Changes in some key biological parameters of the northern benguela sardine stock

Abstract

During the past 50 years, more than 15 million tons of sardine have been harvested from the northern Benguela ecosystem. The sardine population has undergone changes in abundance estimated to range over more than two orders of magnitude, but for the past two decades it is estimated to have remained at less than 10% of former levels of abundance. Some key changes in biological parameters, notably age composition and rates of natural mortality, are discussed in relation to the changes in abundance. Literature values for the period before the 1990s are compared to values calculated from acoustic survey population estimates thereafter. Although these recent data are potentially biased, and often lack estimates of precision, it is argued that they are sufficient to demonstrate general trends. The likelihood of the sardine stock recovering is seemingly reduced owing to the recent high rate of adult natural mortality.