Evidence for a clustered spatial distribution of clupeid fish schools in the Norwegian Sea and off the coast of southwest Africa

Abstract

Abstract To quantify and characterize the spatial distribution of clupeid fish schools, sonar data were collected during surveys off the coast of Namibia in 1994 (pilchard (Sardinops sagax), anchovy (Engraulis capensis), and round herring (Etrumeus whiteheadi)), off Angola in 1995 (sardinella (Sardinella sp.)) and in the Norwegian Sea in 1997 and 1998 (Norwegian spring-spawning herring (Clupea harengus L.)). The two-dimensional distances between clupeid schools were calculated in the order that the different schools were observed along the survey vessels transect lines. In all four surveys, two different modes (frequency distribution maximums) were observed. The first mode, representing the most usual interschool distance, was about 60 m. The second mode, around 1600 m, probably represented the distances between different clusters. The distances between clupeid schools and between different clusters were found to be about the same for separate pelagic clupeid species, locations, and years of observation. The mean diameters of the school clusters were estimated to vary between 450 and 1450 m.