Recruitment patterns and factors affecting recruitment of five species of short-lived clupeoids in the tropical South Pacific

Abstract

The temporal and spatial patterns of recruitment of the short-lived anchovies Encrasicholina devisi and Encrasicholina heterolobus, and the clupeoids Spratelloides delicatulus, Spratelloides gracilis and Spratelloides lewisi between 1984 and 1989 were examined at one or more sites in the Solomon Islands, Papua New Guinea and Maldives. At all sites, all species recruited throughout the year. There was no difference between months in the proportion of recruits in the fished population of any species at any site. The relative abundance of recruits of E. devisi, E. heterolobus, S. delicatulus and S. lewisi between 1984 and 1989 was examined at Munda and Tulagi in the Solomon Islands. There were no detectable differences between months or sites for any species, although the interannual variability in recruitment in some months was quite high. Both the relative abundance of recruits and variation in recruitment of both Encrasicholina species were correlated at both sites. Adult stock size was the most important factor that explained variation in recruitment 2 months later and accounted for between 30 and 85% of the variation in recruitment of each species at the two sites. Environmental factors such as Zooplankton biomass, wind or monthly rainfall were not correlated with recruitment of any species at either site. Nor was predation by adults an important source of egg or larval mortality. All species preyed on Encrasicholina eggs and larvae at some time during the year and Encrasicholina species were the most important predators at both sites. However, unlike some temperate clupeoids, these species ate less than 1% of the estimated daily egg production each month during the study. Overall, there was little variation in recruitment of Encrasicholina or Spratelloides species. Most of the monthly estimates 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 compared with temperate clupeoids results from a combination of their multiple-spawning reproductive strategy, rapid growth and early recruitment. For these species, prerecruit mortality appears to be relatively constant.