Coastal Northern Bay of Bengal IMMA

Criterion A – Species or Population Vulnerability

The IMMA supports the world’s largest locally occurring population of Irrawaddy dolphins. This species was up listed as Endangered on the IUCN Red Listed of Threatened Species in 2017, due to a suspected population size reduction of ≥50% over the past 60 years, future 60 years, and encompassing 60 years in both the past and future (Minton et al. 2017). The IMMA also supports among the world’s largest populations of Indo-Pacific finless porpoise and Indo-Pacific humpback dolphins. Both of these species are considered Vulnerable due to a suspected or inferred decline of at least 30% over the last three generations, over three generations into the future, and over a three-generation period that includes both the past and the future (Jefferson et al. 2017, Wang and Reeves, 2017). For all three species, the factor most responsible for population declines is incidental mortality in fisheries. This means that, even though all three populations are relatively large, mortality from entanglements in fisheries and suspected declines make them vulnerable to extinction, thereby meeting Criterion A.

Criterion B: Distribution and Abundance

Sub-criterion B2: Aggregations

Extraordinary bio-productivity, driven by the enormous discharge from the Ganges/Brahmaputra/Meghna river system, redistribution and retention of nutrients in a basin-scale current gyre and upwelling in a submarine canyon, supports among the world’s largest resident populations of three globally threatened species. This gives aggregations of all three primary species occurring in the IMMA vital importance as a potential safety net to safeguard species extinction.

Criterion C: Key Life Cycle Activities

Sub-criterion C1: Reproductive Areas

Frequent sightings of Irrawaddy and Indo-Pacific humpback dolphin calves in the IMMA  combined with their relative high population size implies that the area plays a particularly important role in the reproduction of these species. The cryptic nature of finless porpoises means that calves are rarely identified in the field but the high concentration of these animals in the northern Bay of Bengal surrounded to the east and west by waters that support much lower densities implies that the IMMA also has a significant role as a reproductive area for this species.

Criterion D: Special Attributes  

Sub-criterion D1: Distinctiveness

Humpback dolphins in the IMMA are phylogenetically unique from neighboring populations to the east and west. Levels of genetic divergence indicate that humpback dolphins in the IMMA are as different from the other putative Sousa species as they are from each other. The productive ecological conditions in the northern Bay of Bengal may almost certainly explain the genetic distinctiveness of humpback dolphins in these waters (Amaral et al. 2016).