The origin of "acadja" branches and transport routes
in the Province Atlantique

 

Authors: Stephanie Weinzierl and Karsten Vennemann*

* Institute of Soil Science and Land Evaluation, University of Hohenheim, Stuttgart, Germany, email: vennema@uni-hohenheim.de

Keywords: fish rearing, aquaculture, lagoon, soil degradation, transport, fallow vegetation
 

1 Aims of the work

Acadja is a traditional fish rearing technique which requires a huge amount of bush and tree branches for the establishment of parks. The aim of this work is to determine the export intensity of acadja branches from fallow fields and the associated transport routes in a part of the Province Atlantique. The documentation is divided into two parts. The first part introduces and summarises the business of acadja fish rearing. The second part categorises the importance of acadja branch export from fallow fields. These results are displayed in the map, together with the main transport routes for acadja. Furthermore, ecological problems arising from the current acadja business and the business sectors involved will be discussed.
 

2 Approach

Data sources
The research for this article is based on the results of the Masters thesis of Weinzierl (1997), and the survey of FLOQUET et al. (1995), and on the review of some additional literature. The data for this survey were obtained using the following techniques:

In field surveys the intensity of acadja harvest was estimated. Farmers, acadja dealers, and people working in acadja transport business were interviewed. People were asked about main acadja harvesting areas, to estimate the harvest intensity, and to determine temporal variations in acadja harvest and possible reasons for these variations. The estimations where correlated with field surveys and the results of the interviews. For a more detailed description of the methods used for data collection see WEINZIERL (1997) and FLOQUET et al. (1995).
 

Map production
The original information is extracted from WEINZIERL (1997). There, the results of the above studies are displayed in two separate maps: (1) the intensity of acadja export in different regions of the Province Atlantique, and (2) shipment harbours (inland) and loading locations of acadja branches and respective transport routes. These two maps where digitised and added as two separate layers to a GIS (ARCVIEW). The digital base map includes "layers" for political borders (1), lakes and rivers (2), villages and towns (3).
 

3 Results and Interpretation

3.1 Background: The Acadja-system

Acadja is a traditional aquaculture system of fish rearing in natural lagoons. Both, the branches of shrubs and trees cut and used for placement in lagoons, as well as the fish rearing itself, are called acadja. Artificial habitats for certain types of fish are created with branches placed into the water of the lagoon at a depth of about one or two meters (Photo 1, Photo 7). This provides an artificial habitat distinct of the surrounding lagoon. It provides

For the above reasons, significantly higher populations of fish live in this artificial habitat than in the surrounding lagoon.

3.2 Acadja in southern Benin
Fishers already used this technique in southern Benin for about two hundred years, and it is also used in other countries such as Brazil, Ecuador Mexico, Egypt, Madagascar, Cambodia, Sri Lanka, and Bangladesh (compare IDRC (ed.), 1998).

The local name of an acadja park depends on its specific size and shape. For example plots of 6-8 ha are called "Acadja-Gbo", plots of 1-2 ha size "Acadja-Ava" and small plots (<0.25 ha) are called Acadjavi. To establish one hectare of acadja park, about 7500 bundles of acadja branches are needed in the first year, and about 5000 bundles the following years. The main fish species (Photo 2) in the acadja are the following :

After HOUSSOU (1986) fish catches in lagoons of southern Benin amount to 10-15 tons per ha, whereas VAN THIELEN (1990) states 1.5-8 tons per ha.

The Lake Nokoué is the biggest and most important lake in Benin. It is connected to the Atlantic ocean through an artificial channel. Since the existence of the channel the lagoon is influenced by saltwater and organisms intruding from the Atlantic ocean. Intruding predators and molluscs lead to decreasing fish populations in the acadja systems. The size of the lagoon varies strongly with seasons. It covers about 150 km2 in the dry season and grows to about 450 km2 in the rainy season. The depth varies from an average of 1 m in the dry season to 3 m during the rainy season. In the acadja system fish can be harvested in two ways. Either a single harvest after 12 months, or selective fishing throughout the year is possible. Selective fishing uses nets with holes large enough to allow small fish to escape.

The following steps are describing the processes and people involved building an acadja park:

Traditionally, fields are cultivated for a period of several years and then left fallow to restore soil fertility. Branches for acadja are harvested on fallow fields where shrubs and small trees started to grow shortly after cultivation ceased. Branches of three to four meters in length and one to four centimetres thickness are harvested after several years of fallow. Because of population pressure in southern Benin, intervals for cutting of acadja is getting more frequent and fallow periods are therefore getting shorter. Often, soil fertility is not fully restored when cultivation of fields starts over again and soil degradation is a common result. The cutting of branches is done by farmers themselves or by others who paid a fee (to the land owner) for the permit to cut acadja branches in a certain lot. About 200 branches are put together in a bundle for sale or further transport.
 

3.3 Interpretation of maps and other results

Acadja harvest results
It was observed that the average fallow period of land from which acadja branches were harvested was about 4 years, ranging between two and eight years. The acadja harvest per hectare was strongly dependent on the origin of the bundles. For areas close to the village of Hévie-Zoungo it was determined that about 900 bundles ha-1 are harvested on fertile fallow land (fallow with mainly shrubs growing), but only 300 bundles ha-1 on degraded land (often grass dominated). The average harvest amounted about 600 bundles ha-1. The harvest for areas further away from the village was about 2000 bundles ha-1 (average fallow period 5 years). The observations concerning the estimation of dry mass and of nutrient export from fields to the lagoon lead to the following results: Average gravimetric water content of acadja branches is 52 %, leaf dry mass 14 % and wood dry mass 34 %. Average export (village of Hévie-Zoungo) of a harvest of 600 bundles ha-1 results in a dry mass export of 5640 kg ha-1 (560 g m-2). A detailed table of nutrient export is shown in the annotations. During the survey sixty-seven species used for acadja where found. Most of them are species representative for secondary forest or shrub dominated fallow land.

Transport routes of acadja branches
The main transport routes for acadja in the Province Atlantique are the following:

A third axis used by smaller acadja dealers is Sékou - Glodjigbé - Akassato - (Abomey Calavi). Another route is Ouedo - Abomey Calavi. The acadja are mainly sold to fishers on the markets of Akassato or Abomey Calavi.
 

Regional intensity of acadja export
Three zones of intensity of acadja exported from fallow land in the survey area can be distinguished. The southern region has a low intensity of acadja export. The harvest of acadja from fallow land seems to have reached it¹s limit. This is because of the proximity of Cotonou and a high population pressure and therefore intensive cultivation. The region reaching from Tori-Bossito in the west to Zinvie in the north-east is a zone of medium export intensity. Acadja harvest in this zone seems to be decreasing (quantity and quality). The zone of high acadja export intensity lies in the Subprovince Ze. Towns in this region are Tangbo-Djevie, Sedje-Denou and Ze. The vegetation on fallow land here is more luxurious than in the other two zones. Branches cut in this zone are 4 meters long in average and 4 cm in diameter. Overall the catchment area of acadja branch harvest is expanding northwards.
 

4 Conclusions

The survey shows a positive correlation between the export intensity for acadja of a region and its distance to the destination area (acadja parks in the lagoon). This can be mainly explained by the following factors:

Zone one - low acadja export intensity:

In zone one, species representative for secondary forest that are traditionally used for acadja are getting rare on fallow land. Therefore, increasingly species are harvested which are not very useful for acadja culture (e.g. because of thorns or a certain content of allelopathic substances potentially impeding growth of algae).

Zone two - intermediate acadja export intensity:

The soils in zone two are increasingly at risk to become as degraded as those of zone one if fallow periods are not extended instead of steadily getting abridged. Diversity of species in fallow land is at risk to decline when intensive cultivation of fields and frequent usage of fallow vegetation for acadja will persist.

Zone three - high acadja export intensity:

Soil degradation is yet not as severe, and therefore acadja harvests are richer than in the previously described regions. However, in the future this region is at risk of increasing soil degradation if fallow periods are decreasing and usage of fallow land for acadja harvests is intensified.

The study shows that acadja harvested from fallow land economically supports a significant number of people involved in the business. On the other hand, intensified use of fallow land led to degradation of soil fertility and extension of the acadja harvest area. Nutrients exported from fields in form of acadja branches are a significant factor in the nutrient balance of such agro-ecosystems (see annotations). The described negative effects of acadja harvesting in fallow can be avoided when shrubs for acadja are grown in plantations. Results of a rooting experiment (WEINZIERL, 1997) have shown that the species Millettia thonningii can be propagated easily. Future research should determine optimum procedures for acadja plant propagation and management of plantations as well of fallow vegetation to prevent soil degradation.
 

Limitations of the study
Data used for this study have to be used with precaution due to limited data sources. The data presented are neither overall comprehensive nor in all cases statistically representative for all parts of the study region. Results from the main study area around the village of Hévie-Zoungo are more detailed than the data used to classify the other regions. The results are referring only to the catchment areas for acadja west of Lake Nokoué. At this point data about other sources (e.g. from the south-eastern territories) were not available.
 

5 References

6 Further Readings
7 Related Web sites
International Center for Living Aquatic Resources Management (ICLARM)
Office: No. 10, Lower Level 6 Equatorial Hotel Office Block
1 Jalan Bukit Jambul, Bayan Lepas 11900 Penang, Malaysia
Mail: P.O. Box 500, GPO 10670, Penang, Malaysia
Tel. no. (604) 641-4623, 641-4652, 641-4655, 641-4729
Fax: (604) 643-4463; 643-4496
E-mail: ICLARM@cgiar.org
A Global Information System on Fishes (developed by ICLARM)

International Development Research Centre (IDRC) (March 13, 1998), Ottawa, Canada

SYFIA - Rédaction centrale. Système francophone d'information agricole.
Agence Periscoop-SYFIA. Agropolis International. 34394 Montpellier Cedex 5 &shy; France. Tél. (33) 04 67 04 75 80 - fax (33) 04 67 04 7585. Courriel: syfia@agropolis.fr
SYFIA - Bureau Afrique Côtière. BP 01-3315, Cotonou &shy; Bénin. Tél. (229) 31 18 27 - fax (229) 31 18 29. Courriel : syfia@bow.intnet.bj

Tilapia aquaculture - Proceedings of the Fourth. International Symposium on Tilapia in Aquaculture. Meeing held in Orlando, Florida November 1997.

The Role of Land Tenure and Property Rights in Sustainable Resource Use: The Case of Benin
 

8 Annotations

Income of Acadja harvest per hectare (FCFA) depending on fallow vegetation
 
Fallow type
Coverage %
gross income(FCFA)
net income (FCFA)
Fan
55
59300
50100
Gbozun
42
196500
140000
all (including Acacia plantation)
100
133200
97900

Fan = degraded fallow dominated by grasses, gbozun = fertile fallow with bush vegetation
 
 

Nutrient export ( g m-2) from fallow sites at Hêvié-Zoungo, Benin
 
Fallow type
 
 
Nutrient
 
 
 
N
P
K
Mg
Ca
Average fallow (600 bundles)
5.1
1.1
3.1
1.7
6.0
Fan (300 bundles)
2.5
0.6
1.6
0.8
3.0
Gbozun (900 bundles)
7.6
1.7
4.7
2.5
9.0

Fan = degraded fallow dominated by grasses, gbozun = fertile fallow with bush vegetation
 
 

Different types of organisation of the Acadja system
 
Fallow
Transport I
Harbour
Transport II
Lagoon
1. Owner
Commercial
Commercial
Fisherman
Fisherman
2. Owner
Fisherman
Fisherman
Fisherman
Fisherman
3. Owner
Owner
Owner
Fisherman
Fisherman

 

9 Links to data source

Download data of this project

Includes the following data (if available) compressed into one "zip" file:

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