Citizen and standard monitoring of the Bolivian river dolphin (Inia boliviensis) in the upper Mamoré basin

Standard river dolphin population assessments rely on labor-intensive, infrequent boat surveys
along river transects, resulting in sparse time series data and limited possibility to detect
population trends. This study introduces a complementary citizen science approach involving
fishing boat captains to enhance monitoring efficiency of the Bolivian river dolphin (Inia
boliviensis). We tested this method in the Ichilo River in combination with standard methods. In
September 2022, researchers positioned on the rooftop of a survey boat counted 0.72 dolphins/
km, along 520 km of river. Concurrently, the survey fishing boat captain independently recorded
bow sightings using a smartphone application, detecting 51% of researcher-observed bow
dolphins, and 35% of researcher-observed stern and bow dolphins. Separately, five commercial
fishing boat captains used the app during routine fishing trips from March to October 2022,
collectively recording five times more dolphins than the number observed by researchers in the
single standard survey along the same river stretch. During a second survey along a 237 km river
stretch in October 2024, researchers registered an encounter rate of 0.40 ind./km. This survey
included an experienced fisher, positioned on the boat roof, who independently detected 54%
more bow- and stern dolphins than researchers. The survey fishing boat captain recorded 51%
of the dolphins observed by researchers on bow, and 38% of the researcher-observed bow and
stern dolphins. We demonstrate that fishing boat captains can reliably record dolphins during
routine activities, that an optimally positioned fisher observer significantly outperforms research
teams, and that year-round citizen science data vastly exceed the coverage of single surveys.
Integrating citizen science with standardized surveys has strong potential to enable more cost-effective,
large-scale monitoring of population status, seasonal dynamics, and long-term trends
of river dolphins, while further promoting inclusive conservation in the future.