Population structure, reproductive biology and maintenance of Euphausia lucens in the southern Benguela Current

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Abstract
This study investigates the population structure and reproductive biology of the euphausiid Euphausia lucens in relation to temporal and spatial variations in the abiotic and biotic environment in the St Helena Bay region off the west coast of South Afnca. This is an area of high biological productivity and is important for recruitment to the pelagic fishery. Gravid females (stage IV) and young larvae were collected throughout the year, suggesting continuous breeding. Spawning was most intense from August to October (late winter to early spring) just prior to the onset of upwelling and an associated increase in phytoplankton. Recruitment was high until early summer (August-January) and decreased to a low level throughout autumn and early winter (February-June). The proportion of gravid females increased with distance offshore despite relatively low chlorophyll a concentrations offshore. Multiple spawning is inferred from the high frequency of gravid females in the population. The reproductive strategy and vertical distribution of all developmental stages of E.lucens is related to the current regime of the study site in order to formulate mechanisms most likely to play an important role in maintaining coastal populations of E.lucens in the southern Benguela Current.

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