Most dolphins live in the ocean. However, there are still a few species of freshwater dolphin struggling to survive in an increasingly developed world. Recent news from Cambodia raises worries that the endangered Mekong dolphin may not be one of the success stories.
The Mekong dolphin is a subpopulation of the Irrawaddy dolphin (Orcaella brevirostris), now found only in the upper Mekong River. This group is listed as critically endangered. They feed on many species, including small fish, crustaceans, and squid. These small dolphins are fairly slow swimmers, putting them in some danger around human activities (although they typically avoid boats). Conservation measures have included photo identification of individual dolphins.
In 2006, the Cambodian government banned fishing nets from critical parts of the river. The dolphin population seemed to rebound, from 90 to 150 over several years. However, in the last few months, the annual survey counted very few baby dolphins compared to previous years. These young animals also had dramatically lower weights than in previous years, and one of the three was found dead. When observed, many adult groups had no offspring, raising concerns about reproductive problems.
One factor that may affect health and reproduction is an increase in water temperature. The result is a decline in fish populations and less potential food for dolphins. Water quality is also impacted by pollution, logging, agriculture, and development. Like other marine mammals, river dolphins are vulnerable to habitat degradation. Rising water temperatures may be a result of a general warming trend, such that conditions are unlikely to reverse in the near future.
