Reviewing evidence of marine ecosystem change off South Africa

Recent changes have been observed in South African marine ecosystems. The main pressures on these ecosystems are fishing, climate change, pollution, ocean acidification and mining. The best long-term datasets are for trends in fishing pressures but there are many gaps, especially for non-commercial species. Fishing pressures have varied over time, depending on the species being caught. Little information exists for trends in other anthropogenic pressures. Field observations of environmental variables are limited in time and space. Remotely sensed satellite data have improved spatial and temporal coverage but the time-series are still too short to distinguish long-term trends from interannual and decadal variability. There are indications of recent cooling on the West and South coasts and warming on the East Coast over a period of 20 - 30 years. Oxygen concentrations on the West Coast have decreased over this period. Observed changes in offshore marine communities include southward and eastward changes in species distributions, changes in abundance of species, and probable alterations in foodweb dynamics. Causes of observed changes are difficult to attribute. Full understanding of marine ecosystem change requires ongoing and effective data collection, management and archiving, and coordination in carrying out ecosystem research.DHE

Serial spawning and batch fecundity of merluccius capensis and m. Paradoxus

Histological analysis of the ovaries and the presence of multiple modes in oocyte size frequency distribution of Cape hake Merluccius capensis and M. paradoxus indicates that they are serial spawners. Batch fecundity,calculated by means of the “hydrated oocyte method”, was positively correlated to ovary-free fish mass and total fish length. The mean relative fecundity (ovary-free mass) of M. capensis and M. paradoxus was 160 ± 12and 306 ± 25 eggs.g-1 respectively