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Fish tagging programs are a vital part of a fishery manager's tools for assessing fish populations. Conducted properly, tagging can yield a wealth of information, including data about movement patterns, population structure, and mortality rates.

Tagging programs are usually designed by scientists, but any angler can contribute to this important research! The most important action that anglers can take to aid tagging programs is to return/report tags with important information about the tagged fish (Caught a Tagged Fish?).

Tags come in all shapes, sizes, and colors, from simple streamer tags to sophisticated — and expensive — pop-off archival tags. Here are some of the tags you may come across while you're fishing. Different tags are used for different species and to get different kinds of information.

Different kinds of streamer tags.
Different streamer tags T-bar tags, another kind of streamer tag

These long, thin tags that stick out of a fish's body are often referred to as dart and anchor tags, streamer tags, or spaghetti tags. These are the most commonly used tags because they are cheap and easy to apply. If you get involved with a volunteer-angler tagging program, these are probably the kind of tags you'll be putting on fish. The dart-like tip or the bar at the end are inserted into the muscle of the fish's body to secure the tag. Depending on the type of tag and where on the fish it is placed, the anchor can lock into place under or between bones to hold the tag more securely.

A tagged red drum, about to be released.
A tagged red drum, about to be released.

These tags have a unique number printed on them, along with the contact information of the tagging program. When a fish is first tagged, basic information, such as when and where it was tagged and its size at release, is recorded along with the tag number. When the fish is recaptured, scientists can use the tag number to match up the release information with the recapture information and learn how long the fish was at large, how far the fish traveled and how much it grew during that time period.

Disc tag on a horseshoe crab.
Disc tag on a horseshoe crab.
Tags need to interfere as little as possible with an animal's behavior. Tags are placed so they stay securely attached and don't add extra drag. For some animals, especially those with a shell like sea turtles and crabs, a streamer tag like those above is difficult to attach and will stick out at a weird angle. These disc tags lie flat against the body of the tagged animal and can be secured directly to the shell. This one has just been placed on a horseshoe crab, but they are used on fish as well. They include the same kind of information as a streamer tag: contact information, instructions, and a unique number.

Any tag that is attached to the outside of an animal is exposed to the wear and tear of the environment and thus can be damaged or lost. External tags can also affect an animal's behavior, especially in smaller fish, or cause injury by rubbing or tearing the flesh where it's attached. One solution to this problem is to use tags that are implanted under the fish's skin, like coded wire tags or visual implant tags.

A coded wire tag on a researcher's fingertip (left) and examples of visual implant tags (center, right).
Coded wire tagApplying a visual implant tagA visual implant tag

Coded wire tags are tiny pieces of metal with microscopic unique codes that are inserted into fish, usually in the snout. They are often used to tag hatchery-reared fish that are released as juveniles into the wild. The fish are very small themselves at this stage and couldn't handle an external tag. These fish may also have one or more fins clipped to distinguish them visibly from untagged fish, so that anglers know the fish has a coded wire tag, too. When the fish is recovered, researchers can remove the tag and read the number to find out when and where it was released.

Since coded wire tags aren't visible from the outside of the fish, they may be overlooked by anglers who recapture the fish. Visual implant tags are also implanted internally, but are placed very close to the surface so they are visible. Visual implant tags are made of a brightly colored plastic-like substance that is injected underneath the skin, usually near the eye of the fish. Some tags may have a number on them, but many are simply color-coded to represent the year or body of water they were released in. When they are recaptured, scientists know which "batch" of released fish they came from, but not which individual fish are returned.

An acoustic tag
Acoustic tag

These conventional tags only tell you where a fish was released and where it was caught. To get more detailed information on the movement patterns of a tagged fish, researchers turn to acoustic tags. These tags are implanted surgically into the fish, where they send out unique radio signals on a preprogramed frequency. Researchers set up an array of receivers in the area where the fish are tagged. These listening stations record the time and signal they receive. When the researchers retrieve the data, they can plot out where the fish went and even how fast it was travelling. This extra information comes with a price: acoustic tags are more expensive and difficult to deploy than conventional tags.

However, if the fish goes outside the array of listening stations, it essentially disappears, so acoustic tags are best for species that stay close to home. If researchers want to tag large pelagic fish that travel long distances, like tunas, billfish, and sharks, they can use an archival tag, which stores data on a computer chip inside the tag.

A pop-off satellite archival tag (PSAT)
Pop-off archival tag

An internal archival tag is implanted inside the fish (sometimes with a light-sensor sticking out). When the fish is caught again and the tag returned, researches can download the data to reconstruct where the fish has been. But some fish are rarely caught again once they've been tagged (for example, less than 2% of all billfish have been recaptured, and people have tagged thousands of them). For those fish, researchers can use a pop-off archival tag. These tags are attached outside the fish and take readings of environmental conditions like temperature, depth, and light level. After a specified amount of time - anywhere from a couple of days to several months - the tag pops off and floats to the surface. At the surface, it broadcasts the information it has collected to a satellite, and that satellite sends the information to the scientist's computer. These kinds of tags provide a lot of data about the movement and diving behavior of these rarely seen animals, but a single pop-off archival tag and the necessary satellite time cost thousands of dollars. Usually, these pop-off tags can be used only once; they're lost at sea once they've transmitted their information. However, they do occasionally wash back up on shore, so keep an eye out -- a scientist will be very happy to get that tag back. In addition to having a lot of data on it, the tag can be reprogrammed and used again.


For questions about fish tagging in freshwater, contact your state agency.
For additional information about tagging in marine waters contact Jeff Kipp at jkipp@asmfc.org