Scientists track dolphin health using DNA in seawater
Scientists have demonstrated that environmental DNA floating in seawater can reveal both the presence of dolphin species and the genetic health of their populations. The finding marks a major step in marine conservation, offering a non-invasive way to monitor cetaceans without capturing or physically tagging animals.
The study, published in Frontiers in Marine Science and led by researcher Frederick Archer at the NOAA Southwest Fisheries Science Center in La Jolla, California, shows that repeated seawater sampling can reliably estimate genetic diversity in dolphin groups. Researchers say this genetic diversity acts as a key indicator of population size and resilience to environmental change.
Fieldwork conducted between October and December 2021 focused on 15 dolphin groups near Santa Catalina Island, off the coast of Southern California. Scientists collected two-liter seawater samples within 10 meters of animals, capturing mitochondrial DNA shed through skin cells, mucus, feces, and respiratory exhalations. The analysis identified hundreds of distinct mitochondrial sequence variants, reflecting multiple cetacean species in the region, including long-beaked common dolphins, short-beaked common dolphins, common bottlenose dolphins, and Risso’s dolphins.
The results showed clear differences in genetic diversity across species. Long-beaked common dolphins exhibited the highest variability, while Risso’s dolphins and bottlenose dolphins showed lower diversity in the same study area. Researchers also found that collecting between 60 and 72 liters of seawater per survey could produce a representative snapshot of genetic diversity, although requirements vary by species and environmental conditions.
Scientists say the approach could transform how marine populations are monitored. Traditional methods rely on expensive ship-based surveys or physical tagging, both of which limit coverage and frequency. Environmental DNA sampling could instead allow continuous monitoring of species distribution and genetic shifts linked to climate change, pollution, and other ecological pressures.
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