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.)

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