Mission: Dugong Survey December 2009
Date: 18
December 2009
Requesting organisation: Dr Almeida Guissamulo
Location: Bazaruto Archipelago National Park, Inhambane Province
Pilot: Ivan Marx

Report from the beneficiary:
Report on the 18th December 2009 Dugong Aerial Survey at Bazaruto Archipelago
by Dr Almeida Guissamulo of the University Eduardo Mondlane, Maputo

The marine mammal researcher Dr Almeida Guissamulo submitted to The Bateleurs a request to sponsor an aerial survey to monitor dugong numbers and fishing nets at Bazaruto Archipelago National Park, Inhambane Province.

The Bateleurs approved the flight request and offered a flight on a  twin engine, high wing- 4 seat airplane Albatross belonging to Dr  Ivan Marx.  The plane had a co-pilot. The two observers during the survey were Dr  Almeida Guissamulo and Mr Janneman Conradie. Dr Guissamulo also acted as recorder, because the plane could not accommodate a third person due to weight limitations. A french film crew preparing a documentary on dugongs at Bazaruto also came onboard the plane and filmed the survey.

The research and film team met Dr Ivan Marx at the Indigo Bay hotel, Bazaruto Island at 08h00 on the morning of 18th November, and prepared the plane for the dugong survey flight at the Indigo Bay airfield. The flight was started at 09h41 and finished at 11h38. The survey was flown at a height of 500 feet.

The size of the Albatross airplane meant that the team was offered a flight time of 2.5 hours, rather than the 5 hours which would have been possible in a smaller plane.  This limited flight time imposed a change in the survey procedure:  the expected two miles spaced perpendicular survey lines to the coast over an area of 120 km were altered to a long shore flight in the north between Inhassoro and Ponta Nhamábue and a four miles spaced perpendicular survey lines in the south, between Inhassoro Village and Vilanculos Wildlife Sanctuary.

Weather conditions during the flight were not good but were adequate for a survey: the sky was partially overcast, the wind speed was strong (15 knots), and while the water visibility was good the sea surface was choppy, reducing the ability to sight dugongs.

The flight path was divided into 2 sections: a coastal flight between Bazaruto Island and Ponta Nhamabue (Bartolomeu Dias), and the flight inside Bazaruto Archipelago between Inhassoro and Vilanculos Sanctuary. During the coastal flight, the plane flew north to Ponta Nhamábue at about 500 m from shore and returned along the coast southward until Inhassoro village along the shoreline. From Inhassoro village, the plane route changed. The plane flew 8 km spaced perpendicular survey lines between the mainland and Islands of Bazaruto Archipelago. The survey was terminated in the Vilanculos sanctuary and the plane landed at Vilanculos Airport.

During the flight very few dugongs were observed (3 groups: 2 single dugong offshore at Nhamabue Point) and 4 dugongs north of Santa Carolina Island.  Four groups of the Indian Ocean bottlenose dolphins were observed (in total 17 dolphins), and three groups of indo-pacific humpback dolphins (six dolphins). Beach seine fishing nets were observed along the whole coastline between Nhamabue and Inhassoro. A total of nine long beach seine nets were observed operating within a 4 km stretch. It was not possible to count nets in the area South of Inhassoro towards Vilanculos, because the survey was not parallel to the coast and the perpendicular lines were too far apart, leaving large gaps. No gill nets were observed in the sea during the survey, which is a good indication for dugong conservation.

In the south, at Vilanculos Wildlife Sanctuary several fishing boats were observed using beach seine nets in the channels.

As an overall comment, the flight offered by the Bateleurs on 18th November 2009 was well flown, no mechanical problems occurred. The flight allowed the research team and the film crew to have an overview of the dugongs and especially fishing activity in some sections of the Bay.  However, the limited flight time and the changes in the survey route imposed by the type and size of plane available did not allow the precise evaluation of the dugong population numbers over the entire research area.

In addition the setting of the passengers’ seats was not appropriate, as the observers were not aligned and were searching different sections.  Communication between observers was sometimes deficient because one of the headsets failed to operate, at times, distracting the observers during the survey.

The research team is very grateful for the efforts and support of The Bateleurs and their volunteer  pilot, Dr  Ivan Marx, for his kindness in offering to do this flight to support dugong research and awareness, at short notice and during the holiday season.