Jakarta. A researcher has warned that Indonesia's population of Irrawaddy dolphins (Orcaella brevirostris) is increasingly coming under threat.
"There are estimated to be only between 75 and 80 dolphins left in the rivers of Kutai Kartanegara district [in East Kalimantan]" Danielle Kreb, of conservation group Rare Aquatic Species of Indonesia (RASI), told state news agency Antara on Monday (02/01).
Kreb said the specific number of remaining dolphins is unknown because previous research in 1997 used a different method to determine population size.
Her research, which was conducted between 2005 and 2016, used a fin calculation method, while in 1997, population size was determined by observing density and deployment.
"The number still cannot be specified as more in-depth research is needed and the method we have been using from 2005 to 2016 has a margin of error. The highest number we counted was 90 dolphins," the researcher said.
Kreb said the mortality rate of Irrawaddy dolphins was not significant between 2005 and 2015, with an average of about five per year. Birth rates remained normal, at around five or six calves per year.
The dolphins are often found in the Mahakam River in East Kalimantan, where water quality does not play a role in mortality rates, Kreb said.
"Unlike the Mekong River [in Indochina], we did not find any deaths of newborn dolphins. Most deaths of adult dolphins are caused by them getting entangled in nets or being hit by pontoons," she explained.
Fishermen's nets caused the deaths of five individuals in 2016.
There were also two recorded cases of dolphins having died after being struck by pontoons in 2016. This has become a new threat for the marineaquatic mammals, due to the large number of coal mines and palm oil operations, which use pontoons to transport their products.
"The dolphins mostly hang around in the tributaries because it's easier there for them to catch fish, but now with the pontoons in the area, it's becoming a new threat for the species," Kreb said.
Irrawaddy dolphins are generally found in Muara Kaman, Kota Bangun and tributaries of the Mahakam River – Kedang Rantau, Kedang Kelapa and Belayan – all in Kutai Kartanegara district.
"When we were in Muara Pahu, West Kutai, last, we could see these dolphins almost every day," Kreb said. "But now they are only in Kutai Kertanegara and in only a few locations. And even there you will only rarely spot them because the population has really gone down."
Populations of Irrawaddy dolphins are also declining in the Mekong River due to commercial fishing activities, according to the International Union for Conservation of Nature (IUCN).
In the Mekong area, habitat degradation is another factor due to deforestation and mining – something Indonesia should look out for.
Kreb called on corporations using the river, as well as the Indonesian government, to act to protect the species.