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In the wild, abalone population has been
declining. One way of replenishing this is through stock enhancement in
marine reserves, sanctuaries or other protected areas. One way of
determining the activity’s success is by monitoring tagged abalones
after they are released in the wild. And therein lies the problem: the
lack of effective tagging or marking methods.
Ideally, tags used in stock enhancement
should be able to mark small individuals, detectable in other life
stages, is unique to the local population, and suitable for
identification of individuals from particular releases. Tags should also
be inexpensive to apply and detect, could be transmitted to subsequent
generations, should not harmful to the tagged abalone and people, and
acceptable to the public.
Wenresti Gallardo and his colleagues at
SEAFDEC/AQD studied the ways to meet the above-mentioned requirements.
While they have noted that tagging methods for abalone exist, these were
usually labor-intensive and either results in irritation to the abalone
or the loss of tags. One possible alternative to existing methods is
diet-tagging, an idea that came up when they saw green bands on abalone
that had been fed formulated feeds in the hatchery. Wild stocks do not
have such bands, and the only difference between wild and hatchery-held
abalone was their diets.
In their research, they fed abalone
juveniles daily with a SEAFDEC-formulated diet at 5% of body weight,
After three weeks, when a bluish-green shell band was observed, the
abalone were given Gracilaria bailinae for two months to produce the
normal brownish shell after the bluish-green band. The control setup was
fed only with liberal servings of G. bailinae. Abalone were then
stocked in outdoor tanks and in a marine reserve to observe any color
changes in the shells.
Eighteen months after, the researchers noted
that the bluish-green band in abalone fed formulated diets remained
distinct, and they could be distinguished from the seaweed-eating
abalone in both the outdoor tank and marine reserve habitats. This could
be due to the presence of pigments in some of the ingredients of the
formulated feed.
Diet-tagging is a step in the right
direction for researchers and stakeholders intent on determining the
success or failure of abalone stock enhancement efforts. Although it
could take some time, this method is perhaps the most painless procedure
for the abalone, who need the least amount of stress in their new
habitats.
Read more from the journal Aquaculture Research (2003)
34: 839-842.
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