Fisheries Management and Ecology, 2001, 8, 173±186
Factors determining the structure of ®sh
1 communities in Pantanal lagoons (MS, Brazil)
8
 AREZ
Y. R. SU
UEMS/Unidade de Ivinhema, Ivinhema ± MS, Brazil
M. PETRERE Jr
UNESP ± Departamento de Ecologia, Rio Claro ± SP, Brazil
A. C. CATELLA
Embrapa/Pantanal, Corumba ± MS, Brazil
Abstract The ®sh communities of lagoons in the NhecolaÃndia Pantanal were studied to
determine the factors which are responsible for the composition and abundance of species.
Fishes were collected in 19 lagoons during August 1997, after their isolation from the
River Negro, using beach seines (15 ´ 1.5 m; 2 mm mesh). A total of 51 species were
collected. In the lagoons, or in parts with dense macrophytes, a screened box trap was used.
Fishing was also accomplished with hooks of several sizes. Species richness was estimated
by the jack-knife procedure, after adjustment to the log-normal distribution and with von
Bertalan€y's equation (asymptotic). The most important factors in the community
organization were macrophyte cover, piscivore abundance and depth of the lagoons. The
role of these habitats in the Pantanal ecosystem was discussed.
KEYWORDS:
Brazil, ®sh communities, ¯oodplains, lagoons, Pantanal.
Introduction
Floodplain environments are highly productive and support important inland ®shing
activities (Goulding 1980; Bayley & Petrere 1989). They are spawning grounds and nursery
grounds for many ®shes, as a result of the diversity of habitats, supplying food and shelter
against predators (Goulding 1979; Lowe-McConnell 1987).
Pantanal is an alluvial plain in the centre of South America, with a ¯oodplain of about
140 000 km2 (Alho, Lacher Jr. & GoncËalves 1988). There is a diversi®ed ¯ora and fauna,
in the varied aquatic habitats such as rivers, intermittent creeks, lagoons and swamps
(MouraÄo 1989). The ¯ooding pattern is of fundamental importance for the ichthyofauna
of the Pantanal. The area and residence time of water in the surrounding lands determines
habitat availability and the food of the ®shes, thus a€ecting their abundance (Catella
1992).
Correspondence: Yzel R. SuÂarez, UEMS/IVINHEMA, Av. Brasil no. 679, Centro. CEP 79.740±000, Ivinhema
(MS), Brazil (e-mail: [email protected])
Ó 2001 Blackwell Science Ltd
173
174
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Y. R. SU
Although the importance of ®sh in this ecosystem is well recognized, few studies have
attempted to characterize the ®sh communities and to elucidate the processes responsible
for their composition and abundance (Catella 1992; Catella & Petrere 1996). The
objectives of this paper were to:
± establish whether ®sh species composition and abundance are determined by the `species
pool' in the lagoons during the connection period or if the characteristics of these
lagoons in¯uence this organization;
± which are the most important factors that determine the distribution and abundance of
the ®sh species;
± using presence/absence data and the cumulative increase of species as a function of the
number of lagoons sampled, what would be the total richness of species in the lagoons of
the Pantanal of NhecolaÃndia area.
Materials and methods
A total of 19 lagoons were sampled during August 1997, in the Pantanal of NhecolaÃndia,
CorumbaÂ, MS (Fig. 1). These lagoons are visited by aquatic birds for shelter and mainly
for feeding in the dry season. At least 32 species out of the 656 of all bird species listed for
the Pantanal, feed exclusively upon ®sh (Coutinho, Campos, MouraÄo & Mauro 1997). The
area of the lagoons studied ranges from 179 to 44 178 m2, with depth from 0.3 to 2 m and
distance from River Negro from 0.1 to 34 km. Macrophyte cover varied from 1 to 97% of
the lagoon area and the river isolation varied from 2 to 13 weeks.
A trap specially developed to catch ®sh in areas covered with aquatic macrophytes was
used for sampling. The trap consisted of two 2-m long, 1-m wide and 1-m deep rectangular
iron frames, with the bottom and sides of the trap covered with a 2-mm mesh mosquito
screen. For ®sh sampling the trap was manoeuvred under the vegetation in a collapsed
state, with the side walls folded under the upper frame. Soon after, the upper frame was
lifted quickly above the surface, trapping ®sh in the box thus formed. In areas without or
with little vegetation, a 15 ´ 1.5 m, 2-mm mesh beach seine and ®shhooks of di€erent sizes
were used. Fishes were identi®ed according to Britski, Silimon & Lopes (1999).
The lagoons were grouped using the simple matching coecient (presence/absence of
species) and the Morisita±Horn index based on percentage abundance (Krebs 1999), to
verify similarities on composition and abundance of ®sh species.
The simple matching coecient (SSM) is expressed as:
SSM ˆ …a ‡ b†=…a ‡ b ‡ c ‡ d†
where a is the number of common species in lagoons A and B; b, the number of species in
lagoon B but not in lagoon A; c, the number of species in lagoon A but not in lagoon B
and d, number of species absent in both lagoons
The Morisita±Horn index (Cij) is expressed as:
,
!
n
X
X X
2
2
2
2
Xki ; Xkj
Xkj Nj Ni Nj
Xki =Ni ‡
Cij ˆ
k
Ó 2001 Blackwell Science Ltd, Fisheries Management and Ecology 2001, 8, 173±186
FISH COMMUNITIES IN PANTANAL LAGOONS
175
Figure 1. Location of the study area: NhecolaÃndia Pantanal in Mato Grosso do Sul State, Brazil. Shaded area
represents extent of Negro River high inundation ¯oodplain.
where Xki, Xkj are the number of individuals of species k in lagoons i and j; Ni, the total
number of individuals in lagoon i; Nj, total number of individuals in lagoon j.
The simple matching coecient was used because it is sensitive to double absences.
Once the lagoons are connected, any ®sh will decide in which lagoon it will remain. A
given species may also not choose either of the two lagoons if none is suitable. They were
also grouped by their characteristics (depth, area, distance from the main river,
macrophyte covering, piscivore abundance in weight and isolation time) using the Bray±
Curtis' coecient, as a metric and the unweighted pair group method average (UPGMA)
as the clustering method. The cophenetic coecient of correlation was calculated in order
to assess the appropriateness of the dendrograms.
The Bray±Curtis coecient (B) is expressed as:
X
. X
Yij ÿ Yik …Yij ‡ Yik †
Bˆ
Ó 2001 Blackwell Science Ltd, Fisheries Management and Ecology 2001, 8, 173±186
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 AREZ ET AL.
Y. R. SU
where Yij is the lagoon characteristic i in lagoon j; Yik, the lagoon characteristic i in
lagoon k.
Similarity matrices were compared using the Mantel test (Mantel 1967). Species
richness was estimated by the jack-knife procedure (Heltshe & Forrester 1983) and by
®tting the log-normal distribution (Krebs 1999).
The lagoons were randomized generating 50 groups of one, two, ¼, 19 lagoons, to
calculate the asymptote richness. The average richness, for each of the 50 randomizations,
was plotted as cumulative richness as a function of the number of sampled lagoons.
These results were adjusted to the von Bertalan€y growth equation, using an algorithm
of non-linear regression.
The species frequency of occurrence (FO) was calculated according to:
FO ˆ …Number of lagoons with the species i = Number of lagoons† 100
If FO is ³ 50%, the species is termed a primary species; if 25% £ FO £ 50%, the species is
termed a secondary species; if FO £ 25%, the species is termed an incidental species.
The relative abundance of the 14 primary species and the already mentioned
characteristics of the lagoons were used in the communities ordering through Canonical
Correspondence Analysis (CCA). CCA scatterplots describe the ecological associations
between the samples and species along an environmental gradient (Jongman, Ter Braak &
Van Tongeren 1995). A Monte Carlo simulation procedure was also performed (1000
permutations) to test the statistical signi®cance of the variable e€ects in the observed
distribution (Manly 1994).
Results
Characiformes was the most represented order by number, weight and number of
species. However, its dominance was less accentuated in a number of species (Table 1).
A total of 30 662 individuals were recorded representing 51 species (Table 2). The ®ve
most abundant species represented 86% of all individuals collected. The Characidae
family represented 92% of the individuals. Of these, Odontostilbe calliura represented
59.7% of the individuals, followed by Psellogrammus kennedyi (11.1%). There are more
incidental species (51%) than primary species (27%) and secondary species (22%). Of
the 51 species, 14 occurred in one lagoon and 6 occurred in two lagoons. This
community mainly consists of adults of small sized ®sh species and not by juveniles of
large sized species.
Table 1. Relative number of species (RNSP), relative abundance by number (RANI) and relative abundance
weight (RAWT) for the ®sh orders in 19 lagoons of the NhecolaÃndia Pantanal, August 1997
Order
RNSP
RANI
RAWT
Characiformes
Siluriformes
Perciformes
Synbranchiformes
54.90
29.41
13.72
1.97
96.47
0.85
2.64
0.04
82.26
5.71
11.80
0.23
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FISH COMMUNITIES IN PANTANAL LAGOONS
177
Table 2. List of species and their respective number of individuals, weight (g) and frequency of occurrence (FO)
sampled in 19 lagoons of the NhecolaÃndia Pantanal, August 1997
8 Species
Characiformes
Characidae
Aphyocharax anisitsi
Astyanax bimaculatus
Acestrorhynchus pantaneiro
Aphyocharax paraguayensis
A. rathbuni
Bryconamericus exodon
Characidium a€. zebra
Gymnocorymbus ternetzi
Hyphessobrycon eques
Holoshestes pequira
Hemigrammus ulreyi
Metynnis maculatus
M. mola
Markiana nigripinnis
Moenkhausia sanctae-®lomena
Odontostilbe calliura
O. microdon
Psellogrammus kennedyi
Piaractus mesopotamicus
Pygocentrus nattereri
Roeboides paranensis
Serrasalmus spilopleura
Triportheus nematurus
Curimatidae
Curimatopsis myersi
Erythrinidae
Erythrinus erythrinus
Hoplias malabaricus
Authorities
Number
Eigenmann & Kennedy
Linnaeus
Menezes
Eigenmann
Eigenmann
Eigenmann
Eigenmann
Boulenger
Steindachner
Steindachner
Boulenger
Kner
Eigenmann & Kennedy
Perugia
Steindachner
Boulenger
Eigenmann
Eigenmann
Rolmberg
Kner
Pignalberi
Kner
Kner
1621
971
11
822
4
1849
59
319
37
2
6
4
2
17
549
18 293
63
3412
±
±
9
2
70
Vari
Schneider
Bloch
4
Weight (g)
641.65
2285.9
45.52
115.53
1.07
566.57
15.87
476.42
15.38
13.18
0.51
2.3
10.3
278.39
357.85
2008.93
8.72
1974.28
±
±
5.93
11.92
149.38
FO (%)
94.73
73.68
26.31
89.47
10.52
68.42
36.84
52.63
31.57
5.26
5.26
10.52
10.52
36.84
42.1
100
5.26
78.94
5.26
10.52
5.26
5.26
36.84
27.1
15.78
1
143
0.47
419.41
5.26
84.21
1292
372.57
89.47
Lebiasinidae
Pyrrhulina australis
Eigenmann & Kennedy
Rivulidae
Rivulus punctatus
Boulenger
8
0.71
21.05
Perciformes
Cichlidae
Apistogramma borellii
Aequidens plagiozonatus
Bujurquina vittata
Cichlassoma dimerus
Crenicichla edithae
Gymnogeophagus balzanii
Regan
Kullander
Heckel
Heckel
Ploeg
Perugia
200
368
44
6
25
1
37.77
781.22
252.37
74.02
90.48
16.87
73.68
78.94
36.84
15.78
57.89
5.26
Ó 2001 Blackwell Science Ltd, Fisheries Management and Ecology 2001, 8, 173±186
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 AREZ ET AL.
Y. R. SU
Table 2. (Continued)
8 Species
Siluriformes
Aspredinidae
Amaralia hypsiura
Auchenipteridae
Parauchenipterus striatulus
Authorities
Weight (g)
FO (%)
Kner
1
0.02
5.26
Steindachner
8
229.97
26.31
157
2
16
3
13.2
56.5
32.76
55.13
68.42
5.26
31.57
10.52
8
7.9
10.52
41
2
79.97
0.21
36.84
5.26
1
4
2
95.53
5.14
7.06
5.26
5.26
10.52
12
15.03
26.31
4
1
8.12
0.34
15.78
5.26
10
27.44
21.05
Callichthyidae
Corydoras hastatus
Hoplosternum littorale
Hoplosternum pectorale
H. personatus
Eigenmann & Eigenmann
Hancock
Boulenger
Ranzani
Doradidae
Anadoras weddellii
Castelnau
Hypopomidae
Hypopomus sp. 1
Hypopomus sp. 2
Loricariidae
Lyposarcus anisitsi
Hypostomus sp.
Loricariithys platymetopon
Number
Eigenmann & Kennedy
IsbruÈcker & Nijsen
Gymnotidae
Gymnotus gr. carapo
Linnaeus
Sternopygidae
Eigenmannia trilineata
E. virescens
Lopez & Castello
Valenciennes
Synbranchiformes
Synbranchidae
Synbranchus marmoratus
Bloch
Lagoons were more similar in the composition of species when a quantitative coecient
was used (Fig. 2; cophenetic correlation r ˆ 89.9; P < 0.01) than when a simple matching
coecient was used (Fig. 3; cophenetic correlation r ˆ 92.7; P < 0.01). Using the
Morisita±Horn coecient, six of the 19 lagoons studied (B. Anhuma 2, B. Sede,
B. PocËo, B. Anhuma 1, B. Logrador, B. Alegria) were similar in the abundance of the species,
a pattern that does not occur with the coecient of simple matching. The lack of grouping
of the two similarity coecients was veri®ed by the Mantel test (r ˆ 0.103; P ˆ 0.29).
The Mantel test showed that there was no correlation between the similarity among
species abundance of the communities (Morisita±Horn) and the geographical distance
(km) between the lagoons (r ˆ 0.073; P ˆ 0.37). However, signi®cant correlation existed
between the similarity matrix calculated with the species abundance in lagoons and the
matrix of their physical characteristics (r ˆ )0.293; P ˆ 0.008). Closer lagoons tended to
be more similar in species composition (simple matching) (r ˆ 0.470; P < 0.001), but the
Ó 2001 Blackwell Science Ltd, Fisheries Management and Ecology 2001, 8, 173±186
FISH COMMUNITIES IN PANTANAL LAGOONS
179
Figure 2. Similarity dendrogram (Morisita±Horn) of the ®sh communities in the 19 lagoons studied at the
NhecolaÃndia Pantanal, August 1997.
Figure 3. Similarity dendrogram (simple matching) of the ®sh communities in the 19 lagoons studied at the
NhecolaÃndia Pantanal, August 1997.
Ó 2001 Blackwell Science Ltd, Fisheries Management and Ecology 2001, 8, 173±186
180
 AREZ ET AL.
Y. R. SU
similarity among the lagoons based on physical characteristics does not in¯uence the
composition of species (r ˆ )0.088; P ˆ 0.23).
At the level of 60% similarity the lagoons separated into 4 groups using the Morisita±
Horn coecient (Fig. 2), while for the coecient of simple matching the ponds were divided
into 11 groups, with 9 groups represented by just a single lagoon (Fig. 3). The higher the
number of ®sh species in lagoons the lower the similarity in species composition (Fig. 3).
The estimated species richness for lagoons of the NhecolaÃndia Pantanal as ®tted by
log-normal distribution was of 63 species. With the jack-knife the estimated richness was
64 species (CI (0.05%): 56±71). The asymptotic richness, estimated by von Bertalan€y's
equation was 50 species (CI (0.05%): 48±52) (Fig. 4), according to:
Richness ˆ 50:44‰1 ÿ exp…ÿ0:224† …number of lagoons†Š:
The ®rst three axes of the CCA explained 40.2% of the variation of the species abundance.
The ®rst axis explained 23.5% of the variation based on macrophyte cover and piscivore
abundance. The second axis was associated mainly with lagoon depth and it explained
9.9% of the variation. The third axis explained 6.8% of variation and it was associated
with lagoon area (Fig. 5; Table 3). Monte Carlo simulation showed that only axes 1 and 3
were signi®cant.
Discussion
The ichthyofauna of South American rivers is characterized by the dominance of
Characiformes over Siluriformes (Lowe-McConnell 1987; Agostinho 1993). However, in
lagoons and dams this dominance is intense (Cordiviola de Yuan 1980; Bonetto, RoldaÂn &
VeroÂn 1981; Castro & Arcifa 1987; VerõÂ ssimo 1994; Okada 1995). VerõÂ ssimo (1994),
studying the icthyofauna of lagoons of the ¯oodplain of the Parana river attributed this to
Figure 4. Mean number of species as a function of the number of lagoons sampled in the NhecolaÃndia Pantanal.
Ó 2001 Blackwell Science Ltd, Fisheries Management and Ecology 2001, 8, 173±186
FISH COMMUNITIES IN PANTANAL LAGOONS
181
Figure 5. Scatterplot of the ®rst two axis of the Canonical Correspondence Analysis of the ®sh species in the
NhecolaÃndia Pantanal lagoons. The arrows indicate the importance of the environmental variables.
Table 3. Canonical Correspondence Analysis (CCA) for the ®sh communities in the lagoons of the NhecolaÃndia
Pantanal, August 1997
Axis 1
Axis 2
Axis 3
Canonical coecients for the standardized variables
Macrophyte cover (%)
Depth
Lagoon area
Piscivores (%)
River distance
Isolation time
)0.339
0.062
)0.280
0.275
)0.327
)0.109
0.250
)0.213
)0.034
0.462
0.171
)0.013
)0.220
)0.316
)0.317
)0.428
)0.125
0.028
Correlation among groups of variables
Macrophyte cover (%)
Depth
Lagoon area
Piscivores (%)
River distance
Isolation time
)0.697
0.163
)0.329
0.599
)0.489
)0.396
0.170
)0.472
)0.303
0.403
0.303
0.092
)0.038
)0.440
)0.508
)0.251
0.101
0.241
Statistical summary for the ®rst 2 axes
Eigenvalue
Explained variation (%)
Species/environment correlation
Monte Carlo simulation (1000 permutations) P
0.253
23.5
0.861
0.008
0.106
9.9
0.647
0.083
0.073
6.8
0.760
0.031
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the small Characiformes being able to exploit oxygen in the upper layers of the water
column. The present study con®rmed this high dominance.
In the NhecolaÃndia lagoons, 51 (19%) of the 263 ®sh species listed to the Pantanal
¯oodplain were found (Britski et al. 1999). Although the relationship between the number
of species ´ number of sample lagoons quickly approaches the asymptote
(k ˆ 0.224 lagoons±1), suggesting that a small number of lagoons is sucient to
represent NhecolaÃndia ®sh diversity, other considerations are in order: in the present
study it was observed that a large number of incidental species (51%), albeit these were
rare representing only 0.49% of individuals. This is responsible for the di€erences
identi®ed in the simple match groupings (Fig. 3), and it can be interpreted as a
complementary measure of the b diversity (between habitats), provided that a high
frequency of incidental species indicates a large di€erence in the composition of species
between the lagoons. This suggests that it is necessary to preserve several lagoons and
di€erent habitats to assure the survival of a viable number of individuals for conservation
purposes. However, although the lagoons were di€erent in species composition, the
abundance of the main species leads to a tighter grouping of the ponds, as shown by the
dendrogram using the Morisita±Horn formula.
The lagoons with low richness tend to be more similar in their simple matching
coecients. This raises two hypotheses regarding the diversity in these ponds: (1) the low
similarity observed among the lagoons using the simple matching coecient is mainly a
function of the di€erence in richness and not of species abundance; (2) the lagoons with
low richness and most similarities in species composition, are those that endured larger
stress caused by drought and retained the most resistant species. In comparison, those that
revealed greatest diversity were the deepest ones and had been isolated from the river more
recently. MouraÄo, Ishii, & Campos (1988) studied the ichthyofauna of NhecolaÃndia
Pantanal lagoons, and Catella (1992) found 75 species in BaõÂ a da OncËa, a perennial
marginal lake of Aquidauana River, Pantanal, and they concluded that richness is a result
of the lake±river connection (distance, height, continuance and frequency of the
connection), water quality and lake area.
In the present study neighbouring lagoons tended to be more alike in species
composition (simple matching), but they were not more similar in the species abundance
(Morisita±Horn). These results suggest that the species composition is determined by the
`pool' of available species during the period in which the lagoons are connected. However,
the characteristics of each lagoon (depth, macrophyte cover, macrophyte dominant
species) will determine the abundance of the species. This was con®rmed by the CCA.
Jackson & Harvey (1989) veri®ed a negative correlation between ®sh community structure
and the geographical distance between lakes of the Ontario region. Jackson & Harvey also
veri®ed that lakes in the same region presented similarities in typology (pH, depth and
area). In the Orinoco ¯oodplain ponds, RodrõÂ guez & Lewis (1997) veri®ed that the
similarity among the ®sh communities was not signi®cantly correlated with the
geographical distance. They commented that the morphometry of each lake allied to the
predator/prey interaction, would be the main factors responsible for the community
structure, independent of the distance between the ponds. Catella (1992) observed in BaõÂ a
da OncËa a low similarity between the communities during two serial isolation periods
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FISH COMMUNITIES IN PANTANAL LAGOONS
183
(1988, 1989), and changes in numerical dominant species (Moenkhausia dichroura and
Auchenipterus nigripinnis), but they represented species with the same dietary habits. This
suggests that the arrangement of the species may be a function of the resources available,
and the lagoon can be exploited by di€erent combinations of ecologically equivalent
species.
The results of the CCA indicated that macrophyte cover and piscivorous abundance
were the most important biotic factor structuring ®sh communities. Tejerina-Garro,
Fortin & Rodriguez (1998) demonstrated that water transparency and maximum lake
depth were the most important factors structuring the ®sh communities in ¯oodplain
lagoons of the Araguaia river in Brazil. Besides these two factors, RodrõÂ guez & Lewis
(1997) suggested the piscivory as another determining trait in the Orinoco ¯oodplain.
It was anticipated that this study would contribute to understanding the role ecological
factors play in structuring the ®sh communities of these habitats. This knowledge is
important in the decision making about community management (e.g. to decide which
species may be collected for aquarium trade) and land use.
The jack-knife species richness estimator is positively biased (Heltshe & Forrester 1983).
In the present work, its 95% estimated con®dence interval (56±71 species) overlapped
with the estimate by the log-normal model (63) suggesting that the list of species in the
lagoons (51) may be incomplete. Therefore, these estimates are considered more realistic
than the asymptotic richness value (50). Bastos & MouraÄo (1986), studying the
composition of ®sh species in the lagoons of the Nhumirim farm (NhecolaÃndia
Pantanal), made four collections of ®sh from a number of lagoons, and identi®ed 53 species.
Welcomme (1985) commented that the best habitats for ®sh feeding rarely coincide
with the best for reproduction, resulting in seasonal migrations between these areas.
During ¯ooding in the Pantanal, the ®sh species invade the ¯oodplain in search of food.
The moment the level of the rivers begins to drop, there is the inverse migration back to
83 the main channel (Ferraz de Lima 1986). VerõÂ ssimo (1994) and Okada (1995) found that
with isolation, the water recedes and ®sh density increases together with biotic and abiotic
pressures, although Catella (1992) detected an opposite trend. There can be drastic
changes in some physical and chemical water characteristics (e.g. reduced oxygen), quickly
killing the less tolerant species (VerõÂ ssimo 1994; Okada 1995).
In this study, some lagoons were far from the river, so they may dry out completely
before the next ¯ood. Catella (1992) suggested that the species that remain are represented
by: (1) individuals that did not return (or did not have the opportunity) to the river before
isolation; (2) species that would exhibit some adaptation to the pool characteristics (e.g.
hypoxia, presence/absence of sheltering macrophytes, desiccation), and therefore may be
able to survive until the next ¯ood. However, in the present set of lagoons there are some
which do not dry out sustaining ®sh populations, whose characteristics allow the survival
of a small number of species among the 263, that would possibly explain the low diversity.
It has been veri®ed that the NhecolaÃndia lagoons hosts mainly species of small size and
not small specimens of large species, but what is the role of these lagoons in the Pantanal?
Probably, one important function is to provide an amenable habitat for these small-sized
®shes, easily caught in shallow waters by aquatic birds and reptiles, mainly in the dry
season. In contrast, Catella (1992) remarks that marginal lagoons as BaõÂ a da OncËa
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 AREZ ET AL.
Y. R. SU
(perennial and deeper) shelter these small forms in the dry season, providing potential prey
for predatory ®sh when the lake connects to the river. These lagoons are more important
as feeding locations for aquatic mammals than for birds and reptiles.
The ®sh communities of these lagoons are not exploited by subsistence nor commercial
®sheries. They are only exploited by ®shermen looking for bait for sport ®sheries, mainly
the tuvira (Gymnotus gr. carapo), which lives in macrophyte roots. In this activity the
macrophytes are frequently brought to the lagoon margin, destroying this important
habitat. It has been increasing since the 1980s as a result of intensi®cation of sport ®shing
in the Pantanal. During 1979±1981, there were an estimated 17 000±20 000 sport
®shermen (Silva 1986), but this reached 44 000 in 1995, being responsible for a catch of
960 t, representing 69% of the total catches in the Pantanal of Mato Grosso do Sul State
(Catella, Albuquerque, Peixer & Palmeira 1999).
Although the ®sh fauna is diverse, with a great potential for aquarium trade, with some
species already scattered all over the aquarist world, e.g. Hyphessobrycon eques
( ˆH. callistus) and Gymnocorymbus ternetzi, there is no regular exploitation of these
®sh. Future management of these species requires knowledge of their habitats and the
environmental factors structuring ®sh communities. There is an important question. If
most of the lagoons dry out every year killing the vast majority of its ®sh, would it not be
worthwhile collecting the ornamental ®sh just before they are lost?
The habitats studied are intimately related to the main river and su€er from any
in¯uence of possible alterations in the channel. The most severe threat to the whole
Pantanal ecosystem is the proposed Paraguay±Parana water-way, for grain and cattle
84 transport from Brazil's Centre-west (Cunha 1998). The project will alter the ¯ow regime,
as a result of dredging, deepening and widening of channel, rock removal, embankments,
etc. There is considerable debate about the social bene®t of such a dramatic environmental
impact, compared with a possible railway connecting the South Cone.
Other threats are hydroelectric reservoirs in the upland, as Manso reservoir, which also
interfere with water regime; levees for drying out the ¯oodplain for cattle raising; river
siltation because of inappropriate land occupation in the high plateau and the use of
pesticides.
Acknowledgments
This paper is a part of a dissertation submitted by YRS to the Universidade Federal de
Mato Grosso do Sul (UFMS) as a partial requirement for a Master Degree in Ecology and
Conservation advised by MPJ. We thank CAPES, UNESP, EMBRAPA/CPAP
and CNPq for the ®nancial support and thank Gary R. SuÂarez and Robson de Souza
for the help in the ®eld work. We also thank EMBRAPA/CPAP for use of the ®eld station
at Leque Farm and laboratory facilities during this project.
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