Let’s talk smell.
Hawaiian monk seals have two vertical slits for nostrils that are adapted to close when they dive, begging the question how much do Hawaiian monk seals rely on a sense of smell when flipping over rocks on the ocean floor in search of, say, flat fish like flounder? Or when they stick their nose in a puka in rock, hopeful to snag a lobster or eel for a good meal? For that matter, what about when Hawaiian monk seals are hauled out on the beach, and their nostrils are open?
Turns out there are probably more questions at this point in time than there are published scientific papers on Hawaiian monk seals and their sniffing prowess.
Let’s tackle the use of smell on land (air) by taking a look at other seal species.
Take Antarctic fur seals. According to The Wire, when this species gives birth, mothers nurse their young for some four months. During that time, mothers leave their pups on the beach and head to the sea to search for food. They may be gone for up to 10 days. When they return, researchers suggest mothers rely on smell to sniff out their own pup from the many others on the beach.
Researchers believe the same is true of Harbor seals.
More closely related to Hawaiian monk seals, the Mediterranean monk seal is also thought to use smell in mother-pup bonding. According to the Eastern Adriatic Monk Seal Project, “…sense of smell plays an important role in the life of a Mediterranean monk seal as scent and sniffing is used intensively in the first weeks of a newborn pup’s life in order to communicate and find its mother in the dark caves where they live.”
Compared to Antarctic fur seals, Hawaiian monk seals nurse their young for a fraction of time—four to six weeks instead of four months. While nursing, Hawaiian monk seals don’t leave their pups alone on the beach to forage. And Hawaiian monk seals birth their pups on beaches, not in caves like Mediterranean monk seals. Interestingly, especially at islands and atolls in Papahānaumokuākea Marine National Monument, it’s not uncommon for pup-switches to occur among Hawaiian monk seals. That is, moms and pups get mixed up. It happened on Kauai in 2018 when there were three moms and pups on the same beach.
Researchers propose there are more uses of smell among Antarctic fur seals. They may rely on “signature scents” to mate with unrelated seals, according to the same article in The Wire. Because fur seals tend to colonize, they may use smell as a way to form stable social groups.
But what about when foraging? How might smell be involved? Steller sea lions possess a large number of olfactory receptor genes, possibly because they are more terrestrial, that might help them hunt for food.
This unique research paper posits that “aquatic carnivores” forage “noseblind,” that is without airborne chemical cues and, thus, have reduced olfactory anatomy, especially among deep-divers, relative to closely related land-based carnivores. That is, if sense of smell isn’t a critical component to their way of life, the anatomy that supports it diminishes over time in an adaptive response. Why build it if it’s not needed?
Over millennia, Hawaiian monk seals have adapted to their tropical ecosystem in unique ways. They don’t “colonize” in the same ways as some seals. They don’t birth their pups in caves. They spend the vast majority of their lives at sea. They can dive as deep as 1,800 feet; however, average foraging dives of several hundred feet. So, just how great—or not—is Hawaiian monk seals’ sense of smell? Good question.
This will be updated as more information come to light.
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