zooplankton species that was rare before elimination of the planktivores,
became abundant.
The use of
to eliminate fish in a reservoir may not be feasible
due to the large area to be treated, the possibility of damage to downstream
communities,
the possibility of reinvasion from upstream, and the use of water
for drinking.
According to Bennett
a dose of 1.0 mg
will produce
a-complete fish kill if applied when the weather is warm (water temperature
20" C or warmer).
No toxicity to fish should remain after 7 days, although
this must be checked by placing caged fish in the reservoir.
may not
be used in potable waters.
Water level
can be ver.y effective in restructuring fish
.
munities, as well as in eliminating certain species of macrophytes (see
Part IX).
Pierce, Frey, and Yaun (1963) and Lantz (1974) describe the
enhancement of piscivorous fish populations through drawdown.
Small fish are
trapped in vegetation and killed.
Forage-size bluegills, which are among the
planktivores,
decline conspicuously, apparently due to bass predation in the
remaining pool (Herman, Campbell, and Redmond 196.9; Bennett 1970).
Lantz
et al. (1964) report that winter
can remove gizzard shad
sunfish
when spring
and that summer
can prevent their spawning.
to 15" C has been used effectively to kill
water temperature reaches
Hulsey (1958) recommended that new reser-
common carp eggs (Shields 1958).
voirs have a deep channel or harvest basin that will support fish during
down.
Then, seining or use of
could take place without endangering
downstream fish communities.
Restocking of a reservoir must be done with the objectives of the reser-
voir users in mind.
Highly productive water bodies are usually ideal for
fishing, but often have low transparency, high algal biomass, and problems
associated with dense algae.
Fish stocking in a fishery reservoir should be
However, in those cases in which other
directed toward that activity.
of recreation are important, a drinking water supply is involved, or an
oxygen-free hypolimnion poses a problem, fish stocking to enhance zooplankton
grazing and stocking to reduce or eliminate nutrient recycling by fish such as
common carp or bullheads would be an important consideration.
The use of
planktivores such as shad as forage for game fish would be inconsistent with
an objective of high water transparency or potable water free of taste and
odor.
145
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