Dolphin researchers with the Wildlife Conservation Society have been scanning the waters of the Indian Ocean between the islands of Pemba and Misali for humpback dolphins since dawn, when suddenly a pod surfaces for air.
The excitement is palpable. Straightaway, the team starts taking pictures of the dorsal fins and record the exact sighting location with their GPS. The exercise will continue for two weeks, 11 hours a day, using a local dhow, come rain or shine.
Gill Braulik, head of the WCS dolphin team, has been studying dolphins for most of her adult life. She set up a dolphin research project in Pakistan, to study one of the world’s most endangered species — the Indus River dolphin.
In Tanzania, the focus is on the humpback dolphin — the rarest of the dolphin found in the western Indian Ocean.
Dr Braulik says the project is the first complete survey of dolphins and whales in the Pemba Conservation Area.
“The Indian Ocean humpback dolphin is endangered throughout its range in the Indian Ocean. When we first started the survey, we didn’t even know we would find any, but the habitat was good so we were hopeful,” she says. “I was relieved when we found humpback dolphins here.”
From our vantage point, the pod of four humpback dolphins surface every few minutes to breathe, gliding in and out of the blue waters in bursts of speed within metres of the coastline, where local fishermen spread out their fishing nets.
“They live in very shallow water, always near the coast,” the dolphin scientist adds.
In contrast, the following day far out at sea, spinner dolphins — almost 400 in several pods leap and spin out of the water. They are more common and much less elusive.
The gill nets are the marine mammals’ greatest threat. As mammals, dolphins need to surface for air, so should they get caught in the nets, they drown.
“It’s still a mystery to us why they get caught in the nets,” says Dr Braulik.
One theory could be that at the speed they move, they may not see the nets until it is too late, or perhaps they just get careless and don’t realise the risks, she adds.
Another intriguing aspect of this research is to find out if this population of humpback dolphins ever leave Pemba island for Unguja island (popularly called Zanzibar Island) or the African mainland coast of Kenya, given that Pemba island and its smaller islands are isolated, separated from Africa by the 1,000-metre deep Pemba Channel.
“We think that they could be trapped here but we have no proof of that yet,” Dr Braulik says, adding: “We want to find out if this is an isolated small population.”
This is vital because small populations that are so isolated and face numerous threats like the fishers’ nets are more likely to decline and disappear if they suffer high mortalities.
“At this point we don’t know how many humpback dolphins are here,” she says “So this survey is designed to estimate the population size by photographing the dorsal fins.”
Most dolphins have unique marks and scars on the dorsal fin similar to a human finger print.
“So far our research suggests that yes, most of the humpback dolphins live in the Pemba Channel and that the population is very small, probably only a few hundred animals,” says Dr Braulik.
WCS is setting up a photo ID catalogue of the dorsal fins to compare with already existing catalogues of dorsal fins from Unguja set up by the University of Dar as Salaam and Newcastle University, and in Kenya with the Watamu and Shimoni catalogue compiled by Watamu Marine Association under the same project.
“The long term aim is to set up an East African Cetacean Working Group and agree how to work together to save these rare dolphins and others,” says Dr Braulik.
Once the dolphin researchers have evidence of whether humpback dolphins move several hundred kilometres between Kenya and Tanzania, they can look at the core areas where high numbers regularly occur and work with governments on protecting those locations, this may involve transboundary projects between the two countries to reduce threats to these endearing mammals.
Research is increasingly showing that as top predators, dolphins can shed light on human and ocean health. Pollutants such as pesticides that are harmful to wildlife and humans accumulate in the fat of whales and dolphins, and can occur at very high levels with potential negative health effects.
“This can point to ways that human health could also be affected and as environmental indicators, so it’s time we made the seas safer for our marine cousins,” says Dr Braulik.
A 2006 survey proved what was already suspected — that the Yangtze River dolphin is the first of its kind to be driven to extinction by humans. It declined and disappeared due to extensive fishing and pollution.