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A significant portion of CWT use is concentrated in
<br />Pacific coast salmon research (25 million tags per year
<br />as quoted in a Northwest Marine Technology 1987
<br />Newsletter). Coded wire tagging is also more organized
<br />and closely monitored in this Fishery than anywhere else
<br />in the world. The Pacific Marine Fisheries Commission
<br />has taken on the responsibility of coordinating the
<br />returns as they are reported. Due to the volume and
<br />variety of tags and codes being released and
<br />subsequently returned (500,000 CWT's have been
<br />recovered to date) and the number of governmental and
<br />private agencies currently involved, data processing has
<br />understandably been delayed.
<br />The logistics of coordinating a CWT recovery program
<br />for the Atlantic salmon fishery are complicated by the
<br />comparativelywide-ranging habitat of the species and the
<br />many nations involved. Coded wire tags are currently
<br />implanted in Atlantic salmon as a means of identifying the
<br />country of origin of salmon caught on the high seas.
<br />However, the basic reason for tagging salmon has varied
<br />through the years, resulting in a reduction of the data base
<br />needed to evaluate long-term tag retention and return
<br />information (Victor Segarich, personal communication).
<br />Researchers at the Salmon Genetic Research Group
<br />reported using CWT's with various other external tagging
<br />methods, such as pheasant wing tags and a newly
<br />developed form of tattooing or panjed marking (Atlantic
<br />Salmon Federation 1985-1986). The consensus of
<br />Atlantic salmon researchers is that the CWT program will
<br />expand in the future. Because fewer Atlantic salmon (in
<br />comparison with Pacific salmon} are produced and
<br />tagged annually, the initial cost of the tagging and
<br />decoding equipment has delayed the large-scale use of
<br />CWT systems by Atlantic salmon researchers.
<br />Coded wire tags have also been used to identify stocks
<br />of cyprinids, ictalurids, and percids (Northwest Marine
<br />Technology 1987 Newsletter). Klar and Parker (1986),
<br />who compared the usefulness of CWT's and
<br />microtaggants in marking fingerling striped bass (Morone
<br />saxatilu), reported 100% tag retention when CWT's were
<br />implanted in the cephalic portion of the adductor
<br />mandibularis (a small muscle below the eye) and superior
<br />overall results compared to those with microtaggants.
<br />Although the passive integrated transponder tagging
<br />system is considered state of the art, the flat CWT and
<br />ray technology should not be considered far behind.
<br />Id fact, the CWT system will probably continue to be the
<br />ost widely used technique due to its lower long-term
<br />c ~ st per tagged fish.
<br />Passive Integrated Transponders
<br />(PI'1~ Tags
<br />Implantable transponders were first used in the early
<br />1970's to identify livestock, specifically horses. Today,
<br />Destron Identification Devices Inc., Boulder, CO,
<br />markets the tags and decoding equipment, which have
<br />been used to mark and identify not only livestock, but
<br />artwork, machinery, and (for the last several years) fish.
<br />Much of the information presented in the following
<br />review of this tagging system was obtained from three
<br />sources:
<br />1. Documentation provided by Destron Identification
<br />Devices Inc.
<br />2. Victor Segarich, U.S. Fish and Wildlife Service,
<br />Nashua National Fish Hatchery, Nashua, NH.
<br />3. Annual reports prepared by the National Marine
<br />Fisheries Service (NMFS) for the Bonneville Power
<br />Authority, currently investigating the potential of PIT
<br />tags for use in research on anadromous salmonids.
<br />The reader is advised to refer to these reports
<br />(Prentice and Park 1984; Prentice et a1.1985, 1986) for
<br />a detailed review of various aspects of baseline
<br />biological testing with regard to these tags.
<br />The PIT tag is inert, consists of a microchip and an-
<br />tenna,and is 12 mm long x 2.1 mm wide. It was original-
<br />ly encapsulated in polypropylene, which unfortunately
<br />permitted moisture to enter and foul the electronic cir-
<br />cuiitry, causing an unacceptable failure rate in early tags
<br />(P'rentice et al. 1986). Today the tags are encapsulated
<br />in glass, which apparently remedied the moisture
<br />problem. The tags or transponders are implanted in the
<br />bc-dy cavity with a modified hypodermic syringe and 12-
<br />ga,uge needle or semi-automatic tag injector. Once ac-
<br />tivated, the tag emits a low frequency radio signal (40-
<br />50~ kHz), which is translated into a 10-digit alphanumeric
<br />code (there are 34 billion possible codes). The tag is
<br />decoded in vivo, which eliminates handling of both
<br />tagged and nontagged fish. Since there is no self-con-
<br />taiined energy source, the tag's lifetime is indefinite.
<br />Passive Integrated Transponders are currently being
<br />tested in juvenile and adult salmonids in the Pacific
<br />Northwest (Prentice and Park 1984; Prentice et a1.1985,
<br />1986) and on a smaller scale in adult Atlantic salmon at
<br />the Nashua National Fish Hatchery.
<br />From 1983 to 1985, NMFS researchers in Seattle,
<br />WA, experimented with various anatomical locations
<br />for PIT tag implantation. Dummy (nonfunctional) PIT
<br />tal;s were injected into the body cavity, opercular region,
<br />and the dorsal and caudal musculature of juvenile
<br />salmonids. Adult salmonids were also tested for
<br />injection in the nose. The body cavity was chosen as the
<br />best anatomical site for implantation for all life stages.
<br />Passive Integrated Transponders implanted in the body
<br />cavity of adult Atlantic salmon were not as easily
<br />decoded as those implanted in the nose; however,
<br />glaiss-encapsulated tags seemingly can be read easily
<br />while in the body cavity (Earl Prentice, personal
<br />co:mmunication). Further testing with the dummy tags
<br />and subsequent work with functional tags (Prentice et
<br />a1.1985, 1986) yielded the following guidelines for body
<br />ca~~ity implantations:
<br />
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