Morphology of nares associated with stereo-olfaction in baleen whales

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.