A coded wire tag (CWT) is an animal tagging device, most often used for identifying batches of fish. It consists of a length of magnetized stainless steel wire 0.25 mm in diameter and typically 1.1 mm long. The tag is marked with rows of numbers denoting specific batch or individual codes. The tag is usually injected into the snout or

cheek The cheeks () constitute the area of the face below the eyes and between the nose and the left or right ear. ''Buccal'' means relating to the cheek. In humans, the region is innervated by the buccal nerve. The area between the inside of th ...

of a

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

so that it may be tracked for research or

fisheries management The management of fisheries is broadly defined as the set of tasks which guide vested parties and managers in the optimal use of aquatic renewable resources, primarily fish. According to the Food and Agriculture Organization of the United Nation ...

. Fish, crustaceans, insects, gastropods, and many other animals have been successfully tagged with Coded Wire Tags. The coded wire tag program in the Pacific Northwest has been described as the largest animal tagging program in history, with over 1 billion salmon tagged.

Data retrieval

The CWT is not visible once inside the fish; its presence is detected at close range by using a handheld wand or tunnel type detector that can sense the magnetized metal. A number code unique to either a group of fish or an individual fish is etched into the surface of the CWT, and to read the code the fish is killed first so that the tag can be removed and inspected under a

microscope A microscope () is a laboratory equipment, laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic ...

. Upon insertion, information about the fish such as hatching date, release date, location, species, sex, and length are recorded along with the corresponding tag code into a database, so that codes on recovered tags can be matched to information within that database. Coded wire tags have been used to research fish species from over 40 different families.Vander Haegen, G., Blankenship, H.L., Knutzen, D., McKenzie, J.R., Parsons, B., Seitz, A.C., Kopf, R.K., Mesa, M., Phelps, Q., 2011
Advances in coded wire tag technology: meeting changing fish management objectives
in: Advances in Fish Tagging and Marking Technology. American Fisheries Society, Symposium.

History

Coded wire tags were first introduced in the 1960s as an alternative to fin clipping. The first CWTs used colored stripes and allowed about 5000 different color combinations to uniquely identify groups of tags. The next development was binary codes marked on tags by electrical discharge machining in 1971. Binary codes allowed 250,000 unique code combinations. The sequential coded wire tag was introduced in 1985, which allowed tags with sequentially increasing numbers, or codes, to be cut from the same spool of wire, so that individual or small groups of fish could be uniquely identified. With advancements in laser technology, digits could be etched on tags, which caused the switch from binary to decimal codes. Currently, coded wire tags are marked using a decimal system, which is a row of numbers. The decimal system allows 1 million unique codes for batch tags, and 100,000 unique codes for individual sequential tags.Solomon, D.J., 2005.
Coded Wire Tag Project Manual
'.

Use

Salmon fry weighing less than 1 gram can be successfully tagged, and different sized tags are used depending on the length of the fish to be tagged. A small handheld injector is portable and can be used where small numbers of fish will be tagged. For large scale tagging projects, an automatic tag injector is used, which cuts and magnetizes the wire. In manual tagging, a juvenile fish's snout is pressed into a molded guide so that the tag will be positioned correctly and the tag is automatically injected by the machine. These automatic injectors can be integrated into a fully automated process inside of a mobile trailer called an AutoFish trailer, or "autotrailer", where fish are mechanically sorted,

adipose Adipose tissue (also known as body fat or simply fat) is a loose connective tissue composed mostly of adipocytes. It also contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, Blood vessel, vascular endothel ...

fin clipped, and tagged. Autotrailers do not require anesthetic or the fish to be removed from water. When fish are tagged, their tag code and other information such as release date and location are entered into a database. In the

Pacific Northwest The Pacific Northwest (PNW; ) is a geographic region in Western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Though no official boundary exists, the most common ...

, the Regional Mark Information System is used.

Applications

Coded wire tags are used to track groups or individual fish for research and fishery management purposes. Commonly tagged species are

coho COHO, short for Coherent Oscillator, is a technique used with radar systems based on the cavity magnetron to allow them to implement a moving target indicator display. Because the signals are only coherent when received, not transmitted, the concept ...

, chinook, steelhead, chum, sockeye, and pink salmon.Nandor, G.F., Longwill, J.R., Webb, D.L., 2010
Overview of the coded wire tag program in the Greater Pacific Region of North America
PNAMP Special Publication: Tagging, Telemetry and Marking Measures for Monitoring Fish Populations—A compendium of new and recent science for use in informing technique and decision modalities: Pacific Northwest Aquatic Monitoring Partnership Special Publication 2, 5–46. In

Alaska Alaska ( ) is a non-contiguous U.S. state on the northwest extremity of North America. Part of the Western United States region, it is one of the two non-contiguous U.S. states, alongside Hawaii. Alaska is also considered to be the north ...

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

, Washington,

Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...

, and

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

, the adipose fin is removed from CWT tagged salmon as a visual indicator of the presence of the tag. However, in Washington the adipose fin is removed from nearly all hatchery salmon in mass marking programs to distinguish them from wild fish. In order to study the impacts of mark selective fisheries, where marked hatchery salmon are selected by fisheries rather than unmarked wild fish, some fish receive what is called a double index tag. In double index tagging, some hatchery fish are tagged with a CWT but do not have their adipose fin clipped. This means that the adipose fin clip cannot always be depended on as an indicator that a tag is there, since some fish with adipose fin clips will not actually have tags, and some fish with intact adipose fins will have tags. In places where mass marking or double index tagging is practiced, an electronic detector such as a wand or tunnel must be used to determine if a tag is present so the snout can be dissected to read the tag. Electronic tag detection is used in Washington, Oregon, and Idaho. Alaska and California depend on the adipose fin clip to indicate the presence of a tag. Coded wire tags have also been used to track the diet of

piscivorous A piscivore () is a carnivorous animal that primarily eats fish. Fish were the diet of early tetrapod evolution (via water-bound amphibians during the Devonian period); insectivory came next; then in time, the more terrestrially adapted rept ...

birds, because when the head of a tagged fish is eaten, the tag passes through the bird's digestive system.Sebring, S.H., Ledgerwood, R.D., Morrow, M., Sandford, B.P., Evans, A., District, W.W., 2012
Detection of Passive Integrated Transponder (PIT) Tags on Piscivorous Avian Colonies in the Columbia River Basin
2011. Report of the National Marine Fisheries Service to the US Army Corps of Engineers, Portland District. CWTs have also been used in Japan.Ando, D., Nagata, M., Kitamura, T., Shinriki, Y., 2004
Evaluation of loss rate of coded-wire tags implanted into adipose eye tissue of masu salmon Oncorhynchus masou and effect on growth of tagged salmon
Fisheries Science 70, 524–526.

Sources

{{collective animal behaviour Fisheries science Wild animals identification Fish migrations Fisheries databases

Data retrieval

History

Use

Applications

See also

Sources