Occurrence of tuna and mackerel larvae (Family: Scombridae) off the east coast of South Africa

Abstract

Spatial and temporal distribution patterns of scombrid larvae along the east coast of South Africa were investigated from ichthyoplankton collections made during May–June 1990 (winter), October 1990 (spring) and February 1991 (summer). Results were analysed in relation to oceanographic conditions and known spawning localities of tuna and mackerels in the western Indian Ocean. In total, eight species were represented in the samples, with highest diversity in February and lowest numbers in May–June. Larvae of the temperate chub mackerel Scomber japonicus were most abundant at shelf stations during October. Larvae of neritic tunas Auxis sp. and Euthynnus affinis occurred in shelf stations off KwaZulu–Natal in February and extended southward in a plume along the shelf edge. Larvae of skipjack tunaKatsuwonus pelamis were most abundant in the Agulhas Current during February. Only a few larvae of oceanic tunas Thunnus spp., wahoo Acanthocybium solandri and king mackerel Scomberomorus commerson were collected in the Agulhas Current in the north of the study area during February when there was an intrusion of warm Tropical Surface Water. This indicates that spawning of these species probably does not occur off the east coast of South Africa.