The vertical and transverse distribution of larval herring in the River Blackwater estuary, Essex

Abstract

The vertical and transverse distributions of spring‐spawned larval herring were studied in the River Blackwater estuary, Essex. Sampling was undertaken during May when larval densities within the estuary were at a maximum for the year. At this time, larval lengths were in the range 7–16 mm. No clear diel pattern in the vertical distribution was found, although larval distribution at night was more even.The tides were found to influence the vertical distribution. Surface waters (< 1.5 m in depth) were avoided during both flood and ebb tides, but used during slack water. Larval densities at ebb were higher near the sea bed than during the flood tide. It was concluded that this behaviour will tend to transport larvae into and retain them within the estuary.