Dolphins living close to humans face more threats than those that live far from land and far from human intervention. Dolphins found in coastal and riverine environments therefore are in more immediate danger of extirpation.
I recently gave an overview of the situation facing Nepal’s remaining dolphins where the biggest threat to their continued survival has been the construction of dams and irrigation structures throughout the Nepalese river systems. Not only has this led to a reduction in available and suitable habitat including a lowering of the water depth through increased sedimentation and reduced water flow but the reduced available habitat has led to an increased vulnerability to the many human activities. Importantly, the river barrages resulted in dolphin populations being isolated from each other leading to the possibility of inbreeding depression or the worst case scenario, a complete lack of breeding. The best estimate of remaining dolphins in Nepal’s rivers is currently less than 30 individuals and whilst the figure in Pakistan is substantially greater than this, the blind Indus river dolphin, a living fossil of a dolphin existing only in a few stretches of the Indus River in Pakistan is in serious trouble.
As in other rivers, one of the biggest problems facing the Indus River dolphin is an ever-increasing human population that are dependent on the river for drinking water, food and power. Agriculture in Pakistan in reliant on water being diverted from the main Indus River and many dams and/or barrages have sprung up along the length of the river, diverting the water flow into narrow canals that help to irrigate the surrounding Indus plains. So many of these barrages exist that the Indus basin irrigation system is now claimed to be the largest in the world. The dolphins however face a multitude of additional threats. Although hunting is no longer considered to be a problem, accidental entanglement in fishing nets is still a concern, albeit a limited one and the dolphins are known to become trapped in the various barrages at times of low-water. Pesticides used on farms also make their way back into the river, as does untreated waste from cities upstream, the result being that the dolphins tissues and those of their prey, are loaded with pollutants.
The biggest remaining threat however is the actual amount of water being extracted from the river. Not only does this reduce available habitat (areas of the river are known to run dry in the summer months), a reduced water flow brings the dolphins into closer contact with humans and exacerbates the effect of pollutants.
Prior to the construction of the Indus irrigation system, the historical distribution of the Indus river dolphin covered 3,500km of the Indus River system. Today, thanks to human intervention, that figure has been reduced by over 80% with approximately 99% of the remaining population occurring in only 690km of the river. In 2011 the population figure was estimated at approximately 1,450 individuals, split into 6 subpopulations, three of which are probably too small to persist for any length of time.
The papers authors suggest however that all is not lost and that there is hope on the horizon but only if action is taken now. They suggest the translocation of any animals that are trapped in irrigation canals to areas of the river with smaller populations. They support the creation of community based reserves and better river management as well as habitat restoration and management.
Most importantly they note that water conservation is key. With projected demand for water in Pakistan predicted to outstrip availability before 2025 without conservation not only will the dolphins suffer but the human population will too.
(Research recently published in Biological Conservation outlines a comprehensive review of the status, threat and conservation management of the endangered Indus River blind dolphin where all the above information has been taken from).