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Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Author's personal copy Ecological Indicators 23 (2012) 19–26 Contents lists available at SciVerse ScienceDirect Ecological Indicators jo urnal homepage: www.elsevier.com/locate/ecolind River dolphins as indicators of ecosystem degradation in large tropical rivers a,b,∗ a,c a Catalina Gomez-Salazar , Marta Coll , Hal Whitehead a Biology Department, Dalhousie University, Halifax, Nova Scotia, Canada b Fundación Omacha, Colombia c ◦ Institute of Marine Science (ICM-CSIC), Passeig Maritim de la Barceloneta, n 37-49, 08003 Barcelona, Spain a r t i c l e i n f o a b s t r a c t Article history: Human stressors are currently impacting both the Amazon and Orinoco river basins and these are likely Received 18 October 2011 to increase. However, there is a lack of standardized monitoring programs to track these human stressors Received in revised form 27 February 2012 in most of the countries that overlap these basins, and no clear ecological indicators have been identified. Accepted 28 February 2012 In this study we investigated the relationships between measures of ecosystem degradation and river dolphins as potential ecological indicators. The presence of human stressors and their distance from the Keywords: areas surveyed were used to provide an estimate of ecosystem degradation. We tested three ecological River dolphins indicators of freshwater ecosystem degradation using river dolphins: (i) density of river dolphins, (ii) Top predators Amazon mean group size of dolphins, and (iii) dolphin sighting rates. We found a strong negative relationship Orinoco between measures of habitat degradation and river dolphin density estimates in selected locations of Human stressors the Amazon and Orinoco. Therefore, we suggest that river dolphins are good candidates as ecological Freshwater indicators, flagship and sentinel species for monitoring the conservation status of large tropical rivers in Ecosystem degradation South America. We suggest that further effort should be directed toward collecting reliable data on human stressors, creating collaborative networks for compiling existing data, and documenting and monitoring current trends in freshwater ecosystem degradation and indicator species in the Amazon and Orinoco basins with the goal of targeting areas for recovery or sustainable management. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction global conservation strategies, provide scientific knowledge to sup- port policy and management actions, and to restore ecosystem Human stressors can lead to ecosystem degradation (Alcamo services (e.g., Sanderson et al., 2002; Foley et al., 2005). et al., 2005; Foley et al., 2005). Currently, freshwater systems are The reliability of ecosystem degradation measurements at risk, with 65% of global river discharge being considered under depends on our ability to accurately understand and measure moderate to high threat, and water security of 80% of the human the number and intensity of human stressors and their effects population at high risk (Vörösmarty et al., 2010). In addition, bio- on biodiversity and ecosystems. Ecosystem degradation often diversity in freshwater ecosystems is in rapid decline and it is occurs gradually, making it difficult to recognize without repeated considered even more threatened compared to that of terrestrial measures of reliable indicators (Dale and Beyeler, 2001). Fresh- and marine ecosystems (Revenga et al., 2000; Vörösmarty et al., water ecosystem degradation is sometimes measured using a 2010). Rivers are at risk due to the impact of multiple human suite of ecological indicators, such as macro-invertebrates, fishes, stressors, including changes in water quantity and quality, habitat macrophytes, and organisms that live between terrestrial and modification, exploitation of species, climate change, and intro- aquatic ecosystems, such as odonata (e.g., Moya et al., 2010). duced species (Table 1). The current impacts of these stressors Good, carefully selected indicators can provide warning signals of are dramatically increasing and are unsustainable in the long term significant but cryptic changes to ecosystems (Karr, 1999; Noss, (Alcamo et al., 2005). In this context, it is critical to measure and 1999). monitor the status of freshwater ecosystems and the extent of The collection of detailed data on ecological indicators may be their degradation (Revenga et al., 2000; UNEP, 2004). Obtaining this costly, especially in developing countries where funding is limited information is critical to prioritize areas for conservation, develop and where large tropical rivers of exceptionally high biodiversity are located (Revenga et al., 2000). For example, there are at least 5600 identified species of freshwater fish in the Amazon River Basin ∗ and new species are being identified at a rapid rate (Albert and Corresponding author at: Department of Biology, Life Science Centre, Dalhousie Reis, 2011). As an alternative, it has been proposed to collect data University, 1355 Oxford St., Halifax, NS, Canada B3H 4J1. Tel.: +1 902 494 3723. E-mail address: [email protected] (C. Gomez-Salazar). on population trends of specific indicator species (Revenga et al., 1470-160X/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecolind.2012.02.034 Author's personal copy 20 C. Gomez-Salazar et al. / Ecological Indicators 23 (2012) 19–26 Table 1 Principal human stressors that are responsible for freshwater degradation and their impact on the ecosystems. Human stressors Impact of stressors on freshwater ecosystems Water quantity Water withdrawals by domestic, industrial and agricultural needs, reservoir storage capacity Water quality Source point and non-source point pollutants (e.g., organic pollutants, increased nutrients, heavy metals, microbial contamination, toxic organic compounds), suspended particles, temperature Habitat modification Roads, dams, reservoirs, land transformation, land use intensity, agriculture, vegetation cover, fragmentation Exploitation of species Fishing pressure, destructive fishing practices (e.g., blast fishing or fishing using poison or explosives), excessive by-catch and discards, aquaculture Climate change Increasing water temperature, decreasing precipitation, increasing acidification, changes in primary production Introduced species Increasing the rates of species introduced in freshwater systems and the success rate of those introduced Alcamo et al. (2005), Hoekstra et al. (2011), Revenga et al. (2000), Alkemade et al. (2009), Moyle and Randall (1998), Alcamo et al. (2003), GIWA (2002), Milà i Canals et al. (2009), Falkenmark (1997), Bennett et al. (2004), Karr and Chu (1999), Vörösmarty et al. (2010), Vörösmarty et al. (2000). 2000; Noss, 1999). Top predators such as mammalian carnivores, them within four major categories: (I) water quality, (II) habitat sea birds and raptors are among the indicator species suggested modification, (III) species exploitation, and (IV) cities and human (Furness and Camphuysen, 1997; Sergio et al., 2005, 2006, 2008; settlements. Each human stressor was coded according to four Piatt et al., 2007). impact categories: (0) when disturbance is absent/no disturbance, Top predators tend to be concentrated in important biodiver- (1) when disturbance is low, (2) medium and (3) high (Table 2). sity hotspots (Worm et al., 2003; Sergio et al., 2005, 2006). The Score index of freshwater ecosystem degradation for each major reduction or disappearance of top predators is related to significant category (water quality (I), habitat modification (II) and species ecosystem transformations, including impacts on several trophic exploitation (III), Table 2) were the average of those for the human levels and changes in energy flows, marine resources’ removals stressors coded in that category, and an overall score index of from fisheries, and changes in the behavior of prey (Soulé et al., freshwater habitat degradation was obtained by summing over 2005; Heithaus et al., 2008; Baum and Worm, 2009). Moreover, these three major categories (Table 3), with overall value ranges their presence or absence can indicate the extent of the footprint of from 0 to 8.5 (8.5 being the highest degradation). In addition, the human pressures; those areas with low human population and/or information on human population size (cities and human settle- strong conservation and regulations tend to have the highest sight- ments (IV), Table 2) for each river area surveyed was obtained using ing frequencies of top predators (Baum and Worm, 2009; Sandin the databases of the population census for each country surveyed et al., 2008; Ward-Paige et al., 2010). (Table 2, DANE, 2005; INE, 2001a,b; INEI, 2007; INEC, 2010). The River dolphins are top predators that inhabit some of