New research: Determining the sex of whales via environmental DNA samples

For the first time ever, researchers have demonstrated that we can determine the sex of whales via environmental DNA samples. eDNA refers to genetic material shed into an organism’s environment. For whales, this looks like cells, tissues, fluids, and fragments of excrement left behind in the ocean!

The study, by Chloe Robinson, Gary Sutton, Emma Laqua, Michael Judson, Adam Warner, and Karina Dracott, published in the journal Environmental DNA, showed success in accurately determining the sex of both killer whales and humpback whales from water samples, a cost-efficient and non-invasive method.

Knowing the sex of wild whales helps scientists understand how healthy a population is and how well it is likely to recover, further informing conservation efforts. This is especially important for species still bouncing back from population losses experienced during the commercial whaling era.

Traditional methods of determining whale sex — like taking photos of their underside or performing skin biopsies — can be time-consuming, expensive, and invasive.

“The method showed higher overall gene detection success in killer whales (53%), though due to their tight social groupings, only about half of the samples could be confidently linked to the sex of a specific individual. In contrast, gene detection in humpbacks was slightly lower (44%), but all successfully amplified samples accurately matched the known sex of the individual (100%). This suggests that the method shows strong promise, especially for more solitary species like humpbacks or other large whale species.”

Abstract

Anthropogenic pressures on marine ecosystems are intensifying, highlighting the need to bridge knowledge gaps for species at risk. Data deficiencies, particularly for species recovering from historic declines, such as marine megafauna like whales, hinder effective management. Understanding long-term population viability and identifying any sex-biased threats is important for cetacean conservation. Killer whales (Orcinus orca) and humpback whales (Megaptera novaeangliae) are well-studied in the Northeast Pacific, making them ideal for optimizing noninvasive environmental DNA (eDNA) techniques for sex determination. We collected eDNA flukeprint samples from killer whales (n = 67) and humpback whales (n = 18), analyzing ZFX/ZFY gene amplification using conventional PCR to compare results against known sexes. Samples from killer whales exhibited higher ZFX/ZFY PCR amplification success (53%) compared with humpback whales (44%). However, the close social structure of this species likely contributed to only 54% of samples matching the known sex of whales sampled. Conversely, humpback whale samples accurately matched the known sexes of individuals (100%). These findings demonstrate eDNA’s potential to replace more invasive biopsies for sex determination but highlight the need for further optimization regarding sampling protocols and species-specific ZFX/ZFY amplification approaches. Additionally, eDNA flukeprint sampling also shows promise for other solitary cetaceans such as large rorquals (Balaenoptera spp.), which remain among the most data-deficient species.