7937

• UCREFRP Catalog Number: 7937
• Author: Chart, T. E. and E. P. Bergerson.
• Title: Methods for Long-term Identification of Salmonids
• USFW Year: 1988.
• USFW - Doc Type: A Review.
• Copyright Material: NO

contribution of the hatchery stock (Stahl 1987). This
general review has dealt with the use of genetic mazks as
a means of delineating a population structure. Genetic
marking is also used to examine population mixing when
the structure is already known. (For a review of this aspect
of genetic mazking see Pellan and Milner 1987.)
Parasites
The presence of pazasites is sometimes used for iden-
tifying various groups or stocks offish and determining
fish movements and migration patterns (Sindermann
1961). Toward this end, pazasites have been investigated
in the Atlantic salmon (Pippy 1969a,1969b; Nyman and
Pippy 1972; Hare and Burt 1976) and in Pacific salmon
(Margolis 1956; Bailey and Margolis 1987).
Geography, like the trophic status of the lake and
other biotic variables, apparently influences the
chazacteristics of the parasite fauna. In a recent study of
the parasites of sockeye salmon from 15 Fraser River
lakes, statistical clusters of parasites were found
between lakes within biogeoclimatic zones and of
similar trophic status; however, overall there appeared
to be much overlap (Bailey and Margolis 1987).
No pazasite is 100% incident or exclusive within a
stock or depends entirely on host availability and
movement patterns. In addition, the parasite must be
present continually throughout the year and capable of
surviving fluctuating environmental conditions (Moring
and Fay 1984). This technique of stock identification
probably serves best as a secondary or backup method
to more reliable techniques. Moring and Fay (1984) and
Wydoski and Emery (1983) offered the following
advantages and disadvantages.
Advantages
1. Natural.
2. Applies to a large number of fish.
3. No time or cost to apply the tag.
Disadvantages
1. Requires much preliminary parasite survey data to
determine if identification of stocks is possible with the
parasite fauna present.
2. Requires the availability of technicians with a
knowledge of parasitology.
Conclusions
Moring and Fay (1984) reported that they believed
the CWT and fluorescent pigments were probably the
most promising techniques as judged by several
attributes (one of which was cost). Injecting fluorescent
pigments remains one of the least expensive methods to
mark fish; however, the problems of few permutations
and the relatively short retention times remain. From the
recent literature it would seem that the fluorescent
pigment tagging method has not greatly increased in
populazity over the last few yeazs. However, as with all
tagging methods, there remain situations for which
fluorescent pigment tagging is tailored, as well as
researchers who prefer this method.
The CWT program has certainly not declined during
the past few years, as evidenced by Northwest Marine
Technology's recent claim of 200 million tags implanted.
It is currently the marking method of choice in any
high-volume operation. With the advent of the flat tag
and the recently available X-ray detection equipment,
the CWT soon may be the standard mazking method for
ocean-going sahnonids worldwide.
The PIT tag has emerged on the tagging scene in the
past few years, and is still in the experimental stage. The
recently improved encapsulation material and process,
in addition to extensive baseline biological
investigations conducted by NMFS for the Bonneville
Power Administration, account for the increasing
attention this system has received. The costliness of this
system and the current size of the transponder may
prevent the PIT system from equaling the widespread
use of the CWT; however, the PIT system is sure to
become a common tool in the mazking of anadromous
salmonids in the future.
The various methods of stock identification reviewed
here have proven useful in recognizing discrete
populations of fish in several river systems throughout
the world. The degree of resolution associated with
these methods vazies with species and locale; however,
electrophoresis seems capable of routinely
distinguishing European and American stocks of
Atlantic salmon, thus providing the biologist with
another useful technique. As biochemical stock
identification advances (as in the vaziation of
mitochondrial DNA analysis), so should its application
to research on anadromous salmonids.
With recent advances in super-conductor
technology, new materials may soon be developed that
will benefit fish marking. Perhaps powerful new magnets
could be built that would be capable of extracting very
small metal tags (CWT'S?)directly from the fish without
serious injury or death. Perhaps smaller, more powerful
PIT tags will be developed. Satellite tracking of fish
stocks around the world may someday become
commonplace and the possibilities of applying genetic
engineering to fish stock marking seem endless.
Considering the tremendous worldwide investment
and importance of fishery resources and the potential
benefits from development of an effective, economical
marking technique, it would seem that anall-out effort
to develop the "perfect" tag would not be inappropriate.
Unfortunately, as in most reseazch, advances will come
in small increments, probably by individuals or small
groups of workers -and perhaps totally outside fishery
biology. Consequently it behooves all reseazchers to
remain aware of new developments in other disciplines
and to pursue any promising leads that develop.
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