Investigating the diversity, abundance, and distribution of marine mammals in Vietnamese Southwest coast

Little is known about the diversity, distribution, and abundance of marine mammals in Vietnam. Through the country’s history, only few of surveys and scientific expeditions have been conducted to study marine mammals in Vietnamese waters (Smith et al. 1997). Those that were conducted along the Southwest coast of Vietnam resulted in only a small number of sightings (Smith et al. 1997, Hines et al. 2008, Vu et al. 2014, 2015), creating the impression of a paucity of marine mammals in this area. For example, a boat-based survey conducted by Smith et al. (1997) in this area did record any marine mammals. Hines et al. (2008) reported the presence of Dudong (Dugong dugon) in this area but only based on data from interviewing fishermen and dugong hunter. More recently, the primary investigator of this proposed study, conducted boat-based surveys and sighted three species of cetaceans: the Irrawaddy dolphin (Orcaella brevirostris), the Indo-Pacific Humpback dolphin (Sousa chinensis) and the Indo-Pacific finless porpoise (Neophocaena phocaenoides) (Vu et al. 2014, 2015). However, all surveys only focused on the upper part of the southwest coast of Vietnam. The lower part of this area has never been surveyed for marine mammals.

In contradiction to those few available surveys, a large recorded number of marine mammals have been reported by fishermen, either stranded on beaches or entangled in fishing gear in this area during 2000-2018 (Vu et al. 2015, Vu et al. unpublished data). Additionally, the local belief of fishermen along Vietnamese Southwest coast obligates them to preserve the remains (mostly skulls) of whales, dolphins or porpoises, in local whale temples, which has resulted in a unique collection of historical records of marine mammal for this area. Preliminary assessment of marine mammal remains stored in 10 whale temples along the Vietnamese southwest coast suggests that at least nine species of marine mammals may be present in the ocean area nearby (Smith et al. 1997, Vu et al. 2015, Vu et al. unpublished data). Among those, there were two skulls of the rarely sighted Omura’s whale (Balaenoptera omurai) recovered from animals stranded in this area (Vu et al 2015). This finding changes the current knowledge on worldwide distribution range of Omura’s whales, as current IUCN data does not include the Vietnamese southwest coast as a regular distribution range of this species (Reilly et al. 2015).

Addressing these gaps of information and data on the diversity, distribution, and abundance of marine mammals along the Vietnamese southwest coast will advance both marine mammal science and conservation management in this underdeveloped country. For marine mammal science, filling this data gap will provides empirical, scientific data to answer the ecological questions about the distribution, abundance and diversity of marine mammals along the southwest coast of Vietnam. For conservation management, information on diversity, distribution and abundance of marine mammals will answer the question on how important the Vietnamese southwest coast is for global conservation schemes for marine mammals. For instance, these data will help to determine whether this area should be recognized as International Union for Conservation of Nature’s Important Marine Mammal Area (IUCN-IMMA), or an Ecologically or Biologically Significant Area (EBSA) of the Convention on Biological Diversity (CBD).

The overall goal of this project is to fill the gaps of knowledge about the conservation status of marine mammals occurring off the Southwest coast of Vietnam. There are two main research questions, which we will address: (1) how marine mammals distributed along the southwest coast of Vietnam; and, (2) how important is the Vietnamese southwest coast for global conservation schemes for marine mammals.