The Action Plan for South American River Dolphins 2010-2020
F. Trujillo, E. Crespo, P. Van Damme and S. Usma
Gómez-Salazar, C.; Trujillo, F.; Portocarrero, M.; Whitehead, H. 2011. Population, density estimates and conservation of river dolphins (Inia and Sotalia) in the Amazon and Orinoco river basins. Marine Mammal Science.
Click here to see maps with areas where surveys were conducted.
See also: WWF’s Global River Dolphin Initiative
Abstract: This 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 of Inia and Sotalia dolphins 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 of Inia and Sotalia were 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 778 Inia geoffrensis, 1,323 Inia boliviensis, and 764 Sotalia fluviatilis. High-density areas were identified (within200 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.
Gómez-Salazar, C.; Trujillo, F.; Whitehead, H. 2011. Ecological factors influencing groups sizes of river dolphins (Inia and Sotalia). Marine Mammal Science. In press.
Abstract: Living 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 for Inia and Sotalia over a 9-year 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) which receive an influx of blackwaters that are poor in nutrients and sediments. In the Orinoco, largest group sizes occurred during the transitional water season when the aquatic productivity increases. Largest group size of Inia occurred in the Orinoco location which 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.
Hollatz, C., Torres-Vilaça, S., Redondo, R., Marmontel, M., Baker, S., Santos, F. The Amazon River system as an ecological barrier driving genetic differentiation of the pink dolphin (Inia geoffrensis). Biological Journal of the Linnean Society, 2011, 102, 812–827. DOI: 10.1111/j.1095-8312.2011.01616.x
Abstract: The pink dolphin (Inia geoffrensis) is widely distributed along the Amazon and Orinoco basins, covering an area of approximately 7 million km2. Previous morphological and genetic studies have proposed the existence of at least two evolutionary significant units: one distributed across the Orinoco and Amazon basins and another confined to the Bolivian Amazon. The presence of barriers in the riverine environment has been suggested to play a significant role in shaping present-day patterns of ecological and genetic structure for this species. In the present study, we examined the phylogeographic structure, lineage divergence time and historical demography using mitochondrial (mt)DNA sequences in different pink dolphin populations distributed in large and small spatial scales, including two neighbouring Brazilian Amazon populations. mtDNA control region (CR) analysis revealed that the Brazilian haplotypes occupy an intermediate position compared to three previously studied geographic locations: the Colombian Amazon, the Colombian Orinoco, and the Bolivian Amazon. On a local scale, we have identified a pattern of maternal isolation between two neighbouring populations from Brazil. Six mtDNA CR haplotypes were identified inBrazil with no sharing between the two populations, as well as specific cytochrome b(cyt b) haplotypes identified in each locality. In addition, we analyzed autosomal microsatellites to investigate male-mediated gene flow and demographic changes within the study area in Brazil. Data analysis of 14 microsatellite loci failed to detect significant population subdivision, suggesting that male-mediated gene flow may maintain homogeneity between these two locations. Moreover, both mtDNA and microsatellite data indicate a major demographic collapse within Brazil in the late Pleistocene. Bayesian skyline plots (BSP) of mtDNA data revealed a stable population for Colombian and Brazilian Amazon lineages through time, whereas a population decline was demonstrated in the Colombian Orinoco lineage. Moreover, BSP and Tajima’s D and Fu’s Fs tests revealed a recent population expansion exclusively in the Bolivian sample. Finally, we estimated that the diversification of the Inia sp. lineage began in the Late Pliocene (approximately 3.1 Mya) and continued throughout the Pleistocene.
Ryan, G.E., Dove, V., Trujillo, F., Doherty Jr.P. 2011. Irrawaddy dolphin demography in the Mekong River: an application of mark–resight models. Ecosphere 2(5):58. doi:10.1890/ES10-00171.1
Abstract. Riverine Irrawaddy dolphin populations are critically endangered and much uncertainty exists over the population status in the Mekong River of northeast Cambodia and southern Lao People’s Democratic Republic (Lao PDR). We conducted 11 surveys over three years to estimate abundance at each survey as well as survival and the probability of individuals becoming unavailable for detection between surveys. We utilized novel mark–resight estimators to account for the detection process in estimating these parameters. Annual survival was 0.977 (0.040 SE) and movement in (0.060) and out (0.018) of an observable state was low. We estimated abundance at 84.5 (95% CI¼77.9–91.2) with little change over our surveys. We also estimated recruitment and population growth rate for the marked, and presumably older, individuals by estimating seniority using a reverse-time model. Seniority was estimated at 0.999 (0.028 SE), recruitment at 0.001 and population growth rate at 0.978. Although the population size appears to be stable, we believe this represents the slow disappearance of a long-lived animal with no recruitment. Along with the isolated nature of the population and reduced population size as compared to historical estimates, we believe this population is in serious threat of extirpation. We believe there may be as few as 7 or 8 animals in Lao PDR and that the species is at risk of extinction there in the short-term. Although recent management actions (e.g., outlawing of explosive fishing and some restriction on the use of gill-nets) have likely been beneficial we believe identifying population goals to work towards, identifying additional management actions to improve recruitment, and designing the survey methods to best estimate the success of these actions is needed.
WWF 2010. River dolphins and people: Shared Rivers, Shared Future. WWF Internal Report. See report.
Aliaga-Rossel, E., A. Beerman and J. Sarmiento. 2010. Stomach Content of a Juvenile Bolivian River Dolphin (Inia geoffrensis boliviensis) from the Upper Madeira Basin, Bolivia. Aquatic Mammals 2010, 36(3): 284-287DOI10.1578/AM.36.3.2010.284
Loch et al, 2009. Conflicts with fisheries and intentional killing of freshwater dolphins (Cetacea: Odontoceti) in the Western Brazilian Amazon. Biodiversity Conservervation. 18:3979–3988. Japura river, Tefe Lake (Western Brazilian Amazon). Website
Abstract: We report three cases of conflicts with fishing activities of freshwater dolphins Inia geoffrensis and Sotalia fluviatilis in the Western Brazilian Amazon. The animals presented several cuts produced by perforating and cutting objects, especially on the dorsum, sides and flukes. The wounds were probably caused by harpoons and machetes, gear commonly used by local inhabitants for fishing and agricultural practices in the Amazon. The carcasses had not been subsequently used in any way, which suggests that the animals were not killed for consumption. Conflicts with fishermen and persistent cultural taboos may have led to the deaths. These records are an indication of a growing situation of conflict with fishing activities that should be taken into consideration in the conservation policy planning of aquatic mammals in the Amazon.
Smith et al, 2008. Habitat selection of freshwater-dependent cetaceans and the potential effects of declining freshwater flows and sea-level rise in waterways of the Sundarbans mangrove forest, Bangladesh. Aquatic Conservation: Marine and Freshwater Ecosystem. Ganges River (Bangladesh). PDF
Abstract: Generalized additive models of sighting data for cetaceans collected during two surveys of waterways in the Sundarbans mangrove forest of Bangladesh indicated that Ganges River dolphin Platanista gangetica gangetica distribution was conditionally dependent (P50.05) on low salinity, high turbidity, and moderate depth during both low and high freshwater flow; and Irrawaddy dolphin Orcaella brevirostris distribution was conditionally dependent (P50.05) on low salinity during high freshwater flow, high and moderate depths during low and high freshwater flow, respectively; low and high-low extremes of turbidity during low and high freshwater flow, respectively; and high temperature and increasing numbers of large–small channel confluences during low freshwater flow. 2. According to sighting data collected over a 3-year period by the captains of three nature tourism vessels, there were significant differences between the actual and expected frequencies of Ganges River dolphin sightings and individuals according to various channel types (chi-square=64.22, P50.0001 and chi-square=134.14, P50.0001, respectively, df=6) and of Irrawaddy dolphin sightings and individuals (chi-square=15.28, P=0.0182, and chi-square=29.42, P50.0001, respectively, df=6), with shared preferences for wide sinuous channels with at least two small confluences or one large confluence. 3. The dependency exhibited by both species for environmental characteristics associated with abundant freshwater flow, including low salinity and the availability of confluences, make them particularly vulnerable to habitat loss due to upstream water abstraction and sea-level rise.4. Although the results of this study may not affect plans for construction in India of large-scale, inter-basin water transfer projects that will result in further declines in freshwater flows, or decisions within the international community about CO2 emissions affecting global sea levels, they can be used to prioritize locations where protective measures could be employed to benefit the long-term conservation of both species.
Martin et al., 2008. Object carrying as socio-sexual display in an aquatic mammal. Biology Letters. Mamiraua Sustainable Development Reserve (Brazil).Website
Abstract: Amazon river dolphins or botos (Inia geoffrensis Blainville) were observed carrying objects in 221 social groups over a 3-year study period. Sticks, branches and clumps of grass were taken from the water surface and often repeatedly thrashed or thrown. Lumps of hard clay were collected from the river bed and held in the mouth while the carrier rose slowly above the surface and sub- merged again. Carriers were predominantly adult males and less often subadult males. Adult females and young dolphins rarely carried objects. Groups of dolphins in which object carrying occurred were differentially large and comprised a greater proportion of adult males and adult females. Aggression, mostly between adult males, was significantly associated with object carrying. The behaviour occurred year-round, with peaks in March and July. A plausible explanation of the results is that object carrying by adult males is aimed at females and is stimulated by the number of females in the group, while aggression is targeted at adult males and is stimulated by object carrying in the group. We infer that object carrying in this sexually dimorphic species is socio-sexual display. It is either of ancient origin or has evolved independently in several geo- graphically isolated populations.
Mansur, 2008. Two Incidents of Fishing Gear Entanglement of Ganges River Dolphins (Platanista gangetica gangetica) in Waterways of the Sundarbans Mangrove Forest, Bangladesh. Aquatic Mammals. 34(3), 362-366. Sundarbans man- grove forest (Nepal, India, and Bangladesh). Website
Abstract: Incidental mortality in fishing gear, especially gill- nets, is considered among the most severe threats to the endangered Ganges River dolphin (Platanista gangetica gangetica). However, almost no information is available about actual interactions of the species with fisheries. An emaciated adult Ganges River dolphin was found stranded on Katka Beach where the eastern Sundarbans mangrove forest of Bangladesh meets the Bay of Bengal. The dolphin had a piece of fine-thread, mono-filament, 5-cm mesh-size gillnet, used to catch hilsa (Tenualosa ilisha) in large rivers and coastal areas, wrapped tightly around its rostrum. It also had a thicker strand, double-filament, 2.5- to 3.5-cm mesh- size gillnet, used to catch medium-size fin fishes in large rivers and small creeks, entangled in its teeth at the end of the rostrum. The dolphin was disentangled and released. In another incident, the carcass of a nonlactating female Ganges River dolphin was also retrieved from a local fishing boat in the northeast portion of the Sundarbans. The dolphin had become entangled in a long-line fishing gear very similar to the rolling hooks used in the Yangtze River that have been cited as among the primary factors contributing to the probable extinction of the baiji (Lipotes vexillifer). These incidents confirm that Ganges River dolphins are vulnerable to being accidently killed by becoming entangled in gillnets and long-lines. These events also indicate the importance of monitoring mortality rates and establishing a protected area network in channel segments where the species occurs in relatively high numbers.
Gravena et al, 2008. Amazon River dolphin love fetishes: From folklore to molecular forensics. Marine Mammal Science. 24(4): 969–978. Website
Abstract: Traditional Amazonian folklore includes a host of supernatural beings believed to protect its forests and rivers. One of the most powerful and widely recognized of these beings is the Amazon River dolphin Inia geoffrensis, or boto. The boto is traditionally viewed as a mischievous and tempestuous being, both feared and respected. The most sensational folklore concerning botos is that they transform themselves at dusk into handsome Caucasian men, who are skilled at dancing and seducing young women. Botos are also believed to at times enter boats or households, paralyzing their occupants to engage in sexual intercourse. Before first light, the boto returns back into water, reverting into its dolphin form (Cravalho 1999). Indeed, unexpected teenage pregnancies in the Amazon region have been traditionally attributed to seduction by the boto (Cravalho 1999).
Rossi-Santos et al 2007. Residence and site fidelity of Sotalia guianensis in the Caravelas River Estuary, eastern Brazil. Journal of the marine biological Association of the United Kingdom. 87, 207–212. Caravelas River Estuary (Brazil). Website
Abstract: Between April 2002 and April 2005, 210 estuarine dolphin groups were sighted, with 58 animals individually identified. Fifteen dolphins were photo-identified just once, while only two animals were sighted in 15 different months. Some individuals showed long-term residence (more than 3 y). Residence rates showed heterogeneity in the dolphin’s permanence of the estuary, with 60% of the individuals with low numbers (<10) and only 7% showing high values for residence (maximum=45.9). Continued resightings of some dolphins support the regular use of the study area by the animals, despite some individuals that, after a long time without resightings were registered again. Individual range analysis showed that dolphins shared the same common area, the Caravelas River Estuary. A marked fluctuation in the number of photo-identified dolphins was observed in the study area, revealed by the high number of individuals with just a few resightings. The majority of the dolphins (60%) present a yearly residence pattern, as observed in other areas, suggesting that a few individuals show high fidelity for the area, while many other dolphins move constantly between different areas for unknown reasons.
McGuire and Aliaga-Rossel, 2007. Seasonality of Reproduction in Amazon River Dolphins (Inia geoffrensis) in Three Major River Basins of South America. Biotropica. 39(1): 129–135 . Orinoco, Amazon, and Mamore river basins (Bolivia, Peru, and Venezuela). Website
Abstract: Reproduction of Amazon River Dolphins, Inia geoffrensis, is generally reported to be highly seasonal; however, this conclusion is based on studies from only one area of Inia distribution from throughout the Amazon and Orinoco river basins. Our observations of live dolphins from the Orinoco, Amazon, and Mamore river basins (in Venezuela, Peru and Bolivia, respectively) indicate that reproduction in Inia often occurs year-round, with seasonal peaks varying according to geographic location. Inia neonates in Peru and Bolivia were seen in all seasons, and were observed most often in falling water (season was defined by relative water level). Conversely, neonates in Venezuela were seen at the end of low water and in rising water, yet were never observed during falling water. Inia mating behavior in Peru was observed in all seasons, while mating was observed only during falling and low water in Bolivia. Our review of the literature from throughout the range of Inia indicates variation in reproductive seasonality, with year-round reproduction in some areas. Seasonality of peaks in births varied according to study area, and may be more closely associated with local environmental and prey conditions than with taxonomic relatedness, relative seasonal differences in water levels, or broad geographic distribution.
Cunha and Watts, 2007. Twelve microsatellite loci for marine and riverine tucuxi dolphins (Sotalia guianensis and Sotalia fluviatilis).Molecular Ecology Notes. Website
Abstract: Twelve dinucleotide polymorphic microsatellite loci were isolated from the marine tucuxi dolphin (Sotalia guianensis). Levels of genetic diversity were assessed using 34 individuals from the coasts of Rio de Janeiro and Pará, Brazil. Numbers of alleles varied between two and 14, and observed and expected heterozygosities ranged from 0.040 to 0.704, and from 0.093 to 0.818, respectively. Moreover, eight of these loci were variable in the riverine tucuxi Sotalia fluviatilis. This is the first description of microsatellite primers from a dolphin that does not belong to the Delphininae. These loci are currently being used in the analysis of population structure of both tucuxi species.
Caballero et al, 2007. Taxonomic Status of the Genus Sotalia: Species Level Ranking for Tuxcuxi (Sotalia Fluviatilis) and Costero (Sotalia Guianesis) Dolphins. Marine Mammal Science. VOL. 23, NO. 2. Nicaragua Colombian Caribbean, Maracaibo Lake, French Guiana Amazonian Estuary Brazilian Coast, Peruvian Amazon Colombian Amazon, Brazilian Amazon
Abstract: Dolphins of the genus Sotalia are found along the Caribbean and Atlantic coasts of Central and South America and in the Amazon River and most of its tributaries. At present, the taxonomy of these dolphins remains unresolved. Although five species were described in the late 1800s, only one species is recognized currently (Sotalia fluviatilis) with two ecotypes or subspecies, the coastal subspecies (Sotalia fluviatilis guianensis) and the riverine subspecies (Sotalia fluviatilis fluviatilis). Recent morpho- metric analyses, as well as mitochondrial DNA analysis, suggested recognition of each subspecies as separate species. Here we review the history of the classification of this genus and present new genetic evidence from ten nuclear and three mitochondrial genes supporting the elevation of each subspecies to the species level under the Genealogical/Lineage Concordance Species Concept and the criterion of irreversible divergence. We also review additional evidence for this taxonomic revision from previously published and unpublished genetic, morphological, and ecological stud- ies. We propose the common name “costero” for the coastal species, Sotalia guianensis (Van Be ́ne ́den 1864), and accept the previously proposed “tucuxi” dolphin, Sotalia fluviatilis (Gervais, 1853), for the riverine species.
Bonar et all, 2007. A retrospective study of pathologic findings in the amazon and Orinoco River dolphin (Inia geoffrensis) in captivity. Journal of Zoo and Wildlife Medicine . 38(2): 177–191, 2007. Amazon River. Website
Abstract: River dolphins are especially susceptible to negative human impacts. For their conservation, attempts of relocation or procreation ex situ may become important in the future to avoid their extinction. Additional knowledge and medical experiences of river dolphin management in captivity may aid such conservation efforts. The medical records and necropsy and histopathology reports on 123 captive Amazon River dolphins (Inia geoffrensis) were re- viewed. Of these 123 animals, 105 were necropsied and 70 necropsies were supported with histopathology. Eighteen animals were not necropsied. Among wild-born animals, mortality was highest in the first 2 mo immediately postcapture and transport, accounting for 32 of 123 deaths. Pneumonia and skin lesions (cutaneous and subcutaneous ulcerations and abscesses) were the most common findings, found in 44 of 105 (42%) and 38 of 105 (36%) of gross diagnoses, respectively. At least 10 of 44 cases of pneumonia diagnosed grossly included a verminous component. Cachexia, from a variety of causes, was a major gross finding in 21 animals. Fifteen animals had histologic evidence of significant renal pathology, and this was the primary cause of death in 13 cases. Hepatic pathology was found in 18 cases, and bacterial sepsis was confirmed via histology in 16 cases. Based on these findings, it may be concluded that keys to successful maintenance of this species include 1) prophylactic anthelminthic and antibiotic therapy immediately post- capture; 2) maintenance of animals in larger enclosures than in past attempts, in compatible groups, and in facilities capable of separating aggressive animals; 3) maintenance in microbiologically hygienic water quality at all times; and 4) a proactive program of preventive medicine during the immediate postcapture, quarantine, and maintenance period of captivity.
Smith et al, 2006. Abundance of Irrawaddy Dolphins (Orcaella brevirostris) and Ganges River Dolphins (Platanista gangetica gangetica) estimated using current counts made by independent teams in waterways of the sundarbans mangrove forest in Bangladesh. Marine Mammal Science. 22(3): 527–547. Bangladesh. PDF
Abstract: Independent observer teams made concurrent counts of Irrawaddy dolphins Orcaella brevirostris and Ganges River dolphins Platanista gangetica gangetica in mangrove channels of the Sundarbans Delta in Bangladesh. These counts were corrected for missed groups using mark-recapture models. For Irrawaddy dolphins, a stratified Lincoln-Petersen model, which incorporated group size and sighting conditions as covariates, and a Huggins conditional likelihood model, which averaged models that individually incorporated group size, sighting conditions, and channel width as covariates, generated abundance estimates of 397 individuals (CV = 10.2%) and 451 individuals (CV = 9.6%), respectively. For Ganges River dolphins, a stratified Lincoln-Petersen model, which incorporated group size as a covariate, and a Huggins conditional likelihood model, which averaged the same models described above, generated abundance estimates of 196 individuals (CV = 12.7%) and 225 individuals (CV = 12.6%), respectively. Although the estimates for both models were relatively close, the analytical advantages of the Huggins models probably outweigh those of the Lincoln-Petersen models. However, the latter should be considered appropriate when simplicity is a priority. This study found that waterways of the Sundarbans support significant numbers of Irrawaddy and Ganges River dolphins, especially compared to other areas where the species have been surveyed.
Martin et al., 2006. Does radio tagging affect the survival or reproduction of small cetaceans? A test. Marine Mammal Science. 22(1): 17–24. Mamiraua Sustainable Development Reserve (Brazil). Website
Abstract: A long-term study of botos (Inia Geoffrensis) in the Brazilian Amazon permitted the comparison of survival and reproduction between 51 adults fitted with radio transmitters and an equal number that were captured and handled in the same way but released without a transmitter. For both sexes combined, 47 radio tagged botos (92.2%) survived at least three years after release compared with 42 (82.4%) without radios, equating to annual survival of 97.3% and 93.6% respectively. The difference was not statistically significant. Eight of 15 closely monitored radio tagged females were lactating at capture, and all their calves weaned successfully. Two that were pregnant at capture subsequently gave birth. The mean number of calves per year born to these 15 females after first release was 0.172 (SD = 0.107) and to 17 non-tagged was 0.174 (SD = 0.095), again a non-significant difference. These results indicate that the anchoring of packages to the dorsal fin of dolphins can be accomplished with no measurable impact on their subsequent survival or reproductive output. However, botos may be unusually robust to handling, and this study should not be used to justify using similar techniques on other species without customary caution, diligence, and expert guidance.
Martin & da Silva, 2006. Sexual Dimorphism and body scarring in the Boto (Amazon River Dolphin) Inia geofrensis. Marine Mammal Science. 22(1): 25–33.
Abstract: Measurements and quantitative descriptions of a large sample of live adult botos (Inia geoffrensis) were obtained from the Mamiraua Reserve in the central Amazon. Males were on average 16% longer and weighed 55% more than females, demonstrating that this species is one of the most sexually dimorphic of all cetaceans for size. Males were also pinker than females, more heavily scarred by intraspecific tooth rakes, and had more life-threatening injuries. Some larger males had areas of modified skin that may simply be scar tissue, but may also be a heritable characteristic used as a shield or weapon. As in sperm whales, sexual size dimorphism and male-male aggression appear to be linked in botos, suggesting fierce competition for a resource—probably mating opportunities. The boto is unique among river dolphins in that males are larger than females. This distinction implies long evolutionary separation and fundamental differences in social behavior.
Aliaga-Rossel et al, 2006. Distribution and encounter rates of the river dolphin (Inia geoffrensis boliviensis) in the central Bolivian Amazon. Journal of Cetacean research and management.8(1):87–92. Mamore, Tijamuchi, Apere, Yacuma, Rapulo (Department of Beni;Llanos de Mojos).
Abstract: The ecology and conservation status of river dolphins (Inia sp.) distributed in the lowland rivers of Bolivia are poorly understood and only recently have basic studies been conducted to investigate their population size, taxonomic status, distribution, behaviour, environmental threats and ecology in this region. This paper examines the distribution and encounter rates of the bufeo (Inia sp.) in the middle reach of the Bolivian Amazon and was conducted in the Mamoré River and four of its tributaries during the low water season. Methods were employed which can be replicated during future surveys of Bolivian river dolphins and the results can be compared with those from surveys of Inia throughout its range. Sixty-two hours were spent surveying for dolphins, with 68% of the effort in Mamoré River and 32% in its tributaries. The Inia encounter rates reported here (1.6-5.8 dolphins km21) are the highest recorded anywhere in its broad geographic range; and indicate the importance of continuing and expanding surveys in this area. The mean group size was greatest in the Tijamuchi River (3.3±2.96) and smallest in the Yacuma River (1.8±0.75) and the maximum group size was 14. The high bufeo encounter rates in the central Bolivian Amazon can be taken as a reflection of the general environmental status of the region; however, a growing human population, associated with an increase in boat traffic and fishing activity, poses a future threat to bufeos and their aquatic habitats.
Smith et al 2004. New information on the status of finless porpoises Neophocaena phocaenoides and Irrawaddy dolphins Orcaella brevirostris in Bangladesh and Myanmar. Unpublished Report. Sundarbans Delta (Bangladesh).
Abstract: A line-transect survey conducted in February 2004 along 780 km of trackline in the outer Sundarbans Delta of Bangladesh resulted in abundance estimates of 1,382 (CV=54.8%) and 5,383 (CV=39.5) for finless porpoises and Irrawaddy dolphins, respectively. These estimates indicate that the waters of Bangladesh support regionally important populations of both species. The optimistic conservation implications of the survey are tempered by observations of potential unsustainable bycatch in gill net fisheries targeting elasmobranchs. One-way ANOVAs (df = 1, 84) indicated significant differences between the two species for depth (Prob. = 0.001), temperature (Prob. 0.004), salinity (Prob. 0.001) and probably turbidity (Prob. = 0.057). A discriminant analysis pointed towards depth and salinity as the two most important factors that differentiate environmental preferences of the two species. A line transect survey conducted in February/March 2005 along 955 km of trackline in the Mergui Archipelago of Myanmar recorded only two sightings of finless porpoises (one of five and one of two individuals) and one sighting of Irrawaddy dolphins (12 individuals). All three sightings were within 15 km of each other in a small semi- enclosed bay offshore of the Kyaukpa and Tenasserim river mouths and their associated mangrove forests. The paucity of sightings and limited range of finless porpoises and Irrawaddy dolphins recorded during this survey suggest that both species occur only in low densities in the Mergui Archipelago, probably due to the lack of large freshwater inputs and possibly incidental catches in the intensive gillnet fisheries that operate in the area where the animals were observed.
Martin & da Silva, 2004. River dolphins and flooded forest: seasonal habitat use and sexual segregation of botos (Inia geoffrensis) in an extreme cetacean environment. The Zoological Society of London. 263, 295–305. Mamiraua Sustainable Development Reserve (Brazil).
Abstract: Habitat use by the boto, or Amazon river dolphin Inia geoffrensis, was investigated in and around the Mamiraua Reserve, Brazil. Largely forested with numerous channels and lakes, Mamiraua comprises a variety of seasonal floodplain habitats known collectively as várzea. The annual cycle of flooding in this region (amplitude 11–15 m) dominates all life. Profound seasonal differences in dolphin density between habitats were consistent with known fish movements, in turn dictated by changes in water level and dissolved oxygen. An exodus of botos from floodplain to river at low water prevents dolphins being trapped in areas that become entirely dry. Densities of botos in floodplain channels were seasonally higher (up to 18 km−2) than reported for any cetacean worldwide. Adults were largely segregated by sex except at low water. Females and calves dominated in chavascal habitat – the areas most remote from rivers, which were preferred by males. Probable causes of this segregation are the energetic requirements of calves and the safety of females and/or calves from male harassment. Some 80% of botos occurring on rivers were within 150 m of the margins. The reliance of adult females and calves on varzea in a region with exceptional dolphin densities demonstrates the importance of floodplain habitats for the boto, and may be the key determinant of this species’ distribution.
Martin & da Silva, 2004. Riverine habitat preferences of Botos (Inia Geoffrensis) and Tucuxis (Sotalia Fluviatilis) in the Central Amazon. Marine Mammal Science. 20(2):189-200.Japud, Amazon (Brazil).
Abstract: The distribution and density of the Amazon’s two contrasting endemic dolphins-boto, or Amazon river dolphin, lnia geofirensis, and tucuxi, Sotafia fluviatilis were examined on two adjoining large rivers in western Brazil. Using a 17-m river boat as a sightings platform, strip transects were used to cover areas within 150 m of the river margin and line transects were used in all other areas. Highest densities of both dolphins occurred near the margin, and lowest in the center of rivers. Seven different habitats were identified along river margins. The boto and the tucuxi differed in some elements of habitat choice, but they shared a preference for areas with diminished current and where two channels joined. Neither species favored the two most common edge types in this region of the Amazon-mud banks and flooded forest margins. Overall, the most preferred habitat type was the least common, and known as “meeting of the waters.” In these areas a channel of sediment-rich white water meets one carrying acidic black water; the resultant mixing produces particularly productive, and obviously attractive, conditions for dolphins. These results demonstrate that Amazonian dolphins selectively occur in areas known to be favored for gill net deployment by local fishermen, and may explain why entanglement is apparently a common cause of mortality.
Zhang et al, 2003. The Yangtze River dolphin or baiji (Lipotes vexillifer): population status and conservation issues in the Yangtze River, China. Aquatic Conservation: Marine and Freshwater Ecosystem. 13: 51–64. Yangtze River (China).
Abstract: Baiji were sighted 17 times during three recent simultaneous multi-vessel surveys in the Yangtze River, China (November 4–10, 1997; December 4–9, 1998; October 31–November 5, 1999). There were 11 sightings in 1997 (consisting of 17 animals), five in 1998 (seven animals), and two in 1999 (four animals). It was concluded that 13 individuals could be considered as a minimum number of the baiji currently in the Yangtze River. 2. An annual rate of population decrease was roughly estimated as 10%. From the body sizes observed, the proportions of old, adult and immature individuals were approximately estimated at 57, 26, and 17% respectively 3 baiji showed a significant attraction to confluences and sand bars with large eddies. The present distribution range of the baiji is less than 1400 km in length in the Yangtze main river. Distances between the two nearest groups of baiji appear to be increasing 4 two typical sightings are described, in which surfacing and movements of baiji were recorded. Baiji were often found swimming together with finless porpoise. In the surveys they occurred in the same group in 63% of occurrences. Interactions between baiji and finless porpoise are described and discussed. 5. Human activities are the main threats to the baiji. Illegal electrical fishing accounted for 40% of known mortalities during the 1990s. Engineering explosions for maintaining navigation channels have become another main cause of baiji deaths. The last hope of saving the species may be to translocate the remaining baiji into a semi-captive reserve, known as the ‘Baiji Semi-natural Reserve’.
Monteiro-Neto et al, 2003. Concentrations of heavy metals in Sotalia fluviatilis (Cetacea: Delphinidae) off the coast of Ceara , northeast Brazil. Environmental Pollution. 123 (2003) 319–324. Brazil – the coast of Ceara state.
Abstract: Lead (Pb), cadmium (Cd) and mercury (Hg) concentrations on liver and kidney of Sotalia fluviatilis (Cetacea: Delphinidae) stranded in the coast of Ceara , Brazil, were studied from 1996 to 1999. Pb levels were usually lower than the detection limit (0.1 mg/ g). Concentrations of Cd were significantly higher in kidney than liver, averaging 0.8 mg/g. Mercury accumulation took place mainly in liver with an average concentration of 4.6 mg/g. Both metals were significantly higher in larger mature individuals, but differences between sexes were not significant. The detection of Cd, Hg and Pb in tissue samples of S. fluviatilis off the coast of Ceara indicated that heavy metals are locally available in the water, and bioaccumulation may be occurring through the food web. Contamination levels were not considered critical, but could be related to Ceara’s growing industrial development. The associated risks of pollution outfalls may pose a threat to marine organisms in a near future, especially for top predators such as S. fluviatilis.
Aliaga-Rossel, 2003. Current situation of the river dolphin (Inia geoffrensis) in Bolivia. Ecologia en Bolivia. 38(2): 167-177. Ibare, Mamore (Department of Beni).
Abstract: Entre las especies de mamíferos acuáticos, el delfín rosado de río (Inia geoffrensis) o bufeo como es llamado en Bolivia, constituye la única especie de cetáceo que habita exclusivamente en aguas dulces de América. Es considerado “vulnerable” por la IUCN (Klinowska 1991), pero está en mejor condición que otras especies de delfines de río del mundo, cuyo número ha sufrido un marcado descenso debido a conflictos con las poblaciones humanas. Por ejemplo, el baiji (Lipotes vexillifer) de China es el más amenazado con una población estimada menor a cien individuos, mientras que el bhulan (Platanista minor) en Pakistán cuenta alrededor de 500 individuos aislados y divididos en pequeñas sub poblaciones por las represas hidroeléctricas (Reeves et al. 2003, Zhanga et al. 2003, Klinowska 1991). En adición, todos los delfines de río son susceptibles a muertes accidentales por las embarcaciones y actividades de pesca, principalmente con redes y dinamita (Best & Da Silva 1989a, Klinowska 1991, Reeves et al. 2000, Aliaga-Rossel 2002, Reeves et al. 2003.) El bufeo está distribuido ampliamente en Sudamérica, y habita ríos en la cuenca del Orinoco de Colombia y Venezuela, así como del Amazonas, en Brasil, Colombia, Ecuador, Perú, Guyana y Bolivia, cubriendo un área equivalente a siete millones de kilómetros cuadrados (Best & Da Silva 1989a, 1989b). El tamaño de la población aún no es conocido y existen pocos estudios referidos a su ecología, comportamiento, estructura social y biología. La mayoría de éstos son trabajos generales o estimaciones poblacionales, entre los que se tiene a las investigaciones de Trebbau & Van Bree (1974), Schnapp & Howroyd (1992) y Mc Guire & Winemiller (1998) en Venezuela; Magnusson et al. (1980) y Da Silva (1994) en el Brasil; Meade & Koehnken (1991) en la cuenca del Orinoco de Venezuela y Colombia; Hurtado (1996) y Vidal et al. (1997) en el río Amazonas de Colombia. Leatherwood (1996), Zuñiga (1999) y Mc Guire (2002) en el Perú, Herman et al. (1996) en el Ecuador y Aliaga- Rossel (2002), Aliaga- Rossel et al. (en prep.) en Bolivia. Algunas de estas investigaciones son de corto plazo, emplean métodos diferentes y no estandarizados en cada estimación; por ello, no es posible realizar comparaciones precisas entre estos trabajos. Actualmente, se están llevando a cabo proyectos de investigación de largo plazo por Vera Da Silva en Brasil y por La Fundación Omacha en Colombia (T. Mc Guire com. pers., 2003, F. Trujillo 2001 com. pers., Smith 1996), pero en Bolivia no se cuenta con planes de investigación de este tipo.El objetivo del presente trabajo es el de revisar la información actual sobre la situación taxonómica, ecológica, distribución, amenazas y estado de conservación del delfín de río en Bolivia e identificar las prioridades de investigación y conservación.
Aliaga Rossel 2002. Distribution and abundance of the river dolphin (Inia geoffrensis) in the Tijamuchi River, Beni, Bolivia. Aquatic Mammals. 28 (3): 312-323. Tijamuchi (Beni, Bolivia). Website
Abstract: Very few studies have been conducted in Bolivia regarding the distribution, behaviour or ecology of the Amazon river dolphin (Inia geoffrensis). The only published studies of bufeo in Bolivia are from Pilleri (1969) and Pillieri & Gihr (1977) and were not quantitative investigations of river dolphin abundance or distribution. The work presented here consists of an estimate of abundance and description of the seasonal distribution of the bufeo in the Tijamuchi River, Beni, Bolivia. The study was conducted during January 1998-September 199 and represents four hydro-climatic season (i.e., low, high, rising, and falling waters). wo hundred and twelve h were spent in survey effort. The total study area was approximately 185km along the river. Strip transects were used to survey for dolphins. Dolphin distributions among the three habitats were copared; these habitats were riverine-balckwaters, riverine-mixed waters (black and white), and oxbow lakes of the river system. Group size and age structure were recorded. Any dead dolphins were necropsied. On average, 208 bufeos were observed in the Tijamuchi River, with an average encounter rate of 1.12 dolphins/linear km. Dolphins were seen most frequently during low and falling water (56% of total observations) and least often during high waters (22% of total observations). These seasonal differences were statistically significant. Dolphins were seen most often in oxbow lakes, and next often in confluences. Difference in dolphin abundance according to water colour were not statistically significant. There was some evidence of associations between group size and season, and group size and water colour. Fourty two per cent of observations were of solitary dolphins, 32% were of pairs, and maximum group size was 19. Calves were seen most often during falling and low waters. Causes of mortality of dolphins in the study area were identified as entaglement in fishing nets, intra-specific aggression, and collision with outboard motors.
Podos et al, 2002.Vocalizations of Amazon River Dolphins, Inia geoffrensis: Insights into the Evolutionary Origins of Delphinid Whistles. Ethology. 108, 601—612 . Mamiraua Sustainable Development Reserve (Brazil). Website
Abstract: Oceanic dolphins (Odontoceti: Delphinidae) produce tonal whistles, the structure and function of which have been fairly well characterized. Less is known about the evolutionary origins of delphinid whistles, including basic information about vocal structure in sister taxa such as the Platanistidae river dolphins. Here we characterize vocalizations of the Amazon River dolphin (Inia geoffrensis), for which whistles have been reported but not well documented. We studied Inia at the Mamiraua ́ Sustainable Development Reserve in central Brazilian Amazonia. During 480 5-min blocks (over 5 weeks) we monitored and recorded vocalizations, noted group size and activity, and tallied frequencies of breathing and pre- diving surfaces. Overall, Inia vocal output correlated positively with pre-diving surfaces, suggesting that vocalizations are associated with feeding. Acoustic analyses revealed Inia vocalizations to be structurally distinct from typical delphinid whistles, including those of the delphinid Sotalia fluviatilis recorded at our field site. These data support the hypothesis that whistles are a recently derived vocalization unique to the Delphinidae.
Banguera et al., 2002. Molecular Identification of Evolutionarily Significant Units in the Amazon River Dolphin Inia sp. (Cetacea: Iniidae). The American Genetic Association. 93:312–322. Orinoco, Guaviare, Inirida, and Arauca (Colombia). PDF
Abstract: The Amazon river dolphin, genus Inia, is endemic to the major river basins of northern South America. No previous studies have focused on the genetic structure of this genus. In this work, 96 DNA samples from specimens of this genus were collected in the Orinoco basin (four rivers), the Putumayo River, a tributary of the Colombian Amazon and the Mamore, and the Tijamuch and Ipurupuru rivers in the Bolivian Amazon. These samples were used to amplify a fragment of 400 bp of the mitochondrial DNA (mtDNA) control region. In addition, 38 of these samples were also used to sequence 600 bp of the mitochondrial cytochrome b gene. The analysis of the population structure subdivision with an analysis of molecular variance (AMOVA) revealed important aspects about the genetic structure of Inia groups from these three geographically separate regions. By comparing the control region DNA and cytochrome b sequences, distinct types of nonshared haplotypes were observed. The net genetic divergence of control region sequences was 6.53% between the Orinoco and Bolivian rivers, 5.32% between the Putumayo and Bolivian rivers, and 2.50% between the Orinoco and Putumayo rivers. For the cytochrome b gene, these values were 2.48%, 2.98%, and 0.06%, respectively. The nucleotide sequences were analyzed phylogenetically using several genetic distance matrices and applying neighbor joining, maximum likelihood, and maximum parsimony procedures. The results support the proposal to subdivide the Inia genus into at least two evolutionarily significant units: one confined to the Bolivian river basin and the other widely distributed across the Amazon and Orinoco basins.
Schnell & Edwards, 2001. Status and ecology of Sotalia Fluviatilis in the Cayos Miskito Reserve, Nicaragua. Marine Mammal Science. 17(3):445-472. Cayos Miskito Reserve (Nicaragua).
Abstract: In March through May of 1996-1998, we conducted research in the Cayos Miskito Reserve, Nicaragua, to assess the status, ecology, and distribution of Sotalia juviatilis, a dolphin known from southern Brazil to Honduras. Aerial and boat surveys of lagoons, inlets, and coastal areas were conducted and observational information collected on Sotalia activity, behavior, and other factors relating to its ecology. During boat surveys 183 groups (536 individ- uals) were sighted (for areas with Sotalia, mean overall density = 0.604 in- dividuals/km2, coastal areas = 0.647/km2,inlets = 0.578/km2,and lagoons = 0.486/km2). Overall, based on all sightings, mean group size was 3.01 (SD = 1.79, range 1-15) and varied among years(2= 4.20 in 1996, 2.58 in 1997, and 3.39 in 1998), but not for different months. We estimate That 49 Sotalia inhabited the portions of the Reserve we studied. Sightings of Sotalia groups were non-random (nearest-neighbor analysis); clumping of sightings indicates that some areas were preferred. In both Pahara inlet and Wauhta lagoon, sightings were more frequent after 1200 than in the morning. In coastal areas Sotalia were sighted most often within 100 m of shore (54.0%), less often from 101 to 200 m (39.1%), and infrequently from 201 to 300 m (6.8%). Seldom were animals observed in more than 5 m of water, and usually it was considerably shallower ( k ,<2 m). Feeding was the predominant of five recorded activities (ie., traveling, feeding, socializing, resting, and other), based on time of group sighting (70.3%) and during instantaneous sampling (56.3%). Resource distribution appears to be an important factor influencing Sotalia distribution in the Reserve.
Romero et al. 2001. Cetaceans of Venezuela: Their Distribution and Conservation Status. national oceanic and atmospheric administration. Venezuela. PDF
Abstract: Sighting, stranding, and capture records of whales and dolphins for Venezuela were assembled and analyzed to document the Venezuelan cetacean fauna and its distribution in the eastern Caribbean. An attempt was made to con firm species identification for each of the records, yielding 443 that encompass 21 species of cetaceans now confirmed to occur in Venezuelan marine, estuarine, and freshwater habitats. For each species, we report its global and local distribution, conservation status and threats, and the common names used, along with our proposal for a Spanish common name. Bryde’s whale (Balaenoptera edeni) is the most commonly reported mysticete. The long-beaked common dolphin (Delphinus capensis) is the most frequent of the odontocetes in marine waters. The boto or tonina (Inia geoffrensis) was found to be ubiquitous in the Orinoco watershed. The distribution of marine records is consistent with the pattern of productivity of Venezuelan marine waters, i.e., a concentration at 63°07′W through 65°26′W with records declining to the east and to the west. An examination of the records for all cetaceans in the Caribbean leads us to conclude that seven additional species may be present in Venezuelan waters.
Hamilton et al, 2001. Evolution of river dolphins. Proceedings of the royal socitey B: Biological Sciences. 268, 549^556. Brazil, Peru and Bolivia. Website
Janik et al, 2000. Tucuxi (Sotalia Fluviatilis) occurs in Nicaragua, 800km north of its previously known range. Marine Mammal Science. VOL. 16. NO. 2. . Wawa River, Leimus Lagoon, Pahara Lagoon, Waunta Lagoon (Nicaragua). Website
Cassens et al, 2000. Independent adaptation to riverine habitats allowed survival of ancient cetacean lineages. Proceedings of the National Academy of Sciences. Vol 97 (21): 11343–11347. Nicaragua, Colombia, Caribbean, Maracaibo, Lake, French Guiana, Amazonian Estuary, Brazilian Coast, Peruvian Colombian and Brazilian Amazon. Website
Abstract: The four species of ‘‘river dolphins’’ are associated with six separate great river systems on three subcontinents and have been grouped for more than a century into a single taxon based on their similar appearance. However, several morphologists recently questioned the monophyly of that group. By using phylogenetic analyses of nucleotide sequences from three mitochondrial and two nuclear genes, we demonstrate with statistical significance that extant river dolphins are not monophyletic and suggest that they are relict species whose adaptation to riverine habitats incidentally insured their survival against major environmental changes in the marine ecosystem or the emergence of Delphinidae.
Flores, 1999. Preliminary results of a pohotoidentification study of the Marine Tucuxi, Sotalza Fluvzatzilz in southern Brazil. Marine Mammal Science. 15(3):840-847. Colombia and Brazil.
McGuire & Winemiller, 1998. Occurrence Patterns, Habitat Associations, and Potential Prey of the River Dolphin, lnia geoffrensis, in the Cinaruco River, Venezuela. Biotropica. 30(4): 625-638. Cinaruco River (Venezuela). Website.
Abstract: The distribution, habitat association, group size, population structure, and prey availability of river dolphins (Inia geofiensis) were studied from November 1993-June 1994 in the Cinaruco River, a tributary of the Orinoco River that forms the southern boundary of Venezuela’s Santos Luzardo National Park. Dolphins were sampled from a boat using modified strip-width transedts, for a total of 418 h. The study area was 1.67 km2, and contained 20 km of water courses. Like other rivers of this region, the Cinaruco River undergoes a seasonal flood cycle. Dolphins were seen most often during the period of falling water (41% of total sightings) and least often during the rising water period (24% of total sightings). Dolphins were seen most often in confluence areas (35% of total sightings) and were seldom seen in side channels (13% of total sightings). The presence of rocks or sandbanks was associated with a greater frequency of dolphin sightings, and sightings increased with habitat heterogeneity. Average group six for the 8 mo study was 2.0 (t1.0) and was largest during the rising water period. Calves were first sighted during the end of the dry season and became more common during the early flood season. Six individuals were photo-identified and resighted with one sighted eight times over 186 d. The fish diversity of the study area was high, with 161 species documented in our samples. The stomach of one Znia contained 15 fishes representing at least 4 species.
Smith et al., 1998. River Dolphins in Bangladesh: Conservation and the Effects of Water Development. Environmental Management. Vol. 22, No. 3, pp. 323–335. Bangladesh. Website
Abstract: Ganges river dolphins (Platanista gangetica) are threatened in Bangladesh from the effects of dams, large embankment schemes, dredging, fisheries bycatch, di- rected hunting, and water pollution. Visual surveys of the section of the Jamuna River located between the divergence of the Old Brahmaputra River and the confluence of the Padma River and the section of the Kushiyara River located between the Bangladesh–India border and the confluence of the Korangi River recorded a sighting rate of 0.13 sight- ings/km (mean group size 1.8 dolphins) and 0.08 sightings/km (mean group size 3.8 dolphins), respectively. These sections of river were considered to be priority areas for investigation because several water development projects have already been constructed and more are planned for the areas. During the surveys we examined the remains of dolphins caught accidentally in plastic gillnets and observed fishermen catching the fish species Clupisoma garua using dolphin oil and body parts as a fish attractor. Additional studies are needed to assess the status of dolphins and effects of water development and fisheries bycatch. Feasibility studies should be conducted on designating dolphin/fish sanctuaries and creating artificial habitat or enhancing existing habitat in eddy counter current scour pools to mitigate deleterious impacts. The environmental requirements of river dolphins reflect the needs of productive and biotically diverse tropical rivers.
Vidal et al, 1997. Distribution and abundance of the Amazon River Dolphin (Inia Geoffrensis) and the Tucuxi (Sotalia Fluviatilis) in the Upper Amazon River. Marine Mammal Science. VOL. 13. NO. 3. Amazon river (Colombia, Peru and Brazil). Website
Abstract: A boat survey was conducted from 5 to 26 June 1993 to estimate the abundance of the Amazon river dolphin (Inia geoffrensis) and the tucuxi (Sotalia fluviatilis) along ca. 120 km of the Amazon River bordering Colombia, Peru, and Brazil. Two survey methods were used: line transects during 5 d and strip transects during 15 d. The line transects were used to estimate the abundance of both species in the main channels of the Amazon at distances greater than 200 m from river banks and islands, and strip transects were used to estimate abundance in the remainder of the habitat. A total of 29 sightings was obtained using line transects, including 8 of Inia, 15 of Sotalia, and 6 with both species present. The total number of sightings made while using strip transects was 143, including 78 of Inia, 51 of Sotalia, and 14 with both species present. The distributions of sightings with respect to distance from the nearest bank were not significantly different between the two species. Based on the results from the two methods, we estimate that there are 346 (CV = 0.12) lnia and 409 (CV = 0.13) Sotalia in the study area. Overall, the mean group size for Inia was 2.9 individuals and for Sotalia was 3.9 individuals. Inia density (dolphin/km*) was highest in tributaries (4.8), followed by areas around islands (2.7) and along main banks (2.0); while Sotalia density was highest in lakes (8.6), followed by areas along main banks (2.8) and around islands (2.0). These are among the highest densities measured to date for any cetacean.
Romero & Aguido, 1997. The scientific discovery of the Amazon River dolphin Inia Geoffrensis. Marine Mammal Science. 13(3):419-426. Website
Abstract: Analysis of little-known manuscripts revealed that there have been at least two pre-Linnean descriptions of the South American freshwater dolphin lnia geoffrensis (Blainville, 1817). The earliest one that we found was made by Frei Cristbvao de Lisboa in a manuscript written around 1627. The second one was by Pehr Lofling, a disciple of Linnaeus, who wrote a very detailed and accurate description of this mammal in 1755. He used the binomial system to designate this species, and his description was much more complete and sophisticated than the ones used by Linnaeus in the 10th edition of Systema Naturae for other cetaceans. This and other zoological work by Lofling re- mains almost completely unexamined to date. Like the outcome of other field work carried out by many Spanish scientists in America, failure to publish the findings of the expeditions resulted in scientific information being largely lost.
Herman et al, 1996.The Bufeo (Inia geoffrensis) in the Rio Lagarto Cocha of the Ecuadorian Amazon. Marine Mammal Science. 12( 1): 118-125. Rio Lagarto Cocha (Ecuador). Website
Abstract: The world’s river dolphins (Inia, Pontoporia, Lipotes and Platanista) are among the least known and most endangered of all cetaceans. The four extant genera inhabit geographically disjunct river systems and exhibit highly modiced morphologies, leading many cetologists to regard river dolphins as an unnatural group. Numerous arrangements have been proposed for their phylogenetic relationships to one another and to other odontocete cetaceans. These alternative views strongly abject the biogeographical and evolutionary implications raised by the important, although limited, fossil record of river dolphins. We present a hypothesis of river dolphin relationships based on phylogenetic analysis of three mitochondrial genes for 29 cetacean species, concluding that the four genera represent three separate, ancient branches in odontocete evolution. Our molecular phylogeny corresponds well with the rest fossil appearances of the primary lineages of modern odontocetes. Integrating relevant events in Tertiary palaeoceanography, we develop a scenario for river dolphin evolution during the globally high sea levels of the Middle Miocene. We suggest that ancestors of the four extant river dolphin lineages colonized the shallow epicontinental seas that inundated the Amazon, Parana , Yangtze and Indo-Gangetic river basins, subsequently remaining in these extensive waterways during their transition to freshwater with the Late Neogene trend of sea-level lowering.
Vidal, 1994. Aquatic Mammal Conservation in Latin America: Problems and Perspectives. Conservation Biology. Vol 4, No 4 pp 786-795. Website
Abstract: Management of renewable natural resources in developing countries has been hampered by a mix of socio- economic and political difficulties that in turn have resulted in insufficient scientific knowledge, limited environmental awareness and education, and limited commitment to conservation. Aquatic mammals provide good examples. Despite the fact that about 65% of all known living species of aquatic mammals are found in Latin America (including 19 species found nowhere else), local and regional conservation efforts have developed only recently and are isolated. While management of the commercial exploitation of most baleen whales and pinnipeds has been more or less successfully achieved, the lack of comprehensive policies and conservation strategies for small cetaceans, manatees, and otters has allowed several species or populations to become threatened or even endangered. Threats include incidental mortality in fisheries, direct exploitation for human consumption or for use as bait in other fisheries, and habitat loss and degradation. To illustrate these problems, several cases are briefly discussed: (1) the endangered vaquita (Phocoena sinus) in Mexico; (2) the tuna-dolphin problem in the eastern tropical Pacific; (3) the small cetacean fishery in Peru; and (4) the Amazon river dolphin (Inia geoffrensis). Because many aquatic mammal populations are shared by Latin American countries, international cooperation is critical to ensuring their long-term conservation.
Tujillo, 1994. The use of photoidentification to study the Amazon River Dolphin, Inia geoffrensis, in the Colombian Amazon. Marine Mammal Science. 10(3):348-353. Amazon river (Colombia). Website
Best and DaSilva, 1993.The American Society of Mammalogists. 426, pp. 1-8, 3 figs. Website
Harrison, R. 1975. The Gonads of the South American Dolphins, Inia Geoffrensis, Pontoporia Blainvillei, and Sotalia Fluviatilis. Journal of Mammology. rivers near Iquitos, Peru, from Leticia, Colombia, and from Guanare, Venezuela (Peru, Columbia, Venezuela). Website
Abstract: The appearancesof the gonads are described in males and females of 18 Inia geoffrensis, 11 Pontoporiablainvillei, and eight Sotalia fluviatilis from South America. Males of I. geoffrensis become sexually active at a length of about 228 centimeters, females at 175 to 180 centimeters. Length at birth is 76 to 80 centimeters; parturition occurs from about July to September in the upperAmazon.Maleso blainvillei are still sexually immature at a length of 128.5 centimeters, females become sexually active at a length of 137 centi- meters. Off Uruguay, pregnant females have fetuses 6 centimeters in length in Februaryand 61 centimetersin October. Males of S. fluviatilis are sexually active at a length of 148 centimeters, females at 140 centimeters. Gonad weights and details of corpora lutea and albicantia are given. Corpora albicantia appear to persist as in other cetaceans. The ovaries of I. geoffrensis are relatively bulky with the corpora enclosed in the ovarian substance and not pedunculated as in P. blainvillei and S. fluviatilis in which the right ovary is poorly developed.
Hershkovitz, P. 1963. Notes on South American Dolphins of the Genera Inia, Sotalia and Tursiops. American Society of mammalogists. Vol. 44, No. 1 pp. 98-103. Venezuela, Rio Orinoco, Lake Maracaibo. Website Abstract: Presence of the river dolphin Inia geoffrensis Blainville in the Rio Orinoco system is documented for the first time. Sotalia guianensis Van Beneden, known from the Guianan coast, is now shown to range westward into the Lake Maracaibobasin in Venezuela. The Rio Orinoco Sotalia seen by Alexander von Humboldt may be annectant between S. guianensis and the Amazonian S. fluviatilis Gervais and Deville. Present data indicate that the cataracts of the Orinoco and of some Guianan and upper Amazonian streams are not barriers to the distribution of dolphins across the divides during periods of inundation. A skull of bottlenosed dolphin from the Galapagos and another from Talara, Peru, agree with Tursiops nuuanu Andrews of the north Pacific, T. gephyreus Lahille of the southeastern Pacific and T. catalania Gray of the southwestern Pacific. Absolute separation of these forms from T. nesarnack of the northeastern Atlantic does not appear to be indicated. The Pacific bottlenosed dolphin is, therefore, provisionally treated as a subspecies, Tursiops nesarnack catalania Gray. Tursiops gilli Dall of the California coast appears to be distinct.
Layne, 1958. Observations on freshwater dolphins in the upper Amazon. American Society of Mammalogists. Vol. 39, No. 1 pp. 1-22. Surveys conducted in the Amazon River (Colombian and Peru). Website
Smith et al. Identification and channel characteristics of cetacean ‘hotspots’ in waterways of the eastern Sundarbans mangrove forest, Bangladesh. Unpublished Report. Bangladesh. Bay of Bengal, Mongla Port, Baleswar River, and Passur River. PDF
Abstract: Sighting data on two freshwater-dependent cetaceans: the Ganges River dolphin Platanista gangetica gangetica and Irrawaddy dolphin Orcaella brevirostris were recorded by captains of three nature tourism vessels operating in waterways of the eastern Sundarbans mangrove forest, Bangladesh. These data were used to investigate channel-type preferences and identify cetacean ‘hotspots’ according to a scoring system based on group, individual and calf encounter rates, the co-occurrence of both species, and encounter rates in neighboring segments recorded during monsoon, post-monsoon and dry seasons. Six 5-km segments were identified for priority conservation attention from a total of 38 that were transited (surveyed) on at least three occasions during each season. An investigation of habitat preferences evaluated 5-km segments that had been surveyed on five or more occasions (n=69) and assigned them to one of 12 categories defined by channel width, sinuosity and the number of large and small confluences. Significant differences were found between observed and expected frequencies of occurrence in the different segment categories (p<0.01, df=5) for Ganges River dolphin groups and individuals, and for Irrawaddy dolphin individuals. Both Ganges River and Irrawaddy dolphins selected channels with more than two small confluences or at least one large confluence. Understanding the preferred habitat and 1 identifying ‘hotspots’ of freshwater-dependent cetaceans in the Sundarbans is the first step of a planning process for the potential establishment of a network of protected waterways for these threatened species.
Smith et al. Swimming against the rising tide: the use of cetaceans for evaluating the ecological impacts of declining freshwater supplies and global climate change in Bangladesh. Unpublished Report. Bangladesh. Website
Abstract: The effects of climate change are extremely difficult to predict and monitor because they are complex and operate on broad ecological scales. In biological monitoring, the assessment of complex processes is commonly approached through the use of indicator case-populations or species. These are assumed to integrate changes over time and space, thus reducing random variance of physical measurements, and to be sensitive enough to warn about changes earlier than the usual “spot” measurements. Cetaceans are normally considered to be poor indicators species due to their generalist capacity for adapting to environmental changes. However, the manner by which these large, mobile predators respond to environmental changes (e.g., by altering their movement patterns and foraging behaviour) may be particularly informative for identifying biologically significant environmental attributes, and for monitoring alterations in the spatial and temporal availability of these attributes. These responses may then be used to generate targeted and testable hypotheses, prioritize investigative efforts and identify local aggregations of biological productivity for site-based protection. The community of cetaceans inhabiting the inshore waterways of the Sundarbans mangrove forest and adjacent coastal waters in Bangladesh is composed of species that distribute themselves according to the physical characteristics in their environment (e.g. salinity, turbidity, depth, and channel configuration). Cetaceans farther offshore in the Swatch-of-No Ground, a 900m+ deep submarine canyon, may also show distinct distributional responses to a decline in the availability of nutrients associated with reduced freshwater discharge and alterations of current patterns that could suppress upwelling. Given that these waters support a diverse and relatively abundant cetacean community that will be dramatically affected by declining freshwater flows and climate change, it is concluded that the animals may be an efficient model for gauging the effects of these anthropogenic threats on the same species elsewhere in their range, and possibly other cetaceans subject to similar environmental pressures. In addition, studies of this cetacean community may provide fundamental insights on the nature and magnitude of more general ecological effects (e.g. changes in the abundance and species composition of lower-level trophic communities) and a basis for developing appropriate management responses. Baseline information and trained local expertise is available, thus offering a solid ground for long-term studies and monitoring.
This information was compiled by (in alphabetical order):
Last updated: June 2 2011