167
13 Estimating Fish Production in the Itaipu Reservoir (Brazil): The Relationship Between Fish Trophic Guilds, Limnology …
producers (ii), and biomanipulation-induced reduction of
phosphorus (P) available to phytoplankton (iii).
Bell et al. (2003) conducted trophic cascade experiments
in experimental ponds over a period of 4 years. The results of
this study showed further development of phytoplankton related to the increase of piscivore biomass. The authors stress
that most studies, no matter if they are trophic cascade effect
experiments or not, are developed in short-term scale. The
authors emphasize that the result of experimental manipulations in ecology should depend on the duration of the experiment, and this factor is crucial to test the trophic cascade
hypothesis in lakes.
Mehner et al. (2005) compared the data of trophic (limnological) variables with the spatial and temporal distribution
of fishes, zooplankton, and phytoplankton. According to the
analysis (meta-analysis), the distribution of the studied trophic levels was correlated with the temperature of water and
nutrient concentration distributions.
13.1.3 Tropical and Subtropical Trophic
Cascades
According to Lazzaro et al. (2003), the dams in the semiarid northeastern region of Brazil offer excellent opportunities for theoretical comparisons on the relative importance
of the top-down and bottom-up impact structuring forces on
the fish-plankton interactions in tropical environments, including comparisons between the effects of the dominance
of omnivorous and low number of piscivorous species.
However, most of the dams have never been studied, except
for some large public ponds, especially those controlled by
DNOCS—Departamento Nacional de Obras Contra a Seca
(National Department of Works Against Droughts) in the
states of Ceará and Paraíba. Regional reports on fishery
yield, hydrochemistry, and limnology (e.g., Davies 1972;
Gesteira 1978; Silva 1981; Wright 1981; DNOCS 1990;
Molle 1991; Gurgel and Fernando 1994; Paiva et al. 1994;
Bouvy et al. 1998) were rare. The author points out that to
make generalizations it is more appropriate to use a comparative approach based on data from climatology, limnology,
and plankton communities and fish collected in the reservoir,
and studies correlating all these variables are in small number (Regier and Henderson 1980; Quiros 1990). Studies with
this type of approach can provide important practical and
social implications for predictive limnology (Peters 1986),
for the management of fishery yield (Schlesinger and Regier
1982) and/or water quality.
While studying 31 Argentinian reservoirs, Quirós and
Boveri (1999) have shown that in environments in which the
effect of piscivorous stock did not cause a depletion of zooplanktivores, the phytoplankton biomass reduced drastically.
The authors emphasized that human influence can cause
changes in trophic relationships in lakes and reservoirs.
Rejas et al. (2005) evaluated the top-down and bottom-up
effects in a floodplain lake in Bolivia. The authors found two
types of effects on the trophic cascade in experiments in mesocosms, and the effect of these relationships varied among
trophic levels. The effect of planktonic fishes did not show
any positive relationship with zooplankton, mainly with cladocerans, and phytoplankton showed bottom-up effect.
The objectives of this work were to evaluate the water
quality of the Itaipu Reservoir (central body and arms of the
left bank of the reservoir) through the analysis of physical,
chemical, and biological variables, given the multiple uses of
the reservoir during the period from 1999 to 2004; to analyze
the evolution of the trophic levels of the reservoir, including
its left margin arms, and characterize the trophic webs and
the relationship between the relative fish biomass, plankton,
and limnology of the Itaipu reservoir.
13.2 Materials and Methods
13.2.1 Characterization of the Study Area
The Paraná River is the tenth longest river in the world
(4,695 km), and was considered the most important hydrological system of the La Plata River Basin (Borghetti et al.
1988). It is formed by the confluence of the rivers Grande
and Parnaíba (center-south of Brazil), flowing into La Plata
River, north of Argentina (Agostinho and Gomes 2005). The
Paraná River Basin is responsible for more than 70 % of hydroelectric power production in Brazil, has the largest population density in South America and includes other major
rivers, such as the rivers Grande, Tietê, Parnaíba, Paranapanema, and Iguaçu, were approximately 130 dams were constructed (Fig. 13.1).
The Itaipu Reservoir, completed in October 1982, is located
in the Brazil-Paraguay border, between latitudes 24
o
05’S and
25
o
33’S and between longitudes 54
o
00’W and 54
o
37’W (Grw).
It has a surface of 1,350 km
2
in its mean elevation of operation
(220 m) and 1,460 km
2
when in maximum height (223 m). Of
these, 625 km
2
are part of Brazil and 835 km
2
of Paraguay. It
stretches over 151 km (170 km in maximum quote) and separates the cities of Guairá—Salto del Guayra and also Foz do
Iguaçu—Ciudad del Este (Agostinho et al. 1999).
With an average depth of 22 m, and possible depths of
170 m near the dam, the Itaipu reservoir accumulates as normal maximum volume, 29,109 m
3
of water. The residence
time in the main channel is 29 days and the speed of the
water can reach 0.6 m/s. The average residence time is,
however, 40 days. It operates with a maximum annual level
variation of 0.6 m (Itaipu Binacional 2006).
13 Estimating Fish Production in the Itaipu Reservoir (Brazil): The Relationship Between Fish Trophic Guilds, Limnology …
producers (ii), and biomanipulation-induced reduction of
phosphorus (P) available to phytoplankton (iii).
Bell et al. (2003) conducted trophic cascade experiments
in experimental ponds over a period of 4 years. The results of
this study showed further development of phytoplankton related to the increase of piscivore biomass. The authors stress
that most studies, no matter if they are trophic cascade effect
experiments or not, are developed in short-term scale. The
authors emphasize that the result of experimental manipulations in ecology should depend on the duration of the experiment, and this factor is crucial to test the trophic cascade
hypothesis in lakes.
Mehner et al. (2005) compared the data of trophic (limnological) variables with the spatial and temporal distribution
of fishes, zooplankton, and phytoplankton. According to the
analysis (meta-analysis), the distribution of the studied trophic levels was correlated with the temperature of water and
nutrient concentration distributions.
13.1.3 Tropical and Subtropical Trophic
Cascades
According to Lazzaro et al. (2003), the dams in the semiarid northeastern region of Brazil offer excellent opportunities for theoretical comparisons on the relative importance
of the top-down and bottom-up impact structuring forces on
the fish-plankton interactions in tropical environments, including comparisons between the effects of the dominance
of omnivorous and low number of piscivorous species.
However, most of the dams have never been studied, except
for some large public ponds, especially those controlled by
DNOCS—Departamento Nacional de Obras Contra a Seca
(National Department of Works Against Droughts) in the
states of Ceará and Paraíba. Regional reports on fishery
yield, hydrochemistry, and limnology (e.g., Davies 1972;
Gesteira 1978; Silva 1981; Wright 1981; DNOCS 1990;
Molle 1991; Gurgel and Fernando 1994; Paiva et al. 1994;
Bouvy et al. 1998) were rare. The author points out that to
make generalizations it is more appropriate to use a comparative approach based on data from climatology, limnology,
and plankton communities and fish collected in the reservoir,
and studies correlating all these variables are in small number (Regier and Henderson 1980; Quiros 1990). Studies with
this type of approach can provide important practical and
social implications for predictive limnology (Peters 1986),
for the management of fishery yield (Schlesinger and Regier
1982) and/or water quality.
While studying 31 Argentinian reservoirs, Quirós and
Boveri (1999) have shown that in environments in which the
effect of piscivorous stock did not cause a depletion of zooplanktivores, the phytoplankton biomass reduced drastically.
The authors emphasized that human influence can cause
changes in trophic relationships in lakes and reservoirs.
Rejas et al. (2005) evaluated the top-down and bottom-up
effects in a floodplain lake in Bolivia. The authors found two
types of effects on the trophic cascade in experiments in mesocosms, and the effect of these relationships varied among
trophic levels. The effect of planktonic fishes did not show
any positive relationship with zooplankton, mainly with cladocerans, and phytoplankton showed bottom-up effect.
The objectives of this work were to evaluate the water
quality of the Itaipu Reservoir (central body and arms of the
left bank of the reservoir) through the analysis of physical,
chemical, and biological variables, given the multiple uses of
the reservoir during the period from 1999 to 2004; to analyze
the evolution of the trophic levels of the reservoir, including
its left margin arms, and characterize the trophic webs and
the relationship between the relative fish biomass, plankton,
and limnology of the Itaipu reservoir.
13.2 Materials and Methods
13.2.1 Characterization of the Study Area
The Paraná River is the tenth longest river in the world
(4,695 km), and was considered the most important hydrological system of the La Plata River Basin (Borghetti et al.
1988). It is formed by the confluence of the rivers Grande
and Parnaíba (center-south of Brazil), flowing into La Plata
River, north of Argentina (Agostinho and Gomes 2005). The
Paraná River Basin is responsible for more than 70 % of hydroelectric power production in Brazil, has the largest population density in South America and includes other major
rivers, such as the rivers Grande, Tietê, Parnaíba, Paranapanema, and Iguaçu, were approximately 130 dams were constructed (Fig. 13.1).
The Itaipu Reservoir, completed in October 1982, is located
in the Brazil-Paraguay border, between latitudes 24
o
05’S and
25
o
33’S and between longitudes 54
o
00’W and 54
o
37’W (Grw).
It has a surface of 1,350 km
2
in its mean elevation of operation
(220 m) and 1,460 km
2
when in maximum height (223 m). Of
these, 625 km
2
are part of Brazil and 835 km
2
of Paraguay. It
stretches over 151 km (170 km in maximum quote) and separates the cities of Guairá—Salto del Guayra and also Foz do
Iguaçu—Ciudad del Este (Agostinho et al. 1999).
With an average depth of 22 m, and possible depths of
170 m near the dam, the Itaipu reservoir accumulates as normal maximum volume, 29,109 m
3
of water. The residence
time in the main channel is 29 days and the speed of the
water can reach 0.6 m/s. The average residence time is,
however, 40 days. It operates with a maximum annual level
variation of 0.6 m (Itaipu Binacional 2006).