Table of Contents
International Journal of Oceanography
Volume 2011 (2011), Article ID 920414, 10 pages
http://dx.doi.org/10.1155/2011/920414
Research Article

Environmental Influences on South African Fish Catch: South Coast Transition

1Faculty of Science and Agriculture, University of Zululand, KwaDlangezwa 3886, South Africa
2Physics Department, University of Puerto Rico, Mayaguez, PR 00681, USA

Received 12 May 2011; Revised 26 November 2011; Accepted 29 November 2011

Academic Editor: Robert Frouin

Copyright © 2011 Mark R. Jury. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

This study considers environmental factors influencing aggregate fish catch in the South Coast transition of South Africa. The environmental forcing is studied via (i) seasonal analysis of SeaWifs chlorophyll and related variables, (ii) composite analysis of atmospheric and oceanographic reanalysis data, (iii) statistical analysis of annual FAO fish catch with climatic indices, and (iv) analysis of depth-latitude hydrographic sections over the shelf (33–36S, 22–26E). In years of higher fish catch there is a northward shift of the subtropical anticyclones and upwelling that is partially related to Pacific El Nino. Westerly troughs skirt the Agulhas Bank creating onshore Ekman transport. Higher sea surface height inshore, and cooler sea temperatures and lower salinity offshore induce a gradient that weakens the Agulhas Current. These environmental conditions favour the southeastward migration of juvenile fish from west to south coast. A multivariate model of aggregate fish stocks, using four environmental variables: salinity and zonal currents in the Agulhas Current, sea temperature in the Agulhas source region, and geopotential height over the Cape, accounts for 53% of variance at 0-1 year lead. Freshening of the boundary current is a factor influencing aggregate fish catch in the South Coast transition.