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

Carlos Edwar de Carvalho Freitas, Alexandre A. F. Rivas, Caroline Pereira Campos, Igor Sant'Ana, James Randall Kahn, Maria Angélica de Almeida Correa and Michel Fabiano Catarino

Additional information is available at the end of the chapter

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

**1. Introduction**

The Amazon River Basin, which encompasses the world's largest remaining tropical rain‐ forest, has the highest diversity of fish species of any region in the world [1]. Some of these species represent highly abundant fish stocks that have supported an important fishery for many decades, or many centuries if the history prior to European coloniza‐ tion is included. The importance of fishing in the Amazon River Basin can easily be ob‐ served from the high fish consumption, which is mainly attributed to people who live in rural areas near rivers and lakes (Table 1). Regardless of this importance for food, there is no integrative strategy for fishery management, and the activity in this basin as a whole is highly vulnerable to externalities, including those resulting from environmental changes and man-made interventions.

There is a consensus that fishery production is directly related to biological productivity, which is a function of a set of environmental characteristics in the aquatic system. The ma‐ jority of the Rio Amazonas and its tributaries are accompanied by large floodplains, which is where most of the biological production occurs. A key factor for biological production in the floodplains of large Amazonian rivers is the flood pulse [9], which generates tremen‐ dous variation in the input of nutrients over the course of the year, primarily at river head‐ waters located in the pre-Andean areas, such as Madeira, Purus, Juruá, and Solimões. The flood pulse is the driving element that structures the landscape of the floodplains adjacent to

© 2013 de Carvalho Freitas et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 de Carvalho Freitas et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

the river channels, forming a mobile ecotone that is referred to as ATTZ or the aquatic-ter‐ restrial transition zone [9].

consensus that the impact on fish will be species-specific, that is directly related to the bio‐

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

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

177

Nevertheless, the effects on fisheries should be a result of a series of effects that start at the organism level. At an individual level, all fish have an optimal thermal interval that is limit‐ ed on the upper and lower boundaries by their critical thermal maxima and minima, respec‐ tively [18], thus reducing the analysis of the warming effects. Therefore, fish exposed to temperatures within the sub-lethal interval, excluding the optimal thermal interval, may be affected by warming, and the consequences of this temperature effect should be evident by physiological responses. The high energetic cost necessary to compensate for these unfavor‐ able environmental conditions may affect the growth rates or reproduction success of the fish (Figure 1). Realistically, general effects from water warming can be expected. Because biochemical reaction rates are a function of body temperature, all aspects of an individual fish's physiology, including growth, reproduction and activity, are directly influenced by

When the environment changes, these temperature effects should continue to increase and may be perceptible at the population and community levels. Although different species are affected by environmental change in different ways, the abundance patterns of the entire

Dams cause local changes at the sub-basin level but also have the potential to exhibit region‐ al effects. In essence, the impact of dams on the hydrological river cycle, which primarily

community, and thus the fishing production, should be influenced (Figure 1).

**Figure 1.** The effects of global climatic changes on different levels.

logical characteristics of each species.

changes in temperature [19].


**Table 1.** Fish consumption in the Amazon River Basin.

The Amazonian hydrological cycle is annual and quite predictable. The flood intensity and timing is controlled by several factors, including those that act on a global scale. The cyclical phenomenon of warming in the Pacific Ocean near the cost of Peru, termed *El Niño*, is relat‐ ed to severe drought in the Amazon Basin. Alternatively, *La Niña* is associated with strong floods. The simultaneous occurrence of other climatic phenomena, such as the warming of the Tropical North Atlantic Ocean, has been used to explain extreme climatic events [10].

Despite the lack of models describing the relationship between flood intensity and timing and fishing success, the life strategy of many species of Amazonian fish is synchronized with the hydrological cycle. For example, several species of Characiforms, including *Colosso‐ ma macropomum*, *Brycon amazonicus*, *Prochilodus nigricans*, *Semaprochilodus insignis*, *S. taenirus*, *Piaractus brachypomum* and others, begin their reproductive migration at the beginning of the rainy season when the waters begin flooding [11, 12, 13]. This life strategy was most likely developed to ensure the colonization of the floodplain with newly hatched larvae. The avail‐ ability of food and places of refuge in the colonized floodplain may determine the strength of the annual recruitment of these species.

There is ample evidence that the Earth's climate is changing more rapidly now than it has in the past [14], with potential effects on the Amazon basin [15, 16]. These effects include phys‐ ical alterations and changes in nutrient flow [14]. Although uncertainties associated with how local climates change in response to global climate change exist, global circulation mod‐ els employed by the Intergovernmental Panel on Climate Change (IPCC) have found an in‐ creased likelihood of a significant increase in the mean global temperature [14]. A rise in sea level is also predicted, with estimates varying between 0.75 m to 1.90 meters by the end of twenty-first century [17]. Other environmental changes in freshwater systems, such as strati‐ fication, productivity reduction and acidification, have no consistent patterns. These changes are very difficult to generalize based on the available evidence; however, there is a consensus that the impact on fish will be species-specific, that is directly related to the bio‐ logical characteristics of each species.

the river channels, forming a mobile ecotone that is referred to as ATTZ or the aquatic-ter‐

**Reference Sub-basin Social group g/per capita.day Kg/per capita.year** [2] Rio Negro urban 53.95 19.69 [3] Rio Negro urban 121.70 44.42 [4] Rio Amazonas rural 369.00 135.00 [5] Rio Solimões rural 510.00 to 600.00 186.00 to 219.00 [6] Rio Solimões and Rio Japurá rural 509.00 to 805.00 186.00 to 294.00 [7] Rio Madeira rural 243.00 88.00 [8] Rio Amazonas rural 511.00 to 643.00 187.00 to 235.00

The Amazonian hydrological cycle is annual and quite predictable. The flood intensity and timing is controlled by several factors, including those that act on a global scale. The cyclical phenomenon of warming in the Pacific Ocean near the cost of Peru, termed *El Niño*, is relat‐ ed to severe drought in the Amazon Basin. Alternatively, *La Niña* is associated with strong floods. The simultaneous occurrence of other climatic phenomena, such as the warming of the Tropical North Atlantic Ocean, has been used to explain extreme climatic events [10].

Despite the lack of models describing the relationship between flood intensity and timing and fishing success, the life strategy of many species of Amazonian fish is synchronized with the hydrological cycle. For example, several species of Characiforms, including *Colosso‐ ma macropomum*, *Brycon amazonicus*, *Prochilodus nigricans*, *Semaprochilodus insignis*, *S. taenirus*, *Piaractus brachypomum* and others, begin their reproductive migration at the beginning of the rainy season when the waters begin flooding [11, 12, 13]. This life strategy was most likely developed to ensure the colonization of the floodplain with newly hatched larvae. The avail‐ ability of food and places of refuge in the colonized floodplain may determine the strength

There is ample evidence that the Earth's climate is changing more rapidly now than it has in the past [14], with potential effects on the Amazon basin [15, 16]. These effects include phys‐ ical alterations and changes in nutrient flow [14]. Although uncertainties associated with how local climates change in response to global climate change exist, global circulation mod‐ els employed by the Intergovernmental Panel on Climate Change (IPCC) have found an in‐ creased likelihood of a significant increase in the mean global temperature [14]. A rise in sea level is also predicted, with estimates varying between 0.75 m to 1.90 meters by the end of twenty-first century [17]. Other environmental changes in freshwater systems, such as strati‐ fication, productivity reduction and acidification, have no consistent patterns. These changes are very difficult to generalize based on the available evidence; however, there is a

restrial transition zone [9].

176 New Advances and Contributions to Fish Biology

**Table 1.** Fish consumption in the Amazon River Basin.

of the annual recruitment of these species.

Nevertheless, the effects on fisheries should be a result of a series of effects that start at the organism level. At an individual level, all fish have an optimal thermal interval that is limit‐ ed on the upper and lower boundaries by their critical thermal maxima and minima, respec‐ tively [18], thus reducing the analysis of the warming effects. Therefore, fish exposed to temperatures within the sub-lethal interval, excluding the optimal thermal interval, may be affected by warming, and the consequences of this temperature effect should be evident by physiological responses. The high energetic cost necessary to compensate for these unfavor‐ able environmental conditions may affect the growth rates or reproduction success of the fish (Figure 1). Realistically, general effects from water warming can be expected. Because biochemical reaction rates are a function of body temperature, all aspects of an individual fish's physiology, including growth, reproduction and activity, are directly influenced by changes in temperature [19].

When the environment changes, these temperature effects should continue to increase and may be perceptible at the population and community levels. Although different species are affected by environmental change in different ways, the abundance patterns of the entire community, and thus the fishing production, should be influenced (Figure 1).

**Figure 1.** The effects of global climatic changes on different levels.

Dams cause local changes at the sub-basin level but also have the potential to exhibit region‐ al effects. In essence, the impact of dams on the hydrological river cycle, which primarily 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‐ cent floodplains and other wetlands; and blocking fish migrations.

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

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

179

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‐

(a) (b)

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

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

the most critical determinant of the climatic fate of the Amazon [14].

strophic events may disappear at a local level [23].

drought occurred.

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 different fish species.

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 for food and income.

Therefore, the goals of this chapter are as follows:

