Transport of anchovy and sardine eggs and larvae from the western Agulhas Bank to the West Coast during the 1993/94 and 1994/95 spawning seasons

Abstract

The transport of eggs and larvae of anchovy Engraulus capensis and sardine Sardinops sagax from the western Agulhas Bank to the nursery grounds on the Cape west coast was investigated. Samples were taken monthly between August 1993 and March 1994 and September 1994 and March 1995. A comparison of eggs and larval distributions with current features from selected months supports previous studies, indicating that the frontal jet plays an important role in the transport of the early life history stages of anchovy and sardine, but that the position of such transport can vary between the 200 and 500-m isobaths. During October 1994, November 1994 and February 1995, the greatest concentrations of eggs corresponded with areas of strong north-north-westerly flow just beyond the 200 m isobath off the Cape Peninsula, whereas in November 1993 and January 1994 eggs were concentrated farther offshore, increasing the vulnerability of developing larvae to further dispersion offshore. Offshore concentrations, intensified by strong south-easterly winds, occurred during January 1994. Areas of probable egg loss include the western Agulhas Bank, where currents flowing south-south-west can remove eggs before they are transported to the West Coast. Offshore currents also can develop west of the Cape Peninsula, but onshore currents are able to return eggs to the region of the jet, from where they are transported northwards. Other losses may result from offshore transport in the outer branch of the frontal jet off Cape Columbine. Variations in the ability of the jet current flowing north-north-west to transport eggs and larvae to areas favourable for growth and survival may influence recruitment success.