Coded-Wire Tag Program
Coded-wire tag marking of fish by the Michigan Department of Natural Resources Fisheries Division began in the mid-1980s, and oversight of the program moved to the Charlevoix Fisheries Research Station around 1990. Since 1990, more than 15 million trout and salmon have been marked with adipose (Ad) fin clips and coded-wire tags, and more than 75,000 tags have been recovered to provide information critical to the successful management of these important fish populations. On the Great Lakes, coded-wire tag marking of salmon and trout has been used to:
- measure relative return of chinook salmon and steelhead stocked using different methods (net pen v. direct plant) and at different sites (upstream v. downstream, different ports)
- recommend distribution of chinook salmon
- determine movement patterns of lake trout
- measure differences in performance among steelhead strains
- provide known-age fish for a variety of management applications
- evaluate the success of the Atlantic salmon stocking program
- measure relative returns of chinook salmon stocked at different sizes and condition levels
Fish Marking Methods
Fish are marked at all Michigan Department of Natural Resources hatcheries, but most tagging occurs at the Platte River State Fish Hatchery and the Wolf Lake State Fish Hatchery. Marking usually takes place when the fish are fingerlings (3" long, within the first year of life), but sometimes fish are tagged as late as 1 year of age.
Fish are tagged using machines that inject a small piece of wire with an engraved code (coded-wire tag or CWT) into the fish's snout. At the same time fish are coded-wire tagged, they also have their adipose fin removed. This allows anglers and biologists to determine from a quick external examination whether or not the fish is carrying an internal tag. Following tagging, batches of fish are evaluated for fin clip quality and CWT retention, then released at stocking sites throughout the Great Lakes.
Coded-wire tags are collected using a variety of methods and assessment tools. Some of these methods provide proportional samples (vessel collections, weir collections, head-hunter collections, electrofishing, some commercial monitoring, others), whereas other assessments provide only "presence/absence"-type data (creel collections, volunteer returns, fish ladder collections, some commercial monitoring, beach surveys, others). For all methods, fish with missing adipose fins are subject to the following minimum procedures; identification of capture date and location, species identification, total length and weight measurement, fin clip identification. Once appropriate measurements are collected, the snout of adipose fin clipped fish is removed, behind the eyes. Identifying information is included with the biological sample (removed snout), and the sample is frozen until it is transferred to the Charlevoix Fisheries Research Station for processing.
Coded Wire Tag Extraction
All samples for CWT processing are sent to the Charlevoix Fisheries Research Station. Samples are thawed, and CWTs are detected within the snout or head of a salmon or trout with a "V-box detector" or a hand-held wand detector. The sample is serially bisected, and each half of the sample is scanned for the presence of a tag. The procedure is repeated until the tag is visible to the unaided eye; the tag is then removed from the sample using a magnetized "pen" or knife. Once the tag has been extracted, the "code" can be read under a high-magnification dissecting microscope, then entered along with other fish data into the CWT database. If the tag came from a sample returned by an angler, a letter is generated telling the cooperating angler the species, age and stocking location of the fish.
Coded Wire Tag Study Reports: