Trawl and eDNA assessment of marine fish diversity, seasonality, and relative abundance in coastal New Jersey, USA

Abstract Environmental DNA (eDNA) technology potentially improves the monitoring of marine fish populations. Realizing this promise awaits better understanding of how eDNA relates to fish presence and abundance. Here, we evaluate performance by comparing bottom trawl catches to eDNA from concurrent water samples. In conjunction with New Jersey Ocean Trawl Survey, 1-l water samples were collected at surface and depth prior to tows at about one-fourth of Survey sites in January, June, August, and November 2019. eDNA fish diversity from 1 l was same as or higher than trawl fish diversity from 66 M litres swept by one tow. Most (70–87%) species detected by trawl in a given month were also detected by eDNA, and vice versa, including nearly all (92–100%) abundant species. Trawl and eDNA peak seasonal abundance agreed for ∼70% of fish species. In log-scale comparisons by month, eDNA species reads correlated with species biomass, and more strongly with an allometric index calculated from biomass. In this 1-year study, eDNA reporting largely concorded with monthly trawl estimates of marine fish species richness, composition, seasonality, and relative abundance. Piggybacking eDNA onto an existing survey provided a relatively low-cost approach to better understand eDNA for marine fish stock assessment.