Dynamics of growth-based survival mechanisms in Japanese anchovy (Engraulis japonicus) larvae

Abstract

Three growth-based survival mechanisms were tested for multiple cohorts of Japanese anchovy (Engraulis japonicus) larvae in Sagami Bay. Through otolith microstructure analysis, growth trajectories and histories of samples of the survivors were compared with those of the original populations to examine size- and growth-selective mortality to test the “bigger is better” and “growth-selective predation” mechanisms, respectively. The effects of growth rates on the timing of metamorphosis were examined to test the “stage duration” mechanism. The bigger is better and growth-selective predation mechanisms were detected to be effective in two and six of eight seasonal cohorts, respectively. Results contrary to the bigger is better and growth-selective predation mechanisms were obtained from three and two of eight cohorts, respectively. The stage duration mechanism was evaluated to be effective for both of two cohorts that were testable. Overall, none of the three mechanisms were universally appropriate for all of the cohorts. The relative contributions of the three mechanisms were dynamic, although the growth-selective predation mechanism was identified to be the major one in anchovy larvae in the study site.