Monday, January 13, 2014

Understanding the variation in growth rates of the fishes of the Zambezi, Kavango and Kwando rivers, Namibia



 
Floodplain river systems are characterised by a seasonal flood cycle, during which the rivers overflow their banks, inundating the aquatic terrestrial transition zone, creating complex habitats and nutrient rich nursery areas for diverse fish communities (Flood Pulse Concept). (This picture: Kavango river)
  
Research update:
Geraldine Taylor, PhD student, Rhodes University

Supervisors: Dr OLF Weyl; Dr CJ Hay; Dr JM Hill

In conjunction with the Ministry of Fisheries and Marine Resources: Directorate of Aquaculture and Inland Fisheries: Namibia




Funders: National Research Foundation/South African Institute for Aquatic Biodiversity; Press Family Trust; Southern African Science Service Centre for Climate Change and Adaptive Land Management; Nedbank Namibia Go Green 


Floodplain river systems are characterised by a seasonal flood cycle, during which the rivers overflow their banks, inundating the aquatic terrestrial transition zone, creating complex habitats and nutrient rich nursery areas for diverse fish communities (Flood Pulse Concept). As a result of this seasonal inundation, floodplain systems are known for their productive multispecies fish faunas which support subsistence and artisanal fisheries providing food, employment, income and livelihoods for riparian communities. Globally floodplain system integrity is being severely threatened as a result of water abstraction, resource utilisation and climate variability. Research on the drivers of productivity and fish growth on these ecosystems is therefore essential for understanding floodplains, their fisheries and their response to changes in the natural hydrological regime.


The Zambezi and East Kavango Regions of Namibia are home to three large floodplain river systems: the Zambezi, Kavango and Kwando rivers. Prior research has identified growth rate differences of important fisheries species between the systems, and it is hypothesised that differing top down (predation related) and bottom up (productivity related) drivers influence these systems resulting in variable growth rates. The aim of this research is to contribute to understanding African floodplain fish ecology by investigating the cause of the variation in growth rates of fishes representing the three life history strategies; opportunistic, periodic and equilibrium, in the three floodplain rivers. To achieve this aim: fish community structure, nutrient inputs and productivity, and food web dynamics will be quantified and compared between systems. 


To date a limited sample of otoliths and scales have been collected from a number of species from the Zambezi and Kwando rivers, and are being used to determine age. Hard structures are still to be collected from the Kavango River, and additional samples are still needed from the other two rivers, which will be used to determine age and growth and compared between systems. Fish community structure will be described and compared between systems using experimental gill-net catch data collected by the Ministry of Fisheries from 2007-2012, and those collected in 2013 and 2014. Nutrient inputs and productivity will be measured using C13 enrichment experiments during peak and low flow periods in each river system in 2014. The food web dynamics will be described using stable isotope analysis and compared between systems. For this, samples of fish, plant, invertebrate, mollusc, and crustacean species, detritus and particulate organic matter have been collected totalling 403 samples from the Kwando River (August 2013), 425 from the Zambezi River (October 2013) and 236 from the Kavango River (August 2013). 

Read more at:  http://aquaculturenamibia.blogspot.com/2013/09/kwando-and-kavango-river-isotope-field.html
 


No comments: