Ecosystem considerations of the KwaZulu-Natal sardine run

  • L Hutchings
  • T Morris
  • CD van der Lingen
  • SJ Lamberth
  • AD Connell
  • S Taljaard
  • L van Niekerk

Abstract

The annual winter sardine run along the South African east coast impacts the KwaZulu-Natal (KZN) coastal system in a variety of ways. These include ecological impacts, such as enrichment of a largely oligotrophic environment, competition between migrant sardine Sardinops sagax, other migrant and resident small pelagic fish species, and interactions with predators, as well as the socio-economic impacts of the sardine run on the local people. Enrichment of KZN coastal waters with organic nitrogen contained within the sardine is compared with alternative sources of nitrogen such as upwelling, river, sewage and stormwater runoff, and groundwater discharge. The sardine run appears to contribute most nitrogen to this system — 96 000 t compared to 500–3 300 t for each of the other significant sources at trophic level 2, although upwelling estimates are extremely wide. Nonetheless, the majority of surviving sardine, their young and predators return southwards, suggesting that the nett export of nitrogen to KZN waters during the run is likely to be of a similar order of magnitude as that from other sources. Further, whereas the sardine supply of nitrogen is exclusively during winter, the bulk of the riverine input is in summer, thus ensuring that nitrogen supply in the region is maintained at fairly constant levels throughout the year. Competition for food between small pelagic fish is minimised by resource partitioning, but further dietary data are needed for resident species. Although interactions between sardine and top predators must exist, further studies are needed to confirm links between top predator life cycles and the sardine run. The estimated value of sardine as a tourist spectacle is compared to that from a seasonal beach-seine or boat-based purse-seine fishery for this species. Whereas the estimated value of the sardine as a tourist attraction appears substantially higher than could be derived from catching them, the small-scale beach-seine fishery itself draws tourists and also provides limited, seasonal employment opportunities.

Keywords: competition, nitrogen sources, predators, relative economic value, sardine run, South African east coast

African Journal of Marine Science 2010, 32(2): 413–421

Author Biographies

L Hutchings
Oceans and Coasts, Department of Environmental Affairs, Private Bag X2, Rogge Bay 8012, South Africa;  Marine Research Institute, University of Cape Town, Private Bag X3, Rondebosch 7701,South Africa
T Morris
Bayworld, Port Elizabeth Museum, PO Box 13147, Humewood 6013, South Africa
CD van der Lingen
Marine Research Institute, University of Cape Town, Private Bag X3, Rondebosch 7701,South Africa; Branch Fisheries, Department of Agriculture, Forestry and Fisheries, Private Bag X2, Rogge Bay 8012, South Africa
SJ Lamberth
Branch Fisheries, Department of Agriculture, Forestry and Fisheries, Private Bag X2, Rogge Bay 8012, South Africa;  South African Institute for Aquatic Biodiversity, Private Bag 1015, Grahamstown 6140, South Africa
AD Connell
South African Institute for Aquatic Biodiversity, Private Bag 1015, Grahamstown 6140, South Africa
S Taljaard
Council for Scientific and Industrial Research, Environmentek, PO Box 320, Stellenbosch 7599, South Africa
L van Niekerk
Council for Scientific and Industrial Research, Environmentek, PO Box 320, Stellenbosch 7599, South Africa
Section
Articles

Journal Identifiers


eISSN: 1814-2338
print ISSN: 1814-232X