-1
algal grazer, at a copper concentration of about 40
Cu
Concentration
well below that normally used for algal control..
Chelated copper algicides
are somewhat less toxic to Daphnia (Biesinger, Andrew, and Arthur 1974).
The
often observed "rebound" of algal biomass shortly after a copper treatment may
be due to mortality of herbivorous zooplankton.
Fish have been shown to be very significant in the regeneration of
nutrients from sediments to the water column.
The common carp
can
phosphorus to the water column of lakes at rates similar to
the external loading (La Marra 1975).
Similar findings have been made about
the brown bullhead
by Keen and Gagliardi (1981). Con-
trol or removal of these rough fish can improve water clarity by elimination
of their bottom-browsing activities and by lowering the rate at which phos-
phorus is recycled from sediments to water and then to algae.
Several fish management techniques can produce an improvement in the
trophic state of the reservoir.
The first step is to evaluate the reservoir,
as outlined in an earlier section, to establish the types of fish and
zooplankton and thus the likelihood that improvement through fish manipulation
The addition of piscivorous fish to control
fish may
can occur.
meet with limited success, if any (Bennett
but this idea has had little
study as far as trophic state improvement is concerned.
Rough fish removal by
seining has also met with little success, primarily because the technique is
labor intensive and very inefficient.
The use of rotenone, a fish poison, to eliminate all fish may be the
only feasible procedure to correct fish problems, as illustrated by the work
of Shapiro and Wright (1984). Round Lake, Minnesota, a small, shallow, nat-
ural lake, was treated with
to eliminate a fish community dominated
black crappie (Pomoxis
by planktivorous bluegill
nigromaculatus), and the benthivorous black bullhead
Fol-
lowing treatment, the piscivorous largemouth bass
and
walleye
were added, along with channel catfish
to control the reestablishment of the black bullhead, a
A
fish that can increase internal nutrient loading.
marked improvement in
transparency occurred.
Prior to
application, the mean summer Secchi
disc transparency was 2.1 m; in the two subsequent summers, it averaged 4.8 m
Daphnia pulex, a large-bodied herbivorous
and 4.7 m, respectively.
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