Mangrove en garnalenkweek in de Lagune van Chilaw (Sri Lanka): Toestand en perspectieven verlaten garnaalkwekerijen

Abstract

Mangroves are tree species that grow in the subtropical saline intertidal zone. Mangrove
forests fulfil many ecological functions, such as increasing the biodiversity of the water
ecosystems, protection of the coastal areas against erosion and they serve as a natural filter for
the water. Unfortunately, the worldwide area of mangrove forests is decreasing at a very high
rate.

Since 1970 intensive production methods of tropical brackish water aquaculture - in
particular the culture of shrimps - have been developed in South-East Asia. In the beginning
the exploitation of shrimp farms was economic very interesting. This resulted in an
exponential increase in the number of shrimp farms in the tropical coastal areas. But through a
bad management, the outbreak of many diseases and a fluctuating export trade, many farms
were abandoned only 5 to 10 years after the construction of it.

The study area is situated around the Chilaw lagoon at the west coast of Sri Lanka. The past
20 years, many mangrove forests have been cut and replaced by shrimp farms. Currently, the
greatest part of the farms is abandoned. The field work for this study took place during the
months August and September 2006.

In this thesis we try to investigate the relations between fishery, mangrove and aquaculture in
the study area. Especially, we focus on the possible perspectives for the abandoned shrimp
farms. To do this, we have broken up the general objective into three goals.

The first goal was an object-oriented classification of the land use on a very high resolution
satellite image (IKONOS, 2002). We have succeeded to distinguish the classes mangrove and
not-mangrove. But the classification of the mangrove species did not give a good outcome.
The cause of this may be the lack in training data. We didn't manage to classify the shrimp
farms as a separate land use type.

The second goal was to explore the actual state of the aquaculture sector and the traditional
fishery in the study area. At one hand we have interviewed fishermen and people working in

the aquaculture sector. At the other hand a list of attributes was filled in for every visited
shrimp farm. The analysis of this data revealed that 284 ha of the 382 ha visited farms are
abandoned and that the original mangrove vegetation doesn't seem to restore naturally.
The last goal was to formulate recommendations for the restoration of the mangrove in the
abandoned shrimp farms. Based on the results of goal 1 and goal 2 we recommend to break
through the dikes on those places where the recovery of mangrove is opportune. This is a
condition sine qua non to reintegrate those areas in the hydrology of the brackish and saline
water ecosystem. If not, the terrestrialisation of these areas will continue.

Date of Award	14 Sep 2007
Original language	English
Supervisor	Nico Koedam (Promotor), Farid Dahdouh Guebas (Co-promotor) & Diana Di Nitto (Co-promotor)