| Summary: | The sensory mechanisms used by baleen whales (Mysticeti) for locating ephemeral, dense prey patches in vast marine habitats are poorly understood. Baleen whales have a functional olfactory system with paired rather than single blowholes (nares), potentially enabling stereo-olfaction. Dimethyl sulfide (DMS) is an odorous gas emitted by phytoplankton in response to grazing by zooplankton. Some seabirds use DMS to locate prey, but this ability has not been demonstrated in whales. For all 15 extant species of baleen whale, nares morphometrics (imagery from unoccupied aerial systems, UAS) was related to published trophic level indices using Bayesian phylogenetic mixed modelling. A significant negative relationship was found between nares-width and whale trophic level (β = -0.07, Lower 95% CI = -0.12, Upper 95% CI = -0.02), corresponding with a 36% increase in nares-width from highest to lowest trophic level. Thus, species with nasal morphology best suited to stereo-olfaction are more zooplanktivorous. These findings provide evidence that some baleen whale species may be able to localise odorants e.g., DMS. Our results helps direct future behavioural trials of olfaction in baleen whales, by highlighting the most appropriate species to study. This is a research priority, given the potential for DMS-mediated plastic ingestion by whales. Funding provided by: N/A* Crossref Funder Registry ID: 0 Morphometric measurements were made for free-ranging whales mostly using UAS or aircraft-based imagery, including stills from video footage. The selection criteria for images were that they were vertical, in focus and clearly showed the nares. Altitude was typically between 10 – 60 m, however accurate altimetry data were not available for all flights and therefore relative measurements (i.e., pixel counts) were used. Because images were compiled from a range of different studies, the UAS, camera, camera sensor, lens focal length, altitude and thus pixel resolution will have varied among sampling events . Similarly, lens ...
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