Formulation of management strategies for two exploited West African prawn populations

Abstract

The life histories of the estuarine prawn, Nematopalaemon hastatus Aurivillius, and the brackish river prawn, Macrobrachium macrobrachion Herklots, were compared in relation to their seasonal exploitation patterns in the Cross River estuary, Nigeria. The period of intensive exploitation of N. hastatus (March to June) was outside the main spawning season (July to October), because these prawns migrate from the main fishing area in the estuary and near shore coastal waters into the deeper continental shelf waters to spawn. This probably contributes to their reproductive success and conservation of the stock. With M. macrobrachion, the peak spawning period and the major fishing season converge between July and September. These prawns also migrate from the fresh water into the major fishing zone within the estuary during the spawning season. This exposes the spawning population to intense human exploitation. On the basis of their spawning dynamics, M. macrobrachion requires more urgent management attention. An option would be a closed season for M. macrobrachion within the estuary during the spawning period.

The exploited population of the brackish river prawn (<i>Macrobrachium macrobrachion</i> Herklots 1851) in the Cross River estuary, Nigeria

“…M. macrobrachion in the estuary spawns all the year round but this comes to a peak in July to September (Enin, 1997). It is conceivable that during the peak spawning period, much of the ingested food materials may be sequestrated into the development of the gonads, thus resulting in poor somatic growth (Helffman et al, 1997).…”

“…Hence, the spawning adults migrate to the estuaries, where they may be exposed to much fishing pressure. In the Cross River estuary, this exploitation of the spawning biomass has been considered non-conservative to the stock and responsible for the deterioration of the prawn population (Enin, 1997). There is a need to analyse the catch and effort data at least for the last 10 years and to apply other methods of stock assessment in order to estimate the long term trends in the fishery.…”

“…Spawning and recruitment of the species also take place all year round but with seasonal pulses. The major spawning peak occurs between July and September, and a secondary peak in January; while recruitment peaks occur in May and December (Enin, 1997).…”