Spatial and temporal distribution patterns of brown shrimp (Crangon crangon) derived from commercial logbook, landings, and vessel monitoring data

Abstract

In this study, logbook, landings, and vessel monitoring system data of German brown shrimp (Crangon crangon L.) fishers were combined to analyse spatial and temporal distribution patterns. Landings per unit effort (LPUE) were standardized to the efficiency level of a reference vessel. The standardization altered the spatial-Temporal patterns of the LPUE as the vessels differed by a factor of up to 4.7. LPUE data were separated into two size classes according to sieve fractions. Small brown shrimps were characterized by LPUE values increasing early in the year in shallow waters, especially in estuaries in July. Subsequently, peak LPUE values are reached at the end of September in all depths, but with variable spatial patterns between years. LPUE data indicate a general outward migration between early summer and winter. In winter, large shrimp shows a clear increase in LPUE with depths mainly in regions adjacent to the Dutch coast and a reversed pattern close to the Danish coast. The large size class in winter-which consists mainly of mature or egg-bearing females-showed high LPUE values along two persistent diagonal bands in the German Bight. These patterns could lead to local recruitment overfishing, if fishermen are aware of such patterns.