Has climate change disrupted stratification patterns in Lake Victoria, East Africa?

  • BE Marshall
  • CN Ezekiel
  • J Gichuki
  • OC Mkumbo
  • L Sitoki
  • F Wanda

Abstract

Climate change may threaten the fisheries of Lake Victoria by increasing density differentials in the water column, thereby strengthening stratification and increasing the intensity and duration of deoxygenation in the deeper waters. Between 1927 and 2008 the lake’s temperature increased by 0.99 °C at the surface and by 1.34 °C at depths >50 m, with the rate of warming increasing most rapidly between 2000 and 2008. In February 2000 there were marked thermal discontinuities in the water column at a number of deep stations, with marked oxyclines at depths ranging from 30–50 m, and with all stations being anoxic from 50 m downwards. In contrast, in February 2007 the lake’s temperature had risen, especially at the bottom, and both the thermal discontinuities and oxyclines were much reduced, only one station recording a dissolved oxygen concentration of <2.0 mg l–1 at 50 m. This may reflect the fact that deeper waters were warming faster, and the reasons for this are discussed. These data suggest that the impacts of warming on the thermal regime of African lakes may be highly variable and unpredictable and, in this case, may have reduced its threat to the fisheries.

Keywords: deoxygenation, fisheries, global warming, thermocline

African Journal of Aquatic Science 2013, 38(3): 249–253

Author Biographies

BE Marshall
Lake Victoria Fisheries Organisation, PO Box 1625, Jinja, Uganda; current address: 9/4074 Great North Road, Auckland 0602, New Zealand
CN Ezekiel
Tanzanian Fisheries Research Institute, PO Box 475, Mwanza, Tanzania
J Gichuki
Kenya Marine and Freshwater Fisheries Institute, PO Box 1881, Kisumu, Kenya
OC Mkumbo
Lake Victoria Fisheries Organisation, PO Box 1625, Jinja, Uganda; current address: 9/4074 Great North Road, Auckland 0602, New Zealand
L Sitoki
Kenya Marine and Freshwater Fisheries Institute, PO Box 1881, Kisumu, Kenya
F Wanda
National Fisheries Resources Research Institute, PO Box 343, Jinja, Uganda
Published
2013-12-04
Section
Articles

Journal Identifiers


eISSN: 1727-9364
print ISSN: 1608-5914