Population dynamics, distribution and secondary production of the brown shrimp Crangon crangon (L.) in a southern European estuary. Latitudinal variations

Abstract

The population structure, growth, distribution and secondary production of the brown shrimp Crangon crangon (L. 1758) were examined between June 2003 and August 2005 at five stations in the Mondego Estuary, Portugal, using a 2-m beam trawl. Occurrence of immature shrimps suggested almost continuous reproduction with two main recruitment periods in November and March/April; this recruitment pattern is unique and represents a latitudinal transition in the species' life cycle. Severe drought in winter 2004 caused spatial shifts along the north arm of the estuary regarding post-larval settlement in spring 2005. Mean growth of all cohorts was 0.06 mm TL day-1, much lower than rates calculated elsewhere. Secondary production (P) of C. crangon was estimated at 4.6 mg AFDW m-2 y-1 (P/B̄ ratio of 8.7) in 2003/ 2004 and at 2.4 mg AFDW m-2 y-1 (P/B̄ ratio of 10.9) in 2004/2005. High abundances of individuals, predominantly juveniles, were observed in spring/summer with peaks in June 2003, April 2004 and July 2005. This study shows that this species dynamics must be analysed in a latitudinal context, meaning that the contribution of each component of the systems can vary according to environmental and climate variables.