THE ORIGIN AND RECRUITMENT OF BASS, DICENTRARCHUS-LABRAX, LARVAE TO NURSERY AREAS

The distribution of bass, Dicentrarchus labrax (L.), eggs taken in ichthyoplankton surveys of the Bristol channel and eastern Celtic Sea from April 1989 to May 1990 indicates that bass spawned predominantly offshore during March and April. Seventy-two bass larvae were captured by ring net and 16 by high-speed tow net during 19-27 May 1989, and 11 were captured by ring net during April and May 1990. Larvae were most abundant inshore where the water column was unstratified and less than 50 m deep. Back-calculated egg fertilization dates were determined for 58 larvae captured in May 1989 by ring net, using estimates of temperature-dependent egg and larval development rates and counts of daily growth increments on sagittal otoliths. These dates ranged from 5 April to 10 May 1989, later than those for most young-of-the-year bass which first appeared in Welsh estuaries during June 1989. This implies that bass larvae would have been more abundant before the May sampling period, even though these catches are the largest reported from UK waters. Bass larvae of 5-11 mm live notochord length were captured close to estuarine nursery areas, and their mean growth rate was approximately 0.2 mm per day. However, the smallest bass first arriving in the nursery areas during June, July and August were always larger than these larvae, and predominantly 15-20 mm total length. It is suggested that bass larvae hatching offshore either perish or are transported to unstratified coastal waters where they feed and remain for at least 30 days prior to their recruitment to the nurseries. Recruitment is considered to be an active process, whereby larvae reaching a particular developmental stage, and receiving an appropriate environmental cue, actively seek suitable nursery habitats.