Spatial structure and geometry of schools of sardine (Sardinops sagax) in relation to abundance, fishing effort, and catch in northern Chile

We analysed the interrelationships of morphological, energetic, and relational descriptors of schools of sardines in the winter seasons of 1984-1990. A surface occupation index was used to measure the space covered by sardine. These descriptors were then related to catch, fishing effort, and catch per unit effort (cpue). We found that the greater the distance between the schools and the smaller the surface occupation index for schools, the smaller their size, biomass, and density. However, these descriptors were weakly related to the number of schools. The annual catch, fishing effort, and cpue were significantly and directly related to surface occupation index and inversely with the distance between schools. These fishery indices were weakly related to school area, school density, and school biomass. The change in the space occupied by sardine affected their catchability, as shown by the logarithmic relationship between the cpue and acoustic biomass. The lack of linearity can be corrected by taking into consideration the index of surface occupation of the stock so as to produce a corrected cpue (epue*) value, which is directly proportional to stock biomass. (C) 2004 Published by Elsevier Ltd on behalf of International Council for the Exploration of the Sea.