Humpback dolphins, members of the genus Sousa spp., are most common medium-sized delphinids was found along the coastal water of the eastern Atlantic, western Pacific and Indian Oceans. According to Jefferson and Rosenbaum, the genus Sousa comprises of 04 species. According to Cuvier, the Indian Ocean humpback dolphin Sousa plumbeawas treated as Indo-Pacific Humpback dolphin, Sousa chinensis. However, genetic analysis, skeletal and external morphology, and colour have revealed these animals occurring in the Indian Ocean are recognized as taxonomically distinct from those occurring further east. Thus, uncertainty exist w.r.t. the taxonomic affinities of the humpback dolphins that occur in the Bay of Bengal and future studies will help in confirming whether S. plumbea actually occurs east of the Southern tip of India.
According to the International Union for Conservation of Nature (IUCN, 2018) red list category this species is endangered. It belongs to the family Delphinidae and order Cetartiodactyla. Geographically the species is distributed between South African and Indian coast. , Occurrence of Sousa chinensis is frequently reported in Indian coastal waters. Recently, first occurrence of Sousa plumbea was reported at harbour mouth of Kochi which is connected to Arabian Sea Panikar followed by Bopardikar has repored from Sindhudurg coast, Maharashtra. The current finding is the first report of this particular species observed in the Creek waters of Kandla, Gulf of Kachchh. . Along the coastal stretch of Gujarat is concerned, a survey made by Zoological Survey of India (ZSI), four species of dolphins have been reported namely, Spinner Dolphin, Long-Beaked Common Dolphin, Striped Dolphin, and the Indo-Pacific Hump-backed dolphin. A school of Sousa chinensis was reported from southern most region of Gulf Kachchh and Northern Gulf of Kachchh i.e. Jakhau port area.
A major taxonomic change has occurred in Sousa genus during the year 2014. Thereafter, the Indian Ocean humpback dolphin is recognized as a different species S. plumbea. Before change of this species name of humpback dolphin from South Africa to Australia it was recognize as Indo-pacific dolphin as Sousa chinensis The S. plumbea significantly differ from S. chinensis by showing greater length: breadth ratio and highest tooth count 33-39. It also separated from other species by lack of shared mtDNA control region haplotypes with the other species bearing two diagnostic sites .
Geographically Indian Ocean dolphins occurs around 27,000 km coastal border of Indian ocean and also in 21 coastal countries and territories . In Indiathe first occurrence Sousa plumbea was reported in Kochi inner harbour region in all the season and the group sighting increase from monsoon to dry season. In present observation the species was found in Phan creek of Deendayal Port, Kandla region which is outer harbour region during the month of February 2019. The secondary information of the species from literature and inquiry from local fishermen conformed that the reason for the occurrence of Sousa plumbea due to availability of mullet species which is main food for S. plumbea for Foraging. The water depth and salinity are the important factor for distribution of dolphins. At present, the water depth and salinity of study area is about 10 meter and 40 ppt which creates a conducive environment for occurrence of this species as salinity act as an important factor for schooling of different types of fish.