**2. Global climatic changes and dams: What we can expect and what are the potential effects**

Despite the uncertainties at the local level, it is highly likely that there will be more frequent oc‐ currences of extreme climatic events. Most of the global climate models (GCMs) proposed by the IPCC [14] project significant Amazonian drying during the 21st century. Pacific sea sur‐ face temperature (SST) variation, which is dominated by the El Niño–Southern Oscillation (ENSO), is the main driving force for wet-season rainfall. However, dry-season rainfall is strongly influenced by the Tropical Atlantic north-south SST gradient. Therefore, an intensifi‐ cation of this gradient from the warming of northern SSTs relative to those of the south would move the Inter-Tropical Convergence Zone north and strengthen the Hadley Cell circulation. This change would enhance the duration and intensity of the dry season in much of southern and eastern Amazonia, which already has occurred in 2005. Studies indicated that the most ex‐ treme droughts in Amazonia were a result of the strong events of the El Niño-Southern Oscilla‐ tion (ENSO), the large temperature increase of the sea surface in the Tropical North Atlantic or a combination of these events [22]. Changes in precipitation during the dry season are likely the most critical determinant of the climatic fate of the Amazon [14].

involves flood timing, is the most important effect of change in freshwater fisheries because the flood regime is the most important determining force in Neotropical rivers [20]. Dam construction can affect environments and fisheries by changing the timing and quantity of river flows; altering the water temperature, nutrient and sediment transport; reducing adja‐

Currently, there is a large proliferation of hydroelectric dams within the Amazon region. At the western boundary near the Andean and Pre-Andean areas, there are plans for 151 new hydroelectric dams with greater than 2 MW of power over the next 20 years, which is more than a 300% increase [21]. Similarly, in the Brazilian region near the south and southeast boundaries of the Amazon, there are several hydroelectric dam projects that have the poten‐ tial to completely fragment the river basins with headwaters on the Brazilian Plateau. Simi‐ lar to climate change, the impact of dams should be associated with the life strategies of

The most important species captured by small-scale fisheries in the Amazon basin belong to three groups: Characiforms, which are primarily from the Prochilodontidae, Characidae, and Serrasalmidae families; Siluriforms, which are primarily from the Pimelodidae family and include piramutaba (*Brachyplatystoma vailantii*), dourada (*B. rouseauxii*) and piraíba (*B. filamentosum* and *B. capapretum*); and Perciforms, which are primarily from the genus *Cichla*. Over evolutionary time, members of these groups have developed specific life strategies de‐ signed to optimize the survival of Amazonian environmental conditions. Alterations in‐ duced by global changes or man-made interventions may directly influence these strategies, with negative effects on both the recruitment and stock abundance of these species, as well as on the socio-economic conditions of the Amazonian people that exploit these fish stocks

**1.** Review the main scenarios for environmental alterations in the Amazon Basin, which is

**2.** Identify the potential impacts of different scenarios of environmental alterations in the

**3.** Identify the consequences of the predicted impacts on the Amazonian freshwater fish populations, taking into account the main characteristics of the population dynamics. **4.** Illustrate the potential social and economic consequences for the local and regional fish‐

**2. Global climatic changes and dams: What we can expect and what are**

Despite the uncertainties at the local level, it is highly likely that there will be more frequent oc‐ currences of extreme climatic events. Most of the global climate models (GCMs) proposed by

predicted to be a function of global climatic changes and dams.

Amazon Basin on Amazonian freshwater fish populations.

eries and the people who depend on these fisheries.

cent floodplains and other wetlands; and blocking fish migrations.

different fish species.

178 New Advances and Contributions to Fish Biology

for food and income.

**the potential effects**

Therefore, the goals of this chapter are as follows:

These extreme droughts, even if short in duration, can be catastrophic for aquatic organisms because of the strong reduction in the area of the aquatic environments. Floodplain lakes are the most impacted, and the areas of these lakes can be reduced by several orders of magni‐ tude (Figure 2). Although several species of fish are able to relocate to the river channel dur‐ ing the dry season, some lake resident species remain in the lakes and are unable to survive if the drought is severe. Some studies have observed that fish assemblages seemed to recov‐ er rapidly from normal drought seasons [23], but there are indications that extreme droughts occasionally alter fish assemblages. Some species that are vulnerable to these cata‐ strophic events may disappear at a local level [23].

**Figure 2.** A floodplain area of the Rio Amazonas during the flood season (A) and dry season (B) when an extreme drought occurred.

Another likely climatic change is global warming [14]. Over the next two decades, a warm‐ ing of approximately 0.2°C per decade is projected for a range of SRES emission scenarios. Even if the concentrations of all greenhouse gases and aerosols had been maintained at the levels present in the year 2000, a further warming of approximately 0.1°C per decade would be expected [14]. This warming represents an increase of 1-7ºC in the mean global tempera‐ ture within the next one hundred years.

**Temperature change ((C at 2090-2099 relative to 1980-1999)**

B1 scenario 1.8 1.1 - 2.9 0.18 - 0.38 A1T scenario 2.4 1.4 - 3.8 0.20 - 0.45 B2 scenario 2.4 1.4 - 3.8 0.20 - 0.43 A1B scenario 2.8 1.7 - 4.4 0.21 - 0.48 A2 scenario 3.4 2.0 - 5.4 0.23 - 0.51 A1F1 scenario 4.0 2.4 - 6.4 0.26 - 0.59

**Table 2.** Projected global average surface warming and associated sea level rise at the end of the 21st century.

Similarly, Amazonian fish species evolved in a system regulated by an annual and predicta‐ ble flood pulse, developing life strategies to explore the several habitats available during the hydrological cycle. The elimination or change in the timing or duration of this pulse can de‐ stroy signals that trigger reproduction and other life cycle events, which will potentially in‐

The blockage of the fish migration can be critical, with significant impacts for some species that participate in long-distance migrations from the estuary to the headwaters of whitewa‐

The fourth phenomenon concerning the fall in oxygen levels is relatively self-explanatory. The large amount of organic material in the reservoirs will remove a great deal of oxygen from a system that is already low in oxygen content due to the water temperature. The syn‐ ergy between this phenomenon and global warming is quite evident. The results may in‐

Clearly, these phenomena can be completely integrated and synergistic, and their effects on fish communities can be magnified and strongly disruptive. As is most often the case with multiple sources of environmental stress, the combined stress resulting from several sources is greater than the sum of the individual stresses. This point is emphasized by [21], who stat‐ ed that the impact of hydroelectric dams in the Amazon Basin should be considered in a broad perspective, including the planned projects of other Amazonian countries, such as Bo‐ livia, Colombia, Ecuador and Peru. The fragmentation of Amazonian rivers originating in Pre-Andean areas may result in severe nutrient depletion of the rivers because the moun‐ tains and associated uplands are the main source of sediments that form the basis for the

ter rivers to spawn. As a result, some populations may be locally extinct.

clude the loss of species with less tolerance for low oxygen conditions.

high primary productivity observed in the Amazonian floodplains.

Constant Year 2000 concentration

Source: [14]

fluence fish recruitment.

Best estimate Likely range Model-based range excluding future

0.6 0.3 - 0.9 NA

The Potential Impacts of Global Climatic Changes and Dams on Amazonian Fish and Their Fisheries

**Sea level rise (m at 2090-2099 relative to 1980-1999)**

http://dx.doi.org/10.5772/54549

181

rapid dynamic changes in ice flow

Freshwater fish may explore habitats within an optimal thermal interval and thermo-regu‐ late behaviorally and physiologically. Temperature tolerance ranges are species-specific and range from stenothermal species that support only a narrow thermal range to eurythermal species that are able to live in a wide thermal range. Fish populations subjected to changing thermal regimes may increase or decrease in abundance, experience range expansions or contractions or face extinction [19]. There is also an inverse relationship between the temper‐ ature and concentration of dissolved oxygen in water. Thus, an increase in the temperature can exacerbate the hypoxia or anoxia conditions naturally observed in some lentic habitats of freshwater fish.

A direct consequence of global warming is a rise in sea level. Despite the uncertainties relat‐ ed to the dynamics of ice sheets and glaciers, there are models that predict a rise in sea level, which were summarized previously [14]. One model proposed a relationship between glob‐ al sea level variations and the global mean temperature and predicts a rise in sea level rang‐ ing from 75 to 190 cm for the period 1990-2100 [17]. However, some scenarios [14] predict a rise of 4.0 meters (Table 2).

What are the potential effects of a rise in sea level for the Amazon Basin? With regard to its physical characteristics, we can anticipate that the sea will be a hydraulic barrier and will flood areas that are not currently flooded but which are primarily within the floodplain ad‐ jacent to the river channel. Other environmental consequences of this barrier can also be ex‐ pected: a reduction in water flow, an increase in the sedimentation rate and an increase of the flooded area. It is possible that the hydrological cycle will also be affected.

These changes to the hydrological cycle can be magnified by the fragmentation of the envi‐ ronment that will occur as a result of the introduction of hydroelectric dams. We can identi‐ fy at least four phenomena associated with the introduction of dams:


Blockage of the sediments might have a large effect on fish communities. Whitewater rivers originate in Pre-Andean areas and are heavily loaded with volcanic soil sediment. The dams act as a barrier and result in a reduction of water speed, thus improving the rate of decanta‐ tion. The end result is an impoverishment of the river below the dam. Thus, the species that have evolved in the presence of high levels of nutrients will not be able to adapt to the rapid loss in primary productivity that is associated with the reduction of nutrient content. This result will favor a change in the composition of local species and will have serious impacts on fishing activity.


levels present in the year 2000, a further warming of approximately 0.1°C per decade would be expected [14]. This warming represents an increase of 1-7ºC in the mean global tempera‐

Freshwater fish may explore habitats within an optimal thermal interval and thermo-regu‐ late behaviorally and physiologically. Temperature tolerance ranges are species-specific and range from stenothermal species that support only a narrow thermal range to eurythermal species that are able to live in a wide thermal range. Fish populations subjected to changing thermal regimes may increase or decrease in abundance, experience range expansions or contractions or face extinction [19]. There is also an inverse relationship between the temper‐ ature and concentration of dissolved oxygen in water. Thus, an increase in the temperature can exacerbate the hypoxia or anoxia conditions naturally observed in some lentic habitats

A direct consequence of global warming is a rise in sea level. Despite the uncertainties relat‐ ed to the dynamics of ice sheets and glaciers, there are models that predict a rise in sea level, which were summarized previously [14]. One model proposed a relationship between glob‐ al sea level variations and the global mean temperature and predicts a rise in sea level rang‐ ing from 75 to 190 cm for the period 1990-2100 [17]. However, some scenarios [14] predict a

What are the potential effects of a rise in sea level for the Amazon Basin? With regard to its physical characteristics, we can anticipate that the sea will be a hydraulic barrier and will flood areas that are not currently flooded but which are primarily within the floodplain ad‐ jacent to the river channel. Other environmental consequences of this barrier can also be ex‐ pected: a reduction in water flow, an increase in the sedimentation rate and an increase of

These changes to the hydrological cycle can be magnified by the fragmentation of the envi‐ ronment that will occur as a result of the introduction of hydroelectric dams. We can identi‐

Blockage of the sediments might have a large effect on fish communities. Whitewater rivers originate in Pre-Andean areas and are heavily loaded with volcanic soil sediment. The dams act as a barrier and result in a reduction of water speed, thus improving the rate of decanta‐ tion. The end result is an impoverishment of the river below the dam. Thus, the species that have evolved in the presence of high levels of nutrients will not be able to adapt to the rapid loss in primary productivity that is associated with the reduction of nutrient content. This result will favor a change in the composition of local species and will have serious impacts

the flooded area. It is possible that the hydrological cycle will also be affected.

**1.** Blockage of the sediment flow in whitewater systems (e.g., Rio Madeira).

fy at least four phenomena associated with the introduction of dams:

**4.** Reduction in oxygen levels both above and below the dams.

ture within the next one hundred years.

180 New Advances and Contributions to Fish Biology

of freshwater fish.

rise of 4.0 meters (Table 2).

**2.** Change of the flood pulse.

**3.** Blockage of fish migration.

on fishing activity.

**Table 2.** Projected global average surface warming and associated sea level rise at the end of the 21st century. Source: [14]

Similarly, Amazonian fish species evolved in a system regulated by an annual and predicta‐ ble flood pulse, developing life strategies to explore the several habitats available during the hydrological cycle. The elimination or change in the timing or duration of this pulse can de‐ stroy signals that trigger reproduction and other life cycle events, which will potentially in‐ fluence fish recruitment.

The blockage of the fish migration can be critical, with significant impacts for some species that participate in long-distance migrations from the estuary to the headwaters of whitewa‐ ter rivers to spawn. As a result, some populations may be locally extinct.

The fourth phenomenon concerning the fall in oxygen levels is relatively self-explanatory. The large amount of organic material in the reservoirs will remove a great deal of oxygen from a system that is already low in oxygen content due to the water temperature. The syn‐ ergy between this phenomenon and global warming is quite evident. The results may in‐ clude the loss of species with less tolerance for low oxygen conditions.

Clearly, these phenomena can be completely integrated and synergistic, and their effects on fish communities can be magnified and strongly disruptive. As is most often the case with multiple sources of environmental stress, the combined stress resulting from several sources is greater than the sum of the individual stresses. This point is emphasized by [21], who stat‐ ed that the impact of hydroelectric dams in the Amazon Basin should be considered in a broad perspective, including the planned projects of other Amazonian countries, such as Bo‐ livia, Colombia, Ecuador and Peru. The fragmentation of Amazonian rivers originating in Pre-Andean areas may result in severe nutrient depletion of the rivers because the moun‐ tains and associated uplands are the main source of sediments that form the basis for the high primary productivity observed in the Amazonian floodplains.

An unavoidable effect of dams is the shift in species composition and abundance. This shift includes the extreme proliferation of some populations and a reduction, or even elimination, of others [25]. The obstacles in the migratory routes, the loss of natural nurs‐ ery areas placed upstream of dams and the modification of the hydrological regime downstream of dams, in addition to the rheophilic behavior of the community, are fac‐ tors directly linked to failures in recruitment and the limited distribution of adults in res‐ ervoirs [25], which strongly affect fisheries [26].

spawning occurs [13, 32, 33, 34, 35]. The parental schools are very large, containing hun‐ dreds of thousands of individuals, and there is no parental care after spawning [13, 36]. Adult fish move toward flooded areas, which are rich in food, aiming to store energy for a new reproductive cycle. There are some differences between the timing of migration for these species; however, the schematic in Figure 3 shows the synchronism with the rainy sea‐ son when the water starts to rise and the importance of the newly inundated floodplains as

The Potential Impacts of Global Climatic Changes and Dams on Amazonian Fish and Their Fisheries

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183

Lastly, there are species that do not need to migrate to complete their life cycle. These fish are a diversified group with species from several orders; however, some cichlids from the genus *Cichla* are highly important for regional fisheries. These cichlids are called peacock bass and are the main target of recreational fisheries that are located primarily in black wa‐ ter rivers. The peacock bass is also a to predator that moves in several environments for tro‐ phic reasons [37]. Ornamental fish compose another group of non-migratory species that are exploited by fishing. This group is highly diverse, with species belonging to several orders, including Characiforms, Siluriforms, Perciforms, Osteoglossiforms and Gymnotiforms. In

**4. Potential effects of global climatic changes and dams on freshwater**

The intensity and direction (positive or negative) of the potential effects of environmen‐ tal changes will vary among populations and species in the Amazonian fish fauna. Some global scenarios are catastrophic [38], proposing that 75% of global freshwater fish will become extinct before the end of the 21st century due to a reduction in river discharge. Nevertheless, the possible effect is local extinction, which would be a critical event for endemic species. Two species of the small fish *Paracheirodon*, which are exploited as orna‐ mental species, exist in the middle to upper Rio Negro in Brazil and in the upper Rio Orinoco in Colombia and Venezuela. A study conducted at an inter-fluvial palm camp of the Middle Rio Negro found that these two species are rarely observed in the same habi‐ tat. The *P. simulans* habitat water temperature ranged from a low of 24.6 to a high of 35.2 ºC, while the *P. axelroldi* habitat temperature varied between 25.1 and 29.9 ºC [39]. The authors propose that because inter-fluvial areas flood as a function of rainfall, a de‐ crease in regional precipitation could alter the hydrologic balance of these wetlands, es‐ pecially during dry periods, which would lower water levels and increase the water temperature. This scenario would be extremely adverse for *P. simulans*, which exists only in very shallow inter-fluvial areas. A decrease in precipitation could dry out these areas

At the beginning of rising waters season, the adults move down river from tributaries of black and clear waters to spawning in the turbid and rich environment of white water riv‐ ers. After breeding event, these fish move toward the flooded forest for feeding. The larvae

a place of refuge and feeding for the young fish [37].

general, these are small sized fish with high levels of endemism.

completely, ultimately leading to the local extinction of this species.

**amazonian fish**

## **3. Life strategies of freshwater amazonian fish**

In the Amazon Basin, the life strategies associated with migratory and reproductive process‐ es can be employed to distinguish three fish groups. First, groups can be distinguished by their migration length. The fish species that participate in long-distance migrations are from the family Pimelodidae and belong to a unique genus: *Brachyplatystoma rousseauxii*, *B. vailan‐ tii*, *B. filamentosum*, *B. capapretum* and *B. platynemum*[13]. These species migrate up to 3,000 km to complete their life cycle. They migrate from the Amazonian estuary to the border of the Andean mountains in Bolivia, Colombia and Peru [27]. The estuary is the nursery area, and the fish remain there approximately one year prior to beginning their migration. The floodplain areas of the Central Amazon Basin are feeding habitats where the immature fish grow up and store fats prior to their reproductive migration toward the Pre-Andean areas [13, 27, 28, 29]. This process is synchronized with the hydrological cycle. The gonads of *B. rousseauxii* are in an advanced stage of development starting at the beginning of the flood season, while *B. flamentosum*, *B. platynemum* and *B. vailantii* show the highest reproductive activity at the end of the flood season [28].

The short-distance migratory species belong to several groups, including Siluriforms such as *Pinirampus pirinampu*, *Calophysus macropterus*, *Hypophthalmus marginatus*, *H. edentates*, *H. fim‐ briatus*, *Phractocephalus hemiliopterus*, *Pseudoplatystoma punticfer*, *P*. *fasciatum* and *P. tigrinum* [13, 30, 31]. These species are also called floodplain migratory fish because they participate in short-distance migrations between the main stem of the Amazon River and its tributaries and floodplain lakes. Despite the absence of published studies, evidence from field research indicates that the migrations of this group do not appear to exhibit a pattern associated with reproductive events. Because these fish are predator species, these short-distance migrations have trophic causes and are developed to find prey in general small and medium size chara‐ cins.

Another short-distance migratory species is a highly diverse group of Characiformes, which are extensively exploited by the small-scale fishing fleet from the Amazon Basin. Species such as *Colossoma macropomum*, *Prochilodus nigricans*, *Semaprochilodus insignis*, *S. taenirus* and several Myleinae and Curimatidae evolved for a life strategy strongly associated with the hydrological cycle of the Amazon Basin [13, 32, 33]. These species build large schools at the beginning of the rainy season and participate short-distance migrations from their feeding habitat, which is generally within black water tributaries, to white water rivers where spawning occurs [13, 32, 33, 34, 35]. The parental schools are very large, containing hun‐ dreds of thousands of individuals, and there is no parental care after spawning [13, 36]. Adult fish move toward flooded areas, which are rich in food, aiming to store energy for a new reproductive cycle. There are some differences between the timing of migration for these species; however, the schematic in Figure 3 shows the synchronism with the rainy sea‐ son when the water starts to rise and the importance of the newly inundated floodplains as a place of refuge and feeding for the young fish [37].

An unavoidable effect of dams is the shift in species composition and abundance. This shift includes the extreme proliferation of some populations and a reduction, or even elimination, of others [25]. The obstacles in the migratory routes, the loss of natural nurs‐ ery areas placed upstream of dams and the modification of the hydrological regime downstream of dams, in addition to the rheophilic behavior of the community, are fac‐ tors directly linked to failures in recruitment and the limited distribution of adults in res‐

In the Amazon Basin, the life strategies associated with migratory and reproductive process‐ es can be employed to distinguish three fish groups. First, groups can be distinguished by their migration length. The fish species that participate in long-distance migrations are from the family Pimelodidae and belong to a unique genus: *Brachyplatystoma rousseauxii*, *B. vailan‐ tii*, *B. filamentosum*, *B. capapretum* and *B. platynemum*[13]. These species migrate up to 3,000 km to complete their life cycle. They migrate from the Amazonian estuary to the border of the Andean mountains in Bolivia, Colombia and Peru [27]. The estuary is the nursery area, and the fish remain there approximately one year prior to beginning their migration. The floodplain areas of the Central Amazon Basin are feeding habitats where the immature fish grow up and store fats prior to their reproductive migration toward the Pre-Andean areas [13, 27, 28, 29]. This process is synchronized with the hydrological cycle. The gonads of *B. rousseauxii* are in an advanced stage of development starting at the beginning of the flood season, while *B. flamentosum*, *B. platynemum* and *B. vailantii* show the highest reproductive

The short-distance migratory species belong to several groups, including Siluriforms such as *Pinirampus pirinampu*, *Calophysus macropterus*, *Hypophthalmus marginatus*, *H. edentates*, *H. fim‐ briatus*, *Phractocephalus hemiliopterus*, *Pseudoplatystoma punticfer*, *P*. *fasciatum* and *P. tigrinum* [13, 30, 31]. These species are also called floodplain migratory fish because they participate in short-distance migrations between the main stem of the Amazon River and its tributaries and floodplain lakes. Despite the absence of published studies, evidence from field research indicates that the migrations of this group do not appear to exhibit a pattern associated with reproductive events. Because these fish are predator species, these short-distance migrations have trophic causes and are developed to find prey in general small and medium size chara‐

Another short-distance migratory species is a highly diverse group of Characiformes, which are extensively exploited by the small-scale fishing fleet from the Amazon Basin. Species such as *Colossoma macropomum*, *Prochilodus nigricans*, *Semaprochilodus insignis*, *S. taenirus* and several Myleinae and Curimatidae evolved for a life strategy strongly associated with the hydrological cycle of the Amazon Basin [13, 32, 33]. These species build large schools at the beginning of the rainy season and participate short-distance migrations from their feeding habitat, which is generally within black water tributaries, to white water rivers where

ervoirs [25], which strongly affect fisheries [26].

182 New Advances and Contributions to Fish Biology

activity at the end of the flood season [28].

cins.

**3. Life strategies of freshwater amazonian fish**

Lastly, there are species that do not need to migrate to complete their life cycle. These fish are a diversified group with species from several orders; however, some cichlids from the genus *Cichla* are highly important for regional fisheries. These cichlids are called peacock bass and are the main target of recreational fisheries that are located primarily in black wa‐ ter rivers. The peacock bass is also a to predator that moves in several environments for tro‐ phic reasons [37]. Ornamental fish compose another group of non-migratory species that are exploited by fishing. This group is highly diverse, with species belonging to several orders, including Characiforms, Siluriforms, Perciforms, Osteoglossiforms and Gymnotiforms. In general, these are small sized fish with high levels of endemism.
