Weekly variability of clupeoid eggs and larvae in the Benguela jet current: implications for recruitment

Abstract

Weekly sampling of ichthyoplankton, current vectors and surface temperature along a 34-mile transect crossing the jet current off the Cape Peninsula was conducted from August 1995 to July 1996 as part of the third phase of the South African Sardine and Anchovy Recruitment Programme, designed to investigate within-season variability in factors affecting sardine Sardinops sagax and anchovy Engraulis capensis recruitment. Anchovy eggs and larvae were found from October 1995 to February 1996, with most intense spawning from mid-October to early December, Peak abundances of anchovy eggs (717·m⁻²) and larvae (342·m⁻²) were encountered during mid-November. Sardine eggs and larvae were found throughout the year, but were most abundant from August 1995 to February 1996. Numbers were greatest during late September, reaching 630 eggs·m⁻² and 142 larvae·m⁻², with secondary peaks of >200 eggs·m⁻² during August, October and January. Spawning products were low from March onwards, but increased slightly during July 1996. Current vectors indicated that spawning prior to December was most favourable for transport of eggs and larvae to the West Coast nursery area. January and February were characterized by increasingly complex flow patterns, while the frontal jet current was positioned offshore of the transect for most of March and April as a result of prolonged periods of upwelling. Monthly length-frequency distributions of larvae indicated spawning by both species farther east on the western Agulhas Bank later in the season, or more complex transport from that region to the sampling area. Mean monthly (August–March) anchovy and sardine (September–February) egg abundances were significantly correlated (p < 0.05) with the estimated birthdate distribution of recruits, suggesting that frequent monitoring of egg abundance along the transect may be useful for forecasting recruitment strength.