River Dolphin Research Articles

River dolphins as indicators of ecosystem degradation in large tropical rivers

Human stressors are currently impacting both the Amazon and Orinoco river basins and these are likely to increase. However, there is a lack of standardized monitoring programs to track these human stressors in most of the countries that overlap these basins, and no clear ecological indicators have been identified. 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 areas surveyed were used to provide an estimate of ecosystem degradation. We tested three ecological indicators of freshwater ecosystem degradation using river dolphins: (i) density of river dolphins, (ii) mean group size of dolphins, and (iii) dolphin sighting rates. We found a strong negative relationship between measures of habitat degradation and river dolphin density estimates in selected locations of the Amazon and Orinoco. Therefore, we suggest that river dolphins are good candidates as ecological indicators, flagship and sentinel species for monitoring the conservation status of large tropical rivers in 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.

Common pattern of population decline for freshwater cetacean species in deteriorating habitats

Summary1. Freshwater cetacean species, including the baiji (Lipotes vexillifer), Amazon River dolphin (Inia geoffrensis), Ganges/Indus River dolphins (Platanista spp.) and Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis), apex predators in megariver ecosystems, face serious challenges owing to the deterioration of habitat quality.2. We simulated population change of four freshwater cetacean species under increasing habitat deterioration. Carrying capacity (K) was used to represent the habitat quality, and a logistic model was used to describe the rate of habitat deterioration (dK).3. An individual‐based Leslie matrix model showed that population declines and extinctions in freshwater cetaceans under increasing habitat deterioration exhibit a consistent pattern irrespective of the initial level of K or population size. When dK is low, population abundance fluctuates stochastically around initial K, but a rapid increase in dK is accompanied by a sharp population decline, with a residual population ultimately declining continuously to extinction.4. Simulations show that traditional census survey techniques used in cetacean species are unlikely to detect early signs of population decline before a critical level is reached.5. Empirical data of the likely extinction of baiji strongly agree with our simulation exercise, implying that extinction of other freshwater cetacean species may occur sooner than previously considered. Hence, precautionary approaches for habitat restoration and landscape management should be implemented before freshwater cetacean population declines are detected, and ideally, before habitat quality begins to deteriorate.

REPORT OF AN ENCOUNTER WITH A HUMAN-INTENTIONALLY-ENTANGLED AMAZON RIVER DOLPHIN (<i>Inia geoffrensis</i>) CALF AND ITS RELEASE IN TEFÉ RIVER, AMAZONAS STATE, BRAZIL

The Amazon river dolphin or boto ( Inia geoffrensis ) interacts with human fishing activities throughout its range in South America, which causes local communities to have negative reactions to the species’ presence. Here we report the encounter with a human-intentionally-entangled boto calf with a plastic bottle in Tefe river, and its successful release. At least another similar case occurred in 2009 at the nearby Mamiraua Sustainable Development Reserve, which suggests boto calves may be an easy target for human agonistic behavior towards the species. Educational programs at riverside and native communities should be implemented in order to ensure the conservation of this dolphin in the Central Amazon.

O simbolismo e o boto na Amazônia: religiosidade, religião, identidade

This paper discusses the legends and myths about the Amazonian river dolphin by examining their symbolism and selecting as the central aspect the issue of ambiguity. Furthermore, it tries to situate such legends in the religious context of other beliefs and myths, as well as practices related to popular religion, Catholicism and to a type of shamanic worship I call pajelanca cabocla (shamanic healing), a very popular form of medicine among rural, and of rural origin, populations in this Brazilian region. It also includes a brief discussion - related to the aforementioned - about identity, which covers such popular beliefs and practices.

A grave danger for the Ganges dolphin (Platanista gangetica Roxburgh) in the Subansiri River due to a large hydroelectric project

The Ganges River dolphin (Platanista gangetica Roxburgh) of Subansiri River may be in great danger of extinction due to the construction of the 2,000-MW Lower Subansiri Hydroelectric Project, which started in 2006. A recent survey indicates that there are now 29 Ganges dolphins, up from 21 in 2006. It is feared that drastic changes would occur in the downstream hydrology and ecology of the Subansiri River after the installation of the project, scheduled for 2012. The water discharge during a major part of the day in dry months would come down to a meager 6 cumecs from the present average of 450 cumecs (1 cumec is shorthand for cubic meter per second; also cms, or m3/s (m3s–1). Riverine mega fauna like the dolphin would be worst hit by this extremely low discharge. Dumping of an extra amount of sediment from different construction phases has already increased sediment load in the Subansiri downstream and degraded some earlier pockets of dolphin up to 20 km below the dam site. There is reason to believe that high sediment influx might have silted up some of the deeper pools downstream, a preferred habitat of dolphins, forcing them to congregate close to the confluence of the Subansiri.

Factors determining occupancy of Ganges River dolphin (Platanista gangetica gangetica) during differing river discharges in the upper Ganges, India

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River dolphin distribution in regulated river systems: implications for dry‐season flow regimes in the Gangetic basin

ABSTRACT River flow regulation and fragmentation is a global threat to freshwater biodiversity, ecosystem processes, and associated human activities. Large dams in the Ganges river basin of the Indian subcontinent have severely altered natural flow regimes, particularly in the low‐flow dry season. Altered flows could have negative impacts on endangered species such as the Ganges river dolphin Platanista gangetica. Habitat use by river dolphins was investigated in relation to river channel depth and morphology, over 332 km of the flow‐regulated Gandak River in India. Dolphin distribution patterns were compared across multiple spatial scales in the Gandak, Kosi, Chambal, Sone Rivers and the upper and lower sections of the Ganges main stem. Dolphin presence was recorded in 40% of segments in the Gandak river, with a best count of 257 (range 250–267) and average individual encounter rates at 0.75 dolphins km‐1 (SD 0.89). Bayesian zero-inflated spatial models showed that river dolphin abundance was positively influenced by river depth, presence of meanders and corresponded closely with gillnet fishing. Minimum mid‐channel depth requirements were estimated at 5.2 m for dolphin adults and between 2.2 and 2.4 m for mother–calf pairs. Adult dolphins showed highly similar habitat preferences across regulated or unregulated rivers, for depths &gt;5 m, and meandering channels. Dry‐season habitat availability was reduced as the degree of flow regulation increased across rivers, mainly owing to loss of lateral and longitudinal channel connectivity. Overall encounter rates were reduced from &gt;3 km‐1 in less regulated stretches, to &lt;0.3 km‐1 in regulated rivers. Clustering of dolphins in deep pools increased along the gradient of river flow reduction, with dolphins almost absent from intervening segments because of low flow rates. These results indicate the importance of maintaining adequate dry‐season flows to ensure river habitat availability and connectivity for dolphins. Copyright © 2012 John Wiley &amp; Sons, Ltd.

River Cetaceans and Habitat Change: Generalist Resilience or Specialist Vulnerability?

River dolphins are among the world’s most threatened mammals, and indeed the baiji (Lipotes vexillifer), a species endemic to China's Yangtze River, is likely extinct. Exploitation for products such as meat, oil, and skins has been a lesser feature in the population histories of river dolphins compared to most large mammals. Habitat factors are therefore of particular interest and concern. In this paper we attempt to describe the population-level responses of river dolphins to habitat transformation. We find circumstantial but compelling evidence supporting the view that, at a local scale, river dolphins are opportunists (generalists) capable of adapting to a wide range of habitat conditions while, at a river basin scale, they are more appropriately viewed as vulnerable specialists. The same evidence implies that the distributional responses of river dolphins to basinwide ecological change can be informative about their extinction risk, while their local behaviour patterns may provide important insights about critical ecological attributes. Empirical studies are needed on the ecology of river cetaceans, both to inform conservation efforts on behalf of these threatened animals and to help address broader concerns related to biodiversity conservation and the sustainability of human use in several of the world's largest river systems.

A new genus and species of late Miocene inioid (Cetacea, Odontoceti) from the Meherrin River, North Carolina, U.S.A.

ABSTRACT A new genus and species of extinct inioid odontocete (Meherrinia isoni) is based on nine partial crania that probably originated from the late Miocene marine Eastover Formation in North Carolina, U.S.A. They were collected from the riverbed of the Meherrin River, a tributary of the Chowan River. Ossification of the mesethmoid and the tight interdigitation of many sutures indicate that these specimens represent mature individuals. Key characteristics of the new inioid include maxillae that ‘squeeze’ the nasals into a slight hourglass shape and supraoccipital that is deeply wedged between the frontals and maxillae on the vertex. As compared to the extant iniid Inia geoffrensis (Amazon River dolphin) and the extant pontoporiid Pontoporia blainvillei (La Plata dolphin), Meherrinia is more plesiomorphic in having less elevated premaxillary eminences and supraorbital processes. In other respects Meherrinia is intermediate in morphology between the two extant genera of inioids. For example, the essentially symmetrical vertex is intermediate in height between the low and high vertices in Pontoporia blainvillei and Inia geoffrensis, respectively. A cladistic analysis of morphological and molecular data supports a sister-group relationship between Meherrinia and Inia; thus our new taxon is tentatively assigned to the Iniidae. If correct, this is the first iniid represented by diagnostic remains from marine deposits and just the second from North America.

Factors determining occupancy of Ganges River dolphin (Platanista gangetica gangetica) during differing river discharges in the upper Ganges, India

Factors determining occupancy of Ganges River dolphin (Platanista gangetica gangetica) during differing river discharges in the upper Ganges, India

Pattern and timing of diversification of Cetartiodactyla (Mammalia, Laurasiatheria), as revealed by a comprehensive analysis of mitochondrial genomes

The order Cetartiodactyla includes cetaceans (whales, dolphins and porpoises) that are found in all oceans and seas, as well as in some rivers, and artiodactyls (ruminants, pigs, peccaries, hippos, camels and llamas) that are present on all continents, except Antarctica and until recent invasions, Australia. There are currently 332 recognized cetartiodactyl species, which are classified into 132 genera and 22 families. Most phylogenetic studies have focused on deep relationships, and no comprehensive time-calibrated tree for the group has been published yet. In this study, 128 new complete mitochondrial genomes of Cetartiodactyla were sequenced and aligned with those extracted from nucleotide databases. Our alignment includes 14,902 unambiguously aligned nucleotide characters for 210 taxa, representing 183 species, 107 genera, and all cetartiodactyl families. Our mtDNA data produced a statistically robust tree, which is largely consistent with previous classifications. However, a few taxa were found to be para- or polyphyletic, including the family Balaenopteridae, as well as several genera and species. Accordingly, we propose several taxonomic changes in order to render the classification compatible with our molecular phylogeny. In some cases, the results can be interpreted as possible taxonomic misidentification or evidence for mtDNA introgression. The existence of three new cryptic species of Ruminantia should therefore be confirmed by further analyses using nuclear data. We estimate divergence times using Bayesian relaxed molecular clock models. The deepest nodes appeared very sensitive to prior assumptions leading to unreliable estimates, primarily because of the misleading effects of rate heterogeneity, saturation and divergent outgroups. In addition, we detected that Whippomorpha contains slow-evolving taxa, such as large whales and hippos, as well as fast-evolving taxa, such as river dolphins. Our results nevertheless indicate that the evolutionary history of cetartiodactyls was punctuated by four main phases of rapid radiation during the Cenozoic era: the sudden occurrence of the three extant lineages within Cetartiodactyla (Cetruminantia, Suina and Tylopoda); the basal diversification of Cetacea during the Early Oligocene; and two radiations that involve Cetacea and Pecora, one at the Oligocene/Miocene boundary and the other in the Middle Miocene. In addition, we show that the high species diversity now observed in the families Bovidae and Cervidae accumulated mainly during the Late Miocene and Plio-Pleistocene.

Photo-Identification: A Reliable and Noninvasive Tool for Studying Pink River Dolphins (Inia geoffrensis)

2 Foundation Omacha, Calle 86A No. 23-38, Bogota, Colombia Abstract Photo-identification is an important tool for study- ing cetacean residence patterns, population size, movements, and social structure. This knowl- edge directs conservation and management. We examined the reliability of photo-identification studies of pink river dolphins (Inia geoffrensis) with the hope of encouraging long-term popula- tion monitoring programs. From February 2007 to August 2009, 12 surveys were conducted in two locations of the Colombian Amazon and Orinoco river basins. We obtained 795 suitable digital photographs of Inia dolphins. We evaluated the reliability and duration of photo-identification by describing and evaluating the permanence and consistency of eight mark-types. Marks were categorized as reliable (pigmentation patterns on the dorsal ridge, nicks, bends, and wounds) or supplementary based on their prevalence in the population, and gain and loss rates. We created a catalog of well-marked animals, defined as indi- viduals with at least two reliable marks (55% of the images analyzed for this purpose). It contained photographs of the right side of 57 individuals and the left side of 40 individuals. There were 16 individuals with resightings over a 23-mo period. Future field surveys should use digital cameras with long lenses and fast shutter speeds in areas where dolphins are conspicuous when surfacing.

Whale phylogeny and rapid radiation events revealed using novel retroposed elements and their flanking sequences.

BackgroundA diversity of hypotheses have been proposed based on both morphological and molecular data to reveal phylogenetic relationships within the order Cetacea (dolphins, porpoises, and whales), and great progress has been made in the past two decades. However, there is still some controversy concerning relationships among certain cetacean taxa such as river dolphins and delphinoid species, which needs to be further addressed with more markers in an effort to address unresolved portions of the phylogeny.ResultsAn analysis of additional SINE insertions and SINE-flanking sequences supported the monophyly of the order Cetacea as well as Odontocete, Delphinoidea (Delphinidae + Phocoenidae + Mondontidae), and Delphinidae. A sister relationship between Delphinidae and Phocoenidae + Mondontidae was supported, and members of classical river dolphins and the genera Tursiops and Stenella were found to be paraphyletic. Estimates of divergence times revealed rapid divergences of basal Odontocete lineages in the Oligocene and Early Miocene, and a recent rapid diversification of Delphinidae in the Middle-Late Miocene and Pliocene within a narrow time frame.ConclusionsSeveral novel SINEs were found to differentiate Delphinidae from the other two families (Monodontidae and Phocoenidae), whereas the sister grouping of the latter two families with exclusion of Delphinidae was further revealed using the SINE-flanking sequences. Interestingly, some anomalous PCR amplification patterns of SINE insertions were detected, which can be explained as the result of potential ancestral SINE polymorphisms and incomplete lineage sorting. Although a few loci were potentially anomalous, this study demonstrated that the SINE-based approach is a powerful tool in phylogenetic studies. Identifying additional SINE elements that resolve the relationships in the superfamily Delphinoidea and family Delphinidae will be important steps forward in completely resolving cetacean phylogenetic relationships in the future.

Distribution pattern of finless porpoises at the junction of the Yangtze River and Poyang Lake observed by towed passive acoustic device

The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) is an endangered freshwater porpoise subspecies unique to the Yangtze River basin. Without immediate conservation measures, it could soon become extinct, just as the Yangtze River dolphin (baiji, Lipotes vexillifer). We report seasonal change in the local distribution of the porpoises living in the conjunction area of the middle reaches of the Yangtze River, side streams, and appended Poyang Lake. A towed stereo acoustic data-logger, A-tag, was used to detect echolocation signals and sound source bearing angles. The independent sound source directions provided the number of animals present, not just the number of sounds. Passive acoustic surveys were performed regularly from May 2007 to August 2010. The water level was highest in August (summer) and lowest in February (winter) and at mid-level in May (spring) and November (autumn). The average number of porpoises detected in 11 surveys conducted in different seasons varied from 0.53 to 1.26 individuals per km. No significant trend of reducing number of porpoises was detected during 3-y monitoring. The distribution of the porpoises was seasonally site-specific. In May and August, the animals were detected more often at river junctions than in the lake, but vice versa from November to February.

Ecological factors influencing group sizes of river dolphins (Inia geoffrensisandSotalia fluviatilis)

AbstractLiving in groups is usually driven by predation and competition for resources. River dolphins do not have natural predators but inhabit dynamic systems with predictable seasonal shifts. These ecological features may provide some insight into the forces driving group formation and help us to answer questions such as why river dolphins have some of the smallest group sizes of cetaceans, and why group sizes vary with time and place. We analyzed observations of group size forIniaandSotaliaover a 9 yr period. In the Amazon, largest group sizes occurred in main rivers and lakes, particularly during the low water season when resources are concentrated; smaller group sizes occurred in constricted waters (channels, tributaries, and confluences) that receive an influx of blackwaters that are poor in nutrients and sediments. In the Orinoco, the largest group sizes occurred during the transitional water season when the aquatic productivity increases. The largest group size ofIniaoccurred in the Orinoco location that contains the influx of two highly productive whitewater rivers. Flood pulses govern productivity and major biological factors of these river basins. Any threats to flood pulses will likely have an effect on the functionality of these ecosystems and the species living in them.

Seroprevalence of Toxoplasma gondii in free-living Amazon River dolphins (Inia geoffrensis) from central Amazon, Brazil

Toxoplasma gondii is an important pathogen in aquatic mammals and its presence in these animals may indicate the water contamination of aquatic environment by oocysts. Serum samples from 95 free-living Amazon River dolphins (Inia geoffrensis) from the Mamirauá Sustainable Development Reserve (RDSM), Tefé, Amazonas, Central Amazon, Brazil were tested for T. gondii antibodies using the modified agglutination test (MAT). Antibodies (MAT≥25) to T. gondii were found in 82 (86.3%) dolphins with titers of 1:25 in 24, 1:50 in 56, and 1:500 in 2. Results suggest a high level contamination of the aquatic environment of the home range of these animals.

A supermatrix analysis of genomic, morphological, and paleontological data from crown Cetacea.

BackgroundCetacea (dolphins, porpoises, and whales) is a clade of aquatic species that includes the most massive, deepest diving, and largest brained mammals. Understanding the temporal pattern of diversification in the group as well as the evolution of cetacean anatomy and behavior requires a robust and well-resolved phylogenetic hypothesis. Although a large body of molecular data has accumulated over the past 20 years, DNA sequences of cetaceans have not been directly integrated with the rich, cetacean fossil record to reconcile discrepancies among molecular and morphological characters.ResultsWe combined new nuclear DNA sequences, including segments of six genes (~2800 basepairs) from the functionally extinct Yangtze River dolphin, with an expanded morphological matrix and published genomic data. Diverse analyses of these data resolved the relationships of 74 taxa that represent all extant families and 11 extinct families of Cetacea. The resulting supermatrix (61,155 characters) and its sub-partitions were analyzed using parsimony methods. Bayesian and maximum likelihood (ML) searches were conducted on the molecular partition, and a molecular scaffold obtained from these searches was used to constrain a parsimony search of the morphological partition. Based on analysis of the supermatrix and model-based analyses of the molecular partition, we found overwhelming support for 15 extant clades. When extinct taxa are included, we recovered trees that are significantly correlated with the fossil record. These trees were used to reconstruct the timing of cetacean diversification and the evolution of characters shared by "river dolphins," a non-monophyletic set of species according to all of our phylogenetic analyses.ConclusionsThe parsimony analysis of the supermatrix and the analysis of morphology constrained to fit the ML/Bayesian molecular tree yielded broadly congruent phylogenetic hypotheses. In trees from both analyses, all Oligocene taxa included in our study fell outside crown Mysticeti and crown Odontoceti, suggesting that these two clades radiated in the late Oligocene or later, contra some recent molecular clock studies. Our trees also imply that many character states shared by river dolphins evolved in their oceanic ancestors, contradicting the hypothesis that these characters are convergent adaptations to fluvial habitats.

Novel gastric helicobacters and oral campylobacters are present in captive and wild cetaceans

The mammalian gastric and oral mucosa may be colonized by mixed Helicobacter and Campylobacter species, respectively, in individual animals. To better characterize the presence and distribution of Helicobacter and Campylobacter among marine mammals, we used PCR and 16S rDNA sequence analysis to examine gastric and oral samples from ten dolphins ( Tursiops gephyreus), one killer whale ( Orcinus orca), one false killer whale ( Pseudorca crassidens), and three wild La Plata river dolphins ( Pontoporia blainvillei). Helicobacter spp. DNA was widely distributed in gastric and oral samples from both captive and wild cetaceans. Phylogenetic analysis demonstrated two Helicobacter sequence clusters, one closely related to H. cetorum, a species isolated from dolphins and whales in North America. The second related cluster was to sequences obtained from dolphins in Australia and to gastric non- H. pylori helicobacters, and may represent a novel taxonomic group. Dental plaque sequences from four dolphins formed a third cluster within the Campylobacter genus that likely represents a novel species isolated from marine mammals. Identification of identical Helicobacter spp. DNA sequences from dental plaque, saliva and gastric fluids from the same hosts, suggests that the oral cavity may be involved in transmission. These results demonstrate that Helicobacter and Campylobacter species are commonly distributed in marine mammals, and identify taxonomic clusters that may represent novel species.

Population, density estimates, and conservation of river dolphins (IniaandSotalia) in the Amazon and Orinoco river basins

AbstractThis study is part of an on‐going effort to evaluate and monitor river dolphin populations in South America. It comprises the largest initiative to estimate population size and densities ofIniaandSotaliadolphins using statistically robust and standardized methods. From May 2006 to August 2007, seven visual surveys were conducted in selected large rivers of Bolivia, Colombia, Brazil, Ecuador, Peru, and Venezuela in the Amazon and Orinoco river basins. Population sizes ofIniaandSotaliawere estimated for different habitats (main river, tributary, lake, island, confluence, and channel). A total of 291 line and 890 strip transects were conducted, covering a distance of 2,704 linear kilometers. We observed 778Inia geoffrensis, 1,323Inia boliviensis, and 764Sotalia fluviatilis. High‐density areas were identified (within 200 m from the river banks, confluences, and lakes) and we propose that these constitute critical habitat for river dolphins. High densities of river dolphins seem to coincide with well‐managed freshwater protected areas and should be considered as hot spots for river dolphins in South America.

Freshwater Commercial Bycatch: An Understated Conservation Problem

Bycatch from marine commercial fisheries has been regarded as a global conservation concern for decades. Fortunately, some headway has been made in mitigating bycatch problems in marine fisheries. Freshwater commercial fisheries, however, have been relatively understudied. Although freshwater yields comprise 11% of the global commercial catch, bycatch research focusing on freshwater commercial fisheries represents only about 3% of the total bycatch literature. This paucity of research is particularly alarming given that so many of the world's threatened species live in freshwater. The limited literature that does exist includes examples of population declines attributed to commercial bycatch (e.g., the Yangtze River dolphin) and illustrates that bycatch is substantial in some systems (e.g., lake trout in Laurentian Great Lakes fisheries). Encouraging results from the marine realm can serve as models for bycatch research and development in freshwater and can lead to measurable gains in the conservation of ...