Johnson, 1990

Johnson, K. J. 1990. Regional overview of coded wire tagging of anadromous salmon and steelhead in northwest America. American Fisheries Society Symosium 7:782-816.

Coded wire microtags (CWTs) were introduced in the Pacific Northwest in the late 1960s as an alternative to fin clipping and external tags for identification of anadromous salmonids in the region, particularly those of hatchery origin. Coastwide use of CWTs quickly followed, and fisheries agencies in Alaska, British Columbia, Washington, Oregon, and California established ocean sampling and recovery programs. Now, 54 federal, provincial, state, tribal, and private entities release over 50 million salmonids with CWTs yearly. Regional coordination of these tagging programs is provided by the Regional Mark Processing Center operated by the Pacific States Marine Fisheries Commission. The ‘Mark Center’ also maintains a centralized database for coastwide CWT releases and recoveries, as well as for associated catch and sample data. CWT data are provided to users via interactive on-line data retrieval.
The coastwide CWT system proved successful and quite robust despite its piecemeal growth and dependence on cooperative support by all agencies. Not surprisingly, it also has a number of problems that reduce the CWT's effectiveness as a marking tool. Even so, the CWT has proved invaluable as a stock identification tool in marking salmonid hatchery stocks and, to a lesser extent, wild stocks.
Most of the CWT’s limitations have persisted from the beginning. These problems include the need for the establishment of standards for tagging levels, expanded use of replication, improved tag loss estimates, improved accuracy of counts of released fish, resolve under-sampling of fisheries and escapement, and the development of a sound statistical framework for computing the various CWT statistics and the uncertainty associated with those statistics.
There are also a few new problems, some which are major, that have arisen as a direct result of the advent of mass marking with the adipose clip and the subsequent introduction of mark selective fisheries. These new problems include lack of uniformity in electronic sampling, the need to estimate ‘imputed mortalities’ of unmarked DIT fish in mark selective fisheries, and the impact of blank wire on recovery agencies. All of these problems, both old and new, are reviewed, along with changes introduced by the Pacific Salmon Treaty.