Bogotá, Colombia
Bogotá, Colombia

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Ryan G.E.,WWF Cambodia | Ryan G.E.,University of Melbourne | Dove V.,Murdoch University | Dove V.,Apple Inc | And 2 more authors.
Ecosphere | Year: 2011

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% CI=77.9-91.2) 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. Copyright: © 2011 Ryan et al.

Williams R.,University of St. Andrews | Moore J.E.,National Oceanic and Atmospheric Administration | Gomez-Salazar C.,Foundation Omacha | Trujillo F.,Foundation Omacha | Burt L.,University of St. Andrews
Biological Conservation | Year: 2016

Rivers worldwide, particularly in tropical regions, support multiple human uses that can threaten water security and cause species decline. Some tropical rivers are home to obligate freshwater cetaceans (river dolphins) that are vulnerable to exploitation and to upstream and downstream habitat degradation due to limited dispersal opportunities. Assessing vulnerability is complicated by difficulty in reliably estimating abundance, due to the animals' cryptic nature and complex, dynamic habitat. We compared density estimates from surveys conducted in 1993, 2002 and 2007. Surveys were not part of a coordinated monitoring plan and thus were conducted using slightly different methods in different months, which complicated statistical inference. We used information from the most recent survey to account for bias and uncertainty in earlier estimates and used bootstrap and Bayesian approaches to estimate trends, conditional on a plausible range of process variance associated with seasonal movements. For Inia, probability of decline was >. 0.75, even under the highest seasonal movement levels considered. For Sotalia, there was a >. 0.75 probability of population increase. There are 151 proposals pending in the Amazon for large (>. 2. MW) hydroelectric developments that would fragment habitat, and reports suggest that Inia is experiencing illegal killing for fish bait. In this context, our population trend estimates are cause for concern, but improved monitoring is needed to more reliably assess population status. Based on lessons learned from our analysis, future surveys will be standardized in terms of timing (conducted during the transitional water season) and methodology (using our most recent field protocols) to minimize confounding factors and provide more robust inference about population trends. We provide recommendations for ways to distinguish seasonal movements from annual population trends to guide Amazon river dolphin conservation. Until then, two interpretations exist: either Inia is declining, or existing information cannot detect declines unambiguously without additional surveys. Neither explanation bodes well, given the myriad anthropogenic stressors Amazon river dolphins face. © 2015.

Gomez-Salazar C.,Dalhousie University | Gomez-Salazar C.,Foundation Omacha | Trujillo F.,Foundation Omacha | Whitehead H.,Dalhousie University
Aquatic Mammals | Year: 2011

Photo-identification is an important tool for studying cetacean residence patterns, population size, movements, and social structure. This knowledge 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 population 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 individuals 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.

Gomez-Salazar C.,Dalhousie University | Trujillo F.,Foundation Omacha | Whitehead H.,Dalhousie University
Marine Mammal Science | Year: 2012

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 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 of Inia occurred 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. © 2011 by the Society for Marine Mammalogy.

Gomez-Salazar C.,Dalhousie University | Gomez-Salazar C.,Foundation Omacha | Trujillo F.,Foundation Omacha | Portocarrero-Aya M.,Foundation Omacha | And 2 more authors.
Marine Mammal Science | Year: 2012

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 (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. © 2011 by the Society for Marine Mammalogy.

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