Acoustic investigation of the shoaling dynamics of sardine sardinops sagax populations : implications for acoustic surveys

Master Thesis


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University of Cape Town

The total allowable catches (TA Cs) of both anchovy and sardine in South Africa are determined by assessment methods which rely on absolute estimates of recruitment and spawner biomass each year. The validity of the TAC set for each species each year is heavily dependent on the accuracy and precision of the biomass estimates. The method used for both anchovy and sardine has been acoustic surveys on a random stratified grid covering the known range of the species. These surveys have, however, been designed according to the life history patterns of anchovy, which result in a particular occupation of the pelagic environment. This study investigated the shoaling dynamics of sardine at various scales in both the horizontal and vertical dimension in an attempt to ascertain whether these surveys are adequate to characterise the occupation of space by sardine. Hydro-acoustic data collected during 5 meso-scale surveys in 1994 and 1995 was used to study the shoaling dynamics of sardine, Sardinops sagax on the western Agulhas Bank of South Africa. Results of this study indicate the presence of spatial structure in sardine aggregations at both the shoal and meso-scale level.

Bibliography: pages 113-117.