Monday, December 3, 2012

Did you say humpback dolphin?

Even armchair animal enthusiasts have heard of bottlenose dolphins and humpback whales - but few people have heard of humpback dolphins. Summertime is when most of the inland cities of South Africa  plan their routes to their regular holiday destinations, but I wonder if any of them realize that during their vacation they may have the opportunity of spotting this little known species?
So, what exactly is a humpback dolphin and how can you distinguish it from a bottlenose dolphin? As the name suggests, this species of dolphin has a hump upon which the dorsal fin is found. The dorsal fin of a humpback dolphin is not only smaller but their overall colouration is also a lighter shade of grey than that of a bottlenose dolphin. This species also has a distinctive way of surfacing whereby its beak comes completely out of the water before the head. Both species reach lengths over 2.5 meters with males being larger than females.

Three individual humpback dolphins from the Mossel Bay population. Picture by BS James.

Bottlenose dolphins, mother and calf. Photo courtesy of Oceans Research

Where does one look for humpback dolphins? Well, humpback dolphins prefer shallow water between 15 and 30 meters deep and as such are regularly seen close to shore, usually just behind or on the last breaker. They have a preference for reef systems and areas close to river mouths. These represent productive ecosystems that would provide them with food including fish species such as snapper kob, grunter, stumpnose and glassnose depending on where along the South African coast they are.
But why should anybody care about humpback dolphins? In its Indo-Pacific range (between the Bay of Bengal westwards to Danger Point) it is considered Near Threatened according to the International Union for Conservation of Nature (IUCN). This means that there are less than 10 000 of these dolphins left in this exceptionally large area. Off the coast of South Africa it is thought that there are less than 1000 dolphins left. This estimate is based on a technique called mark-recapture which has been applied to a few of the small localised populations along the South African coast. Mark-recapture relies on taking photographs of encountered dolphins while out searching on a boat and then reviewing the dorsal fins to identify distinctive individuals. Once we have an idea of the number of unique individuals we can use this to estimate the size of the entire population.
 But why is this important? This species is found close to shore in areas that are under development and increasing urbanisation. These dolphins may therefore be exposed to large amounts of pollutants from rivers and harbours and boat traffic.
Exposure to large amounts of pollution may result in negative effects to their reproductive abilities and for a species that already has low numbers this may lead to serious losses. Boat traffic, specifically the presence of fast moving vessels in foraging areas, may lead to direct impacts such as collisions or through the animals avoiding these areas due to the large amount of noise produced by the outboard engines.

So what does all of this mean? Enjoy  sightings  of this species while you can because factors like  habitat degradation caused by human activity could make it their last.

Reference: Best, P. 2007. Whales and dolphins of Southern Africa. Cambridge University Press. Pg 167-173 and 181

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