Combining Hydroacoustics and eDNA to Estimate Species-Specific Biomass in a Pelagic Fish Community

Hydroacoustic surveys and eDNA monitoring are rapidly evolving technologies with significant applications for monitoring fish populations. Hydroacoustic technology is capable of enumerating size classes; however, species identification often relies on time-consuming, costly, and lethal supplementary sampling methods. Environmental DNA (eDNA) detection is a nonlethal alternative for ground-truthing hydroacoustic surveys; however, on its own, it does not provide estimates of fish size or stock biomass. We tested the utility of paired hydroacoustic and eDNA surveys by replicating samples over a 12-h period along the depth gradient of pelagic lake habitat where the fish community exhibits diel vertical migration. Generally, we found that (1) the detection and proportion of target species estimated by eDNA was similar to those found in historical gill-netting across depth strata, (2) eDNA-apportioned hydroacoustic data agreed with expected diel patterns in species vertical distributions, and (3) with some exceptions, eDNA-apportioned hydroacoustic estimates of biomass were strongly correlated with expected species biomass. Some species yielded unrealistically high concentrations in the deepest samples, suggesting that benthic accumulation of eDNA can result in inflated biomass estimates near the lake bottom. Combining eDNA and hydroacoustics as complementary noninvasive assessment tools provides a simplified species apportioning protocol for future fish populations and community assessments.