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The role of ichthyoplankton surveys in recruitment research and management of South African anchovy and sardine

C.D. van der Lingen and J.A. Huggett (2003) The role of ichthyoplankton surveys in recruitment research and management of South African anchovy and sardine. The Big Fish Bang. Proceedings of the 26th Annual Larval Fish Conference.

Abstract

Anchovy Engraulis encrasicolus and sardine Sardinops sagax are ecologically and economically important components of the southern Benguela upwelling ecosystem situated off the west coast of South Africa. The importance of these species has resulted in substantial research effort directed towards understanding their population dynamics, with much of this effort going into ichthyoplankton surveys. This review describes the methodologies used and results obtained from ichthyoplankton surveys conducted off South Africa during the past 50 years. This research has allowed the development of a detailed knowledge of the life history cycles of small pelagic species in the southern Benguela, particularly that of anchovy. Spatially distinct spawning and nursery areas have been identified, highlighting the critical influence that transport of eggs and early larvae from the spawning to nursery grounds has on subsequent recruitment strength. Temporal changes in the location of spawning habitat of both anchovy and sardine have been tracked, and environmental parameters characterizing spawning habitat differentiated. Frequent monitoring of early life history stages in the transport region shows promise as a predictor of recruitment success for anchovy but not necessarily sardine, although this predictor is not yet formally incorporated into management procedures. Insights gained from ichthyoplankton surveys have been used to develop individual-based models (IBMs) coupled with a 3D hydrodynamic model of the region; these have allowed the testing of various hypotheses concerning transport success and various physical and biological parameters through experimental simulation. Ichthyoplankton survey data have been used for stock management by application of the DEPM to estimate anchovy spawner biomass from 1986-1993; these absolute estimates were then used to calibrate relative estimates of anchovy biomass made using hydroacoustic methods. These examples demonstrate that ichthyoplankton surveys of anchovy and sardine are widely used off South Africa and have made a substantial contribution toward identifying key mechanisms impacting on recruitment success and hence management of these small pelagic species

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