16 August 2012

The elusive Sousa

I spent July in southern Gabon, collaborating with the Wildlife Conservation Society (WCS) and hoping to collect some data on Atlantic humpback dolphins (otherwise known as Sousa teuszii). It's hard to say that these dolphins are rare, since we actually have not even a vague idea of how large the population is, or where they can still be found. They used to be found along West Africa's coast between Morocco in the north and Angola in the south. These days, they are thought to have a fragmented range, which means that that in some parts of its old range, the population has been wiped out, leaving smaller, disconnected populations in parts of the original range. 

These small dolphins (2 to 2.5 metres in length) are unique for a number of reasons. They are found only on Africa's west coast; one of two endemic species to that general area (the other being the Heaviside's dolphin, the other species I have focused some research on in recent years). They are also found remarkably close to shore; in fact, Atlantic humpback dolphins tend to be seen most often in shallow waters within about 50 metres of the beach! This may be one of their downfalls - they live in area frequented by local (rather than industrial) fishermen, and can often get entangled in fishing nets. Unfortunately, they are also targeted as a food source in some parts of West Africa, probably precisely because they are so accessible to coastal inhabitants. Living in these areas also means that coastal development (construction, increased populations, pollution) can have immediate negative impacts on these animals.

We were lucky enough to sight a group of four humpback dolphins during one of our first surveys in Gabon. This species is notoriously shy, so getting close enough for photographs is not always possible! We also deployed three hydrophones (C-PODs) which will stay in the water until the end of August, collecting data on humpback dolphin clicks. This will allow us to understand how often the dolphins use various parts of the coast, and whether their presence in any given area is linked to time of day or tidal state.

Funding applications have been submitted to continue this work and to extend it to other areas in West Africa where the elusive Sousa is thought to be found. Next stop for me: Guinea-Bissau (a supposedly important area for humpback dolphins), in October. People often report seeing dolphins when travelling between the mainland and the Bijagos islands, so my aim is to find out whether they are Sousa or other species, and where the most important habitats for these dolphins are. Internet will be non-existent out there, so updates will follow after the field season, in December!

Sousa close to the beach in southern Gabon, 2012. Photo by P. Brehony

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