can give a bigger picture of a shark’s movements over time.
Satellite tags are attached to the tip of a shark’s dorsal fin and relay information via radio waves every time the fin breaks the water’s surface. These tags are prone to damage, but they can relay information over a much larger area and do not require underwater receiver stations.
Data logging tags can collect more data over a long period than transmitter tags do. However, these tags have to be retrieved from the shark before the information can be downloaded, so recovery is not guaranteed.
Pop-up Archival Transmitting Tag
The most used datalogger encompasses elements from both types of tags. Pop-up archival transmitting tags or PATs, store data about the shark's environment and then at a preprogrammed time, detach and float to the water’s surface. Once they surface, some of the data can be uploaded to a satellite. If the device can be recovered, the entire onboard memory can be downloaded, and a much more detailed log can be gained.
Business Card Tags
Business card tags or BCTs are a newer form of tag that function as both a transmitter and receiver. Tags can swap information and ID codes with other tags that they pass. This can give information about inter-animal interactions.
pH dataloggers are more used as a way to get information about a shark’s feeding habits. These tags are inserted into a shark’s stomach and record changing acid levels over time.
Sharks are tracked to gather the information that helps researchers, scientists, and conservationists know how to preserve and protect them. There is no evidence that shark tagging causes any harm or behavior changes in the shark.
Tracking sharks gives information about the effectiveness of shark sanctuaries and protected areas, as well as insight into how to coordinate with fishing seasons and areas to protect sharks. Sharks may seem scary, but they are important to the health of our oceans and need to be preserved.