Assessing the potential of eDNA analysis for spawning surveys in marine environments: A case study on Japanese jack mackerel

Understanding spawning ecology is important for species/population management and conservation. However, conventional surveys are often time- and labour-consuming and invasive. To address these challenges, environmental DNA (eDNA) analysis has emerged as a promising method for spawning surveys. This study investigated the spawning season and diurnal changes in eDNA concentrations targeting Japanese jack mackerel in Maizuru Bay, Japan, to assess the potential of eDNA-based spawning surveys in the marine environment. First, to estimate the spawning season, eDNA concentrations at sunset and sunrise were compared monthly for one year at three sites. As Japanese jack mackerel are nocturnal spawners, eDNA concentration will increase at night during the spawning season. A significant increase in eDNA concentration was observed between sunset and sunrise in July, suggesting that this period corresponded to the spawning season. This was confirmed by egg collection surveys using a plankton net. Second, to investigate diurnal changes in eDNA concentrations during the spawning season, time-series sampling was conducted every three hours for 24 h in July. The results indicated that eDNA concentration showed a significant diurnal change with a peak between 9 PM and midnight, which is suggested to be their spawning time window. This study successfully estimated the spawning season of Japanese jack mackerel and demonstrated the potential of eDNA-based spawning surveys for the first time in marine environments. Our findings are expected to facilitate the application of eDNA analysis as a new approach to overcome traditional challenges in marine spawning surveys and contribute to the development of the field. • The potential of eDNA for spawning surveys was assessed in Japanese jack mackerel. • Monthly morning and evening eDNA sampling identified spawning activity in July. • Egg surveys using a plankton net confirmed the spawning event. • Time-series sampling showed a diurnal change in eDNA concentrations in July. • eDNA analysis is thus applicable for detecting spawning in marine species.