External Attached Tags
External tags may also be called: Dangling tags, T-bar anchor tags, Thread, Ribbon, Wire, Dart tags, Spaghetti tags, Colored Vinyl Tubing, Disc tags, Petersen disk, Atkins tags, Batchelor Buttons, Opercle tags, Jaw tags, Carlin tags and more.
External tags are one of the oldest and extensively used marking techniques. Tags may be as simple as colored yarn or thread or may contain additional printed information on disks, plates, or plastic tubing. Tags are most commonly attached through the dorsal musculature with stainless steel wire or nylon thread. Disks or plates are generally affixed flush with the body and may consist of a single plate fastened with wire or two disks held together by piercing the flesh or operculum. Dangling tags also commonly called anchor tags or Floy tags are usually attached to the fish by a nylon monofilament with a T-shaped anchor at the base of the dorsal fin. Dart tags are attached to fish by a sharpened plastic dart with a barb to prevent them from falling off. Jaw tags are metal tags which attach with a locking mechanism around part of the jaw of the fish with a special pair of pliers. They are commonly used for marking salmonid carcasses for escapement studies.
Advantages:
- Inexpensive, simple to produce, or widely available for purchase
- Tags are easy and fast to apply, involving only simple technology for the application and require minimal fish handling
- Tags are available for a large range of fish sizes and applicable to many fish species
- Easily detected and can contain reporting information to fishermen
- Numbered tags enable the identification of individual fish
- Tag retention time can be long, depending on the type of tag
Disadvantages:
- External tags may be difficult to apply to very small fish and may affect behavior of fish
- Tag retention rates may be variable depending on tag type, fish species and experience of the tagging personnel
- Tags may affect growth, health and survival due to penetration of the skin providing an access route for infections, and the continuous drag on the tag
- Tags may become unreadable as a result of algae, crustaceans or abrasion
- Return rates and accuracy of data are often dependent on voluntary recovery and reporting and does not provide information on period between release and recapture