Matching the Tag to the Program


Following is a brief description of the capability of the various NMT tags to satisfy some common requirements:

Individual Identification

Standard CWTs designate "batches" of specimens, (large numbers of specimens with the same code), so they are not used for individual identification. Anatomical location, as determined by Wand detection, can provide a limited numbers of unique codes (Tipping and Heinricher 1993).

Sequential CWTs are used to identify individuals or small batches.

VI Alpha - The alphanumeric code of these tags provides individual identification.

VIE tags are primarily used for "batch" identification but can provide individual identifications by varying locations and colors. For example, two marks per specimen, four colors and six locations could result in 420 unique codes. [See Visible Implant fluorescent Elastomer (VIE).]

External Visibility

Standard CWTs must be excised for the code to be read. Shallow implants into transparent tissue are visible (Oven and Blankenship 1993).

Sequential CWTs provide the same advantages as standard CWTs.

VI Alpha tags are externally visible.

VIE provide external visibility and can be observed by divers (Frederick), and from the surface in free swimming fish (Bonneau, et al. 1995).

Data Recovery from Live Specimens

Standard CWTs are normally dissected from dead fish, however they can be benignly removed from shallow implants (Oven and Blankenship 1993). Also, specific location (e.g., left cheek, right cheek, nape, origin of dorsal fin, etc.) of the implanted CWT, as determined by a Wand Detector, can provide a number of different "codes" (Tipping and Heinricher, 1993).

Sequential CWTs provide the same advantages as CWTs in this regard.

VI Alpha tags can be read in either live or otherwise intact specimens.

VIE tags provide the same advantages as VI Alpha but "reading" is simplified by fluorescence and absence of alphanumerics.

Specimen Size Limitations

Standard CWTs are highly versatile. They are available in various sizes for use in fish as small as newly hatched salmonids and, potentially, for creatures of unlimited size.

Sequential CWTs provide the same advantages as Standard tags except sequential CWTs are not available in half-length format.

VI Alpha tags have definite minimum size and species limitations. (See Visible Implant Alphanumeric tagging.)

VIE tags appear highly versatile in this regard.

Tagging Speed

Standard CWT - Sustained tagging rates of 800 per injector hour are typical for Mark IV production tagging of small salmon and striped bass. Tagging with a hand held multishot injector is about 50% as fast.

Sequential CWT - Similar to Standard CWT but the tag "filing" process (requiring saving the two tags located immediately before and after the individual or identified group) slows down the tagging process. This factor is maximized with individual identification and decreases with increasing group size.

VI Alpha - Sustained tagging rates of 200 per hour can be achieved with VI Alpha tags.

VIE - Sustained tagging rates of 600 tags/marks per hour are achieved with the air injection system, and hand injection is about 50% as fast.

Stock Assessment - Enhancement Evaluation

Standard CWTs offer very high potential for stock assessment. This has been demonstrated for Pacific salmon (Johnson 1990), New Zealand snapper Pagrus auratus (see description in under CWT References, Fishes, Sparidae - porgies), and red drum (Willis et al. 1995). New developments in magnetic detection equipment have increased the potential for automated recovery.

Sequential CWTs provide the same advantages as Standard tags for this purpose.

VI Alpha tags provide individual identification so are not recommended for stock assessment.

VIE - The high application and retention rates of VIE tags provide potential uses for stock assessment.

Voluntary Tag Recovery (See Data Recovery section)

Standard CWT - Adipose fin excision, of coded wire tagged salmonids, have provided a "flag" for tag returns for more than 20 years (Johnson 1990). This usually involves a reward system or qualification for such in a lottery. As demonstrated with paddlefish (Heinricher and Fiss 1996), voluntary recovery does not require a flag. In this case, incentives encourage fishers to return distal portions of all paddlefish rostra - the CWT target area - thereby providing more representative data relating to the occurrence of tagged fish.

Sequential CWTs provide the same advantages as standard tags in this regard.

VI Alpha - Blankenship and Tipping (1993) reported on the voluntary returns of tagged coastal cutthroat trout by anglers.

VIE - Although well suited, there are no known reports of voluntary recovery of VIE tagged specimens.

Systematic Sampling Recovery

Standard CWT - Pacific and Atlantic salmon sampling programs, (as well as those for other salmonids), have primarily involved the use of clipped adipose fins for collection of tagged heads/snouts (Johnson 1990). Tag recovery programs for striped bass, white seabass, lobster, paddlefish and others rely on hand operated magnetic detectors and tubes. The feasibility of automated recoveries from a herring fishery is described by Morrison (1990). The possibility of discontinuing the use of adipose clips for Pacific salmon tag recovery has led to the development of more efficient detectors better adapted to automated tag recovery of many species.

Sequential CWTs provide the same advantages as standard tags in this regard.

VI Alpha - Apart from the visibility of these tags, they provide no special features for recovery.

VIE tags are used with fluorescence enhancing light to identify stocks of adult chinook salmon tagged as yearlings. (See VIE References, Fishes, Salmonidae.)


Northwest Marine Technology, Inc
P.O. Box 427, Ben Nevis Loop Road, Shaw Island, Washington 98286
Telephone (360) 468-3375 Fax (360) 468-3844