Mission: Comparative Count of Dugongs
Date: 4 September 2008
Requesting organisation: Paul Dutton
Location: Mozambique’s Bazaruto National Park
Pilot: Chris Rattray and Etienne Oosthuizen
The Dugong Survey Team: from the left Dr Almeida Guissamulo, Paul Dutton, Etienne Oosthuizen and Chris Rattray
The Bateleurs supported a count of Mozambique’s Dugongs in February this year, when the exercise yielded alarming reports of decreasing numbers of these gentle sea creatures. In September a comparative count was conducted, and this is the short report prepared by Paul Dutton, a Bateleurs pilot and ecologist. The flying for this mission was performed by volunteer pilots Chris Rattray and Etienne Oosthuizen.
“This was my sixth aerial survey, since 1990, of Dugong that occur in the sheltered marine grass environment of the Mozambique’s Bazaruto National Park. I had just graduated with an MSc degree in coastal management and as luck would have it I found Dr John Hanks sitting at the Africa Desk of WWF (International) in Glande, Switzerland and he offered me a contract to formulate a Master Plan for the Bazaruto Archipelago. This opened up an opportunity for me to test the veracity of my MSc dissertation “Traditional Fisheries and Conservation Ethics” whilst gathering a plethora of data required for formulating the Master Plan. However, it was not long after I had pitched my tent on the northern shore of the main island of Bazaruto that my attention was drawn to the presence of the mythical Sirenia or Dugongs that grazed the sea grass meadows throughout the archipelago. To promote the conservation of an ecosystem one needs a flagship species – like the tiger that symbolizes India’s jungle, or the white rhino that assured iMfolozi Game Reserve’s future. The Dugong, because of its rarity and important ecological niche as a bulk grazer of marine grass, fitted into this role.
Dr Almeida Guissamulo, a young graduate of the Mondlane University in Mozambique, and cetacean specialist Dr Vic Cockcroft, accompanied the first aerial survey in 1990 when Dugong were of mixed sexual and age aggregations and were widespread throughout the Archipelago. An estimate of between 150 and 180 animals was based upon a 25% survey sample.
Since then population estimates have followed a roller coaster ride of discrepancies in terms of numbers and distribution. It became apparent that small sample numbers were being extrapolated in relation to our original study when in fact the introduction of gill nets for shark harvesting had caused numerous “accidental” drownings in previously occupied habitats.
Counting a small number of widely distributed animals that can submerge for up to 8 minutes played a major part in the variance in numbers. For example, the survey carried out in February this year accounted for less than 20 animals – all but one occurring close to the islands of Benguerra, Magaruque and miniscule Bangue. Perfect weather on one of the days of the September survey, with the sea clean and mirror calm, resulted in an additional 45 being found close to Santa Carolina. This elevates the population estimate to at least 56 animals, including 6 sub adults and 5 juveniles in 33 localities.
On this occasion flight transects 2 km apart and covering 130 km starting from the Save River Estuary and moving southwards through the national park were flown over a period of 5 days. This produced as near as possible a total figure rather than a statistically generated estimate. A total distance of 3781 km over a period 30 hours was flown by the two aircraft, providing an indication of the intensity of the current survey.
A total of at least 420 Humpback and Bottlenose Dolphins,and 6 Humpback whales were encountered on the survey transects.
We were fortunate to have Dr Almeida Guissamulo design and guide this recent survey which I believe is a definitive estimate of the current status of the Dugong. It will enable initiation of the long term management of the Dugong whose current distribution still places them in the precarious situation of being the proverbial “eggs in just two disparate baskets”.
Our beloved squadron leader Nora Kreher and board members of The Bateleurs – Flying for the Environment in Africa once again showed their commitment to caring for our beleaguered natural environment by funding and fielding two of its proficient member pilots, Chris Rattray and Etienne Oosthuizen, who flew their C182 and Kitfox7 aircraft with utmost precision over Bazaruto National Park’s azure clear water. Sunday Times photographer Darryl Hammond worked hard to capture images of Dugong underwater on known feeding grounds. On one occasion Darryl and I had two Dugongs within a few meters of our dive boat but when we slipped overboard in our scuba gear all we saw was blue water – and no sign of the mythical Mermaid!
The Dugong Trust contributed to the team’s lodgings at the Bazaruto Lodge where managing director Louis Erasmus accommodated the team at a generously reduced rate. Other tourist entrepreneurs namely Gonfishen and the Islands of Benguerra, Indigo Bay and Santa Carolina all helped in various ways to make this survey a pleasant and successful mission. I took a back seat on this, probably my last air survey of Dugong after 18 years.”