**3. Threats and conservation**

Mortality of dolphins in fishing nets and the highest level of water pollution through oil, plastic, and industrial waste are the extreme threats. Illegal fishing such as poisoning or electro fishing and large ship boat, vessel strikes, overfishing, sand and resources mining are also threat for dolphins. In Bangladeshi water, most of the dolphin species death occurs by fishing net specially gill net. Dolphin killing and hunting was extensive in several countries that also threat for the environment [2, 30, 31]. UNDP Bangladesh [16] reported that 130 dolphins were killed from 2007 to 2016 in the waters of Bangladesh which most of the species' death by fishing nets and propellers of ships. GoB [32] also reported a total of 52 dolphins were lost by gillnets in the Sundarban area. Dolphin killing occurred due to collecting body parts has required in fisheries that are used as dolphin oil [33]. Although, several organizations are trying to conserve dolphins but it's not enough, such as SharkLab, United Nations Development Program (UNDP), the Global Environment Facility (GEF), the Forest Department, IUCN Bangladesh, and World Conservation Society (WCS). Dolphin conservation is highly important for other aquatic species in the ecosystem as well as the better health regulator of water. Bangladesh Government has been attentive for the marine protected area (MPA) to conserve cetaceans whereas most of the dolphin sightings occurred in the water. We should concern about bycatch through fishing gear, awareness, and biological data monitoring to conserve dolphins as well as their habitat. Six sanctuaries have been recognized as conservation areas by the Government of Bangladesh for marine mammal and other species. The Swatch of no-Ground is also known as a special conservation area for biological resources.
