Spatial variability in the seasonal trends of ovary weight in the Namibian pilchard population, 1965–1979

Abstract

Seasonal and spatial trends in gonad weight of some 68 000 female pilchard sampled in the northern Benguela system over the period 1952–1979, and especially the better-sampled years 1965–1979, were assessed. There were large variations in fish abundance during the period researched, and there were also changes in spawner potential, in fish condition and in certain environmental parameters. North of 21°S ovary weight increased to a peak during summer, whereas south of that latitude it was high during both winter/spring and summer/autumn. The reason for such spatio-temporal differences is thought to be seasonal differences in the strength and direction of wind stress at different localities. Near Walvis Bay, ovary weight and fish condition were very low prior to 1965, but they increased and remained high after 1969. At specific localities, seasonal trends in the standardized ovary weight of small and large females were similar. © 1990 Taylor and Francis Group, LLC.