Large-scale scientific bottom trawl surveys are still the method of choice to investigate fish-stock densities in marine systems.

While the ecological impacts of these fish and shellfish bottom trawl surveys are comparably minor in terms of biomass extraction or sea floor damage compared to commercial fisheries, negative impacts nevertheless exist and raise ethical questions whether this type of monitoring should be continued. During the last years, the analysis of DNA traces in environmental samples (eDNA, environmental DNA) became a standard method to monitor fish species and abundances in lakes and streams.

In marine systems however, tracing of the local fish community is hampered by the occurring complex multidirectional flow conditions, which together with the observed long stability of eDNA (several days) leads to a blurred and/or translocated signal being in most cases non informative to characterize the local fish communities and their abundances. To overcome these limitations of eDNA analysis in marine habitats, we investigate in the project eRNAmaris, if environmental RNA (eRNA), which is known to be less stable in the environment compared to eDNA, will provide a more localized signal and is thus a better target molecule for non-invasive fish stock assessments in the ocean.

Within this Austrian-French cooperation project, a sequential approach will be followed to elucidate the potential of eRNA for marine biomonitoring. First, a series of non-invasive aquarium and field experiments will be conducted with several fish species to gain insight on shedding and decay rates of different eRNA types and how these rates differ from the ones known for eDNA.

This information will then be used to develop a hydrodynamic computation model describing eDNA/eRNA transport in the ocean, aiming to increase the predictive power of eDNA and eRNA analysis for fish-stock estimates. Finally, the new approach of combining eRNA analysis with high resolution individual-based modelling will be evaluated with samples and data collected during field surveys in the Bay of Biscay and the English Channel.

Combining the complementary expertise of the French and Austrian project partners enables this first project on the eRNA of marine vertebrates to play a pioneering role in advancing and improving non-invasive biomonitoring in marine systems to avoid in the future negative impacts on these sensitive habitats by conventional methods as far as possible.

AAE members involved in eRNAmaris: Daniela Sint (PI) and Michael Traugott

This research is funded by the Austrian Science Fund - FWF.