Sunday, September 8, 2013

Kwando and Kavango river isotope field trip report, September 2013





Participating  researchers: Dr Olaf Weyl and Dr Sven Kaehler, PhD students: Richard Peel and Geraldine Taylor

Introduction

This field trip is part of a larger project on the Zambezi, Kavango and Kwando rivers in Namibia which aims to improve knowledge of the aquatic ecosystems supporting fisheries through studies on fish population dynamics, food webs, nutrients and biodiversity. The research will be undertaken primarily by two PhD students: Richard Peel and Geraldine Taylor through Rhodes University. The students introduced their studies to local staff and students in presentations given at the Kamutjonga Inland Fisheries Institute (KIFI) on the Kavango River on the 26th August 2013. 

Figure 1: Geraldine Taylor introducing an overview of her studies to staff and students at KIFI

The project is funded primarily by the Southern African Science Service Centre for Climate Change and Adaptive Land Management (SASSCAL) and co-funded by the South African National Research Foundation and Nedbank Namibia’s Go Green Fund. The project is administered by the Namibia Nature foundation and involves several collaborating institutions including the South African Institute for Aquatic Biodiversity, Rhodes University, University of Namibia and the Namibian Ministry of Fisheries and Marine Resources.
The field trip was carried out from the 17th to the 27th August 2013.  The objective of the trip was to collect tissue samples from fish and their potential food sources for stable isotope analysis to describe the food webs of the Kwando and Kavango rivers. Understanding floodplain river food webs is important for ecosystem management, as it allows one to assess the importance of the seasonal flood pulse for biodiversity and productivity, and the potential impact of water abstraction and flow regulation that may disrupt the natural flow regime. It is also important for fisheries management as overfishing may alter fish assemblage structure and the structure and dynamics of the food web, with consequences for fish production and sustainability.

Sampling


Sampling was carried out on the Kwando River from the 17th to the 24th August and on the Kavango River from the 25th to the 27th August. Fish samples were collected using gillnets, fyke nets, D-nets, and by angling. Invertebrates were sampled using a SASS net and a drift net. Detritus and benthic invertebrates were sampled using a cone dredge, and aquatic plants were sampled by hand. The minimum number of each species was sacrificed in order to sample different size groups that may utilize different food sources.

Figure 2: Sampling invertebrates and setting fyke nets on the margins of the Kwando River.
Figure 3: The river crab Potamonautes bayonianus, an important prey item for many fishes.
A total of 403 samples were collected from the Kwando River and 238 samples from Kavango River. Fish species sampled are listed in table 1 below. All samples will be analysed at the isotope laboratory at Rhodes University.

Figure 4: The Zambezi parrotfish Cyphomyrus cubangoensis, a common mormyrid in the Kwando River.

Table 1: Fish species sampled in the Kwando and Kavango rivers.

Species
Kwando River
Kavango River
Aethiomastacembelus frenatus
X

Barbus afrovernayi
X
X
Barbus barnardi
X
X
Barbus eutenia

X
Barbus fasciolatus
X
X
Barbus paludinosus

X
Barbus multilineatus
X

Barbus radiates
X
X
Barbus thamalakanensis

X
Barbus unitaeniatus
X
X
Coptostomabarbus wittei
X

Brycinus lateralis
X
X
Chiloglanis fasciatus

X
Clarias gariepinus
X
X
Clarias ngamensis
X
X
Clarias theodorae
X

Cyphomyrus cubangoensis
X

Hemichromis elongates
X

Hemigrammocharax machadoi
X
X
Hemigrammocharax multifasciatus
X
X
Hepsetus cuveiri
X

Hydrocynus vittatus
X
X
Labeo lunatus

X
Marcusenius altisambesi
X
X
Micralestes acutidens
X
X
Micropanchax huterui

X
Micropanchax johnstoni
X
X
Micropanchax katangae
X
X
Mormyrus lacerda

X
Nannocharax macropterus

X
Opsaridium zambezensis
X

Oreochromis andersonii
X
X
Oreochromis macrochir
X

Parauchenoglanis ngamensis
X

Petrocephalus kavangoensis

X
Petrocephalus longicapitas
X

Pharyngochromis acuticeps
X
X
Pollimyrus castelnaui
X
X
Pseudocrenilabrus philander
X
X
Rhabdalestes maunensis
X

Sargochromis carlottae
X
X
Sargochromis codringtonii
X

Sargochromis “dusky”
X

Sargochromis giardi
X
X
Schilbe intermedius
X
X
Serranochromis altus
X
X
Serranochromis angusticeps
X
X
Serranochromis macrocephalus
X
X
Serranochromis robustus

X
Synodontis nigromaculatus
X
X
Synodontis sp.
X
X
Tilapia rendalli
X
X
Tilapia sparrmanii
X
X
Zeirichthys pallidus
X


The results from this survey will be used to describe the food webs of each of these rivers. These will then be compared to results obtained in previous surveys of Lake Liambezi and the Zambezi River to determine what drives the productivity in each of these systems and how they differ from one another. 

Figure 5:  Lab work in the Wet lab at KIFI. Working late into the night...

No comments: