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

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 (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 124 GOMEZ-SALAZAR ET AL.: RIVER DOLPHINS 125 dolphins seem to coincide with well-managed freshwater protected areas and should be considered as hot spots for river dolphins in South America.

Abundance estimate of the Amazon River dolphin (Inia geoffrensis) and the tucuxi (Sotalia fluviatilis) in southern Ucayali, Peru

“…As riverine species, these dolphins are greatly affected by human disturbance (Turvey et al, 2007;Kelkar et al, 2010), yet both are still listed as Data Deficient by the IUCN (Reeves et al, 2011;Secchi, 2012) highlighting one of the key research gaps in cetacean conservation (Parsons et al, 2015). Line and strip transects and mark-recapture techniques have been used to estimate population sizes for both species in certain areas of their distribution but methods have not been standardized, making total estimates unreliable and hard to compare (Gonzalez, 1994;Martin & da Silva, 2004b;Aliaga-Rossel et al, 2006;Gómez-Salazar et al, 2012a, 2012bMcguire & AliagaRossel, 2014) The most extensive survey to date covered the main rivers in six countries resulting in significant insights into habitat preferences for both species (Gómez-Salazar et al, 2012). Bolivia and Peru had the highest overall densities, and confluences and lakes were highlighted in terms of habitat preferences (Gómez-Salazar et al, 2012).…”

Valoración estacional de las amenazas contra la conservación de Inia geoffrensis humboldltiana (Cetartiodactyla Iniidae) en la cuenca del Río Meta, Colombia

“…Las observaciones desde proa fueron independientes de las observaciones en popa, y las posiciones de los observadores en cada plataforma fueron rotadas en un lapso de dos horas. Todos los observadores tenían experiencia previa con estudios de delfines de río (Gómez-Salazar et al 2011).…”

“…Se establecieron cuatro tipos de hábitats con base en las conductas etológicas establecidas para los delfines de río y en criterios limnológicos para la cuenca, como a) río principal, b) confluencias, c) canales, y d) islas. El diseño de muestreo para los tipos de hábitat establecidos empleó una combinación de transectos en banda (paralelos a la orilla que mantenían una distancia de 150 m) y transectos lineales (en un ángulo de 45˚ respecto de la orilla; Gómez-Salazar et al 2011). Los transectos en banda se realizaron en todos los tipos de hábitat y los transectos en línea solo se realizaron en el río principal.…”

Assessing Population Trend and Risk of Extinction for Cetaceans Lacking Long- Term Census Baselines

“…Implementation of systematically-designed census exercise can provide quantitative baselines in an integrative way. The implementation of transect survey, with the information of GPS and animal-sighting records at each sampling sites, does not only estimate the population abundance inside the survey area but also figures the extent of occurrence by minimum convex polygon (MCP) and core/critical distribution site (such as 50% kernel density estimate), information essential for sound protected area design [13,16,[50][51][52][53][54]. Database from individual photo-ID histories can be used to estimate population size, apparent survival rate and, dependent on the temporal scale of database, life history parameters including Am, RI and Ax.…”

“…It is my goal to summarize the techniques frequently used to solve the population trend and status/risk assessment in many cetaceans. This summarization could be helpful for the conservation of cetaceans for forming sound conservation actions, especial for the species inhabiting freshwater habitats and coastal waters under intensive anthropogenic threats [10][11][12][13][14][15][16][17] in developing countries.…”