Spawning overlap of anchovy and sardine in the western North Pacific

Abstract

Spatial and temporal spawning overlaps in Japanese anchovy Engraulis japonicus and sardine Sardinops melanostictus were examined using a long-term data set (1978 to 2004) of monthly egg and larval surveys (total of 102 613 vertical tow samples) off the Pacific coast of Japan. Egg abundance was estimated in 15′ latitude × 15′ longitude squares, and spawning area was calculated by summing areas of squares positive for egg occurrence. Both species had offshore expansion (inshore contraction) of spawning grounds with protracted (shortened) spawning periods during high- (low-) biomass phases. Although anchovy and sardine had different peak spawning periods (April to July and February to March, respectively), their spawnings were coincident from February to June in coastal waters. For anchovy, annual overlapping spawning area percentages of total spawning area and egg abundances in overlapping areas as percentages of total egg abundances were consistently low (6.4 to 30.6% and 7.2 to 39.9%, respectively). In contrast, for sardine these percentages were consistently high and notably increased as population size decreased (21.1 to 80.8% and 1.4 to 86.9%, respectively). Averaged over 5 yr (2000 to 2004), 68.5% of the total area of sardine spawning grounds overlapped with anchovy spawning grounds, and 61.8% of annual sardine egg abundance was produced in spawning grounds that overlapped with anchovy. Thus, Japanese sardine population recovery is likely more difficult than Japanese anchovy population recovery (when interspecific interavtions occur). © Inter-Research 2008.