RECRUITMENT PATTERNS AND FACTORS AFFECTING RECRUITMENT OF 5 SPECIES OF SHORT-LIVED CLUPEOIDS IN THE TROPICAL SOUTH-PACIFIC

The temporal and spatial patterns of recruitment of the short-lived an chovies Encrasicholina devisi and Encrasicholina heterolobus, and the clupeoids Spratelloides delicatulus, Spratelloides gracilis and Sprate lloides lewisi between 1984 and 1989 were examined at one or more site s in the Solomon Islands, Papua New Guinea and Maldives. At all sites, all species recruited throughout the year. There was no difference be tween months in the proportion of recruits in the fished population of any species at any site. The relative abundance of recruits of E. dev isi, E. heterolobus, S. delicatulus and S. lewisi between 1984 and 198 9 was examined at Munda and Tulagi in the Solomon Islands. There were no detectable differences between months or sites for any species, alt hough the interannual variability in recruitment in some months was qu ite high. Both the relative abundance of recruits and variation in rec ruitment of both Encrasicholina species were correlated at both sites. Adult stock size was the most important factor that explained variati on in recruitment 2 months later and accounted for between 30 and 85% of the variation in recruitment of each species at the two sites. Envi ronmental factors such as zooplankton biomass, wind or monthly rainfal l were not correlated with recruitment of any species at either site. Nor was predation by adults an important source of egg or larval morta lity. All species preyed on Encrasicholina eggs and larvae at some tim e during the year and Encrasicholina species were the most important p redators at both sites. However, unlike some temperate clupeoids, thes e species ate less than 1% of the estimated daily egg production each month during the study. Overall, there was little variation in recruit ment of Encrasicholina or Spratelloides species. Most of the monthly e stimates of the relative abundance of recruits of each species did not differ from the long-term mean at each site by more than an order of magnitude. We hypothesise that the lower variability in recruitment co mpared with temperate clupeoids results from a combination of their mu ltiple-spawning reproductive strategy, rapid growth and early recruitm ent. For these species, prerecruit mortality appears to be relatively constant.