Bottlenose Abundance In Kenyan Coastal Waters

Kisite-Mpunguti Marine Protected Area (KMMPA) lies south of Wasini Island (south-coast of Kenya) and covers an area of 39 square kilometres. The KMMPA includes the National Park surrounding Kisite Island and the Marine Reserve surrounding the Mpunguti islands. The KMMPA and the marine wildlife it contains are an important tourist attraction and, as a result, an important resource for Shimoni and surrounding communities. The islands within the KMMPA are surrounded by coral reefs attracting divers and snorkelers to the area. Almost every day dolphin-watching companies operating from Shimoni travel through Wasini Channel to the KMMPA. These tourist dhows most frequently encounter Indo-Pacific bottlenose dolphins (Tursiops aduncus), and less frequently, Indo-Pacific humpback dolphins (Sousa chinensis).

Global Vision International (GVI) Kenya’s main working partner is the Kenya Wildlife Service (KWS). The research conducted by GVI is shaped to satisfy the objectives of KWS, so as to assist them towards better management of the area.  All data collected thus far is made available to KWS to aid in management plans of the study area. The Marine Programme is supporting KWS to collate data by conducting vessel surveys, which was focus on assessing the bottlenose dolphin abundance on the area, during the initial phase.

After three years of cetacean research in Kisite-Mpunguti MPA, GVI has estimated the absolute abundance of bottlenose dolphins around 122 individuals, being the second biggest population of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in East Africa. The largest population of the species inhabits in Kizimkazi (south-coast of Zanzibar), and holds between 139 and 179 individuals (estimation made by University of Stockholm in 1999-2002).  

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Photo-id and mark-recapture methods were the methodology used on both studies to get the estimation. Photo-ID refers to the identification of individuals by distinctive features (shape, outline, natural markings and scarring) of their dorsal fins, flanks and flukes. Some scars will be retained through life, whereas others will be added and may fade through life. The depth and severity of the wound will determine the length of time this may be used for identification. These features allow known individuals to be re-sighted. The re-sighting rate can be plotted on a discovery curve, the plateau of which suggests population size. Photo-ID can also be used to determine residency and demographic data such as inter-birth intervals, patterns of ranging and mortality.

Mark-recapture methods are used to calculate population size from the proportion of known individuals re-sighted over the study period. Mark-recapture models estimate only the size of marked individuals in the population. Therefore, the total population size has been corrected by the correction factor.

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Kenya Wildlife Service applied a code of conduct in 2007 for the tour operators to follow when manoeuvring around the cetacean species; unfortunately it is not being fully adhered to as it has only recently been implemented. The levels of interaction between cetaceans and the tour operators are not being monitored or regulated in any way. The impact these activities may be having is unknown. In particular, it’s not known whether current levels of dolphin tourism are sustainable for the area. The first estimation of Indo-Pacific bottlenose dolphins in KMMPA will allow GVI and KWS to measure the levels of tourism impacts, analysing the population dynamics of this species.

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