The use of a shoal analysis and patch estimation system (SHAPES) to analyse hydro-acoustic data is discussed. SHAPES was used to detect and characterise sardine schools from four echo integration surveys off the coast of South Africa. Methods of school detection and characterisation, assumptions made and corrections applied to school variables are presented. Measurements of school morphology and internal school features are discussed and compared to other relevant works. Significant relationships were established, both between measures of school morphology and internal density structure. Several variables showed significant differences between surveys. Composite factors derived from principle component analyses showed that morphological variables are the most important school descriptors. No differences in the loading of composite factors between surveys are evident. This suggests an inherent spatial and temporal stability in sardine school characteristics. This fact may prove beneficial for comparisons of school structure between co-occurring fish species and possibly aid fish school identification in the future.