SECTION 11 PREPARATION OF A TIDAL ATLAS FOR THE WAKATOBI MARINE NATIONAL PARK

11.1 SUMMARY

Section 11.2 summarises the initial work carried out in 2000 in preparing a tidal atlas for the Wakatobi Marine National Park.

Few data are available on the tidal currents and water movements in the Wakatobi Marine National Park. An initial oceanographic data search in 1999 resulted in a limited amount of information almost all relating to regional oceanography and nothing about the local water circulation in the Park. In August 1999 basic temperature, salinity, eulerian and lagrangian current speed and direction were collected, and tidal height measurements taken as a pilot study for a more extensive research project.

It is well known that the geographical distribution of a species is influenced by a variety of physical and environmental parameters including the length of the larval stage and the pattern of tidal currents. A full knowledge of all contributing factors must be evaluated when deciding upon conservation measures such as the designation of no fishing areas.

The objectives of the project are to describe the physical oceanography in the vicinity of Hoga and Kaledupa Islands. An understanding of the local oceanography would be complementary to an understanding of the chemical and biological processes. Local temperature, an important parameter in coral reef health, can be related to longer term and macro-scale temperatures through satellite derived measurements.

This will comprise the following elements of data collection:

• Eulerian measurements of current speed, direction, temperature, salinity, and density for at least 1 month in both monsoon seasons.
• Lagrangian measurements using drifters to provide an indication of the spatial variation and residual circulation, which is of major importance when considering the dispersion of pollutants or fish larvae, for example.
• Tidal height measurements associated with the above.
• Wind speed and direction measurements associated with the above.
• Bathymetry and hydrographic mapping.

These data will be used to describe patterns of water exchanges, fluxes, residual currents, upwelling, and productivity. A mathematical model will be developed to predict the fate of particles (eg. pollutants, fish larvae), to aid the management strategy under development for the Marine Park. On completion the data will be organised in an Arcview GIS project to allow other data eg. biological distributions, water quality data, larval distribution etc.to be overlaid.

The work programme outlined above is to be completed over the next 3 years. In 2000 Eulerian current speed and direction measurements throughout depth were made using an Acoustic Doppler Current Profiler (ADCP). This instrument transmits high frequency sound waves then determines the Doppler shift of the return signal scattered from the water column. Detailed time-series flow profiles were obtained by deploying the instrument on the seabed at a single location looking up.

The area surrounding Hoga was divided into five sections to allow the vessel mounted ADCP surveys to be completed. Each survey consisted of a predetermined course over a 25 hour period. Accurate positioning was necessary and was achieved using GPS. Wind speed and direction readings were also taken throughout each survey.

Temperature and salinity data was also collected to add to the data collected in 1999. Float tracking was carried out over a 25 hour period.

An interim report entitled Initial Observations on Tidal Patterns and Current Movements Around Hoga Island in the Wakatobi Marine National Park will be completed by February 2001 by Debbie Tyrrell from the Environment Agency.