Biological Monitoring: Fish Eggs, Fish Larvae, and Zooplankton

Abstract

To understand the processes linking environmental variability to fish population dynamics in marine ecosystems, the dynamics of lower trophic levels including zooplankton as fish prey resources needs to be studied. Furthermore, the spawning habitat is the place connecting the life history of spawning adults and offspring and thus reflects the physiological characteristics and stock conditions of the fish resource. The survival rate of fish larvae and juveniles transported from the spawning grounds eventually determines the recruitment success. A long-term monitoring system based on fishery-independent biological sampling is therefore essential to clarify mechanisms of dynamics of the lower trophic organisms and fish spawning habitats. This chapter introduces the technological advances and data applications of fishery-independent monitoring surveys, after briefly reviewing their history and current status in Japan and also worldwide. These reviews include (1) long-term zooplankton monitoring, (2) long-term fish egg and larval surveys and spawning monitoring, and (3) sampling of fish larvae and juveniles (pre-recruit stages). Moreover, the chapter provides recommendations for monitoring systems and perspectives on future directions toward continuity of long-term monitoring.