Tuesday, March 31, 2015

Joint Fish Biodiversity Surveys- Highlights From The Okavango Delta Low Water Survey: December 2014



Joint Fish Biodiversity Surveys- Highlights from the

Okavango Delta Low Water Survey 
Maun, Botswana 
December 2014

Full report available on request

Background

The formation and general mandates of the Joint Permanent Commission of Cooperation (JPCC) between Botswana and Namibia has been reported in previous reports. However, in summary a Trans-boundary Fisheries Management Plan for the Okavango/Kavango/Cubango Basin was formulated under the auspices of the Joint Permanent Commission of Cooperation (JPCC) between Botswana and Namibia, and this serves as a guiding framework and created a platform for establishing a joint fisheries monitoring system for the two countries. The SAREP programme based in Maun, Botswana coordinated and funded meetings that saw the development of the fisheries management plan. The monitoring system is essential for providing a framework for collaborative research and enhances the scientific knowledge base that will direct conservation initiatives and ensure the sustainable use of the fisheries resources of the shared water course. 

       Brief background on joint fish biodiversity surveys 

One of the key activities listed in the management plan and presently ongoing is the joint fish biodiversity surveys. It was planned that two fish biodiversity surveys be conducted in 2014 (during low and high water period). In Namibia the first survey was conducted from the 6th to 19th May 2014 (high water) and the second was conducted between 6-18 October 2014 (low water) while in Botswana the first survey was conducted between June 23 and July 6, 2014 (high water) and the second was conducted between 26 October and 5 November, 2014 (low water). The scope of this report is however limited to the low water Okavango delta fish biodiversity survey.

Survey overall objective                                                          

The main objectives of joint surveys are to standardise fisheries research methods and develop a long term transboundary fisheries database that will facilitate the development of sound and scientific information-driven fisheries management strategies for the Cubango/Kavango/Okavango basin.    

The study area

Description of the Okavango delta

The Okavango delta comprises of a mosaic of permanent marshlands that are interconnected with permanent streams, lagoons, permanent moderate to densely vegetated floodplains, seasonal floodplains and salt islands. Structurally, the delta has two parts; the floodplain system below Popa Falls represents the beginning of the panhandle which becomes progressively more pronounced as the river enters into Botswana while the other part is the delta proper with wide permanent swamp land. 

The Okavango/Kavango/Cubango River altitude is approximately 1100m upon entering Namibia and 1000m when leaving Namibia into Botswana. Therefore, generally the regional terrain is gently undulating with less than 2 m gradient within the Okavango delta. The low topographic gradient of the delta results in low flow velocities with most water flow occurring in streams and partially in vegetated floodplains. Therefore, the flow velocities of the entire system are lowest in the Okavango delta. Also, the flood wave arriving is markedly attenuated as the water spreads through the wider swamp area of the delta while the system in Namibia and Angola comprise of predominantly of narrow floodplains with 95% of the flow carried in the main river. The delta culminates in a dead end so most of the water is lost through evapotranspiration while a small proportion contributes to: ground water recharge, replenishing Lake Ngami water resources and contributing to the closed water balance of Mopipi dam in Orapa via the Boteti River.

Hydrology of the Cubango basin

The basin is home to the Okavango River and its major tributary Cuito River with a total basin area of 530 000 km2 spread along three countries. The magnitude of rainfall events are highly varied along the stretch of the Cubango basin with average annual rainfall gradually decreasing from 1000 mm from the head waters to approximately 500 mm at Rundu and 450 mm within the Okavango delta. The rainfall season in the basin is from November to April while the flood season extends up August in the furthest parts of the Okavango delta.

The water flow is contributed by rainfall events of approximately 1000 mm per year occurring in the upper catchments having a surface area of approximately 135 000 km2 that is situated within Angola. About 95% of the generated water flow is carried by river while the vast distance between the head waters to the Namibia stretch of the river and the delta ensures that a significant period passes between the occurrence of rainfall events in Angola and the arrival of the flood wave in Namibia and the Okavango delta.  

Sampling stations and setting types 
Click on image for better view

No comments: