Biophysical Survey of Mafia Island Marine Reserves

As with the other data collection methods employed for this report, divers swam
at a constant depth, following contours of the reef rather than a specific bearing. Data
were collected at a range of depths, as with the transect methodologies, to allow
differences across the depth gradients to be observed. In some cases, fish appear on both
the reef fish census, and on the commercial fish census, highlighting their importance
within the reef community. Some species listed in Table 5 have been identified only to
family level for simplicity of the survey method and to ensure data accuracy.
3. Seagrass Habitats
Shallow seagrass beds (< 2m deep) within the inner and outer lagoon areas were
assessed. Inner lagoon sites were located within 300m of the island shoreline and outer
lagoon sites were within 300m of the reef edge. In addition deep (> 4m) seagrass habitats
were assessed for fish abundance where they were found to be particularly extensive. A
minimum of four lagoon sites were selected at each island, two inner and two outer. Each
site consisted of 10 points chosen to form a grid pattern within an area extending to
250m². Each of the 10 points selected had the centre point GPS marked. Four 1m²
quadrats were thrown out from the centre point at 90° to each other, within a 10m
diameter circular area. Each quadrat area was visually inspected for substrate and benthos
composition based on estimates of percent cover. Invertebrate species present, and their
abundance, were also recorded.
Fish abundance on the deep seagrass beds was also assessed for some sites. Fish
were recorded in 22 different categories (Table 6) during 5 minute swims over seagrass
habitats on given bearings. Types and density of seagrass species were also recorded.
Sites were studied where accessible and extensive seagrass habitats were found at depths
of 4m or deeper.
Table 6. Fish species list used for collection of abundance of fish species found on seagrass habitats.
Common name Latin name Common name Latin name
Damselfish SIGANIDAE Rabbitfish SIGANIDAE
Goatfish MULLIDAE Surgeonfish ACANTHURIDAE