Skip to content

Research at St Andrews

Searching for trends in river dolphin abundance: designing surveys for looming threats, and evidence for opposing trends of two species in the Colombian Amazon

Research output: Contribution to journalArticle


Robert Williams, Jeffrey E. Moore, Catalina Gomez-Salazar, Fernando Trujillo, Mary Louise Burt

School/Research organisations


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.


Original languageEnglish
Pages (from-to)136-145
Number of pages10
JournalBiological Conservation
Early online date14 Jan 2016
Publication statusPublished - Mar 2016

    Research areas

  • Abundance, Cryptic, Habitat loss, River dolphin, Inia, Sotalia, Amazon, Bayesian methods, Monitoring

Discover related content
Find related publications, people, projects and more using interactive charts.

View graph of relations

Related by author

  1. Loggerhead turtle Caretta caretta density and abundance in Chesapeake Bay and the temperate ocean waters of the southern portion of the Mid-Atlantic Bight

    Barco, S. G., Burt, M. L., DiGiovanni, R. A., Swingle, W. M. & Williard, A. S., 13 Dec 2018, In : Endangered Species Research. 37, p. 269-287 19 p.

    Research output: Contribution to journalArticle

  2. Quantifying the Power to Detect Change: methodological development and implementation using the R package MRSeaPower.

    MacKenzie, M. L., Scott-Hayward, L. A. S., Paxton, C. G. M. & Burt, M. L., 27 Oct 2017, Quantifying the Power to Detect Change: methodological development and implementation using the R package MRSeaPower.. The Scottish Government, p. 1 139 p. CREEM-13804-2016-1. Provided to the Scottish Government and Marine Scotland Science (USA/012/15

    Research output: Chapter in Book/Report/Conference proceedingOther contribution

  3. Estimating cetacean density and abundance in the Central and Western Mediterranean Sea through aerial surveys: implications for management

    Panigada, S., Lauriano, G., Donovan, G., Pierantonio, N., Cañadas, A., Vázquez, J. A. & Burt, L., Jul 2017, In : Deep Sea Research Part II: Topical Studies in Oceanography. 141, p. 41-58 18 p.

    Research output: Contribution to journalArticle

  4. Statistical analysis of SAMBAH survey and associated data

    Thomas, L. & Burt, M. L., 1 Mar 2016, University of St Andrews. 130 p. (CREEM Technical Report; no. 2016-1)

    Research output: Book/ReportOther report

Related by journal

  1. Factors affecting feelings of justice in biodiversity conflicts: towards fairer jaguar management in Calakmul, Mexico

    Lecuyer, L., Calmé, S., Blanchet, F. G., Schmook, B. & White, R. M., Sep 2019, In : Biological Conservation. 237, p. 133-144

    Research output: Contribution to journalArticle

  2. Implications of farmland expansion for species abundance, richness and mean body mass in African raptor communities

    Shaw, P., Kibuule, M., Nalwanga, D., Kaphu, G., Opige, M. & Pomeroy, D., Jul 2019, In : Biological Conservation. 235, p. 164-177 14 p.

    Research output: Contribution to journalArticle

  3. Uses, cultural significance, and management of peatlands in the Peruvian Amazon: implications for conservation

    Schulz, C., Martín Brañas, M., Núñez Pérez, C., Del Aguila Villacorta, M., Laurie, N., Lawson, I. T. & Roucoux, K. H., Jul 2019, In : Biological Conservation. 235, p. 189-198 10 p.

    Research output: Contribution to journalArticle

  4. Basin-scale distribution of harbour porpoises in the Baltic Sea provides basis for effective conservation actions

    Carlén, I., Thomas, L., Carlström, J., Amundin, M., Teilmann, J., Tregenza, N., Tougaard, J., Koblitz, J. C., Sveegaard, S., Wennerberg, D., Loisa, O., Dähne, M., Brundiers, K., Kosecka, M., Kyhn, L. A., Ljungqvist, C. T., Pawliczka, I., Koza, R., Arciszewski, B., Galatius, A. & 9 others, Jabbusch, M., Laaksonlaita, J., Niemi, J., Lyytinen, S., Gallus, A., Benke, H., Blankett, P., Skóra, K. E. & Acevedo-Gutiérrez, A., Oct 2018, In : Biological Conservation. 226, p. 42-53 12 p.

    Research output: Contribution to journalArticle

  5. Marine protected areas show low overlap with projected distributions of seabird populations in Britain and Ireland

    Critchley, E. J., Grecian, W. J., Kane, A., Jessopp, M. J. & Quinn, J. L., Aug 2018, In : Biological Conservation. 224, p. 309-317 9 p.

    Research output: Contribution to journalArticle

ID: 240327574