Sousa plumbea

Common Name: Indian Ocean humpback dolphin

Humpback Dolphin
Humpback dolphins size.svg

Size comparison against an average human

Scientific Classification
Kingdom Animalia
Phylum Chordata
Class Mammalia
Subclass Eutheria
Order Cetacea
Suborder Odontoceti
Family Delphinidae
Genus Sousa
Species

Humpback Dolphin Cetacea range map

Pacific Humpback Dolphin (Chinese White Dolphin) range


Humpback Dolphin Cetacea range map Indian

Indian Humpback Dolphin range


Humpback Dolphin Cetacea range map Atlantic

Atlantic Humpback Dolphin range

Source:  Wikipedia

Humpback dolphins (Sousa sp.): Two genetic variations of humpback dolphins occur along the Indian coastline,the Indian Ocean humpback dolphin (Sousa plumbea) along the west coast and the Indo Pacific humpback dolphin (Sousa chinensis) by the east coast. As genetic studies provide newer results this might change further.

General Description: The general appearance of Indian Ocean humpback dolphins is similar to that of Indo Pacific humpback dolphin with a slightly different coloration. These dolphins have more of a uniform dark-grey (plumbeous or lead coloured) colour with white mottling interspersed with slight pink pigmentation in certain individuals. The belly or the ventral surface of the body is lighter.

plumbeaIndian Ocean Humpback dolphins showing the large hump which the dorsal fin sits & the dark grey colouration. @ Dipani Sutaria

Size: The largest length in an adult humpback dolphin was recorded at about 3.5 m. Variation in length over sex have not yet been studied. New born calves measure up to about a metre in length.

Appearance At Sea: Their appearance is very similar to the Indo Pacific humpback dolphins. Group sizes appear to be slightly larger than the Indo Pacific humpback dolphins. Large groups of about 50-100 individuals are with smaller sub-groups are generally observed.

Found In: The Indian Ocean humpback dolphins are found in localised areas of patchy distributions mainly in shallow waters very close to the shore (<20m depth, <1.5 km from shore) and around river mouths and estuaries.

The Indian Ocean humpback dolphins primarily feed on fish like mackerel, mullet, sardines and pomfret found along the shallow estuarine areas.

These dolphins have been recorded to feed from and around active fishing gear like gill nets, shore seines, purse seine, Chinese fishing nets, dip nets etc. In several instances they have been known to use these gear as barriers to herd prey. In some regions, dolphin depredation causes economic losses to the local fisheries.

Early Records from India: Indian Ocean humpback dolphins are thought to occur along the west coast of India from Gujarat to Kerala. About a little south-east of Kerala, the population then differentiates into “chinensis” type dolphins (Indo pacific humpback dolphins).

DateDetailsSources
[?] Eleven animals caught in gillnets off Calicut coast. R.S. (1985) Observations on the by-catch of dolphins Stenella longirostris
[?] One cast ashore near Dhanu,Tanna district. Sinclair
31-03-1901 Young specimen Sotalia fergusoni measuring 1 m (3 feet 6 inches) cast ashore at Trivandrum beach. R.(1904) On two dolphins from Madras.Journal of the Bombay Natural History Society
01-01-1903 Sotalia lentiginosa (Syn. Sotalia fergusoni). The speckled dolphin. An immature animal was obtained in 1903 and though it resembled Sotalia lentiginosa in many respects the absence of pear·shaped flecks on the body and certain other characteristics, led Mr. Lydekker of the British Museum to provisionally call it S. fergusoni; but when in August 1908 another animal measuring 7 feet 2 inches was also sent, he arrived at the conclusion that this was the adult of what he once described as Sotalia fergusoni R.S.N. (1926) List of cetaceans taken in Travancore from 1902 to 1925.Journal of the Bombay Natural History Society
09-06-05 Live specimen caught in gillnet off Calicut. Anonymous (1987a) - Marine Fisheries Information Service Technical & Extension Series
15-06-05 Two females and three males entangled in gillnets at Calicut coast. R.S. (1995) Age determination of dolphins entangled in gillnets along the Kerala coast.Journal of the Bombay Natural History Society.
01-08-1908 Sotalia lentiginosa specimen measuring 2.15 m (7 feet 2 inches) obtained from Travancore. R.S.N. (1926) List of cetaceans taken in Travancore from 1902 to 1925.Journal of the Bombay Natural History Society
??-07-1983 245 kg of this dolphin landed at Fisheries Harbour. Cochin
??-09-1996 Twelve dolphins observed in 25 km of coast from Elathur to Quilandy river. Lal Mohan
16-10-2014 A dead adult female Indo-Pacific humpback dolphin (Sousa chinensis) washed ashore on 16th October, 2014 morning at Mithapur coast (22° 25.137' N; 68° 59. 482' E) Self report
15-03-2016 A pod of 6 dolphins sighted around 1:30 pm. Dolphins were around 0.5 km off-shore and were actively swimming. B.M.Praveen Kumar

 

World Distribution: These dolphins have a wide distribution range from the South Africa to the southern Bay of Bengal.

Could Be Confused With: Indian Ocean humpback dolphins can be confused with the Indo Pacific humpback dolphins due to the similarity in morphological features and Bottlenose dolphins.

Diagnostic Features: At sea, prominent dorsal fin placed on a large hump in the middle of the back; long, slender beak.

Stranded Specimens: A dead adult can be easily identified by the size of its hump and number of teeth. There may be 29 to 38 pairs of peg-like teeth in each jaw.