Biophysical Survey of Mafia Island Marine Reserves

II. STUDY SITES
The Mafia Island Marine Reserves are located in Mafia District, Tanzania, to the North-
west of Mafia Island. They are situated in the Western Indian Ocean in the shallow
stretch of water that separates Mafia Island from the mainland of Tanzania,
approximately 35km off the Tanzanian coast. This area is located in the mouth of the
Rufiji delta, and is therefore heavily influenced by the outflow from this major river
system. It is also affected by the East African Current and both the north-eastern and
south-western monsoons. The NE monsoon (Kaskazi) runs from November to March and
brings strong northerly winds, which is followed later in the year by a period of heavy
rains which run until May. The wind direction is then reversed with the coming of the SE
monsoon (Kusi) which blows from June to October and brings steady winds and good
weather. Another period of shorter rains also follows this monsoon. The East Africa
current is a major influencing factor on the area, and runs approximately south to north.
The current can flow at between 1 and 4 knots, depending on physical conditions, water
depth and season.
Tides are another important factor in the physical makeup of the reserves. Tides in this
region are mixed semi-diurnal, and average spring tidal range is approximately 3-4m,
varying throughout the year. Currents are heavily influenced around the reserves by tidal
state, with slack water negating currents to a negligible amount, and other states
magnifying them to a maximum of 2-3kts in some cases. There is some evidence to
suggest that tides were exceptionally high throughout January and February 2009, to the
extent that the islands were washed over in parts. These high tides are almost certainly
responsible for the morphology of the steep beaches that characterise the two smallest
islands. Low tides expose shallow reef flat and sea grass areas to view around both
Shungimbili and Mbarakuni Islands.