Four Years of Marine Turtle Monitoring (2002-2006)



Posted on 05 July 2006  | 
By Bas Verhage and Eustache Beodo Moundjim and Suzanne Rachel Linvingstone


Largest leatherback populations in the world
Gabon holds one of the largest leatherback (Dermochelys coriacea) populations in the world, but still little is known about their population dynamics, foraging behaviour, nest ecology and threats. In Total, we find four species of marine turtles nesting on its beaches. The leatherback and the olive ridley are regular nesters and the green turtle and the hawksbill turtle are rare.

Protection, monitoring, scientific research, building capacity & awareness raising
Since 2002 WWF and Ibonga have set up a Marine Turtle Monitoring Programme in the Gamba Complex of Protected Areas, in the south-west of Gabon. The main objective of our Marine Turtle Programme is to conserve marine turtles by assisting the Government of Gabon in developing capacity to effectively manage the parks and reserves in the Gamba Complex. Our activities include protection, monitoring, scientific research, building capacity and awareness raising. The main focus of this programme is on leatherbacks because of its predominant presence in the area.

75 km of beach monitored on a weekly basis
The monitoring Programme is executed on a daily, weekly and quarterly basis. The daily monitored zone is 5,75 km of beach near Gamba. 75 km of beach to the north and south of the daily monitored zone, is monitored on a weekly basis by quad. During the 2005/2006 season, the whole Gabonese coastline was monitored by plane every month between November and March in cooperation with all the partners working on marine turtles in Gabon. Furthermore, the migration of leatherbacks is monitored in the Atlantic Ocean using satellite transmitters, initiated by WWF-LAC.

Decrease in nesting numbers in 1st 3 years, increase in 4th
Over the four years of intensive monitoring (2002-2006) the results show a steady decrease in the leatherback nesting numbers over the first three years, followed by an increase in the fourth season. The population nesting in the Gamba Complex the fourth year is estimated at 2,500 individuals.

Human activities in the Complex mostly concern egg poaching, as well as pollution of the beach with trash, light and oil. A permanent presence of MEF and WWF are of great importance to monitor these threats. Thanks to their presence since 1985, human activities are not at a level that endangers the survival of marine turtles today. However a wave of dead turtles was found on the beaches in the south of Gabon between September and October 2005. This might have been caused by one of the many, and still very little monitored, marine threats (fisheries, pollution).

Threats: erosion, inundation, destructive roots & predation.
The greatest threat to the eggs and the hatchlings on the beach are natural threats; erosion, inundation, destructive roots and predation. The common predators are ghost crabs, monitor lizards and the civet cat. The hatchery showed its effectiveness to protect the eggs from these threats and served at the same time as tool to raise awareness amongst school children and tourists.

The nest temperatures were higher in the nests in the hatchery than on the beach which led to shorter incubation periods. Though the temperature was not so high as to cause an impediment for development of the eggs, as the hatching success in the nests in-situ on the beach was not significantly different from that in the nests in the hatchery.

Three transmitters deployed during the 2005-2006 season
The leatherbacks covered at least 100 km during intra-seasonal migrations and inter-seasonal migrations covered the whole Atlantic basin. The latter was proved by the capture of a leatherback near the coast of Argentina in 2005 tagged in Gamba in 2003 (Billes et al. 2006). The exact migration routes will be better known thanks to three transmitters deployed during the 2005-2006 season.

Protection team and tourists
The combined efforts of WWF, Ibonga and PSVAP, with financial support from Protomac have resulted in the recruitment and training of 20 people as marine turtle researchers, and a successful tourist package, attracting at least 90 tourists during the fourth season. The collaboration with local and international partners have created a solid foundation for a long term monitoring programme. Only long term monitoring of nesting beaches and migration patterns will lead to a coherent approach for conservation of these highly migratory

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