Management strategies for enhanced fisheries production in Sri Lankan and Australian lakes and reservoirs - Extension Project

• Kelaniya University, Sri Lanka
• National Aquaculture Development Authority, Sri Lanka
• National Aquatic Resources Agency, Sri Lanka
• University of Paradeniya, Sri Lanka

Capture fishery in perennial reservoirs is the backbone of Sri Lanka's inland fishery. The government and development agencies are now also promoting the use of seasonal reservoirs (known as village tanks) for fish production by local communities, using a stock and recapture strategy referred to as culture-based fishery. Most of the village tanks are located in the dry zone of Sri Lanka; they retain water for six to nine months of the year and are ideally suited for fish production.
Fisheries in reservoirs are increasingly seen as an integral part of whole watershed management, making geographic information systems (GIS) an ideal tool for fisheries management. An earlier project used GIS land-use data to predict yields from capture fisheries. This project validated the GIS-based models and disseminated information about the nature, scope and applicability of the models to relevant stakeholders.
For culture-based fisheries, the initial project found that the lack of availability of suitably sized fingerlings for stocking was a major constraint, and that minor cyprinids (a type of freshwater fish) from perennial reservoirs could provide the feed needed to rear fish fry to the fingerling stage in cages. This project studied how to improve the preparation of this type of feed, the growth and survival of seed stock, and the economic viability of cage culture operations.

This project extended the work of an earlier project (FIS/1994/040) to increase inland fish production in perennial and seasonal reservoirs. One aim was to validate models for predicting yield of capture fisheries in perennial reservoirs, and also show how the research findings could be used to improve fisheries management. For culture-based fisheries in seasonal reservoirs, the aim was to develop a best practice model that could be used to popularise such fisheries in the dry zone of Sri Lanka.

The capture fishery component used GIS data collated by an independent authority (National Aquatic Resources Agency) for six perennial reservoirs. Catchment land-use patterns were digitised by GIS and combined with limnological data (e.g. pH and temperature) and irrigation data, to predict fish yields. Information on how to apply the models was passed on to government officers and other stakeholders through small workshops and through publications.
The project team developed a best practice model for the culture-based component, through field trials with farmers over two full production cycles, in four districts with high numbers of seasonal reservoirs. The researchers investigated optimal species combinations, stocking density, and the influence of staggered harvesting on yields - staggered harvesting could prevent an oversupply of fish during a short period. GIS methodology was used to investigate land use in catchment areas, and the information gained was combined with a wide range of data on physical, biological and social factors.
The project team consulted widely with stakeholders throughout the project to ensure that the recommendations were practical, easily transferable and suitable for adoption by the rural community.

Capture fisheries As a follow-up to a national workshop held in May 2001, and based on a major recommendations thereof, the findings on catchment land-use patterns on fish yield in Sri Lankan reservoirs, and the use of relevant models in management were rewritten in simplified form comprehensible to fishery extension workers. The findings were submitted for implementation by the National Aquaculture Development Authority.
Validation of the yield-predictive models based on catchment land-use patterns was completed, using catch data collated by an independent body (the National Aquatic Resources Agency). This study confirmed the robustness and the validity of the models, thereby proving the possibility that such models could used in managing the fishery resources in reservoirs. This validation was published in a peer-reviewed journal; Fisheries Management & Ecology, Vol. 9 (2002). In view of the increasing interest both in use of GIS in fishery studies and in catchment affects on fish yields, the team reviewed all the findings and made a presentation at the Second International Symposium on GIS in Fisheries, held in Sussex, UK, in September 2002.
Recommendations arising from the project were implemented by the National Aquaculture Development Authority. Selected reservoirs were stocked in October-November 2002, as planned, with two stocking densities and four different species combinations at each density. Since stocking, scientists have monitored the water quality parameters each month by testing each reservoir.
Culture fisheries Forty-four non-perennial reservoirs were stocked (three species combinations and three stocking densities) over two culture cycles and the growth of the stock, yields and the limnology (physical, biological and geographical properties) of each of the reservoirs were monitored. In addition the size of each of the non-perennial reservoirs used in the study, together with their catchments, was determined using GPS and 1:50,000 scale maps. The land-use patterns of the latter were determined using satellite imagery and confirmed with random ground-truthing.
Of the 44 reservoirs, reliable stocked data could be obtained only from 36. The yield data and the growth data are being analysed and it is believed the study will enable the development of a best-practice model, incorporating water quality features, stocking density, species combination and the socio-economic conditions of the village community, for culture-based fisheries in Sri Lanka. Socio-economic criteria and biological criteria were incorporated into the model using the Analytical Hierarchical Process.
The project activities brought about cooperation and integration between governmental departments that have jurisdiction over the utilisation of the water bodies, namely the Department of Agrarian Services and National Aquaculture Development Authority. Consequently, the Agrarian Services Statute is being amended to permit fishery activities in non-perennial reservoirs - these had never had legal status, and this was a hindrance to further fisheries developments.
Extension booklets on the technical and management aspects on culture-based fisheries were developed and provided to all the stakeholders. A workshop in 2002 focused on culture-based fisheries. The overwhelming consensus at the workshop was that the project has stimulated the development of a new and useful activity for the community and that culture-based fisheries development should be extended to other regions in the country.