1. Jaw tags: Researchers use these external tags, about the size of a quarter, to identify whether a fish has an internal tracker implanted in it. It’s usually fit onto a fish’s lower mandible.
2. Pop-up satellite archival tag: This external tag collects detailed data on fish vitals, location and environmental information, such as light levels.
3. Acoustic transmitter: Internal or external tag that’s ideal for tracking fish in deeper water. These transmitters produce a unique set of pings that get assigned to an individual fish. To collect data, researchers either go out in a vessel to pick up signals or download the information from receivers stationed in the fish’s environment.
4. Cinch tags: This type of external tag indicates the fish bearing it is part of a study and lists contact information for the agency monitoring it. If recreational fishers reel in a catch with a cinch tag, they should report it to the agency listed on the tag.
5. Large-scale model of coded wire: Unlike the model shown here, these internal tags have a true diameter similar to that of mechanical pencil lead. The wire comes on a spool and is lined with imprinted numbers. When a biologist cuts off a piece to make a tag, a unique serial number will be paired with a fish. To read this number, researchers need magnification equipment.
6. T-bar tags: External tags that come in a variety of colors. Similar to cinch tags, T-bars flag the fish as part of a study.
7. Radio telemetry tag: Internal tag for tracking fish in shallower waters. Researchers use an antenna, either handheld or secured beneath a plane or boat, to pick up the tag’s radio signal.
8. Visual Implant (VI) tags: Internal tags mixed with brightly colored biocompatible substances that researchers implant into translucent sections of a fish. While it’s possible to spot them with the naked eye, researchers typically need fluorescent light or magnification to see VI tags. Different colors can indicate details such as the year a fish was tagged for study.
9. Hydrostatic tags: Much like cinch tags, these external tags flag the fish as being part of a study.
10. Passive integrated transponder (PIT) tags: An internal tag that biologists must scan to activate. PITs relay data on fish growth rates and movement patterns to a receiver.
[This article originally appeared in print as "Tag, They're It."]