Humpback dolphin: mad hattery

Name: Australian humpback dolphin (Sousa sahulensis)

Size: Length2-2.5m, weigh up to 260kg

Diet: Carnivore, variety of fish

Habitat: Tropical coastal waters of Northern Australia including WA, NT and Queensland

Conservation status: Vulnerable

Superpower: Males are known to swim around with giant sea sponges on their heads as offerings (likened to a bunch of flowers) to impress the females and coerce mating.

Humpback dolphin
Humpback dolphin. Credit: Holly Raudino

The Australian humpback dolphin was only recognised as its own species in 2014. Let’s hope that doesn’t mean too little help too late, as it’s thought there are less than 10,000 surviving adults.

Australian humpback dolphins are sometimes observed in mixed species groups socialising with bottlenose and snubfin dolphins, and there is evidence of hybridisation with the latter. They have a longer, more slender and toothier beak than the bottlenose dolphin. The fin on their back is stumpier and more triangular -meaning that if only their fin is visible, they may be mistaken for a shark or snubfin dolphin. These dorsal fins accumulate unique marks from injuries over time and are used as “natural tags” by scientists, making it handy to track them and work out population size and life history events. The injuries can come from from multiple sources, including interactions with each other, predators such as sharks, strikes by boats, and entanglement in fishing gear and debris.

This species loses pigment in the dorsal fin over time so that the older ones, particularly males, have distinctive snowy caps to their fins. This is also helpful to scientists studying them to classify older ones and also tell males and females apart, although this can also be confirmed through DNA samples taken through remote biopsy and adult females by the presence of a dependent calf.

Humpback dolphin
Humpback dolphin. Credit: Alizada Studios/Getty Images

Humpback dolphins can best be observed in river systems, a preferred habitat to catch a fish snack on the change of tide. The humpback dolphin is notoriously boat shy and does not bow ride, making it difficult to observe in the wild. For this reason it has received less attention than the better-known bottlenose dolphin and snubfin dolphin, but it can be equally acrobatic with its leaping, particularly when socialising with mates.

Its most endearing behaviour is perhaps sponging. Sea sponges are used routinely by bottlenose dolphins in Shark Bay as protective gloves for their beaks during foraging, but male humpback dolphins use sea sponges in a social context. They have been seen to emerge with humongous sea sponges on their head and beaks. Female humpback dolphins are apparently enamoured by these impressive offerings and may be more inclined to mate with the bearer. The revelation of this complex courtship behaviour in recent years is proof that such displays are not exclusive to the bird world.

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