School of Natural and Environmental Sciences


Population ecology of humpback whales off Zanzibar, Tanzania

The humpback whale research project in Zanzibar, Tanzania was initiated in 2006. The objectives are to research the seasonal occurrence and population ecology of humpback whales and investigate if the humpback whales encountered off Zanzibar constitute a discrete breeding population. To address this research is also conducted on migration, movement, behaviour and social structure of the humpback whales in the study area. The project further aims to aid the development of community based sustainable whale watching to bring much needed income to the local coastal communities in the area. Finally, efforts are made to mitigate bycatch in local gillnet fisheries.

Fishing activities around Zanzibar are a potential threat to humpback whales; in the late 1980s fishermen were encouraged to switch to bottom set and drift gillnets in an effort to prevent the use of destructive fishing methods e.g. using dynamite, to protect coral reefs. The use of gillnets pose a serious new threat to marine mammals that get entangled (bycaught) and die in the nets. The entanglement is a concern and the project is working with the local communities to try to minimise this problem through education, the use of weak links (for whales to break free from the nets) and training fishermen in methods to disentangle whales from nets. These activities create capacity building for the local communities; by educating and involving the communities living and working alongside the humpback whales it is more likely conservation activities will continue into the future. 

We conduct boat surveys in a 350km2 off the south coast of Zanzibar to collect photo-identification data (each whale can be identified from photographs of their dorsal fins and tail flukes), skin biopsy samples for genetic and stable isotope analyses, recordings of singing males and group structure and behaviour of the whales encountered. We have excellent help from a network of local fishermen that report sightings of whales and any entangled animals directly by calling our mobile or sending a text message.

From previous years’ field seasons (2006-2012) a catalogue of 500+ photo-identified adult whales has been compiled. The presence of newborn calves in the study area (2-5% in 2009-2012), as well as observations of competitive groups and recordings of singing males indicate that the waters off Zanzibar is a breeding area for humpback whales in East Africa. However, the relatively low number of whales resighted within and between years further indicates that the area is likely part of a much larger breeding ground in East Africa.