We realize that there is a lot of controversy over tagging sharks, you might be for or against using tags to capture data on sharks. So we thought we would enlighten everyone about the different types of tags and what they are used for. This article was written by Rachel Jacobson who is currently studying marine biology and sharks at Stony Brook University.
Observing sharks in their natural habitat is one of the best ways to learn about the species. While in the water with sharks, you can directly observe their behavior in their natural environment. But what you see while in the water with a shark may not be their natural behavior – sharks alter their behavior while being observed just as humans do. So how do we observe how sharks interact in their habitat while limiting the risk of changing their behavior?
Tagging is an important tool in learning shark behavior. Dart tags and PIT tags are easily to deploy and the data is easy to retrieve. Deploying dart tags is not strictly for scientists. Volunteers can also get in on the action and contribute to science.
Tags are an important tool used to study the behavior of sharks. Tagging sharks provides data ranging from movement to how deep a shark dives. Tags can last for a shark’s entire life or can be recovered after a specific amount of time. Regardless of what tag is used the information gained from tagging sharks is invaluable.
There are many different types of tags used in the study of sharks. They range from relatively inexpensive numbered tags that uniquely identify individual sharks to more expensive satellite tags that can track sharks in real time.
One of the simplest forms of tags is the dart tag, most commonly the National Marine Fisheries Service (NMFS) M-Type dart tag. This tag is made up of a dart head, a single piece of monofilament line, and a plexiglass capsule that contains an identification code and return instructions. These tags are simply used as a “name tag” for individual sharks. When a shark is caught recreationally, commercially, or for research it can be tagged with one of these identifying dart tags. Each tag has a corresponding card to gather data about the shark; date and location of capture, what gear was used to catch the shark, and the size and sex of the shark. After the shark has been tagged and the card is filled out, the card is returned to NMFS. Dart tags are placed at the base of the shark’s dorsal fin, in the muscle that runs along their back for a secure and long lasting fit, and are visible with the naked eye. If a shark is recaptured, the same data is recorded and the information is sent to NMFS where location and size of the shark can be compared to when it was caught previously.
This form of tagging is simple and relatively inexpensive. The tag is placed at the end of a thick needle that is pushed into the dorsal muscle of the shark. A dart tag is easy to see and easy to read for quick and lasting identification and as long as the tag remains intact, the shark can be identified for many years. Invaluable information can be gathered using dart tags such as including movement and migration, age and growth, population, and behavior.
On the other hand dart tags are strictly identification tags – there is no satellite or acoustic capability meaning that in order to gather information the shark needs to be recaptured. Dart tags are not appropriate for all sizes of sharks. If a shark is too small, the muscle may not be developed enough for the tag to remain for long periods of time. Also, the growth of small sharks and juvenile, or younger, sharks may be stunted by the use of dart tags which was observed by Doctors Manire and Gruber by comparing the growth of juvenile lemon sharks that were fitted with the dart tags to lemon sharks that were fitted with PIT tags.
One of the largest and oldest dart tagging programs for sharks is the NMFS Cooperative Shark Tagging Program (CSTP). This program began in 1962 with less than 100 volunteers and has now grown to many thousands. In addition to scientists and researchers volunteers include recreational anglers and commercial industries that are distributed along the Atlantic and Gulf coast of North America and Europe. NMFS supplies the tags to be used by those participating in the tagging program. Since 1962, over 243,000 sharks comprising 52 species have been tagged and 14,000 sharks comprising 33 species have been recaptured and data recorded. A shark can be tagged and not seen for years but the original data is kept for the shark for when the shark is recaptured. The record for the longest period of time a shark has gone without being reported to the CSTP was set by a sand bar shark that was at liberty for 27.8 years.
A passive integrated transponder (PIT) tag is another means of tagging and identifying sharks. A PIT tag may be familiar to many pet owners as it is the same technology used to microchip pets. PIT tags are similar to the dart tags in that they are only used for individual identification. Like dart tags, PIT tags consist of a small glass container with an identification code but instead of being outside the body PIT tags are inserted into the dorsal muscle of the shark. A scalpel is used to make a shallow incision nd a hollow needle loaded with the PIT tag is used to insert the tag into the dorsal muscle of the shark. PIT tags are read with a PIT tag reader that is used to scan the shark until it detects the chip and displays the identification number. PIT tags are often used by researchers conducting independent studies and the data is not forwarded to the NMFS.
PIT tags are small enough to be used on juvenile and small sharks as well as fish species and have not been found to stunt the growth of sharks as can dart tags. Since a PIT tag is read with a tag reader any shark recaptured is identified and the tag does not need to be removed. With the use of PIT tags, sharks can be tagged at a younger age making it possible to record data for a greater range of a shark’s life cycle.
A problem with PIT tags, like dart tags, is that a shark must be recaptured in order to collect data. There is also the possibility that the tag can fail.
One way to passively track sharks is through the use of a passive acoustic tag. These tags are cylindrical and come in a variety of sizes to fit the animal that is being tagged. Passive acoustic tags are surgically implanted in a shark’s abdominal cavity and give off an ultrasonic identification code unique to that shark. Placing the tags requires the capture of the shark and a quick surgical procedure that entails an approximately one inch incision and a suture. Once placed, acoustic tags can last months to years and will record data on a shark’s location which can be used to construct a movement pattern. The location of sharks is recorded by receivers placed in the study area. Receivers are laid out by researchers in a pattern that will cover as much area as possible. The receivers are placed on the sea floor through the use of moorings in the sand. When a shark comes into range of a receiver the receiver detects and records the unique identification code along with the date and time. Depending on the transmitter type, the detection radius of these receivers is up to one kilometer.
Acoustic tags can also be placed on the outside of a shark through the use of a dart tag and tagging gun. This method can be used on sharks that are free swimming and does not require the shark to be caught to implant the device. This method is used with great hammerheads as hammerheads stress easily and using a dart gun reduces the amount of stress.
This form of tagging allows a shark to be tracked and data recorded without the need for recapture.
On the other hand, the use of acoustic tags not only requires the capture of the shark but also a surgical procedure. Also, if the tag is on the outside of the shark, there is a risk of the tag becoming damaged or falling of prematurely.
A big name in the tag world is VEMCO. Many researchers and scientists use VEMCO tags in an array of studies of sharks and fish. As long as there is a VEMCO receiver in the area a transmitter can be recorded. This means that researchers can collaborate and communicate with one another to learn if any of their animals has traveled to a different area.
SPOT tags and PAT tags are both a type of satellite tag. Satellite tags are useful because, depending on the tag type, they can record more information and are not subject to receiver placement so information can be sent over a broader range.
SPOT tags, Smart Position or Temperature Transmitting tag, can give location estimates across the globe. These tags use radio transmissions to transmit data and must have contact with air to do so. Because of that these tags are attached to a shark’s dorsal fin so that data can be transmitted as the fin breaks the surface. This data is transmitted to the Argos satellite system, a system used to collect meteorological and oceanographic data as to track animals on land as well as at sea. The data collected can then be accessed through email, websites, or extracted from virtual globe systems like Google Earth. Because these tags are attached externally they are prone to damage and can be lost from the shark early if there is premature shedding of the skin.
PAT tags, Popup Archival Transmitting tag, record more than location. These tags record temperature, depth, and light intensity which gives a more in depth look at the activities of a shark while traveling. These tags are placed toward the back and to either side of the dorsal fin and are preprogramed with a specific date and time. On that date and at that time the tag will pop off the shark and float to the surface where it will transmit the information it gathered to the Argos satellite array. These tags store large volumes of data but summarize it to transmit to the satellite. If a researcher wants to download all the data they have to locate the tag on the surface and retrieve it which can be a difficult and time consuming task since the tag does not transmit its exact location.
PAT tags work best for sharks that travel long distances such as great whites. This is because the tags do not record specific location but instead record light intensity. Since day length changes with latitude and sunrise and sunset changes with longitude the general movement of the shark can be determined. Depth and temperature paint a picture of the daily behavior of the shark and temperature preferences respectively.
Satellite tags are very useful as they offer a wider range for tracking and can collect more data than just location.
Like some acoustic tags, there is the potential for the tag to become damaged or to release from the shark prematurely.
Regardless of the type of tag, any tag that is visible on a shark is at risk of being tampered with. Some photographers will cut off the tags from a shark so that the tags are not in a photo. This results in the loss of precious data that can further help protect sharks for years to come. Only a handful of sharks are tagged and these sharks serve as ambassadors for their species by giving researchers and scientist’s data on their movement and whereabouts allowing people to work towards better protection of sharks with legislation and understanding. I know many photographers who are excited when they are able to photograph a tagged sharks because they know that specific shark is giving valuable data to researchers. Some people see tags as a fault in the picture, they should be viewed as something amazing as you are able to photograph an animal that is contributing to science and the preservation of its species simply by living its daily life as it always does.
Tagging methods, both active and passive, allow for in depth study of individual sharks and the species as a whole. By learning about movement patterns it is possible to set protected areas to help preserve sharks and learn more about shark in their ecosystem. These simple tags deliver a wealth of information. So next time you see a tagged shark just think, “Right on shark, you are helping to advance the survival of your species!”
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