Needles in an ocean haystack: using environmental DNA to study marine mammals in the North Atlantic

Abstract

Marine mammals in the North Atlantic have experienced severe depletions due to overexploitation. While some species and populations have now recovered, there are numerous other anthropogenic activities impacting their North Atlantic ecosystem. Studying marine mammals is often associated with logistical challenges, and many species have an elusive nature, resulting in substantial knowledge gaps on the distribution, abundance and diversity of marine mammals in the North Atlantic. Environmental DNA (eDNA) is an emerging tool in biodiversity monitoring and has successfully been demonstrated to complement traditional monitoring methods for a wide range of marine taxonomic groups. The promising potential of seawater eDNA is owe to advances within an array of molecular methods used to extract, detect and/or sequence the genetic material of marine organisms from a single seawater sample. 
 We present a literature review of eDNA studies of marine mammals and discuss the potential applications and practical challenges of eDNA in marine mammal research, management and conservation. 
 Environmental DNA has already been introduced to a wide range of applications within marine mammal science, from detection of endangered species to population genetic assessments. Furthermore, eDNA has the power to capture other biologically important species in the marine ecosystem and food web, which could facilitate insight into the spatiotemporal variation of different marine communities in a changing environment. With methodological and technological standardization, eDNA based approaches have a promising potential to be integrated into regular monitoring practices and management strategies.

Determination of polar bear (Ursus maritimus) individual genotype and sex based on DNA extracted from paw-prints in snow

“…Initial applications of e-DNA collection methods focused on detecting species from among FIGURE 1 mixed samples in aquatic systems (Skinner et al, 2020). The presence of aquatic mammals has also been identified (Padgett-Stewart et al, 2016;Szeḱely et al, 2022). DNA has also been detected in paw-prints in snow (Daleń et al, 2007;Bellemain, 2017 unpublished report;Franklin et al, 2019;Hellström et al, 2019 unpublished report;Barber-Meyer et al, 2020;Barber-Meyer et al, 2022) and used to determine species presence.…”

Environmental DNA reveals fine scale spatial and temporal variation of prey species for marine mammals in a Scottish marine protected area

“…Dietary metabarcoding studies have uncovered previously unknown marine mammal diets (Sonsthagen et al, 2020; Zhang et al, 2023), whilst eDNA metabarcoding has revealed spatiotemporal availability of prey species and detected co-occurrences between cetaceans and their prey (Djurhuus et al, 2020; Visser et al, 2021). However, few studies have harnessed eDNA to elucidate marine mammal trophic interactions to date (Székely et al, 2021).…”

“…Recent advances in environmental DNA metabarcoding offer the opportunity to simultaneously monitor cetaceans and their prey, enabling long-term tracking of distributions, and to enhance our understanding of their dynamics (Székely et al, 2021). eDNA can expand the spatiotemporal scope of marine mammal monitoring where visual or acoustic monitoring are infeasible, i.e., at night or in adverse weather conditions and for cetaceans that vocalise infrequently or have unknown vocalisations (Baumgartner et al, 2019;Valsecchi et al, 2021).…”