Mission critical: monitoring the Mekong dolphins in the wild, photo-ID based survey

Posted on 19 February 2020

Cambodia’s Dolphin Conservation Team conducted an annual population survey of the Irrawaddy dolphin in the Mekong River.
Cambodia’s Dolphin Conservation Team conducted an annual population survey of the Irrawaddy dolphin in the Mekong River.
Hopping on board wooden boats, a crew of seven researchers in early February 2020 began their journey from Kratie Town to the Cambodia-Lao PDR border and back again, tracing along the Mekong River stretch of approximately 190 km long.
The research team comprising of staff of WWF, the Fisheries Administration and Kratie and Stung Treng Fisheries Administration Cantonments embarked on a nine-day survey trip on the Mekong River to observe the Irrawaddy dolphins, listed as critically endangered by the IUCN Red List. Equipped with highly professional photo cameras and other survey equipment, the research team took thousands of pictures of the animals, their​ dorsal fins to support photo-identification of individuals’ that when combined with mark-recapture methodology allows for the determination of individual dolphins. By doing so, the research team is able to estimate the population of the Irrawaddy dolphin in Cambodia.
“A photograph is taken of each dolphin sighted and the image of the dorsal fin is used to identify individual dolphins. A mathematical equation is then applied to estimate dolphin numbers. Additionally, a photo ID database of dolphins is produced and can be used to monitor future mortality, distribution, and social patterns of these rare animals,” explained Dr Mark Drew, Director of Conservation Programme with WWF.
The team surveyed upriver through all of the nine dolphin pools and then travelled back downriver to recapture images of the animal throughout the locations. The survey route stops in Kratie Town, which is the current downstream range of the animal’s habitat. Scientists however have observed that the dolphins could occasionally swim downstream out of the range to follow their prey.
Throughout the trip, the researchers spent days on their wooden boats traveling up and down the Mekong River with prolonged sunlight exposure, observing the water with their binoculars and camera machines, and spending nights sleeping in hammocks on the islands they stop by.
This trip requires a huge amount of patience from the team, primarily for the observation of dolphins in the deep pool areas, given the lengthy and complex procedures and protocols they are required to follow during the identification surveys. On the boat, every team member has a task to do: some scan the horizon ready to photograph the dolphins while others collect environmental data like the river depth, weather conditions, water turbidity (visibility) and GPS coordinates.
“All the conditions are favourable during our entire trip since the level of the river is low making it easier for us to observe the dolphins,” said Mr Sam Un Eam, Biodiversity Research and Monitoring Manager with WWF based in the Mekong Flooded Forest landscape (MFF). “We hope we can even photograph dolphin calves during this survey,” he added.
The field surveys will be conducted during the next three months enabling the research team to implement a repeated measures type of approach to ensure robust data are collected.
It was arduous work in the height of the hot season, with the sun blaring down on the team working in an open top boat. After the field work comes the next phase of the research taking place back in the office-– sorting through the thousands of photos and utilizing computer software to produce clear dorsal fin images to identify individual dolphins and provide a specific ID number to each animal. A database will be created to identify the characteristics of each dorsal fin and record location of sighting.
“Each dorsal fin is unique and has particular recognizable characteristics—their shapes can vary, the angle of the fins need to be calculated, they can be rounded or triangular, with notches at the tip of the fin or without,” Mr Sam Un explained.
The team’s efforts were rewarded by an exciting record of two newborn dolphins, becoming the first calf births to be recorded by the team at the beginning of this year. This new dolphin members were spotted swimming among other adult animals in Kampi deep pool, north of Kratie town.
The results from the annual survey will be used to produce a report on population estimate of the Irrawaddy dolphin in the Mekong River. Next population report of the Mekong dolphin is expected to be available mid this year.
“Understanding dolphin population is a critical component for determining appropriate measures for effective conservation and protection of the species,” Dr Drew said.
Conserving the majestic population of Mekong dolphins represents collaborative efforts between WWF and the Fisheries Administration, Kratie and Stung Treng Fisheries Administration Cantonments, as well as local communities and partners.
Read more about Mekong dolphin.
By Laura Dehaene, Field Communications and Community Awareness Officer with WWF-Cambodia
Dolphin's dorsal fin identification