Tags are used to monitor, track and locate sharks in their natural habitat. Tagging provides scientists with important information on life histories, population sizes, movement and migratory patterns, all of which are important for shark conservation. Scientists also use tags to better understand growth rates, survivorship and food webs. Additionally, tagging can be used to identify key areas for protection, such as nurseries and mating grounds, and to better understand how climate change is impacting shark movement and distribution. They can also determine areas where sharks are more likely to encounter fishing activities. All of this data is critical for shark conservation and management.
There are several types of tags which range from simple numbered tags that identify sharks individually using a unique ID code to satellite tags that allow us to track the sharks in real time. Scientists use different tags depending on what species they are studying, the size of the shark, the sex of the shark and the questions they want to answer.
Read below to learn more about the various tags used.
PIT Tags (Passive Integrated Transponders)
These tags are very similar to those used by veterinarians for identifying household pets and for tracking livestock and zoo animals. A PIT tag is between 8-32mm long and 1-4mm in diameter, and consists of an electronic microchip encased in biocompatible glass, the glass protects the electronic components and prevents tissue irritation. PIT tags are inserted with a needle into the base of the dorsal fin with a PIT tag inserter ( similar to a syringe). They essentially act like a lifetime bar code; a social security number and provided they are scanned by a PIT tag reader when the shark is recaptured, they are as reliable as a fingerprint.
These tags were originally manufactured for livestock tagging but have been adapted for marine and wildlife studies. They are semi rectangular in shape and have an identification number on them. Once the shark has been caught, a Roto tag is applied with an applicator through a pre-punched hole in the dorsal fin. This identification number is added to a data base where it can easily accessed and used to identify the shark every time it is re-captured. There is an ID number on one side and either a phone number or email on the reverse side. This allows us who people might see or catch the shark to let the original researcher.
Dart tags or the National Marine Fisheries Service (NMFS)
M-Type dart tag are very simple tags made of a dart head, a single piece of mono filament and a capsule which contains an identification number and return instructions. Each tag has a data card on which data about the shark is documented; date and location of capture, size and sex and the method by which the shark was caught. Darts are placed at the base of the shark’s dorsal fin using a scalpel to make the small incision. The tag is placed into the muscle to ensure a long lasting fit.The data cards are sent back to NMFS where is the information is stored. When a shark is recaptured, the information is recorded again and sent to NMFS, the previous data is then compared to the new data, the size of the shark and location can be compared to when it was previously caught.
These tags are small battery-powered sensors that record acceleration in 1, 2 or 3 spatial axes. They can measure acceleration in the whole animal or a specific body part such as tail beats. You can think of these as 'Fit Bits' for sharks. By understanding movement, scientists can learn how sharks spend their day. Are they resting, avoiding predators or chasing lunch?
Acoustic transmitters are electronic tags that send out a series of ‘pings’ into the surrounding waters that are heard by underwater tracking systems (receivers). As sharks swim through a network of the receivers, which can detect a shark passing from 300-1000 meters away, their movement and behavior patters are revealed. Tags can either be surgically implanted into the abdomen or attached externally at the base of the dorsal fin. When the shark is released, the tag can be heard by any receiver in its range. They come in a variety of shapes and sizes and can last up to a decade. Some tags have added sensors that can collect environmental data such as water temperature and depth. The receivers are small data-logging computers that are anchored on the ocean floor that listen” for tagged sharks swimming close by. The tags transmit a ping every 1-3 minutes, when detected the tag’s unique ID number is stored with the date and time. This provides a record of each visit to that location by a tagged shark.
Pop-off Satellite Archival Tags
PSAT or PAT tags are constructed of several components; a data logger, a float, an antenna and a release section. The tag records temperature, light level, oxygen levels and pressure at specific intervals. This data provides insight on the the activities of a shark while it's traveling. They are placed on the dorsal fin and are pre-programmed with an activation and release date. On the release date they will pop off and float to the surface where they will begin transmitting the data to a satellite. From sea surface temperature and light level data it is possible to estimate the latitude and longitude and recreate the track of the shark. These tags can stay attached from 6 months to 2 years. They measure around 125 mm and must not weigh more than 3-5% of the total shark weight so as not to interfere with the sharks normal behavior.
Smart Position and Temperature Tag
SPOT tags are secured to the shark with plastic bolts and can stay on the shark for up to five years. They use radio transmission to transmit the shark’s location via satellite whenever the shark’s fin breaks the surface during a period in which a satellite is overhead. The tags are positioned on the top of the first dorsal fin to ensure contact with the air. There is a wet/dry sensor within the tag that senses when the shark’s fin is at the surface and out of the water. The satellite can then locate the location of the tag and send the detail to the researchers via email. This enables the researchers to receive daily updates on the shark’s movements. SPOT tags allow scientists to track the shark actively and more precisely.
VMS Virginia Institute of Marine Science. Dart and Roto tags.
Idaho Department of Fish and Game. History of PIT tags for fisheries studies. https://idfg.idaho.gov/blog/2017/01/clone-history-and-utility-passive-integrated-transponders-pit-tags-fisheries-studies
NOAA FISHERIES. Shark Tagging. https://swfsc.noaa.gov/textblock.aspx?Division=FRD&ParentMenuId=87&id=918
Using Accelerometers to Record Movement and Behavior in Aquatic Animals. https://biopixeloceans.org/whats-cracking-tracking/
Electronic Tags Review. http://www.himb.hawaii.edu/ReefPredator/Tools.htm